Glacier

A glacier ( in the Tyrol and Bavaria also Furthermore, in Austria scenic Kees ) is an emerged from snow ice with a clearly defined catchment area, which due to slope, Structure of ice, temperature and out of the mass of the ice and the other factors resulting shear stress independently moved.

Glaciers are the largest freshwater reserve in the world, after the oceans, the largest water reservoir of the earth. They cover in the polar regions, large parts of the land. Therefore, glaciers are also important as a water supplier for many river systems and have a decisive influence on the global climate.

Glaciers are also important landscape shaper, especially in the cold periods of the Pleistocene, in which the northern hemisphere ice sheets up in the northern part of Central Europe lasted well. The glaciers of the Alps, which could advance even to the foothills of the Alps in the cold periods, formed vast trough valleys and dominate the landscape today.

Since the mid-19th century is almost worldwide a significant retreat of glaciers observed ( see glacier retreat since 1850).

3.1 Eisfließen; deformation flow
3.2 Basal sliding
3.3 crevasses, seracs and ogives
3.4 Eissturz with Sturzeis

5.1 Erosion and deposition forms 5.1.1 Gletscherschliff and glacier scrapes
5.1.2 Deterministic Sion and Detraktion
5.1.3 Talformung
5.1.4 Nunatak
5.1.5 Fjell

5.2.1 glacial deposits

Etymology; Synonyms

The word glacier was first glatscharju of the Alemanni from the Western Alps -Roman term " glacier, [ actually: ] ice bucket " borrowed. This in turn is a derivative of the base word Glatsch ( from Latin glacies " ice ").

In the Eastern Alps the designation Furthermore (see firn ) is common from the Upper Inn Valley to the Zillertal ( Zamser reason); so therefore the snow was first away, that is from last year called. To the east of the Ziller Valley ( Venice Group, Hohe Tauern ), use the name Kees, which probably comes from a pre-Indo language.

Formation of glaciers

Glaciers require a number of key factors to their formation. Thus, a long term sufficiently low temperature necessary so that it comes to snowfall. The contour line from the long-term average more snow falls than to melt there is the climatic snowline. This may vary due to shading or sun exposed locations (eg south-facing slope in a mountain range in the northern hemisphere ) locally by several hundred meters from the actual mean value of the region. One speaks in this case of orographic snow line. Only above this boundary lines may fall as much snow at appropriate relief in the long run that it can undergo a metamorphosis.

Accumulation and metamorphosis

The process of accumulation of snow is called accumulation, and consequently the formation of a glacier area and accumulation area ( accumulation area ). Presented the snow thickness from that are pressed together by the static load of the upper the deeper layers, the metamorphosis of the snow begins towards glacial ice. Here is the in depth ever increasing pressure that still 90 % of the volume making up the snow, trapped in cavities air pressed out. In glacial ice can thus drop to about 2 % of the air content. Ice with such a low proportion of air usually has a bluish, rarely, slightly greenish color.

Higher temperatures affect the metamorphosis positively in two ways. On the one form in warmer ( tempered ) glaciers usually smaller ice crystals, which here and also in the preliminary stages of the ice as snow and granular ice ( in some literature also Firneis called ) easier movement is possible, to be released in the air more easily can. In addition, can melt even superficial material and freeze again, without leaving the glacier. Thus, at least in small quantities even in the daily cycle, a metamorphosis of snow take place on ice without the usual pressure metamorphism in the intermediate stages.

It requires 10 m of fresh snow at a density of 0.1 g/cm3 to 1.10 m glacial ice to produce a density of 0.9 g/cm3. This in turn corresponds to a hydrostatic head of 1 m.

Equilibrium line

The equilibrium line is a height limit of Glaciology. Below this line in the so-called ablation zone ( ablation ) of the glacier is the mass loss by ablation greater than the increase in glacial ice. In the above -lying accumulation area ( accumulation area ) more glacial ice is formed as is lost through ablation. In many areas, the equilibrium line is largely in the Firngrenze. The equilibrium line is called in the jargon as Equilibrium Line Altitude (ELA ).

Ablation and sublimation

Meltwater can leave the glacier surface or at its bottom ( subglacial ) and is extracted from the mass balance of the glacier. Subglacial meltwater usually occur out of a glacier called a hole in the glacier tongue, which is located in the so-called ablation zone, the counterpart to the accumulation area above the equilibrium line. If such a drain blocked or does not occur under the ice creates a befindlicher, hidden glacial lake, the so-called water bag.

In particular, polar glaciers lose through the process of sublimation to the ground, where water passes directly from solid to gaseous state.

