1.
Polymer degradation
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The changes in properties are often termed aging. In a finished product such a change is to be prevented or delayed, Degradation can be useful for recycling/reusing the polymer waste to prevent or reduce environmental pollution. Degradation can also be induced deliberately to assist structure determination, polymeric molecules are very large, and their unique and useful properties are mainly a result of their size. Any loss in chain length lowers tensile strength and is a cause of premature cracking. Today there are primarily seven commodity polymers in use, polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polystyrene, polycarbonate and these make up nearly 98% of all polymers and plastics encountered in daily life. Each of these polymers has its own characteristic modes of degradation and resistances to heat, light, polyethylene, polypropylene, and poly are sensitive to oxidation and UV radiation, while PVC may discolor at high temperatures due to loss of hydrogen chloride gas, and become very brittle. PET is sensitive to hydrolysis and attack by acids, while polycarbonate depolymerizes rapidly when exposed to strong alkalis. For example, polyethylene usually degrades by random scission—that is by a breakage of the linkages that hold the atoms of the polymer together. When this polymer is heated above 450 Celsius it becomes a complex mixture of molecules of various sizes that resemble gasoline, other polymers—like polyalphamethylstyrene—undergo specific chain scission with breakage occurring only at the ends, they literally unzip or depolymerize to become the constituent monomers. Most polymers can be degraded by photolysis to give molecular weight molecules. Electromagnetic waves with the energy of light or higher, such as ultraviolet light, X-rays. Chain-growth polymers like poly can be degraded by thermolysis at high temperatures to give monomers, oils, gases, the degradation takes place by, Step-growth polymers like polyesters, polyamides and polycarbonates can be degraded by solvolysis and mainly hydrolysis to give lower molecular weight molecules. The hydrolysis takes place in the presence of water containing an acid or a base as catalyst, polyamide is sensitive to degradation by acids and polyamide mouldings will crack when attacked by strong acids. For example, the surface of a fuel connector showed the progressive growth of the crack from acid attack to the final cusp of polymer. The problem is known as stress cracking, and in this case was caused by hydrolysis of the polymer. It was the reaction of the synthesis of the polymer. Tiny traces of the gas in the air will attack double bonds in chains, with Natural rubber, polybutadiene, Styrene-butadiene rubber. Ozone cracks form in products under tension, but the strain is very small
2.
Weather testing of polymers
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Weather testing of polymers is the controlled polymer degradation and polymer coating degradation under lab or natural conditions. Just like erosion of rocks, natural phenomena can cause degradation in polymer systems, the elements of most concern to polymers are ultraviolet radiation, moisture and humidity, high temperatures and temperature fluctuations. Polymers are used in life, so it is important for scientists and polymer producers to understand durability. Paint, a polymer coating, is used to change the colour, change the reflectance. The structure of paint consists of pigments in a matrix of resin, a typical example is painted steel roofing and walling products, which are constantly exposed to harmful weathering conditions. Figure 1.1 shows typical weathering results of a sample of painted steel, the sample on the left had been placed in an outdoor exposure rack, and weathered for a total of 6 years. It can be seen that the sample has an appearance and has undergone a colour change in comparison to the unweathered sample on the right. Colour is determined by light-reflecting chemical particles, pigments, in the paint and these particles can have very different physical sizes, as shown in the diagram in figure 1.2. In this example, the pigments are the small black dots, red pigments are larger spheres. This combination of pigments produces the original brown colour, the upper diagram has had no weathering, and the surface is still smooth and undamaged. The lower diagram shows the surface after weathering has occurred. The surface has eroded with significant loss of the black and red pigments from the surface layer, the pitted surface scatters light, therefore reducing the gloss and creating the chalky affect. The larger acicular yellow pigments are more difficult to remove, resulting in a change towards a more yellowy appearance. Weather testing was paramount in discovering this mechanism, pigment composition has recently been modified to help minimise this effect. There are 3 main testing techniques, Natural Weathering, Accelerated Natural Weathering, because natural weathering can be a slow process, each of the techniques is a tradeoff between realistic weathering results and the duration of testing before results are collated. Natural Weathering involves placing samples on inclined racks oriented at the sun, in Northern hemisphere these racks are at an angle of 45 degrees in a southerly direction. In Southern hemisphere these racks are at an angle of 45 degrees in a northerly direction and this angle ensures exposure to the full spectrum of solar radiation, from infrared to Ultra violet. Sites used for type of testing are usually in tropical areas as high temperature
3.
Natural arch
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A natural arch, natural bridge or, less commonly, a rock arch is a natural rock formation where an arch has formed with an opening underneath. Natural arches commonly form where inland cliffs, coastal cliffs, fins or stacks are subject to erosion from the sea, most natural arches are formed from narrow fins and sea stacks composed of sandstone or limestone with steep, often vertical, cliff faces. The formations become narrower due to erosion over time scales. The softer rock stratum erodes away creating rock shelters, or alcoves, on sides of the formation beneath the relatively harder stratum, or caprock. The alcoves erode further into the formation eventually meeting underneath the harder caprock layer, the choice between bridge and arch is somewhat arbitrary. The Natural Arch and Bridge Society identifies a bridge as a subtype of arch that is primarily water-formed, by contrast, the Dictionary of Geological Terms defines a natural bridge as a natural arch that spans a valley of erosion. The largest natural arch, by a significant margin, is the Xianren Bridge in China, on coasts two different types of arches can form depending on the geology. On discordant coastlines rock types run at 90° to the coast, wave refraction concentrates the wave energy on the headland, and an arch forms when caves break through the headland. Two examples of type of arch are London Arch—previously known as London Bridge—in Victoria, Australia. When these arches eventually collapse, they form stacks and stumps, on concordant coastlines rock types run parallel to the coastline, with weak rock such as shale protected by stronger rock such as limestone. The wave action along concordant coastlines breaks through the strong rock, good examples of this type of arch are the Durdle Door and Stair Hole near Lulworth Cove on Dorsets Jurassic Coast in south England. When Stair Hole eventually collapses it will form a cove, weather-eroded arches begin their formation as deep cracks which penetrate into a sandstone layer. Erosion occurring within the cracks wears away exposed rock layers and enlarges the surface cracks isolating narrow sandstone walls which are called fins, alternating frosts and thawing cause crumbling and flaking of the porous sandstone and eventually cut through some of the fins. The resulting holes become enlarged to arch proportions by rockfalls and weathering, the arches eventually collapse leaving only buttresses that in time will erode. Many weather-eroded arches are found in Arches National Park, Canyonlands National Park, some natural bridges may look like arches, but they form in the path of streams that wear away and penetrate the rock. Pothole arches form by chemical weathering as water collects in natural depressions, Natural Bridges National Monument in Utah protects the area surrounding three large natural bridges all of which were formed by streams running through canyons. The largest of which is named Sipapu Bridge with a span of 225 feet, Natural bridges can form from natural limestone caves, where paired sinkholes collapse and a ridge of stone is left standing in between, with the cave passageway connecting from sinkhole to sinkhole. Like all rock formations, natural bridges are subject to continued erosion, one example of this was the double-arched Victorian coastal rock formation, London Bridge, which lost an arch after storms increased erosion
4.
Rock (geology)
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Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a rock, is a combination of the minerals quartz, feldspar. The Earths outer solid layer, the lithosphere, is made of rock, rock has been used by mankind throughout history. The minerals and metals found in rocks have been essential to human civilization, three major groups of rocks are defined, igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is a component of geology. At a granular level, rocks are composed of grains of minerals, the aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed, many rocks contain silica, a compound of silicon and oxygen that forms 74. 3% of the Earths crust. This material forms crystals with other compounds in the rock, the proportion of silica in rocks and minerals is a major factor in determining their name and properties. Rocks are geologically classified according to such as mineral and chemical composition, permeability, the texture of the constituent particles. These physical properties are the end result of the processes that formed the rocks, over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock, igneous, sedimentary, and metamorphic, the three classes of rocks are subdivided into many groups. However, there are no hard and fast boundaries between allied rocks, hence the definitions adopted in establishing rock nomenclature merely correspond to more or less arbitrary selected points in a continuously graduated series. Igneous rock forms through the cooling and solidification of magma or lava and this magma can be derived from partial melts of pre-existing rocks in either a planets mantle or crust. Typically, the melting of rocks is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, igneous rocks are divided into two main categories, plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earths crust, a common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, the chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowens reaction series. Most major igneous rocks are found along this scale, about 64. 7% of the Earths crust by volume consists of igneous rocks, making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, only 0. 6% are syenites and 0. 3% peridotites and dunites
5.
Soil
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Soil is a mixture of minerals, organic matter, gases, liquids, and countless organisms that together support life on Earth. Soil is called the Skin of the Earth and interfaces with the lithosphere, the hydrosphere, the atmosphere, the term pedolith, used commonly to refer to the soil, literally translates ground stone. Soil consists of a phase of minerals and organic matter, as well as a porous phase that holds gases. Accordingly, soils are often treated as a system of solids, liquids. Soil is a product of the influence of climate, relief, organisms, Soil continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering with associated erosion. Given its complexity and strong internal connectedness soil has been considered as an ecosystem by soil ecologists. Most soils have a dry bulk density between 1.1 and 1.6 g/cm3, while the particle density is much higher. Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic, Soil science has two basic branches of study, edaphology and pedology. Edaphology is concerned with the influence of soils on living things, pedology is focused on the formation, description, and classification of soils in their natural environment. In engineering terms, soil is referred to as regolith, or loose material that lies above the solid geology. Soil is commonly referred to as earth or dirt, technically, as soil resources serve as a basis for food security, the international community advocates its sustainable and responsible use through different types of soil governance. Soil is a component of the Earths ecosystem. The worlds ecosystems are impacted in far-reaching ways by the carried out in the soil, from ozone depletion and global warming, to rainforest destruction. Following the atmosphere, the soil is the next largest carbon reservoir on Earth, as the planet warms, soils will add carbon dioxide to the atmosphere due to its increased biological activity at higher temperatures. Thus, soil carbon losses likely have a positive feedback response to global warming. Since soil has a range of available niches and habitats. A gram of soil can contain billions of organisms, belonging to thousands of species, mostly microbial, Soil has a mean prokaryotic density of roughly 108 organisms per gram, whereas the ocean has no more than 107 procaryotic organisms per milliliter of seawater. Since plant roots need oxygen, ventilation is an important characteristic of soil and this ventilation can be accomplished via networks of interconnected soil pores, which also absorb and hold rainwater making it readily available for plant uptake
6.
