Ice is water frozen into a solid state. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color. In the Solar System, ice is abundant and occurs 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 is abundant on Earth's surface – in the polar regions and above the snow line – and, as a common form of precipitation and deposition, plays a key role in Earth's water cycle and climate. It occurs as frost, icicles or ice spikes. Ice molecules can exhibit more different phases that depend on temperature and pressure; when water is cooled up to three different types of amorphous ice can form depending on the history of its pressure and temperature. When cooled correlated proton tunneling occurs below −253.15 °C giving rise to macroscopic quantum phenomena. All the ice on Earth's 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 liquid water is cooled below 0 °C at standard atmospheric pressure. It may 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 including cooling, winter sports and ice sculpture; as a occurring crystalline inorganic solid with an ordered structure, ice is considered to be a mineral. It possesses a regular crystalline structure based on the molecule of water, which consists of a single oxygen atom covalently bonded to two hydrogen atoms, or H–O–H. However, many of the physical properties of water and ice are controlled by the formation of hydrogen bonds between adjacent oxygen and hydrogen atoms. An unusual property of ice frozen at atmospheric pressure is that the solid is 8.3% less dense than liquid water. The density of ice is 0.9167–0.9168 g/cm3 at 0 °C and standard atmospheric pressure, whereas water has a density of 0.9998–0.999863 g/cm3 at the same temperature and pressure.
Liquid water is densest 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 with decreasing temperature and has a value of 0.9340 g/cm3 at −180 °C. When water freezes, it increases in volume; the effect of expansion during freezing can be dramatic, ice expansion is a basic cause of freeze-thaw weathering of rock in nature and damage to building foundations and roadways from frost heaving. It is 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, an important feature in Earth's biosphere. It has been argued that without this property, natural bodies of water would freeze, in some cases permanently, from the bottom up, resulting in a loss of bottom-dependent animal and plant life in fresh and sea 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 a sheltered environment for algal colonies; when sea water freezes, the ice is riddled with brine-filled channels which sustain sympagic organisms such as bacteria, algae and annelids, which in turn provide food for animals such as krill and specialised fish like the bald notothen, fed upon in turn by larger animals such as emperor penguins and minke whales. 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 hydrogen 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.
As with water, ice absorbs light at the red end of the spectrum preferentially as the result of an overtone of an oxygen–hydrogen bond stretch. Compared with water, this absorption is shifted toward lower energies. Thus, ice appears blue, with a greener tint than liquid water. Since absorption is cumulative, the color effect intensifies with increasing thickness or if internal reflections cause the light to take a longer path through the ice. Other colors can appear in the presence of light absorbing impurities, where the impurity is dictating the color rather than the ice itself. For instance, icebergs containing impurities can appear grey or green. Ice may be any one of the 18 known solid crystalline phases of water, or in an amorphous solid state at various densities. Most liquids under increased pressure freeze at higher temperatures because the pressure helps to hold the molecules together. However, the strong hydrogen bonds in water make it different: For some pressures higher than 1 atm, water freezes at a temperature below
Snow refers to forms of ice crystals that precipitate from the atmosphere and undergo changes on the Earth's surface. It pertains to frozen crystalline water throughout its life cycle, starting when, under suitable conditions, the ice crystals form in the atmosphere, increase to millimeter size and accumulate on surfaces metamorphose in place, melt, slide or sublimate away. Snowstorms develop by feeding on sources of atmospheric moisture and cold air. Snowflakes nucleate around particles in the atmosphere by attracting supercooled water droplets, which freeze in hexagonal-shaped crystals. Snowflakes take on a variety of shapes, basic among these are platelets, needles and rime; as snow accumulates into a snowpack, it may blow into drifts. Over time, accumulated snow metamorphoses, by sintering and freeze-thaw. Where the climate is cold enough for year-to-year accumulation, a glacier may form. Otherwise, snow melts seasonally, causing runoff into streams and rivers and recharging groundwater. Major snow-prone areas include the polar regions, the upper half of the Northern Hemisphere and mountainous regions worldwide with sufficient moisture and cold temperatures.
