Perito Moreno Glacier Patagonia Argentina

Aletsch Glacier, Switzerland

Icebergs breaking off glaciers at Cape York, Greenland

"Glacial" and "Glaciation" redirect here. For the geological periods, see glacial period. A glacial period is an interval of time within an Ice age that is marked by colder temperatures and Glacier advances For the story by Alastair Reynolds, see Glacial (short story). Alastair Preston Reynolds (born in 1966 in Barry, Wales) is a Welsh Science fiction author. Galactic North (ISBN 057507910X published by Gollancz) is a collection of short stories by the science fiction author Alastair Reynolds.

A glacier is a large, slow-moving river of ice, formed from compacted layers of snow, that slowly deforms and flows in response to gravity. "Snowfall" redirects here For other uses see Snow (disambiguation or Snowfall (disambiguation. Gravitation is a natural Phenomenon by which objects with Mass attract one another The processes and landforms caused by glaciers and related to them are glacial (adjective); this term should not be confounded with glacial (noun), a cold period in ice ages (see glacial period). In Grammar, an adjective is a word whose main syntactic role is to modify a Noun or Pronoun, giving more information about the An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets A glacial period is an interval of time within an Ice age that is marked by colder temperatures and Glacier advances The process of glacier growth and establishment is called glaciation.

The word glacier comes from French via the Vulgar Latin glacia, and ultimately from Latin glacies meaning ice. French ( français,) is a Romance language spoken around the world by 118 million people as a native language and by about 180 to 260 million people Vulgar Latin (in Latin sermo vulgaris, "folk speech" is a Blanket term covering the popular Dialects and Sociolects of the Latin Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. ^[1]

Overview

Glacier ice is the largest reservoir of fresh water on Earth, and second only to oceans as the largest reservoir of total water. Freshwater is a word that refers to bodies of water such as Ponds lakes rivers and streams containing low concentrations of dissolved Salts and other Total dissolved EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 An ocean (from Greek, ''Okeanos'' (Oceanus) is a major body of saline water, and a principal component of the Hydrosphere. Glaciers cover vast areas of polar regions but are restricted to the highest mountains in the tropics. Earth's polar regions are the areas of the globe surrounding the poles also known as frigid zones.

Many geologic processes are interrupted or modified significantly by glaciers. Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit Geologic features created by glaciers include end, lateral, ground and medial moraines that form from glacially transported rocks and debris; U-shaped valleys and cirques at their heads, and the glacier fringe, which is the area where the glacier has recently melted into water. Moraine refers to any glacially formed accumulation of unconsolidated glacial debris (soil and rock which can occur in currently glaciated and formerly glaciated regions such as those In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere Debris (ˈdeɪbriː/ /dɛˈbriː is a word used to describe the remains of something that has been otherwise destroyed In Geology, a valley (also called a vale, dale, glen or strath and near or in Appalachia, a draw) is A cirque ( French for " Circus " is an Amphitheatre -like Valley, or valley head formed at the head of a Glacier by Much precipitation becomes trapped in the glaciers instead of flowing immediately back to the oceans, causing sea level drops and greatly modifying the hydrology of streams. In Meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric Hydrology (from Greek Yδωρ hudōr, "water" and λόγος logos, "study" is the study of the movement distribution and quality of A stream is a body of Water with a current, confined within a bed and stream-banks The Earth's crust is pushed down by the weight of the ice, and meltwater commonly collects and forms lakes along the ice margins. In Geology, a crust is the outermost solid shell of a planet or moon A lake (from Latin lacus) is a Terrain feature (or Physical feature) a body of Liquid on the surface of a world that is localized to the

Glacial epochs have come and gone repeatedly over the last million years. Presently, Earth is in a relatively warm period, called an interglacial, exacerbated by global warming with the resulting retreat of the glaciers. An interglacial is a geological interval of warmer global average temperature that separates Glacial periods within an Ice age. Global warming is the increase in the average measured temperature of the whitechuck glacier 2006jpg|right|thumb|320px|The same view as seen in 2006 where this branch of glacier retreated 1 The Earth has been cyclically plunged into cold episodes, however, called glacials, in which the extent of glaciers is expanded, colloquially referred to as ice ages. An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets

Types of glaciers

Main article: Glacier morphology

Mouth of the Schlatenkees Glacier near Innergschlöß, Austria. Glacier morphology, or the form a Glacier takes is influenced by Temperature, precipitation, Topography, and other factors Austria (Österreich ( officially the Republic of Austria (Republik Österreich

There are two main types of glaciers: alpine glaciers, which are found in mountain terrains, and continental glaciers, which can cover larger areas. Most of the concepts in this article apply equally to alpine glaciers and continental glaciers.

A temperate glacier is at melting point throughout the year, from its surface to its base. The ice of polar glaciers is always below freezing point with most mass loss due to sublimation. Sublimation of an element or compound is a transition from the Solid to Gas phase with no intermediate liquid stage Sub-polar glaciers have a seasonal zone of melting near the surface and have some internal drainage, but little to no basal melt.

Thermal classifications of surface conditions vary, so glacier zones are often used to identify melt conditions. The dry snow zone is a region where no melt occurs, even in the summer. The percolation zone is an area with some surface melt, and meltwater percolating into the snowpack, often this zone is marked by refrozen ice lenses, glands, and layers. Meltwater is the water released by the Melting of Snow or Ice, including glacial ice and Ice shelfs over oceans "Snowfall" redirects here For other uses see Snow (disambiguation or Snowfall (disambiguation. The wet snow zone is the region where all of the snow deposited since the end of the previous summer has been raised to 0°C. The superimposed ice zone is a zone where meltwater refreezes as a cold layer in the glacier forming a continuous mass of ice.

The smallest alpine glaciers form in mountain valleys and are referred to as valley glaciers. A mountain is a Landform that extends above the surrounding Terrain in a limited area with a peak Larger glaciers can cover an entire mountain, mountain chain or even a volcano; this type is known as an ice cap. Plate tectonics and hotspots Divergent plate boundaries At the An ice cap is an Ice mass that covers less than 50 000 km² of land area (usually covering a highland area Ice caps feed outlet glaciers, tongues of ice that extend into valleys below, far from the margins of those larger ice masses. Outlet glaciers are formed by the movement of ice from a polar ice cap, or an ice cap from mountainous regions, to the sea. A polar ice cap is a high- Latitude region of a Planet or moon that is covered in Ice.

The largest glaciers are continental ice sheets, enormous masses of ice that are not visibly affected by the landscape and that cover the entire surface beneath them, except possibly on the margins where they are thinnest. An ice sheet is a mass of Glacier Ice that covers surrounding terrain and is greater than 50000 km² (20000 mile²) Antarctica and Greenland are the only places where continental ice sheets currently exist. Greenland (Kalaallit Nunaat meaning "Land of the Greenlanders" Grønland is a self-governing Danish Province located between the These regions contain vast quantities of fresh water. The volume of ice is so large that if the Greenland ice sheet melted, it would cause sea levels to rise some six meters (20 feet) all around the world. The Greenland Ice Sheet is a vast body of ice covering 171 million km² roughly 80% of the surface of Greenland. If the Antarctic ice sheet melted, sea levels would rise up to 65 meters (210 feet). The Antarctic ice sheet is one of the two Polar ice caps of the Earth.