Mineral
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A mineral is a naturally occurring chemical compound, usually of crystalline form and abiogenic in origin. A mineral has one specific chemical composition, whereas a rock can be an aggregate of different minerals or mineraloids, the study of minerals is called mineralogy. There are over 5,300 known mineral species, over 5,070 of these have been approved by the International Mineralogical Association, the silicate minerals compose over 90% of the Earths crust. The diversity and abundance of species is controlled by the Earths chemistry. Silicon and oxygen constitute approximately 75% of the Earths crust, which translates directly into the predominance of silicate minerals, minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species, changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals. Minerals can be described by their various properties, which are related to their chemical structure. Common distinguishing characteristics include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, tenacity, cleavage, fracture, parting, more specific tests for describing minerals include magnetism, taste or smell, radioactivity and reaction to acid. Minerals are classified by key chemical constituents, the two dominant systems are the Dana classification and the Strunz classification, the silicate class of minerals is subdivided into six subclasses by the degree of polymerization in the chemical structure. All silicate minerals have a unit of a 4− silica tetrahedron—that is, a silicon cation coordinated by four oxygen anions. These tetrahedra can be polymerized to give the subclasses, orthosilicates, disilicates, cyclosilicates, inosilicates, phyllosilicates, other important mineral groups include the native elements, sulfides, oxides, halides, carbonates, sulfates, and phosphates. The first criterion means that a mineral has to form by a natural process, stability at room temperature, in the simplest sense, is synonymous to the mineral being solid. More specifically, a compound has to be stable or metastable at 25 °C, modern advances have included extensive study of liquid crystals, which also extensively involve mineralogy. Minerals are chemical compounds, and as such they can be described by fixed or a variable formula, many mineral groups and species are composed of a solid solution, pure substances are not usually found because of contamination or chemical substitution. Finally, the requirement of an ordered atomic arrangement is usually synonymous with crystallinity, however, crystals are also periodic, an ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form, hardness, and cleavage. There have been recent proposals to amend the definition to consider biogenic or amorphous substances as minerals. The formal definition of an approved by the IMA in 1995, A mineral is an element or chemical compound that is normally crystalline. However, if geological processes were involved in the genesis of the compound, Mineral classification schemes and their definitions are evolving to match recent advances in mineral science
7.
Earth's atmosphere
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The atmosphere of Earth is the layer of gases, commonly known as air, that surrounds the planet Earth and is retained by Earths gravity. The atmosphere of Earth protects life on Earth by absorbing solar radiation, warming the surface through heat retention. By volume, dry air contains 78. 09% nitrogen,20. 95% oxygen,0. 93% argon,0. 04% carbon dioxide, and small amounts of other gases. Air also contains an amount of water vapor, on average around 1% at sea level. The atmosphere has a mass of about 5. 15×1018 kg, the atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. The Kármán line, at 100 km, or 1. 57% of Earths radius, is used as the border between the atmosphere and outer space. Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around 120 km, several layers can be distinguished in the atmosphere, based on characteristics such as temperature and composition. The study of Earths atmosphere and its processes is called atmospheric science, early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann. The three major constituents of air, and therefore of Earths atmosphere, are nitrogen, oxygen, water vapor accounts for roughly 0. 25% of the atmosphere by mass. The remaining gases are often referred to as gases, among which are the greenhouse gases, principally carbon dioxide, methane, nitrous oxide. Filtered air includes trace amounts of other chemical compounds. Various industrial pollutants also may be present as gases or aerosols, such as chlorine, fluorine compounds, sulfur compounds such as hydrogen sulfide and sulfur dioxide may be derived from natural sources or from industrial air pollution. In general, air pressure and density decrease with altitude in the atmosphere, however, temperature has a more complicated profile with altitude, and may remain relatively constant or even increase with altitude in some regions. In this way, Earths atmosphere can be divided into five main layers, excluding the exosphere, Earth has four primary layers, which are the troposphere, stratosphere, mesosphere, and thermosphere. It extends from the exobase, which is located at the top of the thermosphere at an altitude of about 700 km above sea level, to about 10,000 km where it merges into the solar wind. This layer is composed of extremely low densities of hydrogen, helium and several heavier molecules including nitrogen, oxygen. The atoms and molecules are so far apart that they can travel hundreds of kilometers without colliding with one another, thus, the exosphere no longer behaves like a gas, and the particles constantly escape into space. These free-moving particles follow ballistic trajectories and may migrate in and out of the magnetosphere or the solar wind, the exosphere is located too far above Earth for any meteorological phenomena to be possible
8.
In situ
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In situ is a Latin phrase that translates literally to on site or in position. It means locally, on site, on the premises or in place to describe an event where it takes place, in the aerospace industry, equipment on-board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may work but interference from nearby equipment may create unanticipated problems, special test equipment is available for this in situ testing. In archaeology, in situ refers to an artifact that has not been moved from its place of deposition. In other words, it is stationary, meaning still, an artifact being in situ is critical to the interpretation of that artifact and, consequently, of the culture which formed it. Once an artifacts find-site has been recorded, the artifact can then be moved for conservation, further interpretation, an artifact that is not discovered in situ is considered out of context and as not providing an accurate picture of the associated culture. However, the out of context artifact can provide scientists with an example of types, when excavating a burial site or surface deposit in situ refers to cataloging, recording, mapping, photographing human remains in the position they are discovered. The label in situ indicates only that the object has not been newly moved. Thus, an archaeological in situ find may be an object that was looted from another place, an item of booty of a past war. Consequently, the in situ find site may not reveal its provenance. It is also possible for archaeological layers to be reworked on purpose or by accident, for example, in a Tell mound, where layers are not typically uniform or horizontal, or in land cleared or tilled for farming. The term in situ is used to describe ancient sculpture that was carved in place such as the Sphinx or Petra. This distinguishes it from statues that were carved and moved like the Colossi of Memnon, which was moved in ancient times. In art, in situ refers to a work of art made specifically for a host site, for a more detailed account see, Site-specific art. The term can refer to a work of art created at the site where it is to be displayed, rather than one created in the artists studio. In architectural sculpture the term is employed to describe sculpture that is carved on a building, frequently from scaffolds. A fraction of the star clusters in our galaxy, as well as those in other massive galaxies. The rest might have been accreted from now defunct dwarf galaxies, in biology and biomedical engineering, in situ means to examine the phenomenon exactly in place where it occurs
9.
Erosion
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In earth science, erosion is the action of surface processes that remove soil, rock, or dissolved material from one location on the Earths crust, then transport it away to another location. Eroded sediment or solutes may be transported just a few millimetres, the rates at which such processes act control how fast a surface is eroded. Feedbacks are also possible between rates of erosion and the amount of eroded material that is carried by, for example. Processes of erosion that produce sediment or solutes from a place contrast with those of deposition, while erosion is a natural process, human activities have increased by 10-40 times the rate at which erosion is occurring globally. At well-known agriculture sites such as the Appalachian Mountains, intensive farming practices have caused erosion up to 100x the speed of the rate of erosion in the region. Excessive erosion causes both on-site and off-site problems, on-site impacts include decreases in agricultural productivity and ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, the end result is desertification. Off-site effects include sedimentation of waterways and eutrophication of bodies, as well as sediment-related damage to roads. Intensive agriculture, deforestation, roads, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regard to their effect on stimulating erosion, however, there are many prevention and remediation practices that can curtail or limit erosion of vulnerable soils. Rainfall, and the surface runoff which may result from rainfall, produces four types of soil erosion, splash erosion, sheet erosion, rill erosion. Splash erosion is generally seen as the first and least severe stage in the erosion process. In splash erosion, the impact of a falling raindrop creates a crater in the soil. The distance these soil particles travel can be as much as 0.6 m vertically and 1.5 m horizontally on level ground. If the soil is saturated, or if the rate is greater than the rate at which water can infiltrate into the soil. If the runoff has sufficient flow energy, it will transport loosened soil particles down the slope, sheet erosion is the transport of loosened soil particles by overland flow. Rill erosion refers to the development of small, ephemeral concentrated flow paths which function as both sediment source and sediment delivery systems for erosion on hillslopes, generally, where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are typically of the order of a few centimetres or less and this means that rills exhibit hydraulic physics very different from water flowing through the deeper, wider channels of streams and rivers. Gully erosion occurs when water accumulates and rapidly flows in narrow channels during or immediately after heavy rains or melting snow
10.
Ice age
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An ice age is a period of long-term reduction in the temperature of Earths surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Within a long-term ice age, individual pulses of cold climate are termed glacial periods, in the terminology of glaciology, ice age implies the presence of extensive ice sheets in both northern and southern hemispheres. In 1742 Pierre Martel, an engineer and geographer living in Geneva, two years later he published an account of his journey. He reported that the inhabitants of that valley attributed the dispersal of erratic boulders to the glaciers, later similar explanations were reported from other regions of the Alps. In 1815 the carpenter and chamois hunter Jean-Pierre Perraudin explained erratic boulders in the Val de Bagnes in the Swiss canton of Valais as being due to glaciers previously extending further. An unknown woodcutter from Meiringen in the Bernese Oberland advocated a similar idea in a discussion with the Swiss-German geologist Jean de Charpentier in 1834, comparable explanations are also known from the Val de Ferret in the Valais and the Seeland in western Switzerland and in Goethes scientific work. Such explanations could also be found in parts of the world. When the Bavarian naturalist Ernst von Bibra visited the Chilean Andes in 1849–1850, meanwhile, European scholars had begun to wonder what had caused the dispersal of erratic material. From the middle of the 18th century, some discussed ice as a means of transport, the Swedish mining expert Daniel Tilas was, in 1742, the first person to suggest drifting sea ice in order to explain the presence of erratic boulders in the Scandinavian and Baltic regions. In 1795, the Scottish philosopher and gentleman naturalist, James Hutton, two decades later, in 1818, the Swedish botanist Göran Wahlenberg published his theory of a glaciation of the Scandinavian peninsula. He regarded glaciation as a regional phenomenon, only a few years later, the Danish-Norwegian geologist Jens Esmark argued a sequence of worldwide ice ages. In a paper published in 1824, Esmark proposed changes in climate as the cause of those glaciations and he attempted to show that they originated from changes in Earths orbit. During the following years, Esmarks ideas were discussed and taken over in parts by Swedish, Scottish, at the University of Edinburgh Robert Jameson seemed to be relatively open to Esmarks ideas, as reviewed by Norwegian professor of glaciology Bjørn G. Andersen. Jamesons remarks about ancient glaciers in Scotland were most probably prompted by Esmark, in Germany, Albrecht Reinhard Bernhardi, a geologist and professor of forestry at an academy in Dreissigacker, since incorporated in the southern Thuringian city of Meiningen, adopted Esmarks theory. In a paper published in 1832, Bernhardi speculated about former polar ice caps reaching as far as the zones of the globe. When he read his paper before the Schweizerische Naturforschende Gesellschaft, most scientists remained sceptical, finally, Venetz convinced his friend Jean de Charpentier. De Charpentier transformed Venetzs idea into a theory with a limited to the Alps. In fact, both men shared the same volcanistic, or in de Charpentiers case rather plutonistic assumptions, about the Earths history, in 1834, de Charpentier presented his paper before the Schweizerische Naturforschende Gesellschaft
11.
