Ice

views updated May 21 2018

Ice

Structure of ice

Physical properties of ice

Natural ice occurrence

Current glaciology research

Resources

Ice is the solid state of water, and the amount of water on the surface of Earth includes ice in the Polar regions and at high elevations. The relative proportion of each of the three states of water on Earth is the consequence of a balanced equilibrium controlled by the amount of incoming solar energy and the amount of reflection, known as albedo, from clouds, water, ice caps, etc. The amount of ice at any location on Earth varies seasonally, over the long term with climatic change, and even with movements of tectonic plates. One of the most abundant of Earths substances, ice manifests itself in a variety of forms including snow, hail, glaciers, icebergs, and sea ice, along with the artificially produced ice cube. Ice and water behave differently from other materials in a number of important ways.

Structure of ice

Because they share a common composition with their liquid state, ice molecules also consist of the same 2 to 1 ratio of hydrogen and oxygen atoms, the H2O molecule. The shape of this molecule, the oxygen atom at the center with the two hydrogen atoms separated by an angle of 104.52°, dictates the structure of ice. All naturally occurring ice crystals are hexagonal in shape and all snowflakes reflect this six-sided crystal habit. The crystal lattice consists of linked hexagonal rings of water molecules with considerable open space in the center of the ring.

Under artificial laboratory conditions of very high pressures and low temperatures, ice can be forced to crystallize in a number of allotropic forms that are stable only under those particular conditions. Crystallization can occur in these laboratory situations in one of several non-hexagonal forms. This is similar to the way that carbon atoms may crystallize to form graphite or, under more extreme conditions, diamond. The conditions under which the alternate forms might be created do not occur naturally on Earth. They may, however, be present on other bodies in space.

The crystalline structure of ice may be deformed by stress, such as the weight of overlying ice on the deeper portions of a glacier. One type of deformation involves shearing of the crystal lattice along parallel planes. Recrystallization, a different kind of deformation, entails the change in the shape and orientation of crystals within the solid. Both of these processes produce the phenomenon known as creep or creeping flow, responsible for the flowing motion of massive ice bodies such as glaciers.

Physical properties of ice

Pure liquid water is transformed to its solid state, ice, at a temperature of 32°F (0°C) when the pressure is at one atmosphere. The density of liquid water at the freezing point is 62.418 lb/ft3 (0.99984 g/cm3) but decreases to 57.23 lb/ft3 (0.9168 g/cm3) when that water organizes itself into crystalline ice at 32° F (0°C). This density difference is due the large open spaces within the crystal lattice of ice. The increased volume of the solid lattice causes pure water to expand by approximately 9% upon freezing, which can rupture pipes or damage engines if the expanding water has no outlet. Ice is one of a few solid substances that is lower in density than the corresponding liquid state. Surface ice floating on a lake or pond helps to insulate the water below, reduces mixing, and can prevent the water body from freezing solid. This fact has often been cited as an important factor in the development and evolution of life in freshwater.

The freezing point of water containing dissolved solids decreases proportionately to the amount of solute. For example, as the salinity of the water increases its freezing point decreases. This is the principle behind the practice of road and sidewalk salting in some areas during winter. Salt lowers the freezing point of water and, at temperatures near the freezing point of pure water, can cause snow or ice to melt.

When pressure is exerted on ice crystals at temperatures near the melting point, the edges of those crystals may melt. When that pressure is released, the water refreezes. This process, called regelation, may be familiar to those that have formed snowballs. The loose snowflakes are partially melted by the pressure of the hands. When the pressure is released, the refreezing water hardens and causes the cohesion of the flakes into a ball. On very cold days, however, the pressure that can be exerted by the hands is insufficient to cause melting, and the snowball is more difficult to form.

Natural ice occurrence

Most of the natural ice on Earth occurs at extreme latitudes, for example the Greenland ice sheet and sea

ice at the North Pole and the Antarctic ice sheet. Sea ice, massive ice sheets, valley and mountain glaciers all combine to form the polar ice caps. Large areas of the polar and subpolar regions are underlain by permafrost. Polar ice caps and glaciers contain a large proportion of Earths freshwater resource. Over 75% of all freshwater, or 2.15% of all water on Earth, presently exists in the form of ice. This proportion was significantly greater during past glacial epochs.

Glacial ice is a particularly sensitive indicator of climatic change. The rapid retreat of mountain glaciers has been cited as evidence of global warming. If all ice at the poles and in glaciers melted, sea level would rise approximately 260 ft (80 m).