Plateau glaciers resemble ice sheets, but on a smaller scale. They cover some plateaus and high-altitude areas. This type of glacier appears in many places, especially in Iceland and some of the large islands in the Arctic Ocean, and throughout the northern Pacific Cordillera from southern British Columbia to western Alaska. Iceland, officially the Republic of Iceland ( ( Ísland or Lýðveldið Ísland ( The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region is the smallest and shallowest of the world's five major The Pacific Coast Ranges are the series of Mountain ranges that stretch along the west coast of North America from Alaska to northern and central Mexico British Columbia (ˌbrɪtɨʃ kəˈlʌmbiə ( BC) ( (la Colombie-Britannique C Alaska ( Аляска Alyaska) is a state in the United States of America, in the northwest of the North American continent

Tidewater glaciers are glaciers that flow into the sea. As the ice reaches the sea pieces break off, or calve, forming icebergs. An iceberg is a large piece of freshwater Ice that has broken off from a snow-formed Glacier or Ice shelf and is floating in open water Most tidewater glaciers calve above sea level, which often results in a tremendous splash as the iceberg strikes the water. If the water is deep, glaciers can calve underwater, causing the iceberg to suddenly explode up out of the water. The Hubbard Glacier is the longest tidewater glacier in Alaska and has a calving face over ten kilometers long. Hubbard Glacier is a tidewater Glacier in the US state of Alaska and the Yukon Territory of Canada. Yakutat Bay and Glacier Bay are both popular with cruise ship passengers because of the huge glaciers descending hundreds of feet to the water. Yakutat Bay is a 29-km-wide (18 mi bay in the US state of Alaska, extending southwest from Disenchantment Bay to the Gulf of Alaska. The area around Glacier Bay in southeastern Alaska was first proclaimed a U This glacier type undergoes centuries-long cycles of advance and retreat that are much less affected by the climate changes currently causing the retreat of most other glaciers. The tidewater glacier cycle is the typically centuries-long behavior of tidewater glaciers that consists of recurring periods of advance alternating with rapid retreat and punctuated

Formation

Low and high contrast images of the Byrd Glacier. The Byrd Glacier is a major Glacier in Antarctica about 136 km long and 24 km wide draining an extensive area of the polar plateau and flowing eastward between the Britannia The low-contrast version is similar to the level of detail the naked eye would see — smooth and almost featureless. The bottom image uses enhanced contrast to highlight flow lines on the ice sheet and bottom crevasses.

Formation of glacial ice

The snow which forms temperate glaciers is subject to repeated freezing and thawing, which changes it into a form of granular ice called névé. Névé ( is a young granular type of Snow which has been partially melted refrozen and compacted Under the pressure of the layers of ice and snow above it, this granular ice fuses into denser firn. Firn is partially-compacted Névé, a type of Snow that has been left over from past seasons and has been recrystallized into a substance denser than Over a period of years, layers of firn undergo further compaction and become glacial ice. In addition, a few hours after deposition, snow will begin to undergo metamorphism because of the presence of temperature gradients and/or convex and concave surfaces within individual crystals (causing differential vapour pressure). This causes the sublimation of ice from smaller crystals and the deposition of water vapour onto larger crystals, so many crystals become progressively more rounded over time. Depending on the type of metamorphism, the snowpack may become stronger or weaker as a result.

The distinctive blue tint of glacial ice is often wrongly attributed to Rayleigh scattering which is supposedly due to bubbles in the ice. Rayleigh scattering (named after Lord Rayleigh) is the elastic Scattering of Light or other electromagnetic radiation by particles much smaller The blue color is actually created for the same reason that water is blue, that is, its slight absorption of red light due to an overtone of the infrared OH stretching mode of the water molecule [1]. Water is a common Chemical substance that is essential for the survival of all known forms of Life. An overtone is a natural resonance or vibration frequency of a system Infrared spectroscopy (IR spectroscopy is the subset of Spectroscopy that deals with the Infrared region of the Electromagnetic spectrum.

The lower layers of glacial ice flow and deform plastically under the pressure, allowing the glacier as a whole to move slowly like a viscous fluid. Glaciers usually flow downslope, although they do not need a surface slope to flow, as they can be driven by the continuing accumulation of new snow at their source, creating thicker ice and a surface slope. The upper layers of glaciers are more brittle, and often form deep cracks known as crevasses or bergschrunds as they move. A crevasse is a Fracture in a Glacier caused by a large Tensile stress at or near the glacier's surface A bergschrund is a Crevasse that forms where the moving glacier ice separates from the stagnant ice above

Crevasses form due to internal differences in glacier velocity between two quasi-rigid parts above the deeper more plastic substrate far below. As the parts move at different speeds and directions, shear forces cause the two sections to break apart opening the crack of a crevasse all along the disconnecting faces. Projected in effect over three dimensions, one may settle and tip, the other upthrust or twist, or all such combinations due to the effects of each floating on the plastic layers below and any contact with rock and such. Hence the distance between the two separated parts while touching and rubbing deep down, frequently widens significantly towards the surface layers, many times creating a wide chasm.

These crevasses make travel over glaciers hazardous. Subsequent heavy snow may form a fragile snow bridge, increasing the danger by hiding their presence at the surface. For another meaning see Avalanche snow bridge Snow bridge is an arc across a Crevasse, a crack in rock a Creek, or some other Glacial meltwaters flow throughout and underneath glaciers, carving channels in the ice (called moulins) similar to cave formation through rock and also helping to lubricate the glacier's movement. A moulin or glacier mill is a narrow tubular chute hole or Crevasse through which water enters a Glacier from the surface A cave is a natural underground void large enough for a human to enter

Anatomy

The Upper Grindelwald Glacier and the Schreckhorn, in Switzerland, showing accumulation and ablation zones

The upper part of a glacier that receives most of the snowfall is called the accumulation zone. Grindelwald is a municipality in the district of Interlaken in the canton of Bern in Switzerland. The Schreckhorn (4078 m is a Mountain in the Aarmassif in the Bernese Alps. Switzerland (English pronunciation; Schweiz Swiss German: Schwyz or Schwiiz Suisse Svizzera Svizra officially the Swiss Confederation In general, the accumulation zone accounts for 60-70% of the glacier's surface area. Glacier ice accumulation occurs through accumulation of Snow and other frozen precipitation, as well as through other means including Rime ice (freezing The depth of ice in the accumulation zone exerts a downward force sufficient to cause deep erosion of the rock in this area. Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind After the glacier is gone, this often leaves a bowl or amphitheater-shaped isostatic depression called a cirque. Isostatic Depression is the term used by geologists for the sinking of large parts of the earth's crust into the Asthenosphere. A cirque ( French for " Circus " is an Amphitheatre -like Valley, or valley head formed at the head of a Glacier by

On the opposite end of the glacier, at its foot or terminal, is the deposition or ablation zone, where more ice is lost through melting than gained from snowfall and sediment is deposited. Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of The place where the glacier thins to nothing is called the ice front. An ice front is the place where a Glacier thins and ends The ice front's position changes as the glacier moves or melts

The altitude where the two zones meet is called the equilibrium line, also called the snow line. The snow line is the point above which or poleward of which snow and ice cover the ground throughout the year At this altitude, the amount of new snow gained by accumulation is equal to the amount of ice lost through ablation. Due to erosive forces at the edges of the moving ice, glaciers turn V-shaped river-carved valleys into U-shaped glacial valleys.