Aeolian processes
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Aeolian processes, also spelled eolian or æolian, pertain to wind activity in the study of geology and weather and specifically to the winds ability to shape the surface of the Earth. Winds may erode, transport, and deposit materials and are effective agents in regions with sparse vegetation, a lack of soil moisture, although water is a much more powerful eroding force than wind, aeolian processes are important in arid environments such as deserts. The term is derived from the name of the Greek god Aeolus, wind erodes the Earths surface by deflation and by abrasion. Regions which experience intense and sustained erosion are called deflation zones, most aeolian deflation zones are composed of desert pavement, a sheet-like surface of rock fragments that remains after wind and water have removed the fine particles. Almost half of Earths desert surfaces are stony deflation zones, the rock mantle in desert pavements protects the underlying material from deflation. A dark, shiny stain, called desert varnish or rock varnish, is found on the surfaces of some desert rocks that have been exposed at the surface for a long period of time. Manganese, iron oxides, hydroxides, and clay minerals form most varnishes, deflation basins, called blowouts, are hollows formed by the removal of particles by wind. Blowouts are generally small, but may be up to kilometers in diameter. In parts of Antarctica wind-blown snowflakes that are technically sediments have also caused abrasion of exposed rocks, grinding by particles carried in the wind creates grooves or small depressions. Ventifacts are rocks which have cut, and sometimes polished. Sculpted landforms, called yardangs, are up to tens of meters high, the famous Great Sphinx of Giza in Egypt may be a modified yardang. Particles are transported by winds through suspension, saltation and creeping along the ground, small particles may be held in the atmosphere in suspension. Upward currents of air support the weight of suspended particles and hold them indefinitely in the surrounding air, typical winds near Earths surface suspend particles less than 0.2 millimeters in diameter and scatter them aloft as dust or haze. Saltation is downwind movement of particles in a series of jumps or skips, saltation normally lifts sand-size particles no more than one centimeter above the ground and proceeds at one-half to one-third the speed of the wind. A saltating grain may hit other grains that jump up to continue the saltation, the grain may also hit larger grains that are too heavy to hop, but that slowly creep forward as they are pushed by saltating grains. Surface creep accounts for as much as 25 percent of grain movement in a desert, aeolian turbidity currents are better known as dust storms. Air over deserts is cooled significantly when rain passes through it and this cooler and denser air sinks toward the desert surface. When it reaches the ground, the air is deflected forward, crops, people, villages, and possibly even climates are affected by dust storms
12.
Alluvial
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Alluvium is loose, unconsolidated soil or sediments, which has been eroded, reshaped by water in some form, and redeposited in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand, when this loose alluvial material is deposited or cemented into a lithological unit, or lithified, it is called an alluvial deposit. The term alluvium is not typically used in situations where the formation of the sediment can clearly be attributed to another process that is well described. This includes, lake sediments, river sediments, or glacially-derived sediments, sediments that are formed or deposited in a perennial stream or river are typically not referred to as alluvial. Most alluvium is very young, and is often referred to as cover because these sediments obscure the underlying bedrock. Most sedimentary material that fills a basin that is not lithified is typically lumped together as alluvial, alluvium of Pliocene age occurs, for example, in parts of Idaho. Alluvium of late Miocene age occurs, for example, in the valley of the San Joaquin River, alluvium can contain valuable ores such as gold and platinum and a wide variety of gemstones. Such a concentration of ores is termed a placer deposit
13.
Fertile soil
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In lands used for agriculture and other human activities, maintenance of soil fertility typically requires the use of soil conservation practices. This is because soil erosion and other forms of soil degradation generally result in a decline in quality with respect to one or more of the aspects indicated above, bioavailable phosphorus is the element in soil that is most often lacking. Nitrogen and potassium are also needed in substantial amounts, for this reason these three elements are always identified on a commercial fertilizer analysis. For example, a 10-10-15 fertilizer has 10 percent nitrogen,10 percent available phosphorus and 15 percent water-soluble potassium, sulfur is the fourth element that may be identified in a commercial analysis—e. g. 21-0-0-24 which would contain 21% nitrogen and 24% sulfate, inorganic fertilizers are generally less expensive and have higher concentrations of nutrients than organic fertilizers. However, some have criticized the use of fertilizers, claiming that the water-soluble nitrogen doesnt provide for the long-term needs of the plant. Slow-release fertilizers may reduce leaching loss of nutrients and may make the nutrients that they provide available over a period of time. Soil fertility is a process that involves the constant cycling of nutrients between organic and inorganic forms. As plant material and animal wastes are decomposed by micro-organisms, they release inorganic nutrients to the soil solution and those nutrients may then undergo further transformations which may be aided or enabled by soil micro-organisms. The balance between immobilization and mineralization processes depends on the balance and availability of nutrients and organic carbon to soil microorganisms. Natural processes such as lightning strikes may fix atmospheric nitrogen by converting it to, denitrification may occur under anaerobic conditions in the presence of denitrifying bacteria. Nutrient cations, including potassium and many micronutrients, are held in strong bonds with the negatively charged portions of the soil in a process known as cation exchange. In 2008 the cost of phosphorus as fertilizer more than doubled, recently the term peak phosphorus has been coined, due to the limited occurrence of rock phosphate in the world. Photosynthesis is the process whereby plants use light energy to chemical reactions which convert CO2 into sugars. As such, all plants require access to light and carbon dioxide to produce energy, grow and reproduce. While typically limited by nitrogen, phosphorus and potassium, low levels of carbon dioxide can act as a limiting factor on plant growth. Peer-reviewed and published studies have shown that increasing CO2 is highly effective at promoting plant growth up to levels over 300 ppm. Further increases in CO2 can, to a small degree
14.
Abrasion (geology)
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Abrasion is the mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, waves, gravity, running water or erosion. After friction, the moving particles dislodge loose and weak debris from the side of the rock, the intensity of abrasion depends on the hardness, concentration, velocity and mass of the moving particles. Coastal abrasion occurs as breaking waves which contain sand and larger fragments erode the shoreline or headland and this removes material resulting in undercutting and possible collapse of unsupported overhanging cliffs. Abrasion platforms are shore platforms where wave action abrasion is a prominent process, if it is currently being fashioned, it will be exposed only at low tide, but there is a possibility that the wave-cut platform will be hidden sporadically by a mantle of beach shingle. If the platform is exposed above the high-water mark, it is probably a raised beach platform. Erosion Glacial striation Sedimentary Marine terrace
15.
Exfoliation joint
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Exfoliation joints or sheet joints are surface-parallel fracture systems in rock often leading to erosion of concentric slabs. Divide the rock into sub-planar slabs, joint spacing increases with depth from a few centimeters near the surface to a few meters Maximum depth of observed occurrence is around 100 meters. Host rock is generally sparsely jointed, fairly isotropic, and has high compressive strength, can have concave and convex upwards curvatures. Many different theories have suggested, below is a short overview of the most common. This theory was proposed by the pioneering geomorphologist Grove Karl Gilbert in 1904 and is widely found in introductory geology texts. The description of this mechanism has led to terms for exfoliation joints. Laboratory studies show that simple compression and relaxation of rock samples under realistic conditions does not cause fracturing, Exfoliation joints are most commonly found in regions of surface-parallel compressive stress, whereas this theory calls for them to occur in zones of extension. Horizontal stresses become aligned with the current ground surface as the stress drops to zero at this boundary. Thus large surface-parallel compressive stresses can be generated through exhumation that may lead to tensile rock fracture as described below, rock expands upon heating and contracts upon cooling and different rock-forming minerals have variable rates of thermal expansion / contraction. Daily rock surface temperature variations can be large, and many have suggested that stresses created during heating cause the near-surface zone of rock to expand. Large diurnal or fire-induced temperature fluctuations have been observed to create thin lamination and flaking at the surface of rocks, sometimes labeled exfoliation. However, since diurnal temperature fluctuations only reach a few centimeters depth in rock, mineral weathering by penetrating water can cause flaking of thin shells of rock since the volume of some minerals increases upon hydration. This type of fracturing has been observed in the laboratory since at least 1900, fractures formed in this way are sometimes called axial cleavage, longitudinal splitting, or extensional fractures, and are commonly observed in the laboratory during uniaxial compression tests. High horizontal or surface-parallel compressive stress can result from regional tectonic or topographic stresses, recognizing the presence of exfoliation joints can have important implications in geological engineering. Most notable may be their influence on slope stability, Exfoliation joints following the topography of inclined valley walls, bedrock hill slopes, and cliffs can create rock blocks that are particularly prone to sliding. Especially when the toe of the slope is undercut, sliding along exfoliation joint planes is likely if the joint dip exceeds the joint’s frictional angle, foundation work may also be affected by the presence of exfoliation joints, for example in the case of dams. Exfoliation joints underlying a dam foundation can create a significant leakage hazard, finally, exfoliation joints can exert strong directional control on groundwater flow and contaminant transport. Exfoliating granite Media related to Exfoliation joints at Wikimedia Commons
16.
Thermal shock
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Thermal shock occurs when a thermal gradient causes different parts of an object to expand by different amounts. This differential expansion can be understood in terms of stress or of strain, at some point, this stress can exceed the strength of the material, causing a crack to form. If nothing stops this crack from propagating through the material, it cause the objects structure to fail. To measure thermal shock the impulse excitation technique proved to be a useful tool and it can be used to measure Youngs modulus, Shear modulus, Poissons ratio and damping coefficient in a non destructive way. The same test-piece can be measured after different thermal shock cycles, the laser gain medium generates heat. This heat is drained through the heat sink, the transfer of heat occurs at a certain temperature gradient. The non-uniform thermal expansion of a bulk material causes the stress and tension and this phenomenon is also called thermal shock. The robustness of a material to the thermal shock is characterized by the thermal shock parameter. This estimate assumes the unilateral heat drain, as it takes place in the active mirrors, for the double-side sink, the coefficient 4 should be applied. The estimate above is not the only parameter which determines the limit of overheating of a gain medium, the maximal raise Δ T of temperature, at which the medium still can efficiently lase, is also important property of the laser material. The thermal loading, saturation intensity Q and the loss β determine the limit of power scaling of the disk lasers, roughly, the maximal power at the optimised sizes L and h, is of order of P = R2 Q β3. This estimate is very sensitive to the loss β, however, the same expression can be interpreted as a robust estimate of the upper bound of the loss β required for the desirable output power P, β m a x =13. All the disk lasers reported work at the round-trip loss below this estimate, the thermal shock parameter and the loading depend of the temperature of the heat sink. Certain hopes are related with a laser, operating at cryogenic temperatures, the corresponding Increase of the thermal shock parameter would allow to softer requirements for the round-trip loss of the disk laser at the power scaling. Thermal shock testing exposes products to alternating low and high temperatures to accelerate failures caused by cycles or thermal shocks during normal use. The transition between temperature extremes occurs very rapidly, greater than 15 °C per minute, equipment with single or multiple chambers is typically used to perform thermal shock testing. When using single chamber thermal shock equipment, the remain in one chamber. Some equipment uses separate hot and cold chambers with a mechanism that transports the products between two or more chambers
17.
