A Glacier is a mass of more or less wide ice which is formed by the compressing of layers of Neige accumulated. Crushed under its own weight, snow expels the air which it contains, is welded in a mass compacts and transforms themselves into Glace.
The field of plasticity of the ice being particularly wide, a glacier runs out slowly under the effect of the Gravité along a slope or by Fluage.
“Glacier” is a term Francoprovençal which one meets as of the 14th century in Valais and which derives from Latin bottom glacia or of traditional Latin glacies . Starting from the middle of the 18th century, in France, one prefers it at the end “refrigerator” which was then used.
The glaciers account for 98,5% of fresh water of planet.
DescriptionJust like each river is single by its characteristics, no glacier does not resemble another. It is however possible to distinguish certain recurring characteristics and applying in a general way.
One can distinguish three zones in a glacier :
- the zone of accumulation : it is the part of the glacier where precipitations of snow are transformed into ice. It corresponds to the zone of the eternal snow and consequently the ice is seldom exposed. The zone of accumulation corresponds in general to 60 to 70% of the surface of a glacier alpin ;
- the zone of transport : it is the part of the glacier where the cast iron remains limited and where the glacier is thickest. The glacial erosion is there with its maximum ;
- the zone of ablation : it is the part of the glacier where the important cast iron causes the reduction the thickness of the glacier until its total disappearance on the level of the glacial Front which can take the shape of a cliff, a hill, a disorganized cluster of ice,…
The line of balance of a glacier is the limit which separates the zone from the glacier where the weight breakdown is surplus and the zone of the glacier where the weight breakdown is overdrawn. This line of balance is materialized during the hot months by the limit between persistent snow (eternal snow) and freezes apparent. The line of balance is used to mark the end of the zone of accumulation of a glacier.
These three sectors of a glacier are very variable cuts some, even absent on certain glaciers.
The successive layers of snow which form the glacier imprison during their passage in the atmosphere dust, pollens, pollutants and trap bubbles of air which preserve the content of gas composing the atmosphere at the time of trapping. This information makes of a glacier a true book reporting the evolution of the atmosphere lasting of the hundreds of thousands of years. Drillings (Vostok in the Antarctic) make it possible to go up icicles and to analyze the composition of the atmosphere at the time of the formation of the layers.
The darker one ice is, the less it contains bubble of air.
A glacier has other characteristics which are revealing Topographie, Climat, of its erosive activity, of sound passé :
- a glacial Bolt or an increase in the slope can cause on the surface the formation of Crevasse S and Sérac S because the ice sudden of the constraints higher than the limit of its plasticité ;
- a Rimaye can be formed between the zone of accumulation and the zone of transport ;
- a cast iron of surface or an external contribution of water can form Bédière S and mills ;
- of the contributions external or the rock remains increase can cover partially or completely a glacier. These remains protect the glacier from the solar radiation and the atmospheric temperatures what sometimes allows a glacier whose final language is entirely covered with remains to go down low in altitude than if it were deprived by it.
Glacial hydrous assessmentOne can define a seasonal hydrous assessment for a glacier.
This assessment makes the difference between loss and water profit, whether it is in liquid form, solid or gas. During the hottest months, the Précipitation S in the form of snow are with lowest and the increase of the temperatures accelerates the cast iron of the glacier by extending its zone of ablation to more high-altitude. The hydrous assessment of the glacier is then négatif : its mass decreases by losing more water than it does not receive any. Contrary, the most cold months see snow-covered precipitations increasing and the cast iron to reach its minimum. The hydrous assessment of the glacier is positif : its mass increases by reconstituting its stocks of ice which it lost the summer.
The seasonal hydrous assessment of a glacier defines the flow of the emissary torrent whose flood is composed of melt waters. The flow of melt waters is with its maximum the hottest months and is with its minimum the most cold months. It should be specified that this flow of melt waters, even if it strongly influences it, does not correspond to the flow of the emissary torrent which can be grown bigger by the rains or attenuated by evaporation, the refill of the ground water, the taking away for the human activities, etc the flow of melt waters, if he is directly related to snow-covered precipitations, is much more affected by other factors météorologiques : intensity and duration of the sunning and the temperatures which are more stable variables in space and time that precipitations. Thus, one can observe fluctuations day laborers of the flow of water of fonte : the maximum is reached in the afternoon while the minimum is at the end of the night.