The "health" of a glacier is defined by the area of the accumulation zone compared to the ablation zone. When directly measured this is glacier mass balance. See also Retreat of glaciers since 1850 Crucial to the survival of a Glacier is its mass balance, the difference between accumulation Healthy glaciers have large accumulation zones. Several non-linear relationships define the relation between accumulation and ablation.

In the aftermath of the Little Ice Age, around 1850, the glaciers of the Earth have retreated substantially. The Little Ice Age (LIA was a period of cooling occurring after a warmer era known as the Medieval Warm Period or Medieval Climate Optimum Glacier retreat has increased since the 1980s, the coldest decade since 1900. whitechuck glacier 2006jpg|right|thumb|320px|The same view as seen in 2006 where this branch of glacier retreated 1 [2]

Occurrence

Glaciers occur on every continent and in approximately 47 of the world's countries. Extensive glaciers are found in Antarctica, Patagonia, Canada, Greenland and Iceland. Llao LLaojpg|thumb|250px| Lake Nahuel Huapi, near Bariloche, Argentina Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page Greenland (Kalaallit Nunaat meaning "Land of the Greenlanders" Grønland is a self-governing Danish Province located between the Iceland, officially the Republic of Iceland ( ( Ísland or Lýðveldið Ísland ( Mountain glaciers are widespread e. g. in the Andes, the Himalaya, the Rocky Mountains, the Caucasus, the Alps, in Norway, Japan, Turkey and the Iran. The Andes form the world's longest exposed Mountain range. They lie as a continuous chain of highland along the western coast of South America. Mountain peaks of the Rocky Mountains The Rocky Mountains, often called the Rockies, are a Mountain range in western North America. The Caucasus ( also referred to as North Caucasus) is a geopolitical region located between Europe Asia & Middle East Norway ( Norwegian: Norge ( Bokmål) or Noreg ( Nynorsk) officially the Kingdom of Norway, is a Constitutional For a topic outline on this subject see List of basic Japan topics. Turkey (Türkiye known officially as the Republic of Turkey ( is a Eurasian Country that stretches For a topic outline on this subject see List of basic Iran topics. On mainland Australia no glaciers exist today, although a small glacier on Mount Kosciuszko was present in the last glacial period, and Tasmania was widely glaciated. Mount Kosciuszko is a Mountain located in the Snowy Mountains in Kosciuszko National Park. "Last glacial" redirects here For the period of maximum glacier extent during this time see Last Glacial Maximum The last glacial period Tasmania is an Australian island and state of the same name It is located south of the eastern side of the Continent, being separated from it by Bass ^[2] On New Zealand's South Island the West Coast bears the Fox and Franz Josef Glaciers. New Zealand is an Island country in the south-western Pacific Ocean comprising two main landmasses (the North Island and the South Island The South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. Naming To New Zealanders the term 'The Coast' generally refers to the West Coast of the South Island, and 'Coasters' to those that live there The Fox Glacier ( Te Moeka o Tuawe in Māori) is a 12 km long Glacier located in Westland National Park on the West Coast of New Zealand The Franz Josef ( Ka Roimata o Hinehukatere in Māori) is a 12 km long Glacier located in Westland National Park on the West Coast of In New Guinea small glaciers are located on its highest summit massif of Puncak Jaya. New Guinea, located just north of Australia, is the world's second largest island, having become separated from the Australian mainland when the area now known Puncak Jaya (ˈpʊntʃak ˈdʒaja sometimes called Mount Carstensz or the Carstensz Pyramid, is a mountain in the Sudirman Range, the western central Africa has glaciers on Mount Kilimanjaro in Tanzania, on Mount Kenya and in the Ruwenzori Range. Tanzania ˌtænzəˈniːə officially the United Republic of Tanzania (Jamhuri ya Muungano wa Tanzania is a country in East Africa bordered by Kenya Mount Kenya is the highest Mountain in Kenya, and the second highest in Africa (after Mount Kilimanjaro) ^[3]

Permanent snow cover is affected by factors such as the degree of slope on the land, amount of snowfall and the force and nature of the winds. Slope is used to describe the steepness incline gradient or grade of a straight line. Wind is the flow of Air or other Gases that compose an Atmosphere (including but not limited to the Earth's) As temperature decreases with altitude, high mountains — even those near the Equator — have permanent snow cover on their upper portions, above the snow line. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature Altitude is the Elevation of a point or object from a known level or datum (plural data A mountain is a Landform that extends above the surrounding Terrain in a limited area with a peak The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the The snow line is the point above which or poleward of which snow and ice cover the ground throughout the year Examples include Mount Kilimanjaro and the Tropical Andes in South America; however, the only snow to occur exactly on the Equator is at 4,690 m (15,387 ft) on the southern slope of Volcán Cayambe in Ecuador. The Tropics are centered on the Equator and limited in Latitude by the Tropic of Cancer in the northern hemisphere at approximately 23°26' (23 South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a For other uses of Cayambe see Cayambe (disambiguation page Cayambe (or Volcán Cayambe) is the name of a Volcano For a topic outline on this subject see List of basic Ecuador topics.

Conversely, many regions of the Arctic and Antarctic receive very little precipitation and therefore experience little snowfall despite the bitter cold (cold air, unlike warm air, cannot take away much water vapor from the sea). The Arctic is the Region around the Earth 's North Pole, opposite the Antarctic region around the South Pole. In Antarctica, the snow does not melt even at sea level. In addition to the dry, unglaciated regions of the Arctic, there are some mountains and volcanoes in Bolivia, Chile and Argentina that are high (4,500 metres (14,800 ft) - 6,900 m (22,600 ft)) and cold, but the relative lack of precipitation prevents snow from accumulating into glaciers. The Republic of Bolivia (República de Bolivia) named after Simón Bolívar, is a Landlocked country in central South America. Chile, officially the Republic of Chile ( Spanish:) is a country in South America occupying a long and narrow Coastal strip wedged between the For a topic outline on this subject see List of basic Argentina topics. This is because these peaks are located near or in the hyperarid Atacama desert. An aridity index (AI is a numerical indicator of the degree of dryness of the climate at a given location Atacama redirects here for the political-administrative region of Chile, see Atacama Region. Further examples of these temperate unglaciated mountains is the Kunlun Mountains, Tibet and the Pamir Range to the north of the Himalayas in Central Asia. The Kunlun Mountains ( Mongolian: Хөндлөн Уулс is one of the longest Mountain chains in Asia, extending more than 3000 Km. Definitions of Tibet See also Definitions of Tibet Name In English The English word Tibet, like the word for Tibet in most European The Pamir Mountains are located in Central Asia and are formed by the junction or Knot of the Tian Shan, Karakoram, Kunlun, and Central Asia is a region of Asia from the Caspian Sea in the west to central China in the east and from southern Russia in the north to northern Pakistan in the south Here, just like the Andes, mountains in Central Asia can reach above 6,000 m (20,000 ft) and be barren of snow and ice due to the rain shadow effect caused by the taller Himalaya Range. For the Australian television series see Rain Shadow (TV series.