Thermal fatigue
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In materials science, fatigue is the weakening of a material caused by repeatedly applied loads. It is the progressive and localized damage that occurs when a material is subjected to cyclic loading. The nominal maximum stress values that cause such damage may be less than the strength of the material typically quoted as the ultimate tensile stress limit. Fatigue occurs when a material is subjected to repeated loading and unloading, if the loads are above a certain threshold, microscopic cracks will begin to form at the stress concentrators such as the surface, persistent slip bands, and grain interfaces. Eventually a crack will reach a size, the crack will propagate suddenly. The shape of the structure will affect the fatigue life. Round holes and smooth transitions or fillets will therefore increase the strength of the structure. ASTM defines fatigue life, Nf, as the number of cycles of a specified character that a specimen sustains before failure of a specified nature occurs. Engineers have used any of three methods to determine the life of a material, the stress-life method, the strain-life method. One method to predict fatigue life of materials is the Uniform Material Law, UML was developed for fatigue life prediction of aluminium and titanium alloys by the end of 20th century and extended to high-strength steels, and cast iron. Macroscopic and microscopic discontinuities as well as component design features which cause stress concentrations are common locations at which the process begins. Fatigue is a process that has a degree of randomness, often showing considerable scatter even in seemingly identical sample in well controlled environments, Fatigue is usually associated with tensile stresses but fatigue cracks have been reported due to compressive loads. The greater the applied stress range, the shorter the life, Fatigue life scatter tends to increase for longer fatigue lives. Materials do not recover when rested, some materials exhibit a theoretical fatigue limit below which continued loading does not lead to fatigue failure. High cycle fatigue strength can be described by stress-based parameters, a load-controlled servo-hydraulic test rig is commonly used in these tests, with frequencies of around 20–50 Hz. Other sorts of machines—like resonant magnetic machines—can also be used, to achieve frequencies up to 250 Hz, low cycle fatigue is associated with localized plastic behavior in metals, thus, a strain-based parameter should be used for fatigue life prediction in metals. Testing is conducted with constant strain amplitudes typically at 0. 01–5 Hz,1837, Wilhelm Albert publishes the first article on fatigue. He devised a test machine for conveyor chains used in the Clausthal mines,1839, Jean-Victor Poncelet describes metals as being tired in his lectures at the military school at Metz
18.
Stress (physics)
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For example, when a solid vertical bar is supporting a weight, each particle in the bar pushes on the particles immediately below it. When a liquid is in a container under pressure, each particle gets pushed against by all the surrounding particles. The container walls and the pressure-inducing surface push against them in reaction and these macroscopic forces are actually the net result of a very large number of intermolecular forces and collisions between the particles in those molecules. Strain inside a material may arise by various mechanisms, such as stress as applied by external forces to the material or to its surface. Any strain of a material generates an internal elastic stress, analogous to the reaction force of a spring. In liquids and gases, only deformations that change the volume generate persistent elastic stress, however, if the deformation is gradually changing with time, even in fluids there will usually be some viscous stress, opposing that change. Elastic and viscous stresses are usually combined under the mechanical stress. Significant stress may exist even when deformation is negligible or non-existent, stress may exist in the absence of external forces, such built-in stress is important, for example, in prestressed concrete and tempered glass. Stress may also be imposed on a material without the application of net forces, for example by changes in temperature or chemical composition, stress that exceeds certain strength limits of the material will result in permanent deformation or even change its crystal structure and chemical composition. In some branches of engineering, the stress is occasionally used in a looser sense as a synonym of internal force. For example, in the analysis of trusses, it may refer to the total traction or compression force acting on a beam, since ancient times humans have been consciously aware of stress inside materials. Until the 17th century the understanding of stress was largely intuitive and empirical, with those tools, Augustin-Louis Cauchy was able to give the first rigorous and general mathematical model for stress in a homogeneous medium. Cauchy observed that the force across a surface was a linear function of its normal vector, and, moreover. The understanding of stress in liquids started with Newton, who provided a formula for friction forces in parallel laminar flow. Stress is defined as the force across a small boundary per unit area of that boundary, following the basic premises of continuum mechanics, stress is a macroscopic concept. In a fluid at rest the force is perpendicular to the surface, in a solid, or in a flow of viscous liquid, the force F may not be perpendicular to S, hence the stress across a surface must be regarded a vector quantity, not a scalar. Moreover, the direction and magnitude depend on the orientation of S. Thus the stress state of the material must be described by a tensor, called the stress tensor, with respect to any chosen coordinate system, the Cauchy stress tensor can be represented as a symmetric matrix of 3×3 real numbers
19.
Thermal expansion
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Thermal expansion is the tendency of matter to change in shape, area, and volume in response to a change in temperature. Temperature is a function of the average molecular kinetic energy of a substance. When a substance is heated, the energy of its molecules increases. Thus, the molecules begin vibrating/moving more and usually maintain an average separation. Materials which contract with increasing temperature are unusual, this effect is limited in size, the degree of expansion divided by the change in temperature is called the materials coefficient of thermal expansion and generally varies with temperature. If an equation of state is available, it can be used to predict the values of the expansion at all the required temperatures and pressures. A number of contract on heating within certain temperature ranges. For example, the coefficient of expansion of water drops to zero as it is cooled to 3. Also, fairly pure silicon has a coefficient of thermal expansion for temperatures between about 18 and 120 Kelvin. Unlike gases or liquids, solid materials tend to keep their shape when undergoing thermal expansion, in general, liquids expand slightly more than solids. The thermal expansion of glasses is higher compared to that of crystals, at the glass transition temperature, rearrangements that occur in an amorphous material lead to characteristic discontinuities of coefficient of thermal expansion and specific heat. These discontinuities allow detection of the transition temperature where a supercooled liquid transforms to a glass. Absorption or desorption of water can change the size of common materials. Common plastics exposed to water can, in the long term, the coefficient of thermal expansion describes how the size of an object changes with a change in temperature. Specifically, it measures the change in size per degree change in temperature at a constant pressure. Several types of coefficients have been developed, volumetric, area, which is used depends on the particular application and which dimensions are considered important. For solids, one might only be concerned with the change along a length, the volumetric thermal expansion coefficient is the most basic thermal expansion coefficient, and the most relevant for fluids. In general, substances expand or contract when their temperature changes, substances that expand at the same rate in every direction are called isotropic
20.
Forest fires
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A wildfire or wildland fire is a fire in an area of combustible vegetation that occurs in the countryside or rural area. Fossil charcoal indicates that wildfires began soon after the appearance of terrestrial plants 420 million years ago, wildfire’s occurrence throughout the history of terrestrial life invites conjecture that fire must have had pronounced evolutionary effects on most ecosystems flora and fauna. Earth is an intrinsically flammable planet owing to its cover of vegetation, seasonally dry climates, atmospheric oxygen. Wildfires can be characterized in terms of the cause of ignition, their properties, the combustible material present. Wildfires can cause damage to property and human life, but they have beneficial effects on native vegetation, animals. Many plant species depend on the effects of fire for growth, however, wildfire in ecosystems where wildfire is uncommon or where non-native vegetation has encroached may have negative ecological effects. Wildfire behaviour and severity result from the combination of such as available fuels, physical setting. Strategies of wildfire prevention, detection, and suppression have varied over the years, one common and inexpensive technique is controlled burning, permitting or even igniting smaller fires to minimize the amount of flammable material available for a potential wildfire. Vegetation may be burned periodically to maintain species diversity and frequent burning of surface fuels limits fuel accumulation. Wildland fire use is the cheapest and most ecologically appropriate policy for many forests, fuels may also be removed by logging, but fuels treatments and thinning have no effect on severe fire behavior. Wildfires can also be started in communities experiencing shifting cultivation, where land is cleared quickly and farmed until the soil loses fertility, forested areas cleared by logging encourage the dominance of flammable grasses, and abandoned logging roads overgrown by vegetation may act as fire corridors. The most common cause of wildfires throughout the world. In Canada and northwest China, for example, lightning operates as the source of ignition. In other parts of the world, human involvement is a major contributor, in China and in the Mediterranean Basin, human carelessness is a major cause of wildfires. In the United States and Australia, the source of wildfires can be traced both to lightning strikes and to human activities. Coal seam fires burn in the thousands around the world, such as those in Burning Mountain, New South Wales, Centralia, Pennsylvania and they can also flare up unexpectedly and ignite nearby flammable material. The spread of wildfires based on the flammable material present, its vertical arrangement and moisture content. Fuel arrangement and density is governed in part by topography, as land shape determines factors such as available sunlight, overall, fire types can be generally characterized by their fuels as follows, Ground fires are fed by subterranean roots, duff and other buried organic matter
21.
Rocks
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Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a rock, is a combination of the minerals quartz, feldspar. The Earths outer solid layer, the lithosphere, is made of rock, rock has been used by mankind throughout history. The minerals and metals found in rocks have been essential to human civilization, three major groups of rocks are defined, igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is a component of geology. At a granular level, rocks are composed of grains of minerals, the aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed, many rocks contain silica, a compound of silicon and oxygen that forms 74. 3% of the Earths crust. This material forms crystals with other compounds in the rock, the proportion of silica in rocks and minerals is a major factor in determining their name and properties. Rocks are geologically classified according to such as mineral and chemical composition, permeability, the texture of the constituent particles. These physical properties are the end result of the processes that formed the rocks, over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock, igneous, sedimentary, and metamorphic, the three classes of rocks are subdivided into many groups. However, there are no hard and fast boundaries between allied rocks, hence the definitions adopted in establishing rock nomenclature merely correspond to more or less arbitrary selected points in a continuously graduated series. Igneous rock forms through the cooling and solidification of magma or lava and this magma can be derived from partial melts of pre-existing rocks in either a planets mantle or crust. Typically, the melting of rocks is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, igneous rocks are divided into two main categories, plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earths crust, a common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, the chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowens reaction series. Most major igneous rocks are found along this scale, about 64. 7% of the Earths crust by volume consists of igneous rocks, making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, only 0. 6% are syenites and 0. 3% peridotites and dunites
22.
Abisko
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Abisko is a village in Sápmi, in northern Sweden, roughly 250 km within the Arctic Circle, and near Abisko National Park, located 4 km west of the village. It had 85 inhabitants as of 2005, daily passenger electric trains run by SJ AB connect Stockholm with the Norwegian city of Narvik, stopping at both the Abisko village and the Abisko Turiststation. Additional regional trains provide links along the Kiruna-Narvik stretch, Abisko is also reachable by car via the highway E10 which has linked Kiruna and Narvik since the early 1980s. Other local forms of transportation include hiking and dog-sledding in winter, a chair-lift provides access to a point below the summit of nearby Mt. Nuolja. The 425 kilometer-long Kungsleden hiking trail, which follows the Scandinavian mountain range, starts at the Abisko Turiststation, the Nordkalottruta uses trails of the park as part of its longer passage. The national park is known for its Cross-country skiing opportunities, snowshoeing, as its location is 195 km north of the Arctic Circle, summer hikers enjoy the midnight sun, while winter visitors may find the light pollution-free location ideal for viewing the aurora borealis. One of the most recognized natural sights is Lapporten, a U-shaped valley visible from Abisko, Abisko is also located near the 330 square kilometre lake Torneträsk. Abisko is home to the Abisko Scientific Research Station, an important centre for research into Arctic ecology, Abisko travel guide from Wikivoyage Abisko Fjällturer, a tourist business at Abisko
23.