Ice is known to occur on a variety of bodies in space. The origin of water on Earth has been postulated to be a result of collisions with comets and/or meteors containing ice. The presence of ice has been confirmed at the poles of the moon and the planet Mars. The existence of ice on Mars may be an indicator of the potential for the existence of life forms in the warmer and wetter past of that planet. The rings of Saturn and nebulae outside our solar system are thought to contain ice. Europa, a moon of Jupiter, is thought to have a liquid-water ocean beneath a crust of ice. Scientists have also suggested that ice on such bodies might be used to supply the water for manned space missions, as well as being split into its component gases and used for fuel.

Current glaciology research

Current research is focused on reducing the impact of ice on modern society. Ice causes damage to pipes in homes, damages crops, restricts ability to travel, breaks power lines and other property, interferes with the function of airplanes and ships, along with other human considerations, such as contributing to accidental injuries. Engineers study ice to better prepare to build structures that interact with it, such as airplanes, ships, and even oil platforms on the ocean. Climatologists and environmental scientists are working to understand the effects of global warming on the polar ice caps. Meteorologists study the formation of ice in the atmosphere. Other scientists are looking for improved methods by which ice can be controlled on roads. Biologists work to develop

KEY TERMS

Albedo The fraction of sunlight that a surface reflects. An albedo of zero indicates complete absorption, while an albedo of unity indicates total reflection.

Allotropic Said of substances that take multiple forms, such as graphite and diamond, usually in the same phase.

Freezing point The temperature at which a liquid solidifies, 32°F (0°C) for water.

Glaciology The study of all aspects of ice and its associated processes.

Hexagonal crystal system One of six crystal systems. Characterized by one axis that is of unequal length to three identical perpendicular axes, commonly displaying three- or six-fold symmetry.

Melting point The temperature at which a solid becomes liquid, 32°F (0°C) for ice.

Permafrost Permanently frozen soil or subsoil.

Recrystallization The formation of new crystals, while in the solid state.

Regelation A two-fold process involving the melting of ice under pressure and the refreezing of the melt water upon the release of that pressure.

methods of protecting crops from frost damage. Physicists and engineers try to improve understanding of the properties of ice in order to improve the performance of sports equipment such as snow skis and ice skates. Geologists are studying the formation of ice volcanoes along the shores of the Great Lakes. Also, space scientists are looking for additional ice in our solar system and beyond, and planning new techniques and equipment that will allow man to someday utilize that ice in the exploration of other worlds.

See also Ice ages; Icebergs.

Resources

BOOKS

Gosnell, M. Ice: The Nature, the History, and the Uses of an Astonishing Substance. New York: Knopf, 2005.

Hambrey, M., and J. Alean. Glaciers. Cambridge, United Kingdom: Cambridge University Press, 2004.

Tarbuck, E.J., F.K. Lutgens, and D. Tasa. Earth: An Introduction to Physical Geology. Upper Saddle River, NJ: Prentice Hall, 2004.

David B. Goings

Ice

views updated May 29 2018

Ice

Ice is the solid state of water . The great abundance of water on the surface of Earth includes a great quantity of ice in the Polar Regions and high elevations. The relative proportion of each of the three states of water on Earth is a delicately balanced equilibrium controlled by the amount of incoming solar energy and the amount of reflection, known as Aledo, from clouds , water, ice caps, etc. The amount of ice at any one location on Earth varies seasonally, over the long term with climatic change, and even with movements of tectonic plates. One of the most abundant of Earth's substances, ice is especially familiar to residents of high-latitude and alpine regions, and manifests itself in a variety of forms including snow, hail, glaciers , icebergs , and sea ice, along with the artificially produced ice cube. Despite being so familiar, ice and water are anomalous in a variety of respects and behave differently from other materials in a number of important ways. The study of ice, in all forms, and its related processes is known as glaciology.


Structure of ice

Because they share a common composition with their liquid state, ice molecules also consist of the same 2 to 1 ratio of hydrogen and oxygen atoms , the well-known H2O molecule . The shape of this molecule, the oxygen atom at the center with the two hydrogen atoms separated by an angle of 104.52°, dictates the structure of the solid, crystalline ice. All naturally occurring ice crystals are hexagonal in shape and all snowflakes reflect this basic six-sided crystal habit. The crystal lattice consists of linked hexagonal rings of water molecules with considerable open space in the center of the ring.

Under artificial laboratory conditions of very high pressures and low temperatures, ice can be forced to crystallize in a number of allotropic forms that are stable only under those particular conditions. Crystallization can occur in these laboratory situations in one of several non-hexagonal forms. This is similar to the way that carbon atoms may crystallize to form graphite or, under more extreme conditions, diamond . The conditions under which the alternate forms might be created do not occur naturally on Earth. They may, however, be present on other bodies in space.