During glacial periods of the Quaternary, most of Siberia, central and northern Alaska and all of Manchuria, were similarly too dry to support glaciers, though temperatures were as low as or lower than in glaciated areas of Europe and North America. Overview The term Quaternary ("fourth" was proposed by Giovanni Arduino in 1759 for alluvial deposits in the Po river valley in northern Siberia (Сиби́рь Sibir) is the name given to the vast region constituting almost all of Northern Asia and for the most part currently serving The Alaska Interior covers most of that US state 's territory The Alaska North Slope is the region of the US state of Alaska located on the northern slope of the Brooks Range along the coast of two marginal seas Alaska ( Аляска Alyaska) is a state in the United States of America, in the northwest of the North American continent Manchuria ( Romanized Manchu: Manju,, Маньчжурия Mongolian: Манж is a historical name given to a vast geographic region in northeast This was because dry westerly winds from ice sheets in Europe and the coastal ranges in North America reduced precipitation to such an extent that glaciers could never develop except on a few high mountains like the Verkhoyansk Range (which still supports glaciers today). An ice sheet is a mass of Glacier Ice that covers surrounding terrain and is greater than 50000 km² (20000 mile²) The Verkhoyansk Range (Верхоянский хребет is a Mountain range of eastern Siberia, spanning ca

Glaciers on Mars

Elsewhere in the solar system, the vast polar ice caps of Mars rival those of the Earth and show glacial features. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. An ice cap is an Ice mass that covers less than 50 000 km² of land area (usually covering a highland area Especially the south polar cap is compared to glaciers on Earth. ^[4] Other glacial features on Mars are glacial debris aprons and the lineated valley fills of the fretted terrain in northern Arabia Terra. Arabia Terra is a large upland region in the north of Mars. It is densely cratered and heavily eroded ^[5] Topographical features and computer models indicate the existence of more glaciers in Mars' past. ^[6]

Motion

Main article: Ice sheet dynamics

The Perito-Moreno Glacier, showing cracks in brittle upper layer

Ice behaves like an easily breaking solid until its thickness exceeds about 50 meters (160 ft). Ice sheet dynamics describe the motion within large bodies of ice, such those currently on Greenland and Antarctica. The pressure on ice deeper than that depth causes plastic flow. The glacial ice is made up of layers of molecules stacked on top of each other, with relatively weak bonds between the layers. When the stress of the layer above exceeds the inter-layer binding strength, it moves faster than the layer below.

Another type of movement is basal sliding. Basal Sliding is the act of a Glacier sliding over the bed before it due to Meltwater under the ice acting as In this process, the whole glacier moves over the terrain on which it sits, lubricated by meltwater. As the pressure increases toward the base of the glacier, the melting point of water decreases, and the ice melts. Friction between ice and rock and geothermal heat from the Earth's interior also contribute to thawing. In Geology, geothermal refers to heat sources within the planet This type of movement is dominant in temperate glaciers. The geothermal heat flux becomes more important the thicker a glacier becomes.

Fracture zone and cracks

Ice cracks in the Titlis Glacier

Signs warning of the hazards of a glacier in New Zealand

The top 50 meters of the glacier are more rigid. The Titlis (3238  m) is a mountain in the Urner Alps of Switzerland. New Zealand is an Island country in the south-western Pacific Ocean comprising two main landmasses (the North Island and the South Island In this section, known as the fracture zone, the ice mostly moves as a single unit. Ice in the fracture zone moves over the top of the lower section. When the glacier moves through irregular terrain, cracks form in the fracture zone. These cracks can be up to 50 meters deep, at which point they meet the plastic like flow underneath that seals them.

Speed

The speed of glacial displacement is partly determined by friction. Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e Friction makes the ice at the bottom of the glacier move slower than the upper portion. In alpine glaciers, friction is also generated at the valley's side walls, which slows the edges relative to the center. This was confirmed by experiments in the 19th century, in which stakes were planted in a line across an alpine glacier, and as time passed, those in the center moved farther. The 19th century of the Common Era began on January 1, 1801 and ended on December 31, 1900, according to the Gregorian calendar

Mean speeds vary; some have speeds so slow that trees can establish themselves among the deposited scourings. In other cases they can move as fast as meters per day, as in the case of Antarctica's Byrd Glacier, which moves 750-800 meters per year. The Byrd Glacier is a major Glacier in Antarctica about 136 km long and 24 km wide draining an extensive area of the polar plateau and flowing eastward between the Britannia

Many glaciers have periods of very rapid advancement called surges. Glacial surges are short-lived events where a Glacier can move up to velocities 100 times faster than normal and advance substantially These glaciers exhibit normal movement until suddenly they accelerate, then return to their previous state. During these surges, the glacier may reach velocities far greater than normal speed. ^[7] These surges may be caused by failure of the underlying bedrock, the ponding of meltwater at the base of the glacier^[8] - perhaps delivered from a supraglacial lake - or the simple accumulation of mass beyond a critical "tipping point". A supraglacial lake is any pond of liquid water on the top of a Glacier. ^[9]

Moraines

Glacial moraines are formed by the deposition of material from a glacier and are exposed after the glacier has retreated. Moraine refers to any glacially formed accumulation of unconsolidated glacial debris (soil and rock which can occur in currently glaciated and formerly glaciated regions such as those These features usually appear as linear mounds of till, a non-sorted mixture of rock, gravel and boulders within a matrix of a fine powdery material. Till is unsorted glacial sediment Glacial drift is a general term for the coarsely graded and extremely heterogeneous Sediments of glacial origin Terminal or end moraines are formed at the foot or terminal end of a glacier. Lateral moraines are formed on the sides of the glacier. Medial moraines are formed when two different glaciers, flowing in the same direction, coalesce and the lateral moraines of each combine to form a moraine in the middle of the merged glacier. Less apparent is the ground moraine, also called glacial drift, which often blankets the surface underneath much of the glacier downslope from the equilibrium line. Glacial meltwaters contain rock flour, an extremely fine powder ground from the underlying rock by the glacier's movement. Rock flour, or glacial flour, consists of clay-sized particles of rock generated by glacial erosion or by artificial grinding to a similar size Other features formed by glacial deposition include long snake-like ridges formed by streambeds under glaciers, known as eskers, and distinctive streamlined hills, known as drumlins. An esker is a long winding ridge of Stratified Sand and Gravel, examples of which occur in glaciated and formerly glaciated regions of A drumlin (Irish droimnín, a little hill ridge is an elongated whale-shaped Hill formed by glacial action

