Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, the processes by which they change over time. Geology can include the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology overlaps all other earth sciences, including hydrology and the atmospheric sciences, so is treated as one major aspect of integrated earth system science and planetary science. Geology describes the structure of the Earth on and beneath its surface, the processes that have shaped that structure, it provides tools to determine the relative and absolute ages of rocks found in a given location, to describe the histories of those rocks. By combining these tools, geologists are able to chronicle the geological history of the Earth as a whole, to demonstrate the age of the Earth. Geology provides the primary evidence for plate tectonics, the evolutionary history of life, the Earth's past climates. Geologists use a wide variety of methods to understand the Earth's structure and evolution, including field work, rock description, geophysical techniques, chemical analysis, physical experiments, numerical modelling.
In practical terms, geology is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources, understanding of natural hazards, the remediation of environmental problems, providing insights into past climate change. Geology is a major academic discipline, it plays an important role in geotechnical engineering; the majority of geological data comes from research on solid Earth materials. These fall into one of two categories: rock and unlithified material; the majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth. There are three major types of rock: igneous and metamorphic; the rock cycle illustrates the relationships among them. When a rock solidifies or crystallizes from melt, it is an igneous rock; this rock can be weathered and eroded redeposited and lithified into a sedimentary rock. It can be turned into a metamorphic rock by heat and pressure that change its mineral content, resulting in a characteristic fabric.
All three types may melt again, when this happens, new magma is formed, from which an igneous rock may once more solidify. To study all three types of rock, geologists evaluate the minerals; each mineral has distinct physical properties, there are many tests to determine each of them. The specimens can be tested for: Luster: Measurement of the amount of light reflected from the surface. Luster is broken into nonmetallic. Color: Minerals are grouped by their color. Diagnostic but impurities can change a mineral’s color. Streak: Performed by scratching the sample on a porcelain plate; the color of the streak can help name the mineral. Hardness: The resistance of a mineral to scratch. Breakage pattern: A mineral can either show fracture or cleavage, the former being breakage of uneven surfaces and the latter a breakage along spaced parallel planes. Specific gravity: the weight of a specific volume of a mineral. Effervescence: Involves dripping hydrochloric acid on the mineral to test for fizzing. Magnetism: Involves using a magnet to test for magnetism.
Taste: Minerals can have a distinctive taste, like halite. Smell: Minerals can have a distinctive odor. For example, sulfur smells like rotten eggs. Geologists study unlithified materials, which come from more recent deposits; these materials are superficial deposits. This study is known as Quaternary geology, after the Quaternary period of geologic history. However, unlithified material does not only include sediments. Magmas and lavas are the original unlithified source of all igneous rocks; the active flow of molten rock is studied in volcanology, igneous petrology aims to determine the history of igneous rocks from their final crystallization to their original molten source. In the 1960s, it was discovered that the Earth's lithosphere, which includes the crust and rigid uppermost portion of the upper mantle, is separated into tectonic plates that move across the plastically deforming, upper mantle, called the asthenosphere; this theory is supported by several types of observations, including seafloor spreading and the global distribution of mountain terrain and seismicity.
There is an intimate coupling between the movement of the plates on the surface and the convection of the mantle. Thus, oceanic plates and the adjoining mantle convection currents always move in the same direction – because the oceanic lithosphere is the rigid upper thermal boundary layer of the convecting mantle; this coupling between rigid plates moving on the surface of the Earth and the convecting mantle is called plate tectonics. The development of plate tectonics has provided a physical basis for many observations of the solid Earth. Long linear regions of geologic features are explained as plate boundaries. For example: Mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, are seen as divergent boundaries, where two plates move apart. Arcs of volcanoes and earthquakes are theorized as convergent boundaries, where one plate subducts, or moves, under another. Transform boundaries, such as the San Andreas Fault system, resulted in widespread powerful earthquakes.
Plate tectonics has provided a mechan
A cirque is an amphitheatre-like valley formed by glacial erosion. Alternative names for this landform are cwm. A cirque may be a shaped landform arising from fluvial erosion; the concave shape of a glacial cirque is open on the downhill side, while the cupped section is steep. Cliff-like slopes, down which ice and glaciated debris combine and converge, form the three or more higher sides; the floor of the cirque ends up bowl-shaped as it is the complex convergence zone of combining ice flows from multiple directions and their accompanying rock burdens: hence it experiences somewhat greater erosion forces, is most overdeepened below the level of the cirque's low-side outlet and its down slope valley. If the cirque is subject to seasonal melting, the floor of the cirque most forms a tarn behind a dam which marks the downstream limit of the glacial overdeepening: the dam itself can be composed of moraine, glacial till, or a lip of the underlying bedrock; the fluvial cirque or makhtesh, found in karst landscapes, is formed by intermittent river flow cutting through layers of limestone and chalk leaving sheer cliffs.