Joint (geology)
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A joint is a break of natural origin in the continuity of either a layer or body of rock that lacks any visible or measurable movement parallel to the surface of the fracture. Although they can occur singly, they most frequently occur as joint sets, a joint set is a family of parallel, evenly spaced joints that can be identified through mapping and analysis of the orientations, spacing, and physical properties. A joint system consists of two or more intersecting joint sets, the distinction between joints and faults hinges on the terms visible or measurable which depends on the scale of observation. Faults differ from joints in that they exhibit visible or measurable lateral movement between the surfaces of the fracture. Joints are among the most universal geologic structures as they are found in most every exposure of rock and they vary greatly in appearance, dimensions, and arrangement, and occur in quite different tectonic environments. Often, the origin of the stresses that created certain joints and associated joint sets can be quite ambiguous, unclear. The most prominent joints occur in the most well-consolidated, lithified, and highly competent rocks, such as sandstone, limestone, quartzite, Joints may be open fractures or filled by various materials. Joints, which are infilled by precipitated minerals are called veins, Joints result from brittle fracture of a rock body or layer as the result of tensile stresses. These tensile stresses either were induced or imposed from outside, e. g, when tensional stresses stretch a body or layer of rock such that its tensile strength is exceeded, it breaks. When this happens the rock fractures in a parallel to the maximum principal stress. This leads to the development of a single sub-parallel joint set, continued deformation may lead to development of one or more additional joint sets. The presence of the first set strongly affects the orientation in the rock layer, often causing subsequent sets to form at a high angle, often 90°. Joints are classified either by the responsible for their formation or their geometry. The geometry of joints refers to the orientation of joints as either plotted on stereonets, in terms of geometry, three major types of joints, nonsystematic joints, systematic joints, and columnar jointing are recognized. Nonsystematic joints are joints that are so irregular in form, spacing, as a result, they occur as families of joints that form recognizable joint sets. Based upon the angle at which joint sets of systematic joints intersect to form a joint system, systematic joints can be subdivided into conjugate, the angles at which joint sets within a joint system commonly intersect is called by structural geologists as the dihedral angles. When the dihedral angles are nearly 90° within a joint system, when the dihedral angles are from 30 to 60° within a joint system, the joint sets are known as conjugate joint sets. Within regions that have experienced tectonic deformation, systematic joints are typically associated with either layered or bedded strata that has folded into anticlines and synclines
24.
Frost weathering
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Frost weathering is a collective term for several mechanical weathering processes induced by stresses created by the freezing of water into ice. The term serves as a term for a variety of processes such as frost shattering. The process may act on a range of spatial and temporal scales, from minutes to years. Frost weathering is mainly driven by the frequency and intensity of freeze-thaw cycles, certain frost-susceptible soils expand or heave upon freezing as a result of water migrating via capillary action to grow ice lenses near the freezing front. This same phenomenon occurs within pore spaces of rocks, the ice accumulations grow larger as they attract liquid water from the surrounding pores. The ice crystal growth weakens the rocks which, in time and it is caused by the expansion of ice when water freezes, putting considerable stress on the walls of containment. This is actually a common process in all humid, temperate areas where there is exposed rock. Sand can often be found just under the faces of exposed sandstone where individual grains have been popped off and this process is often termed frost spalling. In fact, this is often the most important weathering process for exposed rock in many areas, the traditional explanation for frost weathering was volumetric expansion of freezing water. When water freezes to ice, its volume increases by nine percent, under specific circumstances, this expansion is able to displace or fracture rock. At a temperature of -22 °C, ice growth is known to be able to generate pressures of up to 207MPa, not all volumetric expansion is caused by the pressure of the freezing water, it can be caused by stresses in water that remains unfrozen. When ice growth induces stresses in the water that breaks the rock. Hydrofracturing is favoured by large interconnected pores or large hydraulic gradients in the rock. If there are small pores, a very quick freezing of water in parts of the rock may expel water, since research in physical weathering begun around 1900, volumetric expansion was, until the 1980s, held to be the predominant process behind frost weathering. This view was challenged in 1985 and 1986 publications by Walder, nowadays researchers such as Matsuoka and Murton consider the conditions necessary for frost weathering by volumetric expansion as unusual. Hydrostatic pressure that may also erode in combination with ice blocking outflow routes in mountain regions, pore water pressure Weathering Water Ice Frost heaving Bratschen Solifluction
25.
Scree
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Scree is a collection of broken rock fragments at the base of crags, mountain cliffs, volcanoes or valley shoulders that has accumulated through periodic rockfall from adjacent cliff faces. Landforms associated with these materials are called talus deposits. Talus deposits typically have a concave form, while the maximum inclination corresponds to the angle of repose of the mean debris size. The term scree comes from the Old Norse term for landslide, skriða, formation of scree or talus deposits the results of physical and chemical weathering and erosion acting on a rock face. During the day, water can flow into joints and discontinuities in the rock wall, if the temperature drops enough, for example in the evening, this water may freeze. Since water expands by 9% when it freezes, it can generate forces that either create new cracks or wedge blocks into an unstable position. Special boundary conditions may be required for this to happen, the efficiency of freeze/thaw processes in scree production is debated by scientists. Many researchers believe that ice formation in large open crack systems cannot generate high pressures, many argue that frost heaving, like that known to act in soil in permafrost areas, may play an important role in cliff degradation in cold places. For example, Lech dl Dragon, in the Sella Group of the Dolomites, derives from the waters of a glacier. The melting process of the glacier is slowed by the protective layer of scree. Eventually a rock slope may be covered by its own scree. The slope is then said to be mantled with debris, fellfield Lava stringer Mass wasting Weathering
26.
Frost heaving
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Ice growth requires a water supply that delivers water to the freezing front via capillary action in certain soils. The weight of overlying soil restrains vertical growth of the ice, yet the force of one or more growing ice lenses is sufficient to lift a layer of soil, as much as 1 foot or more. The soil through which passes to feed the formation of ice lenses must be sufficiently porous to allow capillary action. Such soil is referred to as frost susceptible, the growth of ice lenses continually consumes the rising water at the freezing front. Differential frost heaving can crack road surfaces—contributing to springtime pothole formation—and damage building foundations, according to Beskow, Urban Hjärne described frost effects in soil in 1694. e. With little contribution from migration of water within the soil, Ice is unusual among compounds because it increases in molar volume from its liquid state, water. Most compounds decrease in volume when changing phase from liquid to solid, taber showed that the vertical displacement of soil in frost heaving can be significantly greater than that due to molar volume expansion. Taber demonstrated that liquid water migrates towards the line within soil. He showed that other liquids, such as benzene, which contracts when it freezes and this excluded molar volume changes as the dominant mechanism for vertical displacement of freezing soil. His experiments further demonstrated the development of ice lenses inside columns of soil that were frozen by cooling the surface only. The dominant cause of displacement in frost heaving is the development of ice lenses. During frost heave, one or more soil-free ice lenses grow and these lenses grow by the continual addition of water from a groundwater source that is lower in the soil and below the freezing line in the soil. The presence of soil with a pore structure that allows capillary flow is essential to supplying water to the ice lenses as they form. Owing to the Gibbs–Thomson effect of the confinement of liquids in pores and this effect allows water to percolate through the soil towards the ice lens, allowing the lens to grow. Another water-transport effect is the preservation of a few layers of liquid water on the surface of the ice lens. Faraday reported in 1860 on the layer of premelted water. Ice premelts against its own vapor, and in contact with silica, the same intermolecular forces that cause premelting at surfaces contribute to frost heaving at the particle scale on the bottom side of the forming ice lens. The thickness of such a film is temperature dependent and is thinner on the side of the particle
27.
Capillary action
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Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. It occurs because of forces between the liquid and surrounding solid surfaces. If the diameter of the tube is sufficiently small, then the combination of surface tension, the first recorded observation of capillary action was by Leonardo da Vinci. A former student of Galileo, Niccolò Aggiunti, was said to have investigated capillary action, boyle then reported an experiment in which he dipped a capillary tube into red wine and then subjected the tube to a partial vacuum. Some thought that liquids rose in capillaries because air couldnt enter capillaries as easily as liquids, others thought that the particles of liquid were attracted to each other and to the walls of the capillary. They derived the Young–Laplace equation of capillary action, by 1830, the German mathematician Carl Friedrich Gauss had determined the boundary conditions governing capillary action. In 1871, the British physicist William Thomson determined the effect of the meniscus on a liquids vapor pressure—a relation known as the Kelvin equation, German physicist Franz Ernst Neumann subsequently determined the interaction between two immiscible liquids. Albert Einsteins first paper, which was submitted to Annalen der Physik in 1900, was on capillarity, a common apparatus used to demonstrate the first phenomenon is the capillary tube. When the lower end of a glass tube is placed in a liquid, such as water. Adhesion occurs between the fluid and the inner wall pulling the liquid column up until there is a sufficient mass of liquid for gravitational forces to overcome these intermolecular forces. So, a tube will draw a liquid column higher than a wider tube will. Capillary action is essential for the drainage of constantly produced tear fluid from the eye, wicking is the absorption of a liquid by a material in the manner of a candle wick. Paper towels absorb liquid through capillary action, allowing a fluid to be transferred from a surface to the towel, the small pores of a sponge act as small capillaries, causing it to absorb a large amount of fluid. Some textile fabrics are said to use capillary action to wick sweat away from the skin and these are often referred to as wicking fabrics, after the capillary properties of candle and lamp wicks. Capillary action is observed in thin layer chromatography, in which a solvent moves vertically up a plate via capillary action, in this case the pores are gaps between very small particles. Capillary action draws ink to the tips of fountain pen nibs from a reservoir or cartridge inside the pen, in hydrology, capillary action describes the attraction of water molecules to soil particles. Capillary action is responsible for moving groundwater from wet areas of the soil to dry areas, differences in soil potential drive capillary action in soil. Thus the thinner the space in which the water can travel, for a water-filled glass tube in air at standard laboratory conditions, γ =0.0728 N/m at 20 °C, ρ =1000 kg/m3, and g =9.81 m/s2
28.