Stoss-and-lee erosional features are formed by glaciers and show the direction of their movement. Long linear rock scratches (that follow the glacier's direction of movement) are called glacial striations, and divots in the rock are called chatter marks. Glacial striations or glacial grooves are scratches or gouges cut into Bedrock by process of glacial abrasion. A Chatter mark is one or more commonly a series of marks made by vibratory chipping of a bedrock surface by rock fragments carried in the base of a glacier Both of these features are left on the surfaces of stationary rock that were once under a glacier and were formed when loose rocks and boulders in the ice were transported over the rock surface. Transport of fine-grained material within a glacier can smooth or polish the surface of rocks, leading to glacial polish. Glacial polish is a characteristic of rock surfaces where glaciers have passed over bedrock typically Granite or other hard igneous or metamorphic rock Glacial erratics are rounded boulders that were left by a melting glacier and are often seen perched precariously on exposed rock faces after glacial retreat. A glacial erratic is a piece of rock that deviates from the size and type of rock native to the area in which it rests the name " erratic " is based on the In Geology, a boulder is a rock with grain size of usually no less than 256 mm (10 Inches diameter

The term moraine is of French origin, and it was coined by peasants to describe alluvial embankments and rims found near the margins of glaciers in the French Alps. French ( français,) is a Romance language spoken around the world by 118 million people as a native language and by about 180 to 260 million people In modern geology, the term is used more broadly, and is applied to a series of formations, all of which are composed of till.

Drumlins

A drumlin field forms after a glacier has modified the landscape. The teardrop-shaped formations denote the direction of the ice flow.

Drumlins are asymmetrical, canoe shaped hills with aerodynamic profiles made mainly of till. A drumlin (Irish droimnín, a little hill ridge is an elongated whale-shaped Hill formed by glacial action Their heights vary from 15 to 50 meters and they can reach a kilometer in length. The tilted side of the hill looks toward the direction from which the ice advanced (stoss), while the longer slope follows the ice's direction of movement (lee).

Drumlins are found in groups called drumlin fields or drumlin camps. A drumlin field is a cluster of dozens to hundreds of similarly shaped sized and oriented Drumlins also called a drumlin swarm. An example of these fields is found east of Rochester, New York, and it is estimated that it contains about 10,000 drumlins. Rochester is a city in Monroe County, New York State, south of Lake Ontario in the United States.

Although the process that forms drumlins is not fully understood, it can be inferred from their shape that they are products of the plastic deformation zone of ancient glaciers. It is believed that many drumlins were formed when glaciers advanced over and altered the deposits of earlier glaciers.

Ogives

Ogives are alternating dark and light bands of ice occurring as ridges and valleys on glacier surfaces. They only occur below icefalls but not all icefalls have ogives below them. Once formed, they bend progressively downglacier due to the increased velocity toward the glacier's centerline. Ogives are likely linked to seasonal motion of the glacier as the width of one dark and one light band generally equals the annual movement of the glacier. The ridges and valleys are formed because ice from an icefall is severely broken up thereby increasing ablation surface area during the summertime creating a swale and creating space for snow accumulation in the winter creating a ridge. ^[10] Sometimes ogives are described as either wave ogives or band ogives in which they are solely undulations or varying color bands respectively. ^[11]

Erosion

Rocks and sediments are added to glaciers through various processes. Glaciers erode the terrain principally through two methods: abrasion and plucking. Abrasion is mechanical scraping of a rock surface by Friction between rocks and moving particles during their transport in Wind, Glacier, Waves Plucking, in the sense relating to Glaciers is when a glacier erodes away chunks of Bedrock to be later deposited as Glacial erratics Glacial plucking

Diagram of glacial plucking and abrasion

As the glacier flows over the bedrock's fractured surface, it softens and lifts blocks of rock that are brought into the ice. This process is known as plucking, and it is produced when subglacial water penetrates the fractures and the subsequent freezing expansion separates them from the bedrock. When the water expands, it acts as a lever that loosens the rock by lifting it. This way, sediments of all sizes become part of the glacier's load.

Abrasion occurs when the ice and the load of rock fragments slide over the bedrock and function as sandpaper that smooths and polishes the surface situated below. This pulverized rock is called rock flour. Rock flour, or glacial flour, consists of clay-sized particles of rock generated by glacial erosion or by artificial grinding to a similar size This flour is formed by rock grains of a size between 0. 002 and 0. 00625 mm. The Millimetre ( American spelling: millimeter, symbol mm) is a unit of Length in the Metric system, equal to Sometimes the amount of rock flour produced is so high that currents of meltwaters acquire a grayish color.

Another of the visible characteristics of glacial erosion are glacial striations. Glacial striations or glacial grooves are scratches or gouges cut into Bedrock by process of glacial abrasion. These are produced when the bottom's ice contains large chunks of rock that mark trenches in the bedrock. By mapping the direction of the flutes the direction of the glacier's movement can be determined. Chatter marks are seen as lines of roughly crescent shape depressions in the rock underlying a glacier caused by the abrasion where a boulder in the ice catches and is then released repetitively as the glacier drags it over the underlying basal rock. A Chatter mark is one or more commonly a series of marks made by vibratory chipping of a bedrock surface by rock fragments carried in the base of a glacier

A glacier may also erode its environment through katabatic winds. A katabatic wind, from the Greek word katabatikos meaning "going downhill" is the technical name for a drainage Wind, a wind

The rate of glacier erosion is variable. The differential erosion undertaken by the ice is controlled by six important factors:

• Velocity of glacial movement
• Thickness of the ice
• Shape, abundance and hardness of rock fragments contained in the ice at the bottom of the glacier
• Relative ease of erosion of the surface under the glacier.
• Thermal conditions at the glacier base.
• Permeability and water pressure at the glacier base.

Material that becomes incorporated in a glacier are typically carried as far as the zone of ablation before being deposited. Glacial deposits are of two distinct types:

• Glacial till: material directly deposited from glacial ice. Till includes a mixture of undifferentiated material ranging from clay size to boulders, the usual composition of a moraine.
• Fluvial and outwash: sediments deposited by water. These deposits are stratified through various processes, such as boulders being separated from finer particles.

The larger pieces of rock which are encrusted in till or deposited on the surface are called glacial erratics. A glacial erratic is a piece of rock that deviates from the size and type of rock native to the area in which it rests the name " erratic " is based on the They may range in size from pebbles to boulders, but as they may be moved great distances they may be of drastically different type than the material upon which they are found. Patterns of glacial erratics provide clues of past glacial motions.