A common feature for all fluvial-erosion cirques is a terrain which includes erosion resistant upper structures overlying materials which are more eroded. Glacial cirques are found amongst mountain ranges throughout the world. Situated high on a mountainside near the firn line, they are partially surrounded on three sides by steep cliffs; the highest cliff is called a headwall. The fourth side forms the lip, threshold or sill, the side at which the glacier flowed away from the cirque. Many glacial cirques contain tarns dammed by a bedrock threshold; when enough snow accumulates it can flow out the opening of the bowl and form valley glaciers which may be several kilometers long. Cirques form in conditions; these areas are sheltered from heat. The process of nivation follows, whereby a hollow in a slope may be enlarged by ice segregation weathering and glacial erosion. Ice segregation erodes the rock vertical rock face and causes it to disintegrate, which may result in an avalanche bringing down more snow and rock to add to the growing glacier.
This hollow may become large enough that glacial erosion intensifies. The enlarging of this open ended concavity creates a larger leeward deposition zone, furthering the process of glaciation. Debris in the ice may abrade the bed surface; the hollow may become a large bowl shape in the side of the mountain, with the headwall being weathered by ice segregation, as well as being eroded by plucking. The basin will become deeper as it continues to be eroded by ice abrasion. Should ice segregation and abrasion continue, the dimensions of the cirque will increase, but the proportion of the landform would remain the same. A bergschrund forms when the movement of the glacier separates the moving ice from the stationary ice forming a crevasse; the method of erosion of the headwall lying between the surface of the glacier and the cirque’s floor has been attributed to freeze-thaw mechanisms. The temperature within the bergschrund changes little, studies have shown that ice segregation may happen with only small changes in temperature.
Water that flows into the bergschrund can be cooled to freezing temperatures by the surrounding ice allowing freeze-thaw mechanisms to occur. If two adjacent cirques erode toward one another, an arête, or steep sided ridge, forms; when three or more cirques erode toward one another, a pyramidal peak is created. In some cases, this peak will be made accessible by one or more arêtes; the Matterhorn in the European Alps is an example of such a peak. Where cirques form one behind the other, a cirque stairway results as at the Zastler Loch in the Black Forest; as glaciers can only originate above the snowline, studying the location of present-day cirques provides information on past glaciation patterns and on climate change. Although a less common usage, the term cirque is used for amphitheatre-shaped, fluvial-erosion features. For example, an 200 square kilometres anticlinal erosion cirque is at 30°35′N 34°45′E on the southern boundary of the Negev highlands; this erosional cirque or makhtesh was formed by intermittent river flow in the Makhtesh Ramon cutting through layers of limestone and chalk, resulting in cirque walls with a sheer 200 metres drop.
The Cirque du Bout du Monde is another such a feature, created in karst terraine in the Burgundy region of the department of Côte-d'Or in France. Yet another type of fluvial erosion formed cirque is found on Réunion island, which includes the tallest volcanic structure in the Indian Ocean; the island consists of an active shield-volcano and an extinct eroded volcano. Three cirques have eroded there in a sequence of agglomerated, fragmented rock and volcanic breccia associated with pillow-lavas overlain by more coherent, solid lavas. A common feature for all fluvial-erosion cirques is a terrain which includes erosion resistant
Physical geography is one of the two major sub-fields of geography. Physical geography is the branch of natural science which deals with the study of processes and patterns in the natural environment like the atmosphere, hydrosphere and geosphere, as opposed to the cultural or built environment, the domain of human geography. Physical Geography can be divided into several sub-fields, as follows: Geomorphology is the field concerned with understanding the surface of the Earth and the processes by which it is shaped, both at the present as well as in the past. Geomorphology as a field has several sub-fields that deal with the specific landforms of various environments e.g. desert geomorphology and fluvial geomorphology. Geomorphology seeks to understand landform history and dynamics, predict future changes through a combination of field observation, physical experiment, numerical modeling. Early studies in geomorphology are the foundation for pedology, one of two main branches of soil science Hydrology is predominantly concerned with the amounts and quality of water moving and accumulating on the land surface and in the soils and rocks near the surface and is typified by the hydrological cycle.