In the Southern Hemisphere, snow is confined to mountainous areas, apart from Antarctica. Snow affects such human activities as transportation: creating the need for keeping roadways and windows clear. Snow affects ecosystems, as well, by providing an insulating layer during winter under which plants and animals are able to survive the cold. Snow develops in clouds; the physics of snow crystal development in clouds results from a complex set of variables that include moisture content and temperatures. The resulting shapes of the falling and fallen crystals can be classified into a number of basic shapes and combinations, thereof; some plate-like and stellar-shaped snowflakes can form under clear sky with a cold temperature inversion present. Snow clouds occur in the context of larger weather systems, the most important of, the low pressure area, which incorporate warm and cold fronts as part of their circulation. Two additional and locally productive sources of snow are lake-effect storms and elevation effects in mountains.
Mid-latitude cyclones are low pressure areas which are capable of producing anything from cloudiness and mild snow storms to heavy blizzards. During a hemisphere's fall and spring, the atmosphere over continents can be cold enough through the depth of the troposphere to cause snowfall. In the Northern Hemisphere, the northern side of the low pressure area produces the most snow. For the southern mid-latitudes, the side of a cyclone that produces the most snow is the southern side. A cold front, the leading edge of a cooler mass of air, can produce frontal snowsqualls—an intense frontal convective line, when temperature is near freezing at the surface; the strong convection that develops has enough moisture to produce whiteout conditions at places which line passes over as the wind causes intense blowing snow. This type of snowsquall lasts less than 30 minutes at any point along its path but the motion of the line can cover large distances. Frontal squalls may form a short distance ahead of the surface cold front or behind the cold front where there may be a deepening low pressure system or a series of trough lines which act similar to a traditional cold frontal passage.
In situations where squalls develop post-frontally it is not unusual to have two or three linear squall bands pass in rapid succession only separated by 25 miles with each passing the same point in 30 minutes apart. In cases where there is a large amount of vertical growth and mixing the squall may develop embedded cumulonimbus clouds resulting in lightning and thunder, dubbed thundersnow. A warm front can produce snow for a period, as warm, moist air overrides below-freezing air and creates precipitation at the boundary. Snow transitions to rain in the warm sector behind the front. Lake-effect snow is produced during cooler atmospheric conditions when a cold air mass moves across long expanses of warmer lake water, warming the lower layer of air which picks up water vapor from the lake, rises up through the colder air above, freezes and is deposited on the leeward shores; the same effect occurs over bodies of salt water, when it is termed ocean-effect or bay-effect snow. The effect is enhanced when the moving air mass is uplifted by the orographic influence of higher elevations on the downwind shores.
This uplifting can produce narrow but intense bands of precipitation, which deposit at a rate of many inches of snow each hour resulting in a large amount of total snowfall. The areas affected by lake-effect snow are called snowbelts; these include areas east of the Great Lakes, the west coasts of northern Japan, the Kamchatka Peninsula in Russia, areas near the Great Salt Lake, Black Sea, Caspian Sea, Baltic Sea, parts of the northern Atlantic Ocean. Orographic or relief snowfall is caused when masses of air pushed by wind are forced up the side of elevated land formations, such as large mountains; the lifting of air up the side of a mountain or range results in adiabatic cooling, condensation and precipitation. Moisture is removed by orographic lift, leaving drier, warmer air on the leeward side; the resulting enhanced productivity of snow fall and the decrease in temperature with elevation means that snow depth
Rock flour, or glacial flour, consists of fine-grained, silt-sized particles of rock, generated by mechanical grinding of bedrock by glacial erosion or by artificial grinding to a similar size. Because the material is small, it becomes suspended in meltwater making the water appear cloudy, sometimes known as glacial milk; when the sediments enter a river, they turn the river's colour grey, light brown, iridescent blue-green, or milky white. If the river flows into a glacial lake, the lake may appear turquoise in colour as a result; when flows of the flour are extensive, a distinct layer of a different colour flows into the lake and begins to dissipate and settle as the flow extends from the increase in water flow from the glacier during snow melts and heavy rain periods. Examples of this phenomenon may be seen at Lake Pukaki and Lake Tekapo in New Zealand, Lake Louise, Moraine Lake, Emerald Lake, Peyto Lake in Canada, Gjende lake in Norway, several lakes in Chile's Torres del Paine National Park.