Glacial valleys

A glaciated valley in the Mount Hood Wilderness showing the characteristic U-shape and flat bottom. The Mount Hood Wilderness is a protected Wilderness area inside the Mount Hood National Forest which is located in the U

This image shows the termini of the glaciers in the Bhutan Himalaya. The Kingdom of Bhutan (buːˈtɑːn is a Landlocked nation in South Asia. Glacial lakes have been rapidly forming on the surface of the debris-covered glaciers in this region during the last few decades.

Before glaciation, mountain valleys have a characteristic "V" shape, produced by downward erosion by water. In Geology, a valley (also called a vale, dale, glen or strath and near or in Appalachia, a draw) is However, during glaciation, these valleys widen and deepen, forming a "U"-shaped glacial valley. In Geology, a valley (also called a vale, dale, glen or strath and near or in Appalachia, a draw) is Besides the deepening and widening of the valley, the glacier also smooths the valley due to erosion. In this way, it eliminates the spurs of earth that extend across the valley. Because of this interaction, triangular cliffs called truncated spurs are formed. A truncated spur occurs when the action of a Glacier does not follow the original course of the River that wound round Interlocking spurs, but as

Many glaciers deepen their valleys more than their smaller tributaries. A tributary is a Stream or River which flows into a mainstem (or parent river Therefore, when the glaciers recede from the region, the valleys of the tributary glaciers remain above the main glacier's depression, and these are called hanging valleys. In Geology, a valley (also called a vale, dale, glen or strath and near or in Appalachia, a draw) is

In parts of the soil that were affected by abrasion and plucking, the depressions left can be filled by lakes, called paternoster lakes. A Paternoster lake is one of a series of Glacial lakes connected by a single Stream or a braided stream system

At the 'start' of a classic valley glacier is the cirque, which has a bowl shape with escarped walls on three sides, but open on the side that descends into the valley. A cirque ( French for " Circus " is an Amphitheatre -like Valley, or valley head formed at the head of a Glacier by In the cirque, an accumulation of ice is formed. These begin as irregularities on the side of the mountain, which are later augmented in size by the coining of the ice. Once the glacier melts, these corries are usually occupied by small mountain lakes called tarns. A tarn (or corrie loch) is a mountain Lake or pool formed in a Cirque excavated by a Glacier.

There may be two glacial cirques 'back to back' which erode deep into their backwalls until only a narrow ridge, called an arête is left. This article is about a glacial landform See Arete for other meanings This structure may result in a mountain pass. In a range of hills or especially of mountains, a pass (also gap, notch, col, saddle, bwlch,

Glaciers are also responsible for the creation of fjords (deep coves or inlets) and escarpments that are found at high latitudes. A fjord or fiord (fjɔːd|fiːɔːd or fiːɔːd is a long narrow Inlet with steep sides created in a valley carved by glacial activity. In Geomorphology, an escarpment is a transition zone between different physiogeographic provinces that involves a sharp steep Elevation differential characterized

Features of a glacial landscape

Arêtes and horns (pyramid peak)

An arête is a narrow crest with a sharp edge. This article is about a glacial landform See Arete for other meanings The meeting of three or more arêtes creates pointed pyramidal peaks and in extremely steep-sided forms these are called horns. A pyramidal peak, or sometimes in its most extreme form called a glacial horn, is a Mountaintop that has been modified by the action of Ice during A pyramidal peak, or sometimes in its most extreme form called a glacial horn, is a Mountaintop that has been modified by the action of Ice during

Both features may have the same process behind their formation: the enlargement of cirques from glacial plucking and the action of the ice. Horns are formed by cirques that encircle a single mountain.

Arêtes emerge in a similar manner; the only difference is that the cirques are not located in a circle, but rather on opposite sides along a divide. Arêtes can also be produced by the collision of two parallel glaciers. In this case, the glacial tongues cut the divides down to size through erosion, and polish the adjacent valleys.

Sheepback rock

Some rock formations in the path of a glacier are sculpted into small hills with a shape known as roche moutonnée or sheepback. In Glaciology, a roche moutonnée (or sheepback) is a Rock formation created by the passing of a Glacier. An elongated, rounded, asymmetrical, bedrock knob can be produced by glacier erosion. It has a gentle slope on its up-glacier side and a steep to vertical face on the down-glacier side. The glacier abrades the smooth slope that it flows along, while rock is torn loose from the downstream side and carried away in ice, a process known as 'plucking'. Rock on this side is fractured by combinations of forces due to water, ice in rock cracks, and structural stresses.

Alluvial stratification

The water that rises from the ablation zone moves away from the glacier and carries with it fine eroded sediments. On a Glacier, the ablation zone, zone of ablation or zone of wastage is the area in which annual loss of snow through Melting, Evaporation As the speed of the water decreases, so does its capacity to carry objects in suspension. The water then gradually deposits the sediment as it runs, creating an alluvial plain. An alluvial plain is a relatively flat Landform created by the deposition of sediment over a long period of time by one or more Rivers coming from highland regions When this phenomenon occurs in a valley, it is called a valley train. When the deposition is to an estuary, the sediments are known as "bay mud". An estuary is a semi-enclosed Coastal body of Water with one or more Rivers or Streams flowing into it and with a free connection to the open Bay mud consists of thick deposits of soft unconsolidated Silty Clay, which is saturated with Water; these soil layers are situated at the bottom of

Landscape produced by a receding glacier

Alluvial plains and valley trains are usually accompanied by basins known as kettles. A kettle (or kettle hole) is a shallow sediment-filled body of water formed by retreating glaciers or draining floodwaters Glacial depressions are also produced in till deposits. These depressions are formed when large ice blocks are stuck in the glacial alluvium and after melting, they leave holes in the sediment.

Generally, the diameter of these depressions does not exceed 2 km, except in Minnesota, where some depressions reach up to 50 km in diameter, with depths varying between 10 and 50 meters. Minnesota ( Native Americans demonstrated the name to early settlers

Deposits in contact with ice

When a glacier reduces in size to a critical point, its flow stops, and the ice becomes stationary. Meanwhile, meltwater flows over, within, and beneath the ice leave stratified alluvial deposits. Because of this, as the ice melts, it leaves stratified deposits in the form of columns, terraces and clusters. A column in Structural engineering is a vertical structural element that transmits through compression, the weight of the structure above to other structural A terrace deposit is geological term for a flat platform of land created alongside of a River or sea where at some time in the past the river has cut itself a deeper These types of deposits are known as deposits in contact with ice.

When those deposits take the form of columns of tipped sides or mounds, which are called kames. A kame is a geological feature an irregularly shaped Hill or Mound composed of Sand, Gravel and Till that accumulates Some kames form when meltwater deposits sediments through openings in the interior of the ice. In other cases, they are just the result of fans or deltas towards the exterior of the ice produced by meltwater. A delta is a Landform where the mouth of a River flows into an Ocean, Sea, Estuary, Lake or another river

When the glacial ice occupies a valley it can form terraces or kame along the sides of the valley.