Thus the field encompasses water in rivers, aquifers and to an extent glaciers, in which the field examines the process and dynamics involved in these bodies of water. Hydrology has had an important connection with engineering and has thus developed a quantitative method in its research. Similar to most fields of physical geography it has sub-fields that examine the specific bodies of water or their interaction with other spheres e.g. limnology and ecohydrology. Glaciology is the study of glaciers and ice sheets, or more the cryosphere or ice and phenomena that involve ice. Glaciology groups the latter as continental glaciers and the former as alpine glaciers. Although research in the areas are similar with research undertaken into both the dynamics of ice sheets and glaciers, the former tends to be concerned with the interaction of ice sheets with the present climate and the latter with the impact of glaciers on the landscape. Glaciology has a vast array of sub-fields examining the factors and processes involved in ice sheets and glaciers e.g. snow hydrology and glacial geology.
Biogeography is the science which deals with geographic patterns of species distribution and the processes that result in these patterns. Biogeography emerged as a field of study as a result of the work of Alfred Russel Wallace, although the field prior to the late twentieth century had been viewed as historic in its outlook and descriptive in its approach; the main stimulus for the field since its founding has been that of evolution, plate tectonics and the theory of island biogeography. The field can be divided into five sub-fields: island biogeography, paleobiogeography, phylogeography and phytogeography Climatology is the study of the climate, scientifically defined as weather conditions averaged over a long period of time. Climatology examines both the nature of micro and macro climates and the natural and anthropogenic influences on them; the field is sub-divided into the climates of various regions and the study of specific phenomena or time periods e.g. tropical cyclone rainfall climatology and paleoclimatology.
Meteorology is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and short term forecasting. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the eighteenth century. Meteorological phenomena are observable weather events which illuminate and are explained by the science of meteorology. Pedology is the study of soils in their natural environment, it is one of two main branches of the other being edaphology. Pedology deals with pedogenesis, soil morphology, soil classification. In physical geography pedology is studied due to the numerous interactions between climate, soil life, the mineral materials within soils and its position and effects on the landscape such as lateralization. Palaeogeography is a cross-disciplinary study that examines the preserved material in the stratigraphic record to determine the distribution of the continents through geologic time. All the evidence for the positions of the continents comes from geology in the form of fossils or paleomagnetism.
The use of this data has resulted in evidence for continental drift, plate tectonics, supercontinents. This, in turn, has supported palaeogeographic theories such as the Wilson cycle. 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 wave action, sediment movement and weathering, the ways in which humans interact with the coast. Coastal geography, although predominantly geomorphological in its research, is not just concerned with coastal landforms, but the causes and influences of sea level change. Oceanography is the branch of physical geography that studies seas, it covers a wide range including marine organisms and ecosystem dynamics.
A culvert is a structure that allows water to flow under a road, trail, or similar obstruction from one side to the other side. Embedded so as to be surrounded by soil, a culvert may be made from a pipe, reinforced concrete or other material. In the United Kingdom, the word can be used for a longer artificially buried watercourse. Culverts are used both as cross-drains for ditch relief, to pass water under a road at natural drainage and stream crossings. A culvert may be a bridge-like structure designed to allow vehicle or pedestrian traffic to cross over the waterway while allowing adequate passage for the water. Culverts come in many sizes and shapes including round, flat-bottomed, open-bottomed, pear-shaped, box-like constructions; the culvert type and shape selection is based on a number of factors including requirements for hydraulic performance, limitations on upstream water surface elevation, roadway embankment height. If the span of crossing is greater than 12 feet the structure is termed a bridge.
A structure that carries water above land is known as an aqueduct. The process of removing culverts, becoming prevalent, is known as daylighting. In the UK, the practice is known as deculverting. Culverts can be constructed of a variety of materials including cast-in-place or precast concrete, galvanized steel, aluminum, or plastic. Two or more materials may be combined to form composite structures. For example, open-bottom corrugated steel structures are built on concrete footings. Construction or installation at a culvert site results in disturbance of the site soil, stream banks, or streambed, can result in the occurrence of unwanted problems such as scour holes or slumping of banks adjacent to the culvert structure. Culverts must be properly sized and installed, protected from erosion and scour. Many U. S. agencies such as the Federal Highway Administration, Bureau of Land Management, Environmental Protection Agency, as well as state or local authorities, require that culverts be designed and engineered to meet specific federal, state, or local regulations and guidelines to ensure proper function and to protect against culvert failures.