Natural rock flour is formed during glacial migration, where the glacier grinds against the sides and bottom of the rock beneath it, but is produced by freeze-and-thaw action, where the act of water freezing and expanding in cracks helps break up rock formations. Multiple cycles create a greater amount. Although clay-sized, the flour particles are not clay minerals but ground up quartz and feldspar. Rock flour is carried out from the system via meltwater streams, where the particles travel in suspension. Rock flour particles may travel great distances either suspended in water or carried by the wind, in the latter case forming deposits called loess; some agronomists believe. An early experimenter was the German miller, Julius Hensel, author of Bread from Stones, who reported successful results with steinmehl in the 1890s, his ideas were not taken up due to technical limitations and, according to proponents of his method, because of opposition from the champions of conventional fertilisers. John D. Hamaker argued that widespread remineralization of soils with rock dust will be necessary to reverse soil depletion by current agriculture and forestry practice.
While this was an alternative concept, increasing mainstream research has been devoted to soil amendment and other benefits of rock flour application: for instance, a pilot project on the use of glacial rock and basaltic fines by the U. S. Department of Agriculture exists at the Henry A. Wallace Beltsville Agricultural Research Center; the SEER Centre in Scotland is a leading source of information on the use of rock dusts and mineral fines. The Soil Remineralization Forum was established with sponsorship from the Scottish Environment Protection Agency and has commissioned a portfolio of research into the benefits of using mineral fines; the Forum provides an interface among research, environmentalists, industry. Diatomaceous earth Remineralize the Earth - "non-profit organization incorporated to disseminate ideas and practice about soil remineralization". Julius Hensel by John Mann The USGS Glossary of Glacial Terminology
Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure is the pressure relative to the ambient pressure. Various units are used to express pressure; some of these derive from a unit of force divided by a unit of area. Pressure may be expressed in terms of standard atmospheric pressure. Manometric units such as the centimetre of water, millimetre of mercury, inch of mercury are used to express pressures in terms of the height of column of a particular fluid in a manometer. Pressure is the amount of force applied at right angles to the surface of an object per unit area; the symbol for it is p or P. The IUPAC recommendation for pressure is a lower-case p. However, upper-case P is used; the usage of P vs p depends upon the field in which one is working, on the nearby presence of other symbols for quantities such as power and momentum, on writing style. Mathematically: p = F A, where: p is the pressure, F is the magnitude of the normal force, A is the area of the surface on contact.
Pressure is a scalar quantity. It relates the vector surface element with the normal force acting on it; the pressure is the scalar proportionality constant that relates the two normal vectors: d F n = − p d A = − p n d A. The minus sign comes from the fact that the force is considered towards the surface element, while the normal vector points outward; the equation has meaning in that, for any surface S in contact with the fluid, the total force exerted by the fluid on that surface is the surface integral over S of the right-hand side of the above equation. It is incorrect to say "the pressure is directed in such or such direction"; the pressure, as a scalar, has no direction. The force given by the previous relationship to the quantity has a direction, but the pressure does not. If we change the orientation of the surface element, the direction of the normal force changes accordingly, but the pressure remains the same. Pressure is distributed to solid boundaries or across arbitrary sections of fluid normal to these boundaries or sections at every point.