Some glaciers are also forced by the relief for ablation. This is the case if, for example, in a mountain glacier ice plunges over a steep cliff or a Inlandeismasse grows up to a Coast and there can not form ice shelves, but the glacier is here forced to calving. Parts of the ice break off and can then drive as icebergs on the sea. Tabular icebergs are formed when parts of an ice shelf break off, which has formed a very flat top and bottom surface due to its floating starting position. Due to the displacement of the water calving glaciers, dangerous tidal waves, called tsunamis trigger.

Movement of glaciers

Only moving masses of ice are called glaciers. This excludes water drifting ice as icebergs or pack ice. In general, two basic forms of movement of glaciers can be distinguished:

Eisfließen; deformation flow

Practicing the orographic higher-lying parts of a glacier a sufficient shear stress to the lower and thus lie ahead glacier sections, so this pressure is reduced by a flowing movement of the ice. At the molecular level there is ice superposed layers with relatively weak molecular bonding forces between the individual layers. When the voltage applied to the overlying layer exceeds the bonding force between the layers moves the top faster than the underlying layer. In this case, the complete ice so do not move uniformly, but depending on the capabilities of the ice crystals to move within the overall structure. At the glacier sole and the flanks of a glacier, the ice can often freeze at the bedrock, making no movement is possible here. Therefore, the flow rate of a glacier at the surface is higher than at the bottom and on the sides of lower than in the middle.

Basal sliding

Basal sliding occurs only in temperate glaciers with temperatures just below 0 ° C on. Since the melting point of ice per 100 m auflastendem ice decreases by about 0.07 ° C, a temperature- glacier of 500 m thickness must minimally have a temperature of -0.35 ° C. Some glaciers are -1.9 ° C to -32 ° C but much colder.

Due to the anomaly of water, ice can be liquefied at a sufficiently high pressure ( pressure melting point) despite low temperatures. Is the pressure that a glacier exerts on the ground due to its mass, in the present temperature of the ice high enough to cause melting, then a whole section of a glacier slide along this water film. This pressure is reduced again and the water freezing again until a sufficient pressure can be generated.

Crevasses, seracs and ogives

Due relief may result in a glacier different surface forms such as transverse and longitudinal columns, seracs or nose cones, which thereby serve as indicators of the shape of the substrate and the flow behavior of a glacier.

Cross gaps are formed in this case by a longitudinal strain of the glacier surface. This occurs when the front and lower part of a glacier thus may flow faster than the behind and lying higher. This process is called Extending flow. Not always occur at Extending flow and transverse columns, but the columns are reversed cross is always a clear indication of Extending flow. The other hand, longitudinal gaps are formed by a transverse stretching of the glacier surface. This is often observed in foreland glaciers exiting a narrow valley in a vast plain, where the ice can expand far.

Ogives are after the same Gothic style element named regular light-dark pattern transverse to the flow direction. These fringe patterns are formed from beneath some ice falls, when the cycle time of the ice in a fraction approximately coincides with an odd multiple of half a year.

Seasonal mass balance fluctuations in the ice cliff, possibly in conjunction with Compressive flow at the lower end ( higher -lying parts of a glacier move faster than deeper ) may lead to so-called Wave Ogives ( wave ogives ) extending to as Stauchwülste by the outflowing pull glacier.

Called Ogives band ( strip - nose cones ), also Forbes bands are due to seasonally varying intensities dust and pollen entry. Drag in the track as a regular stripe pattern by a relatively smooth glacier surface. The ice in the dark bands has gone through the summer break, with melting processes favor the accumulation of dark particles on the surface of the glacier. The bright streaks are from ice that has passed through the fracture prevalent in winter.

Ogives get their characteristic bow shape by the fact that the flow velocity in the middle of the glacier is higher than at its edges.

Seracs ice towers are caused by the interaction of longitudinal and transverse strain and therefore usually occur together with or near the longitudinal and transverse crevasses.

Eissturz with Sturzeis

A Eissturz is the demolition of larger pieces of ice of a glacier. The abgebroche ice is also called Sturzeis.

Glacier types

Depending on the mode of origin and development stage, a distinction is now following types of glaciers:

From left to right: hanging glaciers, cirque glaciers, valley glaciers, glacier foreland, ice shelf.

A rock glacier is despite its name, no glacier, as it is not clear from snow, but made iced mixed rubble and boulders. He creeps slowly down the valley, which in completely stony surface gives a mostly undulating structure, and is a phenomenon of permafrost ( permanently frozen ground ).