Ice lens
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An ice lens or ice lenses are formed when moisture, diffused within soil or rock, accumulates in a localized zone. Ice lenses grow parallel to the surface and several centimeters to several decimeters deep in the soil or rock, studies between 1990 and present have demonstrated that rock fracture by ice segregation is a more effective weathering process than the freeze-thaw process which older texts proposed. Ice lenses play the key role in frost induced heaving of soils and fracture of bedrock, frost heaving creates debris and dramatically shapes landscapes into complex patterns. Rock fracture in periglacial regions has often attributed to the freezing and volumetric expansion of water trapped within pores. However the majority of frost heaving and of bedrock fracture results instead from ice segregation in ice lenses in the frozen regions. Ice segregation results in rock fracture and frost heave, frost heave is the process by which the freezing of water-saturated soil causes the deformation and upward thrust of the ground surface. This process can distort and crack pavement, damage the foundations of buildings, moist, fine-grained soil at certain temperatures is most susceptible to frost heaving. Frost heave is common in arctic tundra because the permafrost maintains ground frozen at depth and prevents snowmelt, as a result, conditions are optimal for deep ice lens formation with large ice accumulations and significant soil displacement. Differential frost heave producing complex patterns will occur if the correct conditions exist, feedback from one years frost heave influences the effects in subsequent years. For example, a increase in overburden will affect the depth of ice formation. Time-dependent models of the frost heave indicate that over a long period the short-separation perturbations damp out, while mid-range perturbations grow. Bands of sediment or glacial till have been observed below Antarctic ice sheets, in the faster flowing glacial regions, the ice sheet is sliding over water saturated sediments or actually being floated upon a layer of water. The till and water served to reduce friction between the base of the ice sheet and the bedrock and these subglacial waters come from surface water which seasonally drains from melting at the surface, as well as from ice-sheet base melting. Ice lens growth within the bedrock below the glacier is projected during the months when there is ample water at the base of the glacier. Ice lenses will form within the bedrock, accumulating until the rock is sufficiently weakened that it shears or spalls off, layers of rock along the interface between glaciers and the bedrock are freed, producing much of the sediments in these basal regions of glaciers. Since the rate of movement is dependent upon the characteristics of this basal ice. The term premelting is used to describe the reduction in the temperature which results from the surface curvature of water thats confined in a porous medium. Premelted water exists as a layer on the surface of ice
29.
Ice
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Ice is water frozen into a solid state. Depending on the presence of such as particles of soil or bubbles of air. In the Solar System, ice is abundant and occurs naturally from as close to the Sun as Mercury to as far away as the Oort cloud objects, beyond the Solar System, it occurs as interstellar ice. It falls as snowflakes and hail or occurs as frost, icicles or ice spikes, Ice molecules can exhibit up to sixteen different phases that depend on temperature and pressure. When water is cooled rapidly, up to three different types of ice can form depending on the history of its pressure and temperature. When cooled slowly correlated proton tunneling occurs below 20 K giving rise to macroscopic quantum phenomena, virtually all the ice on Earths surface and in its atmosphere is of a hexagonal crystalline structure denoted as ice Ih with minute traces of cubic ice denoted as ice Ic. The most common phase transition to ice Ih occurs when water is cooled below 0°C at standard atmospheric pressure. It may also be deposited directly by water vapor, as happens in the formation of frost, the transition from ice to water is melting and from ice directly to water vapor is sublimation. Ice is used in a variety of ways, including cooling, winter sports, as a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered a mineral. It possesses a regular crystalline structure based on the molecule of water, an unusual property of ice frozen at atmospheric pressure is that the solid is approximately 8. 3% less dense than liquid water. The density of ice is 0.9167 g/cm3 at 0 °C, liquid water is densest, essentially 1.00 g/cm³, at 4 °C and becomes less dense as the water molecules begin to form the hexagonal crystals of ice as the freezing point is reached. This is due to hydrogen bonding dominating the intermolecular forces, which results in a packing of molecules less compact in the solid, density of ice increases slightly with decreasing temperature and has a value of 0.9340 g/cm³ at −180 °C. When water freezes, it increases in volume and it is also a common cause of the flooding of houses when water pipes burst due to the pressure of expanding water when it freezes. The result of this process is that ice floats on liquid water, sufficiently thin ice sheets allow light to pass through while protecting the underside from short-term weather extremes such as wind chill. This creates an environment for bacterial and algal colonies. When ice melts, it absorbs as much energy as it would take to heat an equivalent mass of water by 80 °C, during the melting process, the temperature remains constant at 0 °C. While melting, any energy added breaks the bonds between ice molecules. Energy becomes available to increase the thermal energy only after enough hydrogen bonds are broken that the ice can be considered liquid water, the amount of energy consumed in breaking hydrogen bonds in the transition from ice to water is known as the heat of fusion
30.
Water
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Water is a transparent and nearly colorless chemical substance that is the main constituent of Earths streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen, Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure, but it often refers also to its solid state or its gaseous state. It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, Water covers 71% of the Earths surface. It is vital for all forms of life. Only 2. 5% of this water is freshwater, and 98. 8% of that water is in ice and groundwater. Less than 0. 3% of all freshwater is in rivers, lakes, and the atmosphere, a greater quantity of water is found in the earths interior. Water on Earth moves continually through the cycle of evaporation and transpiration, condensation, precipitation. Evaporation and transpiration contribute to the precipitation over land, large amounts of water are also chemically combined or adsorbed in hydrated minerals. Safe drinking water is essential to humans and other even though it provides no calories or organic nutrients. There is a correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in developing regions of the world. Water plays an important role in the world economy, approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers, lakes, large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a variety of chemical substances, as such it is widely used in industrial processes. Water is also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, Water is a liquid at the temperatures and pressures that are most adequate for life. Specifically, at atmospheric pressure of 1 bar, water is a liquid between the temperatures of 273.15 K and 373.15 K
31.
Alpine climate
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Alpine climate is the average weather for the regions above the tree line. This climate is referred to as a mountain climate or highland climate. There are multiple definitions of alpine climate, one simple definition is the climate which causes trees to fail to grow due to cold. According to the Holdridge life zone system, alpine climate occurs when the mean biotemperature of a location is between 1.5 and 3 °C, which prevents tree growth. Biotemperature is defined as the temperature, except all temperatures below 0 °C are treated as 0 °C, in the Köppen climate classification, the alpine climate is part of Group E, along with the polar climate, where no month has a mean temperature higher than 10 °C. The temperature profile of the atmosphere is a result of an interaction between radiation and convection, sunlight in the visible spectrum hits the ground and heats it. The ground then heats the air at the surface, however, when air is hot, it tends to expand, which lowers its density. Thus, hot air tends to rise and transfer heat upward and this is the process of convection. Convection comes to equilibrium when a parcel at air at a given altitude has the density as its surroundings. Air is a conductor of heat, so a parcel of air will rise. This is known as a process, which has a characteristic pressure-temperature curve. As the pressure gets lower, the temperature decreases, the rate of decrease of temperature with elevation is known as the adiabatic lapse rate, which is approximately 9.8 °C per kilometre of altitude. Note that the presence of water in the atmosphere complicates the process of convection, water vapor contains latent heat of vaporization. As air rises and cools, it becomes saturated and cannot hold its quantity of water vapor. The water vapor condenses, and releases heat, which changes the rate from the dry adiabatic lapse rate to the moist adiabatic lapse rate. The actual lapse rate, called the lapse rate, is not constant. Therefore, moving up 100 metres on a mountain is roughly equivalent to moving 80 kilometres towards the pole and this relationship is only approximate, however, since local factors, such as proximity to oceans, can drastically modify the climate. As the altitude increases, the form of precipitation becomes snow
32.
Periglacial
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Periglaciation describes geomorphic processes that result from seasonal thawing of snow in areas of permafrost, the runoff from which refreezes in ice wedges and other structures. Periglacial suggests an environment located on the margin of past glaciers, however, freeze and thaw cycles influence landscapes outside areas of past glaciation. Therefore, periglacial environments are anywhere that freezing and thawing modify the landscape in a significant manner, tundra is a common ecological community in periglacial areas. Periglaciation became a subject within the study of geology after Walery Łoziński. Łoziński drew upon the work of Johan Gunnar Andersson. According to Alfred Jahn, his introduction of his work at the 1910 International Geological Congress held in Stockholm caused significant discussion, in the field trip to Svalbard that followed the congress participants were able to observe the phenomena reported by Łoziński, directly. Łoziński published his contribution to the congress in 1912, from 1950 to 1970, periglacial geomorphology developed chiefly as a subdiscipline of climatic geomorphology that was current in Europe at the time. The journal Biuletyn Peryglacjalny, established in 1954 by Jan Dylik, was important for the consolidation of the discipline, albeit the definition of what a periglacial zone is not clear-cut a conservativa estimated is that a quarter of Earths land surface has periglacial conditions. Beyond this quarter an additional quarter or fifth or Earths land surface had periglacial conditions at some time during the Pleistocene, in the northern hemisphere larger swathes of northern Asia and northern North America are periglaciated. In Europe parts of Fennoscandia, Iceland, northern European Russia, in addition Alpine areas in the non-arctic northern hemisphere might also be subject to periglaciation. A major outlier in the northern hemisphere is the Tibetan Plateau that stands out by its size, in the southern hemisphere parts of the Andes, the ice-free areas of Antarctica and the sub-Antarctic islands are periglaciated. Since Carl Troll introduced the concept of climate in 1944 there have various attempts to classify the diversity of periglacial climates. Hugh M. Periglacial environments tend to be found in higher latitudes, since there is more land at these latitudes in the north, most of this effect is seen in the northern hemisphere. However, in latitudes, the direct effect of the suns radiation is greater so the freeze-thaw effect is seen. Altitude – Air temperature drops by approximately 1 °C for every 100 m rise above sea level and this means that on mountain ranges, modern periglacial conditions are found nearer the Equator than they are lower down. Conversely, warm currents from tropical seas increases mean temperatures. The cold conditions are found only in more northerly places. This is apparent in western North America which is affected by the North Pacific current, in the same way but more markedly, the Gulf Stream affects Western Europe
33.
Chalk
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Chalk is a soft, white, porous, sedimentary carbonate rock, a form of limestone composed of the mineral calcite. Calcite is a salt called calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the accumulation of minute calcite shells shed from micro-organisms called coccolithophores. Flint is very common as bands parallel to the bedding or as embedded in chalk. It is probably derived from sponge spicules or other organisms as water is expelled upwards during compaction. Flint is often deposited around larger fossils such as Echinoidea which may be silicified, Chalk as seen in Cretaceous deposits of Western Europe is unusual among sedimentary limestones in the thickness of the beds. Most cliffs of chalk have very few obvious bedding planes unlike most thick sequences of such as the Carboniferous Limestone or the Jurassic oolitic limestones. This presumably indicates very stable conditions over tens of millions of years, Chalk has greater resistance to weathering and slumping than the clays with which it is usually associated, thus forming tall steep cliffs where chalk ridges meet the sea. Chalk hills, known as chalk downland, usually form where bands of chalk reach the surface at an angle, because chalk is well jointed it can hold a large volume of ground water, providing a natural reservoir that releases water slowly through dry seasons. Chalk is mined from chalk deposits both above ground and underground, Chalk mining boomed during the Industrial Revolution, due to the need for chalk products such as quicklime and bricks. Abandoned chalk mines remain a popular tourist attraction due to their massive expanse, the Chalk Group is a European stratigraphic unit deposited during the late Cretaceous Period. It forms the famous White Cliffs of Dover in Kent, England, the Champagne region of France is mostly underlain by chalk deposits, which contain artificial caves used for wine storage. Some of the highest chalk cliffs in the occur at Jasmund National Park in Germany. Ninety million years ago what is now the chalk downland of Northern Europe was ooze accumulating at the bottom of a great sea. Chalk was one of the earliest rocks made up of particles to be studied under the electron microscope. Their shells were made of calcite extracted from the rich sea-water, as they died, a substantial layer gradually built up over millions of years and, through the weight of overlying sediments, eventually became consolidated into rock. Later earth movements related to the formation of the Alps raised these former sea-floor deposits above sea level, the chemical composition of chalk is calcium carbonate, with minor amounts of silt and clay. It is formed in the sea by plankton, which fall to the sea floor and are then consolidated and compressed during diagenesis into chalk rock
34.