It is a fundamental parameter in thermodynamics, it is conjugate to volume. The SI unit for pressure is the pascal, equal to one newton per square metre; this name for the unit was added in 1971. Other units of pressure, such as pounds per square inch and bar, are in common use; the CGS unit of pressure is 0.1 Pa.. Pressure is sometimes expressed in grams-force or kilograms-force per square centimetre and the like without properly identifying the force units, but using the names kilogram, kilogram-force, or gram-force as units of force is expressly forbidden in SI. The technical atmosphere is 1 kgf/cm2. Since a system under pressure has the potential to perform work on its surroundings, pressure is a measure of potential energy stored per unit volume, it is therefore related to energy density and may be expressed in units such as joules per cubic metre. Mathematically: p =; some meteorologists prefer the hectopascal for atmospheric air pressure, equivalent to the older unit millibar. Similar pressures are given in kilopascals in most other fields, where the hecto- prefix is used.
The inch of mercury is still used in the United States. Oceanographers measure underwater pressure in decibars because pressure in the ocean increases by one decibar per metre depth; the standard atmosphere is an established constant. It is equal to typical air pressure at Earth mean sea level and is defined as 101325 Pa; because pressure is measured by its ability to displace a column of liquid in a manometer, pressures are expressed as a depth of a particular fluid. The most common choices are water; the pressure exerted by a column of liquid of height h and density ρ is given by the hydrostatic pressure equation p = ρgh, where g is the gravitational acceleration. Fluid density and local gravity can vary from one reading to another depending on local factors, so the height of a fluid column
Purgatory Chasm State Reservation
Purgatory Chasm State Reservation is a state-owned geologic preserve and public recreation area located off Route 146 in the town of Sutton, Massachusetts. The state park is notable for its.25-mile-long, 70-foot-deep chasm of granite bedrock with abrupt precipices and boulder caves where ice lingers into the early summer. It is managed by the Massachusetts Department of Recreation. Various theories have been proposed to account for the chasm's creation. According to one, the chasm was created when glacial meltwater from a burst ice dam ripped out blocks of bedrock at the end of the last Ice Age. Purgatory Chasm was declared a state park in 1919; the park is open year round, although the chasm is closed to hikers and climbers during the winter months because of ice hazards. There are 2 miles of hiking trails around the chasm; the reservation includes picnic areas, a visitors center, playground. A book of poems by Susan Edmonds Richmond titled Purgatory Chasm, a song by Holly Hanson of Neptune's Car titled "Lover's Leap," and Purgatory Chasm, a novel by Steve Ulfelder, were inspired by hikes in the chasm.
Photos of Purgatory Chasm Purgatory Chasm State Reservation Department of Conservation and Recreation Purgatory Chasm State Reservation Map Department of Conservation and Recreation
A subglacial lake is a lake under a glacier an ice cap or ice sheet. There are many such lakes, with Lake Vostok in Antarctica being by far the largest known on Earth at present; the water below the ice remains liquid since geothermal heating balances the heat loss at the ice surface. The pressure causes the melting point of water to be below 0 °C; the ceiling of the subglacial lake will be at the level where the pressure melting point of water intersects the temperature gradient. In Lake Vostok the ice over the lake is thus much thicker than the ice sheet around it. Hypersaline lakes remain liquid due to their salt content; the water in the lake can have a floating level much above the level of the ground threshold. In fact, theoretically a sub-glacial lake can exist on the top of a hill, provided that the ice over it is so much thinner that it creates the required hydrostatic seal; the floating level can be thought of as the water level in a hole drilled through the ice into the lake. It is equivalent to the level at which a piece of the ice over it would float if it were a normal ice shelf.
The ceiling can therefore be conceived as an ice shelf, grounded along its entire perimeter, which explains why it has been called a captured ice shelf. As it moves over the lake, it enters the lake at the floating line, it leaves the lake at the grounding line. For the lake to exist there must be a hydrostatic seal along the entire perimeter, if the floating level is higher than the threshold. A hydrostatic seal is created when the ice is so much higher around the lake that the equipotential surface dips down into impermeable ground. Water from underneath this ice rim is pressed back into the lake by the hydrostatic seal; the ice surface is ten times more important than the bed surface in creating the hydrostatic seal. This means that a 1 m rise in the ice surface at the ice rim is as efficient as a 10 m rise in the bed level below it. In Lake Vostok the ice rim has been estimated to a mere 7 m, while the floating level is about 3 km above the lake ceiling. If the hydrostatic seal is penetrated when the floating level is high, the water will start flowing out in a jökulhlaup.