The crystalline structure of ice may be deformed by stress, such as the weight of overlying ice on the deeper portions of a glacier. One type of deformation involves shearing of the crystal lattice along parallel planes. Recrystallization, on the other hand, entails the change in the shape and orientation of crystals within the solid. Both of these processes produce the phenomenon known as creep, responsible for the flowing motion of massive ice bodies such as glaciers.

Physical properties of ice

Pure liquid water is transformed to its solid state, ice, at a temperature of 32°F (0°C) when the pressure is at one atmosphere. Interestingly, the density of liquid water at the freezing point is 62.418 lb/ft3 (0.99984 g/cm3) but decreases to 57.23 lb/ft3 (0.9168 g/cm3) when that water organizes itself into crystalline ice at 32°F (0°C). This density difference is due the large open spaces within the crystal lattice of ice. The increased volume of the solid lattice causes pure water to expand by approximately 9% upon freezing, resulting in ruptured pipes or damaged engines when the process occurs in a closed vessel. Ice is one of a very few solid substances that is lower in density than the corresponding liquid state. Surface ice floating on a lake or pond helps to insulate the water below, reduces mixing, and can prevent the water body from freezing solid. This fact has often been cited as an important factor in the development and evolution of life in freshwater .

The freezing point of water containing dissolved solids is proportionately reduced below 32°F (0°C) depending on the quantity of solutes. As the salinity of the water increases, the freezing temperature is lowered. This is the principle behind the practice of road salting. The salt causes the freezing point of the water to be lowered, hopefully below the ambient temperature, and the ice or snow is forced to melt.

When pressure is exerted on ice crystals at temperatures near the melting point, the edges of those crystals may melt. When that pressure is released, the water refreezes. This process, called regelation, may be familiar to those that have formed snowballs. The loose snowflakes are partially melted by the pressure of the hands. When the pressure is released, the refreezing water hardens and causes the cohesion of the flakes into a ball. On very cold days, however, the pressure that can be exerted by the hands is insufficient to cause melting, and the snowball is more difficult to form.


Natural ice occurrence

The vast majority of the natural ice on Earth is situated at the extreme latitudes; the Greenland ice sheet and sea ice at the North Pole, the Antarctic ice sheet in the South. Sea ice, massive ice sheets, valley and mountain glaciers all combine to form the polar ice caps . Enormous areas of the polar and subpolar regions are underlain by permafrost . Polar ice caps and glaciers contain a large proportion of Earth's freshwater resource. Over 75% of all freshwater, or 2.15% of all water on Earth, presently exists in the form of ice. This proportion was significantly greater during past glacial epochs.

These vast stores of ice are particularly sensitive indicators of climatic change. The rapid retreat of mountain glaciers has been cited as evidence of global warming . If all ice at the poles and in glaciers melted, sea level would rise approximately 260 ft (80 m).

Ice is known to occur extensively on a variety of bodies in space. The origin of water on Earth has been postulated to be a result of collisions with comets and/or meteors containing a significant quantity of ice. The presence of ice has been confirmed at the poles of the Moon and the planet Mars. The existence of ice on Mars may be an indicator of the potential for the existence of life forms in the warmer and wetter past of that planet. The rings of Saturn and even nebulae outside our solar system are believed to contain ice. Europa, a moon of Jupiter , is thought to have a liquid-water ocean beneath a crust of ice. Scientists also assume that ice on such bodies might be utilized to supply the water needs of manned missions to these bodies, as well as being split into its component gases and used for fuel.

Current glaciology research

Much of the research currently being conducted in glaciology is focused on reducing the impact that ice has on modern society. Ice causes damage to pipes in homes, damages crops , restricts ability to travel, breaks power lines and other property, interferes with the function of airplanes and ships, along with other human considerations, such as contributing to accidental injuries. Engineers study ice to better prepare to build structures that interact with it, such as airplanes, ships and even oil platforms on the ocean. Climatologists and environmental scientists are working to understand the effects of global warming on the polar ice caps. Meteorologists study the formation of ice in the atmosphere. Other scientists are looking for improved methods by which ice can be controlled on roads. Biologists work to develop methods of protecting crops from frost damage. Physicists and engineers try to improve understanding of the properties of ice in order to improve the performance of sports equipment such as snow skis and ice skates . Geologists are studying the formation of ice volcanoes along the shores of the Great Lakes. Also, space scientists are looking for additional ice in our solar system and beyond, and planning new techniques and equipment that will allow man to someday utilize that ice in the exploration of other worlds.