Culverts are classified by standards for their load capacities, water flow capacities, life spans, installation requirements for bedding and backfill. Most agencies adhere to these standards when designing and specifying culverts. Culvert failures can occur for a wide variety of reasons including maintenance and installation related failures, functional or process failures related to capacity and volume causing the erosion of the soil around or under them, structural or material failures that cause culverts to fail due to collapse or corrosion of the materials from which they are made. If the failure is sudden and catastrophic, it can result in loss of life. Sudden road collapses are the result of poorly designed and engineered culvert crossing sites or unexpected changes in the surrounding environment cause design parameters to be exceeded. Water passing through undersized culverts will scour away the surrounding soil over time; this can cause a sudden failure during medium-sized rain events.
Accidents from culvert failure can occur if a culvert has not been adequately sized and a flood event overwhelms the culvert, or disrupts the road or railway above it. Ongoing culvert function without failure depends on proper design and engineering considerations being given to load, hydraulic flow, surrounding soil analysis and bedding compaction, erosion protection. Improperly designed backfill support around culverts can result in material collapse or failure from inadequate load support. For existing culverts which have experienced degradation, loss of structural integrity or need to meet new codes or standards, rehabilitation using a reline pipe maybe preferred versus replacement. Sizing of a reline culvert uses the same hydraulic flow design criteria as that of a new culvert however as the reline culvert is meant to be inserted into an existing culvert or host pipe, reline installation requires the grouting of the annular space between the host pipe and the surface of reline pipe so as to prevent or reduce seepage and soil migration.
Grouting serves as a means in establishing a structural connection between the liner, host pipe and soil. Depending on the size and annular space to be filled as well as the pipe elevation between the inlet and outlet, grouting maybe required to be performed in multiple stages or "lifts". If multiple lifts are required a grouting plan is required which defines the placement of grout feed tubes, air tubes, type of grout to be used and if injecting or pumping grout the required developed pressure for injection; as the diameter of the reline pipe will be smaller than the host pipe, the cross-sectional flow area will be smaller. By selecting a reline pipe with a smooth internal surface, with an approximate Hazen-Williams Friction Factor, C, value of between 140-150, the decreased flow area can be offset and hydraulic flow rates increased by way of reduced surface flow resistance. Examples of pipe materials with high C-factors are HDPE. Undersized and poorly placed culverts can cause problems for aquatic organisms.
Poorly designed culverts can degrade water quality via scour and erosion, as well as restrict the movement of aquatic organisms between upstream and downstream habitat. Fish are a common victim in the loss of habitat du
Cwm Idwal is a cirque in the Glyderau range of mountains in northern Snowdonia, the national park in the mountainous region of North Wales. Its main interest is to hill walkers and rock climbers, but it is of interest to geologists and naturalists, given its combination of altitude and terrain. In a 2005 poll conducted by Radio Times, Cwm Idwal was ranked the 7th greatest natural wonder in Britain. Cwm Idwal is a spectacular product of glaciation, surrounded by high crags, screes and rounded rocks, with a lake on its floor. Cwm Idwal comprises volcanic and sedimentary rock, laid down in a shallow Ordovician sea, folded to give rise to the distinctive trough-shaped arrangement of strata known today as the Idwal Syncline; this fold. The area was eroded by glacial action to form the classic semicircular valley. Given its elevation and north-facing aspect, Cwm Idwal is the most southerly place in Britain where Arctic plants such as moss campion and some alpine saxifrages, such as tufted saxifrage and Micranthes nivalis, can be found.
It is a home of the Snowdon lily, a plant which can only be found in the UK on Snowdon and its surroundings. Evan Roberts, the renowned botanist and explorer from Capel Curig, did as much as any other botanist to document the area; the Snowdonia hawkweed, Hieracium snowdoniense is only known to occur in Cwm Idwal. Rhiwiau Caws and the cliffs around the head of Cwm Idwal are a popular area for rock climbing, they were first climbed in 1897 by Moss. Twll Du has some excellent ice climbing during the winter; the Cwm is popular for hill walking and scrambling, given its proximity to Tryfan and Glyder Fach and Glyder Fawr and their profusion of rocky ridges. In the mid-to-late 1950s and into the 1960s, this was the reunion excursion camp site of the first ascenders of Mount Everest and Kangchenjunga, held at Pen-y-Gwryd, many of whom were keen geologists and botanists. is at coordinates 53.113712°N 4.029927°W / 53.113712.