A third type of deposit formed in contact with the ice is characterized by long, narrow sinuous crests composed fundamentally of sand and gravel deposited by streams of meltwater flowing within, beneath or on the glacier ice. Sand is a naturally occurring Granular material composed of finely divided rock and Mineral particles Gravel is rock that is of a specific Particle size range In Geology, gravel is any loose rock that is larger than two millimeters (2mm After the ice has melted these linear ridges or eskers remain as landscape features. An esker is a long winding ridge of Stratified Sand and Gravel, examples of which occur in glaciated and formerly glaciated regions of Some of these crests have heights exceeding 100 meters and their lengths surpass 100 km. A crest is the point on a Wave with the greatest positive value or upward displacement in a Cycle.

Loess deposits

Very fine glacial sediments or rock flour is often picked up by wind blowing over the bare surface and may be deposited great distances from the original fluvial deposition site. Rock flour, or glacial flour, consists of clay-sized particles of rock generated by glacial erosion or by artificial grinding to a similar size These eolian loess deposits may be very deep, even hundreds of meters, as in areas of China and the Midwestern United States. Aeolian (or Eolian or Æolian) processes pertain to the activity of the Winds and more specifically to the winds' ability to shape the surface of the Loess is a homogeneous typically non stratified porous Friable,slightly coherent often calcareous fine-grained Silty pale yellow or buff windblown ( aeolian

Transportation

• Entrainment is the picking up of loose material by the glacier from along the bed and valley sides. Entrainment can happen by regelation or by the ice simply picking up the debris. Regelation is the phenomenon of melting under pressure and freezing again when the pressure is reduced
• Basal Ice Freezing is thought to be to be made by glaciohydraulic supercooling, though some studies show that even where physical conditions allow it to occur, the process may not be responsible for observed sequences of basal ice.
• Plucking is the process involves the glacier freezing onto the valley sides and subsequent ice movement pulling away masses of rock. As the bedrock is greater in strength than the glacier, only previously loosened material can be removed. Bedrock is the native consolidated rock underlying the surface of a terrestrial planet usually the Earth. It can be loosened by local pressure and temperature, water and pressure release of the rock itself.
• Supraglacial debris is carried on the surface of the glacier as lateral and medial moraines. In summer ablation, surface melt water carries a small load and this often disappears down crevasses.
• Englacial debris is moraine carried within the body of the glacier. Moraine refers to any glacially formed accumulation of unconsolidated glacial debris (soil and rock which can occur in currently glaciated and formerly glaciated regions such as those
• Subglacial debris is moved along the floor of the valley either by the ice as ground moraine or by meltwater streams formed by pressure melting. Moraine refers to any glacially formed accumulation of unconsolidated glacial debris (soil and rock which can occur in currently glaciated and formerly glaciated regions such as those

Deposition

• Lodgement till is identical to ground moraine. Moraine refers to any glacially formed accumulation of unconsolidated glacial debris (soil and rock which can occur in currently glaciated and formerly glaciated regions such as those It is material that is smeared on to the valley floor when its weight becomes too great to be moved by the glacier.
• Ablation till is a combination of englacial and supraglacial moraine It is released as a stationary glacier begins to melt and material is dropped in situ. In situ (ɪn siːˈtuː is a Latin phrase meaning in the place.
• Dumping is when a glacier moves material to its outermost or lowermost end and dumps it.
• Deformation flow is the change of shape of the rock and land due to the glacier.

Glacial deposition takes place in two forms: glaciofluvial deposition and till deposits.

• Glaciofluvial deposition comes from glacial meltwater. The water that is a result from melting glaciers carry material much like a river would and sorts it is it moves along. Examples of these landforms would include outwash plains and kettle holes. A sandur (plural sandar is a glacial outwash Plain formed of Sediments deposited by meltwater at the terminus of a Glacier. A kettle (or kettle hole) is a shallow sediment-filled body of water formed by retreating glaciers or draining floodwaters
• Till deposits are unsorted mounds of sand, gravel and rock that form around a glacier. Examples of these are moraines, kame terraces etc. Moraine refers to any glacially formed accumulation of unconsolidated glacial debris (soil and rock which can occur in currently glaciated and formerly glaciated regions such as those

Isostatic rebound

Main article: Isostatic rebound

Isostatic pressure by a glacier on the Earth's crust

This rise of a part of the crust is due to an isostatic adjustment. Post-glacial rebound (sometimes called continental rebound, isostatic rebound, isostatic adjustment or post-ice-age isostatic recovery) In Geology, a crust is the outermost solid shell of a planet or moon Isostasy (Greek isos = "equal" stásis = "standstill" is a term used in Geology to refer to the state of gravitational equilibrium between the A large mass, such as an ice sheet/glacier, depresses the crust of the Earth and displaces the mantle below. The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided The depression is about a third the thickness of the ice sheet. After the glacier melts the mantle begins to flow back to its original position pushing the crust back to its original position. This post-glacial rebound, which lags melting of the ice sheet/glacier, is currently occurring in measurable amounts in Scandinavia and the Great Lakes region of North America. Post-glacial rebound (sometimes called continental rebound, isostatic rebound, isostatic adjustment or post-ice-age isostatic recovery) Terminology and usage As a cultural term "Scandinavia" has no official definition and is subject to usage by those who identify with the culture in question as well The Laurentian Great Lakes are a chain of freshwater lakes located in eastern North America, on the Canada–United States border.

An interesting geomorphological feature created by the same process, but on a smaller scale, is known as dilation-faulting. It occurs within rock where previously compressed rock is allowed to return to its original shape, but more rapidly than can be maintained without faulting, leading to an effect similar to that which would be seen if the rock were hit by a large hammer. This can be observed in recently de-glaciated parts of Iceland.

Ice ages

Main article: Ice age

Divisions

A quadruple division of the Quaternary glacial period has been established for North America and Europe. An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets Overview The term Quaternary ("fourth" was proposed by Giovanni Arduino in 1759 for alluvial deposits in the Po river valley in northern These divisions are based principally on the study of glacial deposits. In North America, each of these four stages was named for the state in which the deposits of these stages were well exposed. In order of appearance, they are the following: Nebraskan, Kansan, Illinoisan, and Wisconsinan. This classification was refined thanks to the detailed study of the sediments of the ocean floor. "Ocean Floor" redirects here For the 2001 song by Audio Adrenaline, see Lift (Audio Adrenaline album. Because the sediments of the ocean floor are less affected by stratigraphic discontinuities than those on land, they are useful to determine the climatic cycles of the planet. Stratigraphy, a branch of Geology, studies rock layers and layering ( stratification) Climate encompasses the temperatures humidity rainfall atmospheric particle count and numerous other meteorogical factors in a given region over long periods of

In this matter, geologists have come to identify over twenty divisions, each of them lasting approximately 100,000 years. All these cycles fall within the Quaternary glacial period.

During its peak, the ice left its mark over almost 30% of Earth's surface, covering approximately 10 million km² in North America, 5 million km² in Europe and 4 million km² in Asia. The glacial ice in the Northern hemisphere was double that found in the Southern hemisphere. This is because southern polar ice cannot advance beyond the Antarctic landmass. It is now believed that the most recent glacial period began between two and three million years ago, in the Pleistocene era.