Due to melting of the channel the discharge increases exponentially, unless other processes allow the discharge to increase faster. Due to the high head that can be achieved in subglacial lakes, jökulhlaups may reach high rates of discharge. Russian scientist Peter Kropotkin first proposed the idea of fresh water under Antarctic ice sheets at the end of the 19th century, he theorized that the tremendous pressure exerted by the cumulative mass of thousands of vertical meters of ice could increase the temperature at the lowest portions of the ice sheet to the point where the ice would melt. Kropotkin's theory was further developed by Russian glaciologist I. A Zotikov, who wrote his Ph. D. thesis on this subject in 1967. Andrey Kapitsa used seismic soundings in the region of Vostok Station made during the Soviet Antarctic Expeditions in 1959 and 1964 to measure the thickness of the ice sheet. In cooperation with other scientists, Kapitsa discovered a subglacial lake in this region named Lake Vostok, one of the most remarkable geographical discoveries of the 20th century.
Subglacial lakes in Antarctica were suggested by Oswald and Robin and subsequently confirmed theoretically by Oswald. They are identified in radio-echo sounding data as continuous and specular reflectors which dip against the ice surface at around x10 of the surface slope angle, as this is requirement for hydrostatic stability; the largest lakes are clustered in the Dome C-Vostok area of East Antarctica - due to the thick insulating ice and rugged tectonically influenced subglacial topography. The largest is Lake Vostok with other lakes notable for their size being Lake Concordia and Aurora Lake. Several lakes were delineated by the famous SPRI-NSF-TUD surveys undertaken until the mid-seventies. A compilation by Siegert et al. reported 145 subglacial lakes in Antarctica. Since this original compilation several smaller surveys has discovered many more subglacial lakes throughout Antarctica, notably by Carter et al. who identified a spectrum of subglacial lake types based on their properties in radio-echo sounding datasets.
Gray et al. interpreted ice surface slumping and raising from RADARSAT data as evidence for subglacial lakes filling and emptying - termed "active" lakes. Wingham et al. used radar altimeter data to show coincident uplift and subsidence: implying drainage between lakes. NASA's ICESat satellite was key in developing this concept further and subsequent work demonstrated the pervasiveness of this phenomenon. ICESat ceased measurements in 2007 and the detected "active" lakes were compiled by Smith et al. who identified 124 such lakes. In total around 250-300 Antarctic subglacial lakes are known; the realisation that lakes were interconnected created new contamination concerns for plans to drill into lakes. There are three projects to directly sample subglacial lakes in Antarctica; these are the British led Subglacial Lake Ellsworth project, the U. S. led the Russian led Lake Vostok program. No program has gained access but is expected during the austral summer of 2011-12; the role of subglacial lakes on ice dynamics is unclear - on the Greenland Ice Sheet subglacial water acts to enhance basal ice motion in a complex manner.
The "Recovery Lakes" lie at the head of a major ice stream and may influence the dynamics of the region. A modest speed up of Byrd Glacier may have been influenced by a subglacial drainage event (Stea
A glacier is a persistent body of dense ice, moving under its own weight. Glaciers deform and flow due to stresses induced by their weight, creating crevasses and other distinguishing features, they abrade rock and debris from their substrate to create landforms such as cirques and moraines. Glaciers form only on land and are distinct from the much thinner sea ice and lake ice that form on the surface of bodies of water. On Earth, 99% of glacial ice is contained within vast ice sheets in the polar regions, but glaciers may be found in mountain ranges on every continent including Oceania's high-latitude oceanic island countries such as New Zealand and Papua New Guinea. Between 35°N and 35°S, glaciers occur only in the Himalayas, Rocky Mountains, a few high mountains in East Africa, New Guinea and on Zard Kuh in Iran. Glaciers cover about 10 percent of Earth's land surface. Continental glaciers cover nearly 13 million km2 or about 98 percent of Antarctica's 13.2 million km2, with an average thickness of 2,100 m.