Retaining walls are rigid walls used for supporting the soil mass laterally so that the soil can be retained at different levels on the two sides. Retaining walls are structures designed to restrain soil to a slope that it would not keep to, they are used to bound soils between two different elevations in areas of terrain possessing undesirable slopes or in areas where the landscape needs to be shaped and engineered for more specific purposes like hillside farming or roadway overpasses. A retaining wall that retains soil on the backside and water on the frontside is called a seawall or a bulkhead. A retaining wall is a structure designed and constructed to resist the lateral pressure of soil, when there is a desired change in ground elevation that exceeds the angle of repose of the soil. A basement wall is thus one kind of retaining wall, but the term refers to a cantilever retaining wall, a freestanding structure without lateral support at its top. These are cantilevered from a footing and rise above the grade on one side to retain a higher level grade on the opposite side.
The walls must resist the lateral pressures generated by loose soils or, in some cases, water pressures. Every retaining wall supports a "wedge" of soil; the wedge is defined as the soil which extends beyond the failure plane of the soil type present at the wall site, can be calculated once the soil friction angle is known. As the setback of the wall increases, the size of the sliding wedge is reduced; this reduction lowers the pressure on the retaining wall. The most important consideration in proper design and installation of retaining walls is to recognize and counteract the tendency of the retained material to move downslope due to gravity; this creates lateral earth pressure behind the wall which depends on the angle of internal friction and the cohesive strength of the retained material, as well as the direction and magnitude of movement the retaining structure undergoes. Lateral earth pressures are zero at the top of the wall and – in homogenous ground – increase proportionally to a maximum value at the lowest depth.
Earth pressures will overturn it if not properly addressed. Any groundwater behind the wall, not dissipated by a drainage system causes hydrostatic pressure on the wall; the total pressure or thrust may be assumed to act at one-third from the lowest depth for lengthwise stretches of uniform height. Unless the wall is designed to retain water, It is important to have proper drainage behind the wall in order to limit the pressure to the wall's design value. Drainage materials will reduce or eliminate the hydrostatic pressure and improve the stability of the material behind the wall. Drystone retaining walls are self-draining; as an example, the International Building Code requires retaining walls to be designed to ensure stability against overturning, excessive foundation pressure and water uplift. Gravity walls depend on their mass to resist pressure from behind and may have a'batter' setback to improve stability by leaning back toward the retained soil. For short landscaping walls, they are made from mortarless stone or segmental concrete units.
Dry-stacked gravity walls do not require a rigid footing. Earlier in the 20th century, taller retaining walls were gravity walls made from large masses of concrete or stone. Today, taller retaining walls are built as composite gravity walls such as: geosynthetics such as geocell cellular confinement earth retention or with precast facing. Cantilevered retaining walls are made from an internal stem of steel-reinforced, cast-in-place concrete or mortared masonry; these walls cantilever loads to a large, structural footing, converting horizontal pressures from behind the wall to vertical pressures on the ground below. Sometimes cantilevered walls are buttressed on the front, or include a counterfort on the back, to improve their strength resisting high loads. Buttresses are short wing walls at right angles to the main trend of the wall; these walls require rigid concrete footings below seasonal frost depth. This type of wall uses much less material than a traditional gravity wall. Sheet pile retaining walls are used in soft soil and tight spaces.
Sheet pile walls are driven into the ground and are composed of a variety of material including steel, aluminum, fiberglass or wood planks. For a quick estimate the material is driven 1/3 above ground, 2/3 below ground, but this may be altered depending on the environment. Taller sheet pile walls will need a tie-back anchor, or "dead-man" placed in the soil a distance behind the face of the wall, tied to the wall by a cable or a rod. Anchors are placed behind the potential failure plane in the soil. Bored pile retaining walls are built by assembling a sequence of bored piles, proceeded by excavating away the excess soil. Depending on the project, the bored pile retaining wall may include a series of earth anchors, reinforcing beams, soil improvement operations and shotcrete reinforcement layer; this construction technique tends to be employed in scenarios where sheet piling is a valid construction solution, but where the vibration or noise levels generated by a pile driver are not acceptable.
An anchored retaining wall can be constructed in any of the aforementioned styles but i