The glacier, by playing the part of fresh water tank, regularizes the flow of the rivers downstream throughout the year. It thus makes it possible the vegetation downstream from the glacier to have constant water reserves and to avoid or attenuate possible periods of dryness.
Speed of a glacierA glacier starts to become deformed and is thus able to advance by acquiring a certain plasticity when it exceeds fifty meters thickness. It is as for this reason as the surface of the glaciers is covered with seracs and crevasses : the roadbase corresponding to the first fifty meters of the glacier does not become deformed but breakage.
A glacier advances, moves because of gravity or becomes deformed, creeps because of its own weight. The speed and the direction of displacement are function of topography, of the temperature of the glacier, its content of air, the liquid quantity of water which it contains, of the quantity and the nature of rock materials that it transports, of its reaction vis-a-vis the meeting with other glaciers,…
In general, more the slope is strong and regular, the heavy glacier, having a raised temperature and containing liquid water, air and few large rocks, more it will go quickly and reciprocally.
The fact that a glacier is covered or not with a layer of rock remains can influence its rate of flow by the means of melt waters. These melt waters, while running out between the glacier and the rock faces, lubricates the ice which slips better against the rock. By comprising rock remains on its surface, a glacier is isolated from the solar radiations and the atmospheric temperatures, consequently decreasing the cast iron of the ice on its surface. Having less liquid water, the glacier advances less quickly than if its ice were discovered.
The rate of flow is not the same one in any point of a glacier. It varies according to the distance with the walls and according to whether one is in zone of accumulation, transport or ablation. The closer the ice is to the side walls, plus its speed is reduced. In the zone of accumulation and transport, speed is generally maximum in the depths of the glacier, while it is it on the surface of the glacier in the zone of ablation. This differential speed makes that the litage of the layers of snow is horizontal in the zone of accumulation, then becomes vertical in the zone of transport to become again horizontal in the zone of ablation.
The rates of flow of a glacier are very variable. The mean velocity for a traditional glacier is about a few centimetres with a few tens of centimetres per day. Certain glaciers (suspended glaciers or glaciers known as dead ) have a rate of flow almost close to zero. Other glaciers (Ice stream S) can advance several tens of meters per day. Thus, a glacier of Greenland, Kangerdlugssuaq (or Kangerlussuaq located at the south of Nuuk) multiplied its speed by three between 1996 and 2005 and reached on this date of more than fourteen kilometers per annum is an average of forty meters per day.
Retreat and glacial projection
See also: Small Ice Age
The face of a glacier can have to advance or move back in a valley. These movements are the result of an imbalance between contribution of snow and fonte : when the annual hydrous balance sheet is negative, the glacier enters a phase of retreat and reciprocally.
It should be recalled that when one speaks about a glacial retreat, it is not the glacier which moves back, the ice continuing to advance towards the bottom of the valley, it is the position of the glacial face which moves to the top of the valley.
If the contribution of snow, and consequently of ice, is more important than the cast iron of the glacial face, the glacier will progress in the valley. This can be caused by a climatic cooling and/or an increase in the Précipitation S. the opposite effects will be at the origin of a glacial withdrawal.
The consequences of a withdrawal or a glacial projection in the morphology of a glacier can be spectacular and radicales :
- in the case of a glacial withdrawal, the surface of the glacier becomes concave (in hollow ) in the width and in the length, its surface covers bédières, mills and by a Moraine of surface which can cover it entirely under several meters with materials, the zones of accumulation and transport can decrease in the face with the profit of the zone of ablation, the glacial face can in the case of be divided into Digitation S a glacier of piémont ;
- in the case of a glacial projection, surface becomes convex (in bump ) in the length and the width, the ice on the surface remains apparent because not having time to cover remains, the zone of ablation decreases with the profit of the zones of accumulation and of transport, the glacial face transforms into glacial Lobe in the case of a glacier of Piedmont.