Landscape formation by glaciers

Glaciers are important landscape shaper who excel in their effectiveness the wind and the water flowing clearly. In particular, during the Ice Age, glaciers were as large parts of the Northern Hemisphere, huge areas have been reshaped by them. This concerns about the Alps and other high mountains and northern Europe and northern Central Europe, large areas in North America and northern Asia. The effect of the glacier is primarily due to the benefits they carried moraine. A distinction forms of glacial erosion (erosion ) of shapes and sediments in Aufschüttungsgebieten.

Erosion and deposition forms

Gletscherschliff and glacier scrapes

In glacial ice entrained rock material of different grain sizes - from fine clay to boulders several feet measured - may leave significant traces in the rock underground. Fine-grained material causes, as a rule a ground comparable to the effect of sandpaper, while larger particles clear scratch marks and grooves can leave in the rock, supported by the strong pressure and the movement force of the glacier. These grooves are called glacier scrapes.

These forms are testimony to a movement of glacial ice on the ground and are therefore a proof that the former glaciers could move here by basal flow and was not frozen to the ground.

Deter Sion and Detraktion

Glaciers can shape their ground strong. Protrudes from the rocky ground an obstacle in the path of a glacier, the result is a characteristic shape. On the side of the rock, facing the direction of flow of the ice (windward ), the pressure increases in the ice, making easier here is a melting film of water can occur on which the sliding glacier can flow over the rocks. The material carried by the glacier leads to an erosion of the rock. The windward side obtains a streamlined shape similar to a sand dune. This process is called Deterministic Sion. On the opposite side ( Lee), the pressure is much less substantial, which can not form meltwater film here. Instead freezes fixed the ice on rocks and in the further movement of the glacier the ice is carried along while broken parts from the rock. From Deterministic Sion on the windward and the Detraktion at the leeward side creating a so-called round hump. These can be found as legacies of Pleistocene glaciation in the Alps today.

Talformung

Flows occur in mountain ranges usually deeply incised V-shaped V-shaped valleys. In contrast, glaciers are capable of a much stronger lateral erosion, which shaped glacial valleys have a distinctive U-shape and are referred to as U-shaped valleys.

This vorglaziales material was often carved out and carried in the Urtälern of the glaciers. This earlier layers of fluvial sediments were replaced by glacial boulder clay. Clearly visible is often on the valley slopes, the cut boundary, which marks up to what thickness once a glacier had filled the valley.

Nunatak

In Eisstromnetzen how she still finds today, for example, in Alaska, or how they were pronounced in the Pleistocene in the Alps, glaciers able to flow also Talscheiden and these therefore form also erosive.

Extends beyond a mountain out of a Eisstromnetz or a continental glaciation, is referred to this as Nunatak (plural: Nunataker or Nunatakker ). The not shaped by glacial ice tip of a Nunatak is also called horn, which clearly distinguished by its rugged edges of the more rounded lower part of the mountain.

Fjell

As a landscape form in which also peaks were once reshaped by ice and are now available only as a rounded hilltops, the Scandinavian Fjell is very significant for the shaping force of the once auflastenden to Northern Europe ice.

Glacial deposits

Moraines: The moraine is defined as the totality of the transported material from the glacier. Since glaciers are solid bodies, they can all grain size classes, from clay to sand to the coarsest blocks absorb, transport, and redeposit. Depending on the location of the glacier they are referred to as top, side, middle, inner, bottom or end moraine. The term " moraine " refers now more to the corresponding landforms and not on the actual material that is today referred to as glacial till.
Deposit forms: In zurückgetauten mountain glaciers, the moraines are the most widespread deposits, which (if it exists ) must be brought in connection easily with the glacier in question. In the northern part of Central Europe and in the Alpine foothills, the glaciers left as a typical form of society, the glacial deposits with the elements of ground moraine, end moraine, and Sander (only in Northern Germany ) glacial valley. Again, there are many small shapes, such as boulders, drumlins, glacial troughs, Oser (singular Os) and Kames.

Glazialisostasie

Continental plates are normally in a state of equilibrium between the. Due to their mass and the gravitational force and the buoyancy caused by the Earth's mantle This balance is the isostasy. However, it may be disturbed by the fact that attach themselves to a continental plate or parts of large thicknesses of continental glaciation. Due to the extra weight the crust is forced to a vertical compensating movement to again reach the state of isostasy.

The inland ice over Scandinavia caused a significant decrease of the area during cold periods. After the melting of these masses, most of Finland was actually below sea level. Since then, Northern Europe also highlights again again as a compensation motion. The uplift rates reach here up to 9 mm per year.