Dartmoor
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Dartmoor is an area of moorland in southern Devon, England. Protected by National Park status as Dartmoor National Park, it covers 954 km2, the granite which forms the uplands dates from the Carboniferous Period of geological history. The moorland is capped with many exposed granite hilltops known as tors, the highest point is High Willhays,621 m above sea level. The entire area is rich in antiquities and archaeology, Dartmoor is managed by the Dartmoor National Park Authority, whose 22 members are drawn from Devon County Council, local district councils and Government. Parts of Dartmoor have been used as firing ranges for over 200 years. The public is granted land access rights on Dartmoor and it is a popular tourist destination. Dartmoor includes the largest area of granite in Britain, with about 625 km2 at the surface, the granite was intruded at depth as a pluton into the surrounding sedimentary rocks during the Carboniferous period, probably about 309 million years ago. A considerable gravity anomaly is associated with the Dartmoor pluton as with other such plutons, measurement of the anomaly has helped to determine the likely shape and extent of the rock mass at depth. Dartmoor is known for its tors – hills topped with outcrops of bedrock, more than 160 of the hills of Dartmoor have the word tor in their name but quite a number do not. However this does not appear to relate to whether or not there is an outcrop of rock on their summit, the best-known tor on Dartmoor is Haytor,457 m. For a more complete list see List of Dartmoor tors and hills, the high ground of Dartmoor forms the catchment area for many of Devons rivers. As well as shaping the landscape, these have provided a source of power for moor industries such as tin mining and quarrying. The moor takes its name from the River Dart, which starts as the East Dart and West Dart and it leaves the moor at Buckfastleigh, flowing through Totnes below where it opens up into a long ria, reaching the sea at Dartmouth. For a full list, expand the Rivers of Dartmoor navigational box at the bottom of this page, much more rain falls on Dartmoor than in the surrounding lowlands. As much of the park is covered in thick layers of peat. In areas where water accumulates, dangerous bogs or mires can result, some of these, topped with bright green moss, are known to locals as feather beds or quakers, because they can shift beneath a persons feet. Quakers result from sphagnum moss growing over the water accumulates in the hollows in the granite. The vegetation of the bogs depends on the type and location, the valley bogs have lush growth of rushes, with sphagnum, cross-leaved heath, sundews and several other species
35.
Tor (rock formation)
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In the South West of England, the term is commonly also used for the hills themselves – particularly the high points of Dartmoor in Devon and Bodmin Moor in Cornwall. Tors are landforms created by the erosion and weathering of rock, most commonly granites, tors are mostly less than 5 meters high. Many hypotheses have proposed to explain their origin and this remains a topic of discussion among geologists and geomorphologists. It is considered likely that tors were created by processes that differed widely in type and duration according to regional and local differences in climate. For example, the Dartmoor granite was emplaced around 280 million years ago, with the cover rocks eroded away soon afterwards, where joints are closely spaced, the large crystals in the granite readily disintegrate to form a sandy regolith known locally as growan. This is readily stripped off by solifluction or surface wash when not protected by vegetation, where joints happen to be unusually widely spaced, core blocks can survive and escape above the weathering surface, developing into tors. These can be monolithic, as at Haytor and Blackingstone Rock, each stack can comprise several tiers or pillows, which may become separated, rocking pillows are called logan stones. These stacks are vulnerable to frost action and often collapse leaving trails of blocks called clitter down the slopes, weathering has also given rise to circular rock basins formed by the accumulation of water and repeated freezing and thawing. An example is found at Kes Tor on Dartmoor, dating of 28 tors on Dartmoor showed that most are surprisingly young, less than 100,000 years old, with none over 200,000 years old. They probably emerged at the start of the last major ice age and this may reflect a dryer, more arctic climate. Bornhardt Etchplain Inselberg Nubbin List of tors Mercer, Ian, Dartmoor – A Statement of its Time
36.
Coastal geography
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Coastal geography is the study of the dynamic interface between the ocean and the land, incorporating both the physical geography and the human geography of the coast. It involves an understanding of coastal weathering processes, particularly wave action, sediment movement and weather, the waves of different strengths that constantly hit against the shoreline are the primary movers and shapers of the coastline. Despite the simplicity of process, the differences between waves and the rocks they hit result in hugely varying shapes. The effect that waves have depends on their strength, strong waves, also called destructive waves, occur on high-energy beaches and are typical of winter. They reduce the quantity of sediment present on the beach by carrying it out to bars under the sea, constructive, weak waves are typical of low-energy beaches and occur most during summer. They do the opposite to destructive waves and increase the size of the beach by piling sediment up onto the berm, one of the most important transport mechanisms results from wave refraction. Since waves rarely break onto a shore at right angles, the movement of water onto the beach occurs at an oblique angle. However, the return of water is at right angles to the beach and this movement is known as beach drift. The endless cycle of swash and backwash and resulting beach drift can be observed on all beaches, probably the most important effect is longshore drift, the process by which sediment is continuously moved along beaches by wave action. LSD occurs because waves hit the shore at an angle, pick up sediment on the shore, due to gravity, the water then falls back perpendicular to the beach, dropping its sediment as it loses energy. The sediment is then picked up by the wave and pushed slightly further down the beach. This is the reason why long strips of coast are covered in sediment, not just the areas around river mouths, LSD helps create many landforms including barrier islands, bay beaches and spits. Onshore winds blowing up the beach, pick up sand and move it up the beach to form sand dunes, rain hits the shore and erodes rocks, and carries weathered material to the shoreline to form beaches. Warm weather can encourage biological processes to more rapidly. In tropical areas some plants and animals protect stones from weathering, while other plants, temperatures that vary from below to above freezing point result in frost weathering, whereas weather more than a few degrees below freezing point creates sea ice. In tropical regions in particular, plants and animals not only affect the weathering of rocks but are a source of sediment themselves, the shells and skeletons of many organisms are of calcium carbonate and when this is broken down it forms sediment, limestone and clay. The main physical Weathering process on beaches is salt-crystal growth, wind carries salt spray onto rocks, where it is absorbed into small pores and cracks within the rocks. There the water evaporates and the salt crystallises, creating pressure, in some beaches calcium carbonate is able to bind together other sediments to form beachrock and in warmer areas dunerock
37.
Erosion and tectonics
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The interaction between erosion and tectonics has been a topic of debate since the early 1990s. While the tectonic effects on processes such as erosion have long been recognized. The primary questions surrounding this topic are what types of interactions exist between erosion and tectonics and what are the implications of these interactions, the interaction of these processes can form, modify, or destroy geomorphic features on the Earth’s surface. The term tectonics refers to the study of the Earths surface structure, tectonic processes typically occur at plate boundaries which are one of three types, convergent boundaries, divergent boundaries, or transform boundaries. The topography, and general relief, of a given area determines the velocity at which surface runoff will flow, longer, steeper slopes are more prone to higher rates of erosion during periods of heavy rainfall than shorter, gradually sloping areas. Thus, large ranges, and other areas of high relief. Understanding the principle of isostasy is a key element to understanding the interactions, isostatic uplift is both a cause and an effect of erosion. When deformation occurs in the form of crustal thickening an isostatic response is induced causing the thickened crust to sink, the resulting surface uplift leads to enhanced elevations, which in turn induces erosion. Alternatively, when a large amount of material is eroded away from the Earths surface uplift occurs in order to maintain isostatic equilibrium, because of isostasy, high erosion rates over significant horizontal areas can effectively suck up material from the lower crust and/or upper mantle. This process is known as isostatic rebound and is analogous to Earths response following the removal of large ice sheets. Isostatic uplift and corresponding erosion are responsible for the formation of geologic features as well as localized structures. Two such examples include, Continental shields- Generally large areas of low relief in the Earths crust where Precambrian crystalline igneous, initially, a mountain belt is formed at a convergent plate margin. This process of erosion followed by isostatic adjustment continues until the system is at isostatic equilibrium, at this point large-scale erosion can no longer occur because the surface has eroded down to nearly sea-level and uplift ceases due to the systems state of equilibrium. River anticlines- Geologic structures formed through the uplift of rock underlying confined areas of high erosion. Isostatic rebound resulting from the removal of overlying rock, via erosion. In order for the development of structures to occur the erosion rate of the river must exceed both the average erosional rate of the area, and the rate of uplift of the orogen. The two factors influencing the development of structures are stream power of the associated river and the flexural rigidity of the crust in the area. The combination of increased power with decreased flexural rigidity results in the systems progression from a transverse anticline to a river anticline
38.
Granite
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Granite is a common type of felsic intrusive igneous rock that is granular and phaneritic in texture. Granites can be white, pink, or gray in color. The word granite comes from the Latin granum, a grain, in reference to the structure of such a holocrystalline rock. By definition, granite is a rock with at least 20% quartz. The term granitic means granite-like and is applied to granite and a group of igneous rocks with similar textures and slight variations in composition. Occasionally some individual crystals are larger than the groundmass, in case the texture is known as porphyritic. A granitic rock with a texture is known as a granite porphyry. Granitoid is a general, descriptive field term for lighter-colored, coarse-grained igneous rocks, petrographic examination is required for identification of specific types of granitoids. The extrusive igneous rock equivalent of granite is rhyolite, Granite is nearly always massive, hard and tough, and therefore it has gained widespread use throughout human history, and more recently as a construction stone. The average density of granite is between 2.65 and 2.75 g/cm3, its compressive strength usually lies above 200 MPa, and its viscosity near STP is 3–6 •1019 Pa·s. The melting temperature of dry granite at ambient pressure is 1215–1260 °C, it is reduced in the presence of water. Granite has poor primary permeability, but strong secondary permeability, true granite according to modern petrologic convention contains both plagioclase and alkali feldspars. When a granitoid is devoid or nearly devoid of plagioclase, the rock is referred to as alkali feldspar granite, when a granitoid contains less than 10% orthoclase, it is called tonalite, pyroxene and amphibole are common in tonalite. A granite containing both muscovite and biotite micas is called a binary or two-mica granite, two-mica granites are typically high in potassium and low in plagioclase, and are usually S-type granites or A-type granites. A worldwide average of the composition of granite, by weight percent, based on 2485 analyses. Much of it was intruded during the Precambrian age, it is the most abundant basement rock that underlies the relatively thin veneer of the continents. Outcrops of granite tend to form tors and rounded massifs, granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels. Granite often occurs as small, less than 100 km² stock masses
39.