Attention also not to confuse glacial progression and Jökulhlaup which is floods caused by a draining of an intraglacial lake formed during a volcanic eruption.
As for the current trend, and contrary the belief in vogue, the mesures, , , carried out for fifty years has not made it possible to induce a tendency in a direction or the autre : the size of the large glaciers has seemed to grow for twenty-five years, whereas that of certain small glaciers seems to decrease.
Examples of progression of glaciers :
- majority of the glaciers of Norway ;
- majority of the glaciers of New Zealand ;
- the Glacier Maili in Russia ;
- the Glacier Abramov with the Kirghiztan ;
- the Swiss Glacier Silvretta in ;
- the Glacier Perito Moreno in Argentinian ;
- certain glaciers with the the United States, in particular the local cap of the Mount McKinley and the Glacier Hubbard ;
- the Inlandsis of the Greenland thickens.
Examples of regressions of glaciers :
- the Swiss glaciers lost 40% their length, more half of their mass and a hundred disappeared between 1850 and 1999 and continue to lose fifty centimetres thickness each année ;
- the Glacier of the Rhone in Switzerland lost 2,3 kilometers length between 1850 and 1999 ;
- the Glacier of Aletsch in Switzerland lost hundred meters thickness between 1870 and 2001 ;
- the glaciers of Valsorey and Tseudet in Switzerland lost 1,4 kilometers length between 1850 and 1998 ;
- the Glacier of Grindelwald in Switzerland lost 1,6 kilometers length between 1850 and 2000 ;
- the Glacier Furtwängler (local cap of the Kilimandjaro) lost 80% of its volume during 20th century and will disappear between 2015 and 2020.
Engineers have tried for a few years to develop techniques to slow down or stop the cast iron of the glaciers, to even make them regain mass. Thus, an experimental technique consisted, using many drillings in the ice, to inject water in a Swiss glacier which was used for the ski of summer. This water was to make it possible the glacier to regain mass while going down less quickly in the valley. The technique, too expensive and not effective enough, was abandoned. In 2005, the ski station of Andermatt in Suisse packed part of a glacier in foam bands in PVC. According to the results obtained, covered surface will be wide thereafter. Although they can produce encouraging results, these techniques do not solve the source of the problem and do nothing but delay the expiry of a disappearance of these glaciers.
Natural risks related to the glaciersThe glaciers can cause many Catastrophe S related to their nature (solid water and liquid), their characteristics (presence of seracs, cracks, etc) and their capacity (raw glacial, Barrage, etc).
The glaciers can provoquer :
- of the Avalanche S by a fall of seracs or face glaciaire ;
- of the Flood S by an excessive cast iron, a Jökulhlaup, a draining of an intraglacial lake or a lake of surface (formed by the stopping of an adjacent valley by the glacier, a depression on the surface of the glacier, etc) ;
- of the falls of rocks coming from the Moraine s ;
- a destruction of the forests, fields, villages, etc by burial at the time of a glacial projection, a glacial Raw ;
- of the subsidences, crumblings, etc at the time of a glacial retreat on the walls of the valleys which are not maintained by the glacier (exemple  any more;: Ruins of Séchilienne) and on the moraines, in particular side, which are not protected any more from erosion by the glacier.
Records at the glaciersThere exists a multitude small glaciers throughout the world which are connected more with large Névé S compacted than with truths glaciers.
The longest glacier of the world is the Glacier Beardmore in the Antarctic with more than 160 kilometers length.
Largest Inlandsis is that of the Antarctic with 13 586 000 km. They is also thickest with a maximum of 4 700 meters thickness. That of the Greenland makes as for him 1 700 000 km with a maximum of 3 000 meters thickness.
The largest French glacier is the Glacier Cook (Kerguelen).
The longest French glacier of metropolis is the Mer of Ice in the solid mass of the Mont Blanc.
Types of glaciers
Alpine glaciers or confined glaciersThey are glaciers on which morphology is dependant on the relief. They are in general in Montagne and occupy the bottom of the Talweg S.