The last major glacial period began about 2,000,000 years B. P. and is commonly known as the Pleistocene or Ice Age. The Pleistocene ('plaɪstəsin is the epoch from 18 million to 10000 years BP covering the world's recent period An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets During this glacial period, large glacial ice sheets covered much of North America, Europe, and Asia for long periods of time. The extent of the glacier ice during the Pleistocene, however, was not static. The Pleistocene had periods when the glaciers retreated (interglacial) because of mild temperatures, and advanced because of colder temperatures (glacial). Average global temperatures were probably 4 to 5° Celsius colder than they are today at the peak of the Pleistocene. The Celsius Temperature scale was previously known as the centigrade scale. The most recent glacial retreat began about 14,000 years B.P. and is still going on. Before Present (BP years are a time scale used in Archaeology, Geology, and other scientific disciplines to specify when events in the past occurred We call this period the Holocene epoch. The Holocene is a Geological epoch which began approximately 10000 years ago (about 8000 BC

Causes

Generalized glaciations have been rare in the history of Earth. The history of Earth covers approximately 46 billion years (4567000000 years from Earth ’s formation out of the Solar nebula to the present However, the Ice Age of the Pleistocene was not the only glacial event, since tillite deposits have been identified. An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets The Pleistocene ('plaɪstəsin is the epoch from 18 million to 10000 years BP covering the world's recent period Till is unsorted glacial sediment Glacial drift is a general term for the coarsely graded and extremely heterogeneous Sediments of glacial origin Tillite is a sedimentary rock formed when glacial till is lithified.

These deposits found in strata of differing age present similar characteristics as fragments of fluted rock, and some are superposed over bedrock surfaces of channeled and polished rock or associated with sandstone and conglomerates that have features of alluvial plain deposits. Sandstone is a Sedimentary rock composed mainly of Sand -size Mineral or rock grains. A conglomerate (kɒnˈglɒmərət is a rock consisting of individual stones that have become cemented together

Two Precambrian glacial episodes have been identified, the first approximately 2 billion years ago, and the second (Snowball Earth) about 650 million years ago. The Precambrian ( Pre-Cambrian) is an informal name for the supereon comprising the eons of the Geologic timescale that came before the current The Snowball Earth Hypothesis as it was originally proposed]] Evidence The Snowball Earth hypothesis was originally devised to explain the apparent presence of Also, a well documented record of glaciation exists in rocks of the late Paleozoic (the Carboniferous and Permian). The Paleozoic or Palaeozoic Era (from the Greek palaio (παλαιο "old" and zoe (ζωη "life" meaning "ancient life" The Carboniferous is a geologic period and system that extends from the end of the Devonian period about 359 The Permian is a geologic period and system that extends from 299

Although there are several scientific hypotheses about the determining factors of glaciations, the two most important ideas are plate tectonics and variations in Earth's orbit (Milankovitch cycles). Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere Milankovitch cycles are the collective effect of changes in the Earth 's movements upon its climate named after Serbian civil engineer and Mathematician

Plate tectonics

Because glaciers can form only on dry land, plate tectonics suggest that the evidence of previous glaciations seen in tropical latitudes is due to the drift of tectonic plates from tropical latitudes to circumpolar regions. Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the Continental drift is the movement of the Earth 's Continents relative to each other Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere Evidence of glacial structures in South America, Africa, Australia, and India support this idea, because it is known that they experienced a glacial period near the end of the Paleozoic Era, some 250 million years ago. South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a India, officially the Republic of India (भारत गणराज्य inc-Latn Bhārat Gaṇarājya; see also other Indian languages) is a country The Paleozoic or Palaeozoic Era (from the Greek palaio (παλαιο "old" and zoe (ζωη "life" meaning "ancient life"

The idea that the evidence of middle-latitude glaciations is closely related to the displacement of tectonic plates was confirmed by the absence of glacial traces in the same period for the higher latitudes of North America and Eurasia, which indicates that their locations were very different from today. For the superstate in George Orwell 's novel see Nations of Nineteen Eighty-Four.

Climatic changes are also related to the positions of the continents, which has made them vary in conjunction with the displacement of plates. That also affected ocean current patterns, which caused changes in heat transmission and humidity. Since continents drift very slowly (about 2 cm per year), similar changes occur in periods of millions of years.

A study of marine sediment that contained climatically sensitive microorganisms until about half a million years ago were compared with studies of the geometry of Earth's orbit, and the result was clear: climatic changes are closely related to periods of obliquity, precession, and eccentricity of the Earth's orbit. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually Geometry ( Greek γεωμετρία; geo = earth metria = measure is a part of Mathematics concerned with questions of size shape and relative position In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. Precession refers to a change in the direction of the axis of a rotating object In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape

In general it can be affirmed that plate tectonics applies to long time periods, while Milankovitch's proposal, backed up by the work of others, adjusts to the periodic alterations of glacial periods of the Pleistocene. In both mechanisms the radiation imbalance of the earth is thought to play a large role in the build-up and melt of glaciers.

See also

• Aufeis
• Cryoseism
• Effects of global warming
• Erebus Ice Tongue
• Glacial motion
• Glacier Bay National Park and Preserve
• Global warming
• Icefall
• Ice cap
• Ice field
• Ice sheet
• Kenai Fjords National Park
• List of glaciers
• Misty Fjords National Monument
• Quaternary period
• Retreat of glaciers since 1850
• Irish Sea Glacier

Cited references

Uncited references

• This article draws heavily on the corresponding article in the Spanish-language Wikipedia, which was accessed in the version of 24 July 2005. It was translated by the Spanish Translation of the Week collaboration.
• Hambrey, Michael; Alean, Jürg (2004). Glaciers, 2nd ed. , Cambridge University Press. ISBN 0-521-82808-2.   An excellent less-technical treatment of all aspects, with superb photographs and firsthand accounts of glaciologists' experiences. All images of this book can be found online (see Weblinks: Glaciers-online)
• Benn, Douglas I. (1999). Glaciers and Glaciation. Arnold.  
• Bennett, M. R. ; Glasser, N. F. (1996). Glacial Geology: Ice Sheets and Landforms. John Wiley & Sons.  
• Hambrey, Michael (1994). Glacial Environments. University of British Columbia Press, UCL Press.   An undergraduate-level textbook.
• Knight, Peter G (1999). Glaciers. Cheltenham: Nelson Thornes. ISBN 0-7487-4000-7.   A textbook for undergraduates avoiding mathematical complexities
• Walley, Robert (1992). Introduction to Physical Geography. Wm. C. Brown Publishers.   A textbook devoted to explaining the geography of our planet.
• W. S. B. Paterson (1994). Physics of Glaciers, 3rd ed. , Pergamon Press.   A comprehensive reference on the physical principles underlying formation and behavior.

External References

Glaciers shrinking at record rate Retrieved Mar 17 2008

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