Exfoliation (geology)
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Exfoliation joints or sheet joints are surface-parallel fracture systems in rock often leading to erosion of concentric slabs. Divide the rock into sub-planar slabs, joint spacing increases with depth from a few centimeters near the surface to a few meters Maximum depth of observed occurrence is around 100 meters. Host rock is generally sparsely jointed, fairly isotropic, and has high compressive strength, can have concave and convex upwards curvatures. Many different theories have suggested, below is a short overview of the most common. This theory was proposed by the pioneering geomorphologist Grove Karl Gilbert in 1904 and is widely found in introductory geology texts. The description of this mechanism has led to terms for exfoliation joints. Laboratory studies show that simple compression and relaxation of rock samples under realistic conditions does not cause fracturing, Exfoliation joints are most commonly found in regions of surface-parallel compressive stress, whereas this theory calls for them to occur in zones of extension. Horizontal stresses become aligned with the current ground surface as the stress drops to zero at this boundary. Thus large surface-parallel compressive stresses can be generated through exhumation that may lead to tensile rock fracture as described below, rock expands upon heating and contracts upon cooling and different rock-forming minerals have variable rates of thermal expansion / contraction. Daily rock surface temperature variations can be large, and many have suggested that stresses created during heating cause the near-surface zone of rock to expand. Large diurnal or fire-induced temperature fluctuations have been observed to create thin lamination and flaking at the surface of rocks, sometimes labeled exfoliation. However, since diurnal temperature fluctuations only reach a few centimeters depth in rock, mineral weathering by penetrating water can cause flaking of thin shells of rock since the volume of some minerals increases upon hydration. This type of fracturing has been observed in the laboratory since at least 1900, fractures formed in this way are sometimes called axial cleavage, longitudinal splitting, or extensional fractures, and are commonly observed in the laboratory during uniaxial compression tests. High horizontal or surface-parallel compressive stress can result from regional tectonic or topographic stresses, recognizing the presence of exfoliation joints can have important implications in geological engineering. Most notable may be their influence on slope stability, Exfoliation joints following the topography of inclined valley walls, bedrock hill slopes, and cliffs can create rock blocks that are particularly prone to sliding. Especially when the toe of the slope is undercut, sliding along exfoliation joint planes is likely if the joint dip exceeds the joint’s frictional angle, foundation work may also be affected by the presence of exfoliation joints, for example in the case of dams. Exfoliation joints underlying a dam foundation can create a significant leakage hazard, finally, exfoliation joints can exert strong directional control on groundwater flow and contaminant transport. Exfoliating granite Media related to Exfoliation joints at Wikimedia Commons
40.
Tafoni
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Tafoni are small cave-like features found in granular rock such as sandstone, granite, and sandy-limestone with rounded entrances and smooth concave walls, often connected, adjacent, and/or networked. They often occur in groups that can riddle a hillside, cliff and they can be found in all climate types, but are most abundant in intertidal areas and semi-arid and arid deserts. Tafoni have also been called fretting, stonelace, stone lattice, honeycomb weathering, the etymology of the word tafoni is unclear. Tafoni may come from the Greek word taphos, tomb, or it may stem from a Corsican or Sicilian word for holes, taffoni, the earliest known publication of the term “tafoni” was in 1882. Conventionally, the word tafoni is the form of tafone. Honeycomb weathering, a similar weathering feature Stoppato, Marco, ISBN 1-55297-669-6 pp. 30–32 Owen, Athena M.2007, Tafoni Caves in Quaternary Carbonate Eolianites, Examples from the Bahamas. Masters Thesis, Mississippi State University,179 pp. Paradise, T. R.2011
41.
Salt Point State Park
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Salt Point State Park is a state park in Sonoma County, California, United States. The park also features the first underwater preserves in California, the constant impact of the waves forms the rocks into many different shapes. These rocks continue underwater providing a variety of habitats for marine organisms. The activities at Salt Point include hiking, camping, fishing, scuba diving, the weather is cool with fog and cold winds even during the summer. The rocks of Salt Point are sedimentary sandstone, due to the large amounts of sandstone, small cave-like features called tafoni can be found along the shore of Salt Point. This park is named for the formation of crystals in the cracks. The native Kashaya Pomo collected salt from this area for many years and they used abalone chisels to scrape the salt off the rocks. In 1853, Samuel Duncan and Joshua Hendy built a sawmill on a ridge located above Salt Point, a couple of years later they leased the land to a San Francisco company which quarried the sandstone. They used the sandstone to create the streets and buildings in San Francisco along with the facility at Mare Island. It is also possible to see drill holes in the sandstone at Gerstle Cove, in 1870, Duncan sold his property to Frederick Funcke and Lewis Gerstle. They shipped 5,000 cords of wood yearly and used most of the land to graze their cattle, the eyebolts used to anchor ships down are still visible at Gerstle cove. This is where sandstone and wood were loaded onto cargo ships, at first, they used wire cables anchored to the cliff side to load wood and stone onto the ships. Two chutes were eventually made, the Miller chute and the Funcke & Co. chute, there was a horse-drawn railroad that lead from the Miller sawmills to where the boats were loaded. The sawmill had a capacity of 18,000 board feet. Brush and grasslands cover the ground on the terraces, at higher elevations Douglas fir forest dominates. At slightly higher levels, a mixed fir forest of bishop pine and Douglas-fir is present intermixed with second growth coast redwood, madrones. At 1,000 feet there is an open prairie where animals such as elk previously grazed. In addition, at an elevation of about 550 feet within Salt Point State Park is a pygmy forest including the Mendocino cypress, bishop pine and Arctostaphylos
42.
Sonoma County, California
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Sonoma County is a county in the U. S. state of California. As of the 2010 United States Census, its population was 483,878 and its county seat and largest city is Santa Rosa. It is located to the north of Marin County and the south of Mendocino County and it is west of Napa County and Lake County. Sonoma County comprises the Santa Rosa, CA Metropolitan Statistical Area and it is the northwestern county in the nine-county San Francisco Bay Area region. Sonoma is the county and largest producer of California’s Wine Country region, which also includes Napa, Mendocino. It possesses thirteen approved American Viticultural Areas and over 250 wineries, in 2002, Sonoma County ranked as the 32nd county in the United States in agricultural production. More than 7.4 million tourists each year, spending more than $1 billion in 2006. Sonoma County is the home of Sonoma State University and Santa Rosa Junior College, Sonoma County is home to several Native American tribes. By the 1830s, European settlement had set a new direction that would prove to radically alter the course of land use, Sonoma County has rich agricultural land, albeit largely divided between two nearly monocultural uses as of 2007, grapes and pasturage. The voters have twice approved open space initiatives that have provided funding for public acquisition of natural areas, preserving forested areas, coastal habitat, and other open space. The Pomo, Coast Miwok and Wappo peoples were the earliest human settlers of Sonoma County, spaniards, Russians, and other Europeans claimed and settled in the county from the late 16th to mid-19th century, seeking timber, fur, and farmland. The Russians were the first newcomers to establish a permanent foothold in Sonoma County and this settlement and its outlying Russian settlements came to include a population of several hundred Russian and Aleut settlers and a stockaded fort with artillery. However, the Russians abandoned it in 1841 and sold the fort to John Sutter, settler and Mexican land grantee of Sacramento. The Mission San Francisco Solano, founded in 1823 as the last and northernmost of 21 California missions, is in the present City of Sonoma, El Presidio de Sonoma, or Sonoma Barracks, was established in 1836 by Comandante General Mariano Guadalupe Vallejo. The City of Sonoma was the site of the Bear Flag Revolt in 1846, Sonoma was one of the original counties formed when California became a state in 1850, with its county seat originally the town of Sonoma. However, by the early 1850s, the town of Sonoma had declined in importance in terms of commerce and population, its county buildings were crumbling, and it was relatively remote. As a result, elements in the newer, rapidly growing towns of Petaluma, Santa Rosa, the dispute ultimately was between the bigger, richer commercial town of Petaluma and the more centrally located, growing agricultural center of Santa Rosa. Allegedly, several Santa Rosans, not caring to wait, decided to take action and, one night, rode down the Sonoma Valley to Sonoma, took the county seals and records, some of the countys land was annexed from Mendocino County between 1850 and 1860
43.
Salinity
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Salinity is the saltiness or amount of salt dissolved in a body of water. This is usually measured in g salt k g sea water, a contour line of constant salinity is called an isohaline – or sometimes isohale. Salinity in rivers, lakes, and the ocean is conceptually simple, conceptually the salinity is the quantity of dissolved salt content of the water. Salts are compounds like sodium chloride, magnesium sulfate, potassium nitrate, the concentration of dissolved chloride ions is sometimes referred to as chlorinity. Operationally, dissolved matter is defined as that which can pass through a fine filter. Salinity can be expressed in the form of a mass fraction, Seawater typically has a mass salinity of around 35 g/kg, although lower values are typical near coasts where rivers enter the ocean. Rivers and lakes can have a range of salinities, from less than 0.01 g/kg to a few g/kg. The Dead Sea has a salinity of more than 200 g/kg, whatever pore size is used in the definition, the resulting salinity value of a given sample of natural water will not vary by more than a few percent. A bottled seawater product known as IAPSO Standard Seawater is used by oceanographers to standardize their measurements with enough precision to meet this requirement, measurement and definition difficulties arise because natural waters contain a complex mixture of many different elements from different sources in different molecular forms. The chemical properties of some of these depend on temperature and pressure. Many of these forms are difficult to measure with high accuracy, different practical definitions of salinity result from different attempts to account for these problems, to different levels of precision, while still remaining reasonably easy to use. For many purposes this sum can be limited to a set of eight major ions in natural waters, the major ions dominate the inorganic composition of most natural waters. Exceptions include some pit lakes and waters from some hydrothermal springs, the concentrations of dissolved gases like oxygen and nitrogen are not usually included in descriptions of salinity. However, carbon dioxide gas, which when dissolved is partially converted into carbonates and bicarbonates, is often included. Silicon in the form of acid, which usually appears as a neutral molecule in the pH range of most natural waters. The term salinity is, for oceanographers, usually associated with one of a set of measurement techniques. As the dominant techniques evolve, so do different descriptions of salinity, the distinctions between these different descriptions are important to physical oceanographers but are obscure and confusing to nonspecialists. Salinities were largely measured using titration-based techniques before the 1980s, titration with silver nitrate could be used to determine the concentration of halide ions to give a chlorinity
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. PMID 16461674. doi:10.1128/AEM.72.2.1258-1266.2006.