Glacier of valleyThe glaciers of valley are the traditional representation which one has of a glacier : a storing reservoir in form of circus to the feet of peaks exceeding of snow, a mass of lengthened ice occupying all the width of a valley and a glacial face giving rise to a torrent.
A glacier of valley can be formed starting from one only zone of accumulation or several. It can also receive masses of ices which come from glaciers adjacent and coming to enlarge the flood of ice.
Examples of glacier of vallée :
Suspended glacierA suspended glacier is generally small size and is perched on the sides of a mountain. It is made up only of one zone of accumulation, sometimes a short zone of transport but very seldom of a zone of ablation. The ice is evacuated by sublimation or fall of seracs, seracs which can give rise to a glacier regenerated in against-low.
Examples of suspended glaciers:
- the Glacier of Ailefroide in France ;
- the Glacier of the Mummy on the Pelvoux in France ;
- the Glacier of the Large Corridors on the Great Breakage in France.
Regenerated glacierIt is about a glacier whose contributions in snow are provided by falls of seracs coming from a suspended glacier. A suspended glacier being in general low surface, the contributions in snow are limited and the regenerated glaciers are often small and do not manage to form glaciers of valley. Their ice is evacuated by sublimation or the cast iron. The regenerated glacier is to some extent the zone of ablation of a suspended glacier.
Examples of glaciers régénérés :
Glacier of circusA glacier of circus is a glacier which occupies the totality of a circus and not leaving it or very little. It is acted in fact of the part corresponding to the zone of accumulation of a glacier of valley. It has a zone of accumulation, a reduced zone of transport and a zone of ablation.
Example of glaciers of cirque :
Glacier of PiedmontIt is about a glacier of valley which reaches the plain with the foot of the assembly line. It has a zone of accumulation and a traditional zone of transport but its zone of ablation is spread out in the plain either in Digitation S, or in a glacial Lobe more or less wide. In front of the glacial lobe can be formed a Sandur, place favourable with the installation of glacial and perished-glaciaires  formations;: Drumlin S, Esker S, Kame S, Kettle S, erratic blocks, Moraine S,…
Example of glaciers of piémont :
Coastal glacierA glacier of which one of the languages joined the sea or the ocean is generally described as coastal. These situations meet only in raised latitudes, such a glacier requiring an atmospheric average annual temperature with the sea level approaching the temperature of glaciation. One meets some in Norway and Alaska where they are thrown in Fjord S.
Example of glaciers côtiers :
- the glacial language Engabreen of the glacier Svartisen in Norway stops with twenty meters of the Atlantic Ocean ;
- the Glacier Brady in Alaska, length 39 km, it throws in the bay Taylor (Pacific Ocean) ;
- the Glacier Brüggen in Chile which throws in the fjord Eyre (Pacific Ocean) ;
- the Glacier Taku in the South-eastern of Alaska
- the Glacier Chenega in Alaska which throws itself in the Baie of Prince-William (Pacific Ocean).
Local capIn fact glaciers have certain characteristics of the Inlandsis : a large surface, a random form, a great thickness, a relatively weak slope of the rock substrate, an evacuation of the ice by broad glacial faces and/or emissions of glaciers. They are in fact mini-ice caps often perched at the top mountains or volcanos and partly confined by the tops which compose the mountain. They are very often remainders of large the polar icecaps of old the Glaciation S.
Example of caps locales :
Continental glacier or glacier not confinedTheir extent and their thickness are so important that the relief has little incidence on their morphology. They are appeared as an immense cluster of ice to the top forming a not very sloping plate bored time to other by a nunatak, running out of any share by producing glacial lobes, Digitation S and Ice stream S.
See also: Icecap
Their extent is lower than 50 000 km ².
Examples of caps glaciaires :
- the Vatnajökull in Iceland ;
- the Glacier Cook on the island Kerguelen (France) ;
- the Austfonna with the Svalbard (Norway).
See also: Ice cap
Their extent is higher than 50 000 km.