Greenland and Patagonia have huge expanses of continental glaciers. Glacial ice is the largest reservoir of fresh water on Earth. Many glaciers from temperate and seasonal polar climates store water as ice during the colder seasons and release it in the form of meltwater as warmer summer temperatures cause the glacier to melt, creating a water source, important for plants and human uses when other sources may be scant. Within high-altitude and Antarctic environments, the seasonal temperature difference is not sufficient to release meltwater. Since glacial mass is affected by long-term climatic changes, e.g. precipitation, mean temperature, cloud cover, glacial mass changes are considered among the most sensitive indicators of climate change and are a major source of variations in sea level. A large piece of compressed ice, or a glacier, appears blue, as large quantities of water appear blue; this is. The other reason for the blue color of glaciers is the lack of air bubbles. Air bubbles, which give a white color to ice, are squeezed out by pressure increasing the density of the created ice.
The word glacier is a loanword from French and goes back, via Franco-Provençal, to the Vulgar Latin glaciārium, derived from the Late Latin glacia, Latin glaciēs, meaning "ice". The processes and features caused by or related to glaciers are referred to as glacial; the process of glacier establishment and flow is called glaciation. The corresponding area of study is called glaciology. Glaciers are important components of the global cryosphere. Glaciers are categorized by their morphology, thermal characteristics, behavior. Cirque glaciers form on the slopes of mountains. A glacier that fills a valley is called a valley glacier, or alternatively an alpine glacier or mountain glacier. A large body of glacial ice astride a mountain, mountain range, or volcano is termed an ice cap or ice field. Ice caps have an area less than 50,000 km2 by definition. Glacial bodies larger than 50,000 km2 are called continental glaciers. Several kilometers deep, they obscure the underlying topography. Only nunataks protrude from their surfaces.
The only extant ice sheets are the two that cover most of Greenland. They contain vast quantities of fresh water, enough that if both melted, global sea levels would rise by over 70 m. Portions of an ice sheet or cap that extend into water are called ice shelves. Narrow, fast-moving sections of an ice sheet are called ice streams. In Antarctica, many ice streams drain into large ice shelves; some drain directly into the sea with an ice tongue, like Mertz Glacier. Tidewater glaciers are glaciers that terminate in the sea, including most glaciers flowing from Greenland, Antarctica and Ellesmere Islands in Canada, Southeast Alaska, the Northern and Southern Patagonian Ice Fields; as the ice reaches the sea, pieces break off, or calve. Most tidewater glaciers calve above sea level, which results in a tremendous impact as the iceberg strikes the water. Tidewater glaciers undergo centuries-long cycles of advance and retreat that are much less affected by the climate change than those of other glaciers.
Thermally, a temperate glacier is at melting point throughout the year, from its surface to its base. The ice of a polar glacier is always below the freezing point from the surface to its base, although the surface snowpack may experience seasonal melting. A sub-polar glacier includes both temperate and polar ice, depending on depth beneath the surface and position along the length of the glacier. In a similar way, the thermal regime of a glacier is described by its basal temperature. A cold-based glacier is below freezing at the ice-ground interface, is thus frozen to the underlying substrate. A warm-based glacier is above or at freezing at the interface, is able to slide at this contact; this contrast is thought to a large extent to govern the ability of a glacier to erode its bed, as sliding ice promotes plucking at rock from the surface below. Glaciers which are cold-based and warm-based are known as polythermal. Glaciers form where the accumulation of ice exceeds ablation. A glacier originates from a landform called'cirque' – a armchair-shaped geological feature (such as a depressio