See also Ice ages; Icebergs.


Resources

books

Lock, G. S. H. The Growth and Decay of Ice. New York: Cambridge University Press, 1990.

Petrenko, Victor F., and Robert W. Whitworth. Physics of Ice. New York: Oxford University Press, 1999.

Pounder, Elton R. The Physics of Ice. New York: Pergamon Press, 1965.

other

Dolan, Michael, and Paul Kimberly. "Ice Volcanoes of Lake Superior's South Shore." [cited January 10, 2003]. <http://www.geo.mtu.edu/volcanoes/ice/>

NASA. "Found It! Ice on Mars." May 28, 2002 [cited January 10, 2003]. <http://science.nasa.gov/headlines/y2002/28 may_marsice.htm>.

NASA National Space Science Data Center. "Ice on the Moon." December 3, 2002 [cited January 10, 2003]. <http://nssdc.gsfc.nasa.gov/planetary/ice/ice_moon.html>.


David B. Goings

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Albedo

—The fraction of sunlight that a surface reflects. An albedo of zero indicates complete absorption, while an albedo of unity indicates total reflection.

Allotropic

—Said of substances that take multiple forms, such as graphite and diamond, usually in the same phase.

Freezing point

—The temperature at which a liquid solidifies, 32°F (0°C) for water.

Glaciology

—The study of all aspects of ice and its associated processes.

Hexagonal crystal system

—One of six crystal systems. Characterized by one axis that is of unequal length to three identical perpendicular axes, commonly displaying three- or six-fold symmetry.

Melting point

—The temperature at which a solid becomes liquid, 32∞F (0∞C) for ice.

Permafrost

—Permanently frozen soil or subsoil.

Recrystallization

—The formation of new crystals, while in the solid state.

Regelation

—A two-fold process involving the melting of ice under pressure and the refreezing of the melt water upon the release of that pressure.

ice

views updated May 21 2018

ice / īs/ • n. frozen water, a brittle, transparent crystalline solid: the pipes were blocked with ice. ∎  a frozen mixture of fruit juice or flavored water and sugar. ∎ inf. diamonds. ∎ fig. complete absence of friendliness or affection in manner or expression: the ice in his voice was only to hide the pain. ∎ inf. an illegal profit made from scalping tickets. ∎ inf. money paid in graft or bribery. ∎ inf. methamphetamine.• v. [tr.] 1. decorate (a cake) with icing. 2. inf. clinch (something such as a victory or deal). 3. inf. kill: a man had been iced by the police.4. Ice Hockey shoot (the puck) so as to commit icing.PHRASES: break the ice do or say something to relieve tension or get conversation going at the start of a party or when people meet for the first time.on ice1. (of wine or food) kept chilled by being surrounded by ice. ∎ fig. (esp. of a plan or proposal) held in reserve for future consideration: the recommendation was put on ice. 2. (of an entertainment) performed by skaters: Cinderella on Ice.on thin ice in a precarious or risky situation: you're skating on thin ice.PHRASAL VERBS: ice over (of water or an object) become completely covered with ice.ice up (of an object) become coated with or blocked by ice.

ice

views updated May 08 2018

ice
1. Water which has frozen into a crystal lattice. Pure water freezes at 0°C at 1013.24 mb pressure. The presence of salts in solution depresses the freezing point of water. Liquid water has its maximum density at 4°C, in consequence of which ice floats on water. With increasing pressure, a series of denser polymorphs of ice forms, each designated by a Roman numeral, ordinary ice being ice I.

2. Several properties and varieties of ice are important in geomorphological processes. Expansion on freezing (9.05% in specific volume) generates very high pressures. In an enclosed space in the laboratory the pressure reaches 216 MPa (megapascals) at −22°C but reaches only about 10% of this when unenclosed, as in nature. The stresses are, however, sufficient to bring about frost wedging. Such ice I converts into the denser ice III at lower temperatures, but the pressure exerted by it changes little. ‘Ground ice’ forms when interstitial water freezes, and this may bring about heaving as well as frost wedging. ‘Glacier ice’ is a relatively opaque mass of interlocking crystals, and has a density of 0.85–0.91 g/cm3. ‘Regelation ice’ is relatively clear and is formed by the freezing of meltwater beneath a temperate glacier.