There exist only two ice caps in the world:
Criterion of temperatureIn addition to morphology, one can classify the glaciers according to their Température. This one is obviously function of the Altitude and the Latitude of the glacier but also of the presence or not of volcanic activity under the glacier.
- “moderate Glacier” (known as homéotherme) : A moderate glacier is a glacier of which the first meters under surface (ten to twenty meters in general) are found at one time or another of the year likely to exceed the melting point of the ice under pressure. They meet in the low ones and average altitudes of the mountains (the Himalayas, the Alps, Rocheuses, etc).
- “cold Glacier”: A cold glacier is a glacier whose temperature of the base on the surface of the glacier is lower than -30°C throughout the year. This temperature does not make it possible the ice under pressure to exceed its melting point. They meet with the poles and on the tops of the mountains.
- “sub-polar Glacier”: A sub-polar glacier is a glacier whose temperature of the base on the surface of the glacier is lower than -30°C throughout the year. However the zone of accumulation is likely to exceed the melting point of the ice the hottest months.
Formation of the glaciersSo that a glacier is constituted or maintained, one needs that the contribution of snow exceeds or balances the loss of ice due to the cast iron, for the sublimation and the slip of the water mass frozen towards the downstream. Minimal altitude for obtaining the requirements to the formation of a glacier vary according to the Climat and the Latitude of an area.
If it is located almost at the sea level with the pole S, it is on the other hand between 2 700 and 3 500 meters of altitude in the the Alps and beyond under the Tropic S (limiting altitude remains very difficult to currently determine because of the Climate warming).
Modelled and sedimentation glacialThe glaciers leave many traces of their passages in the landscape in the form of deposits of all sorte :
- Moraine : The moraines are formed lengthened material hills of size variable (of clays to the rocks of several tens of tons), transported and deposited by the glacier at the time of its cast iron. The moraines can be is frontal (most current) when it is in front of the glacier, side when it is on its with dimensions and median when it is located in the glacier (formed by the meeting of two lateral moraines of two glaciers which meet). The moraines are of size and very variable height (a few tens of centimetres to several tens of meters) and can create lakes by forming a stopping.
- Drumlin : A drumlin is a lengthened hill of the same composition as the moraines and being formed during a glacial withdrawal.
- Kettle : A kettle is a small lake generally circular formed by the moulding of a block of ice isolated from the glacier and taken in sediments.
- Kame : A kame is a fluvio-lake deposit in the shape of irregular hillock, made up of sediments fine and formed by melt waters of the glacier.
- Esker : A esker is a lengthened hill made up of fluvio-glacial deposits deposited by a subglacial river and reproducing the moulding of the tunnel of ice.
- erratic Block : An erratic block is a rock which can weigh several hundred tons and deposited by a glacier at the time of its cast iron.
- Sandur : A sandur is a glacial plain formed by the accumulation of sediments and remains glacial slackenings by the glacier and deposited by melt waters of the glacier.
- Loess : The loess is a wind deposit made up of fine particles (Argile S, Sable S, etc) taken on the sandurs, sometimes transported on thousands of kilometers and deposited under a periglacial climate.
Glacial erosionThe glaciers, from their weight, the rocks which they contain, the melt waters which they produce, the nature and the hardness of the substrate on which they evolve/move as of their great transport capacity erode and model the landscape by leaving forms characteristic of their passage :
- Glaciated valley : A glaciated valley is a valley formerly occupied by a glacier (of valley in fact) and whose athwartship cut reveals a profile in the shape of “U” called “out of trough”.
- glacial Circus : The zones of ablation of the glaciers can create circuses if erosion is sufficient to accentuate the slopes of the mountain.
- Peaks and arètes : The peaks and the arètes are the resultant of the tops which are not affected by the glacial erosion. The most famous example is the Cervin. In the Ice cap and the icecaps, the equivalents of the peaks are the nunatak.
- moutonnées Rocks : The moutonnées rocks are a rock substrate which acquired an embossed surface of the same aspect as a wool fleece. The moutonnées rocks can are étendrent on kilometers.