3. In planetary geology other ices are important. Water ice condenses at 160 K at solar nebular pressures and appears in abundance forming the surfaces of the Galilean satellites Europa, Ganymede, and Callisto. The satellites of the jovian planets are mostly water ice—rock mixtures. Water ice will exist in high-pressure polymorphs (e.g. ice VIII, density 1670 kg/m3) above about 15–20 kb in satellite interiors. Other possible ices important in satellites (e.g. Titan) include NH3.H2O, CH4.nH2O, and H2O.CO2.

Ice

views updated May 18 2018

Ice

Ice is frozen water , or in other words, water in solid state. Ice is a transparent, colorless substance with some special properties; it floats in water, ice expands when water freezes, and its melting point decreases with increasing pressure. Water is the only substance that exists in all three phases as gas, liquid, and solid under normal circumstances on Earth.

Water, and thus ice molecules, consist of one oxygen and two hydrogen atoms. Water is a polar molecule, with a slight negative charge on the oxygen side, and a slight positive charge on the hydrogen side, which makes it possible to interact with other polar molecules or ions. Thus, a loose chemical connection called a hydrogen bond forms between the water molecules, where each water molecule can bind to other water molecules, forming a complex network. These hydrogen bonds are the main reason for the special properties of water and ice.

Water in the solid state forms a highly ordered hexagonal (six-sided) crystal lattice structure, because it is the most stable arrangement of the water molecules. Although the individual molecules can vibrate, they cannot move fast enough to leave the crystal structure, since the opposite electrical polarities hold them together. This lattice crystal can be visualized as layers of hexagonal rings of the oxygen atoms stacked on each other. Ice has eleven known crystal forms, depending on pressure, temperature , or how quickly the ice forms. Ice cannot form from liquid water at the freezing point, unless there are seeds for the crystal, which dissipate the energy of the colliding water molecules, keeping them locked in the lattice structure. If no seeds are present, spontaneous crystal nucleation begins only if the water is supercooled below the freezing point.

Ice is present in nature in many places and in many forms: icebergs , ice sheets, glaciers , snow, freezing rain, sleet, ice crystals , icicles, hail, rime, graupel, and ice fog . Ice plays an important role in erosion (water fills the cracks of rock , freezes, expands, and breaks the rock), and in atmospheric

energy transport (when water vapor changes into liquid or ice, latent heat is released). The way ice forms in bodies of water (not from the bottom up, but from the top down) protects many organisms in the water from very cold and fast temperature fluctuations.

ice

views updated Jun 27 2018

ice Water which has frozen into a crystal lattice. Pure water freezes at 0°C at 1013.24 mb pressure. The presence of salts in solution depresses the freezing point of water. Liquid water has its maximum density at 4°C, in consequence of which ice floats on water. With increasing pressure, a series of denser polymorphs of ice forms, each designated by a Roman numeral, ordinary ice being ice I. Expansion on freezing (9.05 per cent in specific volume) generates very high pressures, which bring about frost wedging. Such ice I converts into the denser ice III at lower temperatures, but the pressure exerted by it changes little. ‘Ground ice’ forms when interstitial water freezes, and this may bring about heaving as well as frost wedging. ‘Glacier ice’ is a relatively opaque mass of interlocking crystals, and has a density of 0.85–0.91 g/cm. ‘Regelation ice’ is relatively clear and is formed by the freezing of meltwater beneath a temperate glacier.

ice

views updated May 11 2018

ice OE. īs = OS., OHG. īs (Du. ijs, G. eis), ON. íss :- Gmc. *īsam, *īsaz, rel. to AV. isu- icy. Ice cream (XVIII) is for earlier iced cream (XVII).
Hence icy XVI (not continuous with OE. īsiġ). So iceberg †Arctic glacier; detached portion of this in the sea. XVIII. prob. — (M)Du. ijsberg (see BARROW1).

Ice

views updated May 11 2018

ice

views updated Jun 11 2018

ice break the ice do or say something to relieve tension or get conversation going in a strained situation or when strangers meet.
Ice Age the series of glacial episodes during the Pleistocene period.
on thin ice in a precarious or risky situation.

See also the rich man has his ice in the summer.

Ice

views updated May 14 2018

Ice ★★½ 1993 (R)

Charley and Ellen Reed are thieves whose latest heist is $60 million in diamonds from mob boss Vito Malta. There's trouble when they try to fence the goods and Ellen is left with the merchandise and on the run from Malta's henchmen. 91m/C VHS, DVD . Traci Lords, Phillip Troy, Zach Galligan, Jorge (George) Rivero, Michael Bailey Smith, Jamie Alba, Jean Pflieger, Floyd Levine; D: Brook Yeaton; W: Sean Dash.