- Abrupt of wrenching : A precipice of wrenching is a projecting part of the rock substrate whose face downstream presents a break almost perpendicular to the passage of the glacier, signs that the ice output blocks in the rock projection. The precipice of wrenching can reach important dimensions and form cliffs.
- glacial Polish : A glacial polish is a rock surface sometimes of large surface which was completely levelled and worn at the point to become practically smooth.
- Glacial flutings : The glacial flutings are notches and grooves in the rock formed is by the passage of a rock enchased in the ice and which acted with the manner of a graver, that is to say by the passage of a subglacial river which used the rock.
- Lake of origin glaciaire : The lakes formed by the glaciers are placed either in the parts surcreusées by the glacier (glacial Ombilic), or are retained by moraines left by the glaciers during their withdrawal.
- glacial Threshold : A glacial threshold is a projecting rock part in the content of a valley which has gene the glacier in its displacement. The glacial thresholds often comprise on their surface of the moutonnées rocks, the precipice of wrenching, etc and a surcreusée part of the valley upstream.
- glacial Shoulder : A glacial shoulder is a projecting ledge perpendicular to a glaciated valley which was modelled by the passage of a glacier. In general, two shoulders face. One can say that they constitute the vertical equivalent of glacial threshold.
See also: Glaciation
Isostatic rebound and eustasy
See also: Isostasy
TourismThe glaciers constitute an undeniable tourist attraction. Many people move towards the glaciers pour :
- the Panorama ;
- the Ski of été ;
- caves of glace ;
- the climbing of glace ;
- the Alpinism ;
- circuits on the glaciers with motorized machines or in the form of glacial excursion.
Large glaciers by continents
- the Austfonna (Svalbard/Norway).
- the Vatnajökull (Iceland).
- the Glacier of Aletsch (Swiss), larger glacier of the Alps.
- the Glacier Cook (Kerguelen).
- the Mer of ice (France) is the French glacier most famous, it is seven kilometers long.
- the Glacier of Let us work (France).
- the Glacier of Argentière (France).
- the Glacier of Baltoro (Pakistan) (57 kilometers)
- the Glacier of Siachen (India).
- the glacier of Inylchec (Kirghizstan).
- the Glacier Tasman is the longest glacier of New Zealand (29 km). (New Zealand).
- the Glacier Hooker (New Zealand).
- the Glacier Franz Josef (New Zealand).
- the Glacier Fox (New Zealand).
- the Glacier Perito Moreno (Argentinian) is famous to be thrown in a lake and to break periodically under the pressure of water.
- the Glacier Barnard (Alaska).
- the Glacier Malaspina (Alaska).
- the Glacier Beardmore.
- the Glacier Axel Heiberg measurement 48 kilometers length and goes down from the Antarctic plate until the Barrière of Ross.
Extraterrestrial glacierThere exist glaciers on others planètes :
- on Mars, in addition to the polar icecaps, one found traces of glaciers. It could be even that some remain in the hollow of certain craters close to the poles.
- Ganymède, a satellite of Jupiter, has a surface made up of ice of water and of Silicate S.
- Callisto and Europe, two other Jupiter satellites, have a surface made up of water ice.
Seek2007. According to Meier Mark of the University of the Colorado (Boulder, the United States), the cast iron of the ices of the Greenland and Antartcique would contribute only to respective heights of 28% and 12% with the rise in the sea level. The small brooks forming the large rivers, in fact rather the small glaciers of the world, melting from now on at an accelerated speed, would contribute to surplus contributions of 417 billion cubic meters out of water per annum, and should remain the largest contributors until the end of the century. Then the marine level will have risen from 10 to 25 cm.
- Ice cap
- Glaciated valley
- rock Glacier
- Retreat of the glaciers since 1850
- glacial Landscapes, geographical index
- various types of glaciers
- swisseduc.ch - Glaciers online
- '' National Snow and Ice Dated Center '' - Images of glaciers
- Of the glaciers over Mars
- Université of Freiburg - “Operation glacier”
- Université of Neuchâtel - Course of glaciology
- Research center on the environment and the installation of the university of Saint-Etienne
- Glacial Landscapes
Be-X-old: Ледавік Zh-yue: 冰川
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