Glazialeustasie

Due to the massive binding of water in the form of ice on land sank into the cold periods of the sea and lay up to 150 meters lower than today. This, inter alia, fell today's North Sea dry and formed a land bridge between Europe and Britain. Meuse and Thames were tributaries of the Rhine.

If the still existing ice sheets would melt, the sea level would rise by a further 60 to 70 meters. With a particular conditional by melting of ice of the Antarctic sea-level rise is expected in the context of global warming. The forecasts of climate experts still soft it widely. Threatened Stark would secure these very low-lying countries such as Bangladesh or the depression areas in the Netherlands.

Glaciers and Climate

Although glaciers account for only a small part of the earth's surface, is broadly accepted that they influence greatly depending on the size of the local and global climate. Here are two physical properties of importance:

The albedo of the earth's surface increases to a glacier important as long as it is not free of snow: incoming sunlight is reflected back to almost 90 %, which can not unfold its warming energy input into the biosphere. An even more extensive glaciers therefore has a tendency to cool further and further enlarge. Over it arises in connection with low temperatures, high pressure area.
Glaciers act as water reservoirs. It is stored as ice in glaciers and thus removed from the water reservoir temporary or longer lasting. With the melting of glaciers as a result of climate warming may lead to a rise in sea level. This is especially true for the ice sheets of Greenland and Antarctica.

The effect of the increased input of meltwater to the ocean currents, especially the Gulf Stream System, is currently the subject of scientific studies. One theory is that due to the melting of Arctic sea ice or the Greenland ice sheet, the salinity in the Arctic Ocean decreases, thus the density of sea water is reduced and no longer lowers the sea water in Iceland. This can slow down the entire Gulf and even lead to a cooling of the climate in Europe. Whether and to what extent this effect is stronger than global warming, is not clear.

Conversely, glaciers are of course also influenced by climate and are subject to major changes. These are not always predictable. The relationship between glacier retreat and - thrusts with climatic changes is seldom clear, since an advance due to changes in flow rates through stronger ablation causes ( better glide on the melt water ) or can be delayed by increased ice formation in earlier times and slow Plunging flow. More meaningful, therefore, the mass balances - that is, the differences between newly formed and abgeschmolzenem ice. Particularly in large ice sheets depend many factors. So Polarstern was found recently by an expedition of the research vessel that the Antarctica cools in contrast to the current trend and the Antarctic ice sheet is growing. Play a significant role in the precipitation, for an increase due to climate change is predicted. Then the question is whether this increased rainfall comes as snow or as rain down for a glacier. Snow promotes the formation of ice, rain which ablation.

Also, mountain glaciers are subject to substantial fluctuations. In plateau-shaped glaciers such as the Gepatschferner are the catchment areas very flat. With only a slight increase in average temperature and thus increase the snowline large accumulation areas can completely covered by the snow line, which the mass balance of the glacier completely overturns. With the sinking of the glacier surface ( alone in the summer of 2003 at Gepatschferner average 5 m) reaches a subsequent cooling by the same amount no longer sufficient to compensate for the mass loss, since the ice surface is now deeper still remains below the snowline.

Glaciers are an indicator of long-term climate changes. As a result of global warming, there has been a massive glacier melt worldwide.

Glacier as freshwater reserve

Glaciers will in many regions is a safe water supply for the rivers in the low-rainfall summer time as they melt, especially in this time. They operate a balancing effect on the water level, for example the Rhine. In the arid mountainous regions of the Pamir and Karakoram the valley floors and mountain slopes are irrigated almost exclusively using the glacial water and reclaimed. Even in the dry valleys of the Alps ( Val Venosta, Valais) there are extensive networks of canals, some of which are still used today. A hazard can be included from earlier times in ice environmental toxins.

Glacier human use

Due to its imposing appearance glaciers of enormous importance for the tourism in mountains and at high latitudes today. You are always an attraction when they are provision of public transport. Then they are also suitable for winter sports as snow-sure glacier skiing.

Until the general circulation of the glacial ice was cooling systems at several glaciers mined and exported.

Glaciers as a habitat

Glaciers form a Kryal called life space in which, for example, biofilms, snow algae and glacier fleas live.

The Taylor Glacier in Antarctica covers a very rare microbial ecosystem. The Blood Falls are a rotfarbener discharge from the glacier tongue.

Glacier research

History of Research

The idea that glaciers have helped shape the landscape of the world is crucial, not old. Until well into the 19th century most scholars held firmly that the Flood have influenced the shape of the earth and was responsible for legacies like boulders.

The Swiss Society for Natural Sciences wrote in 1817 a prize for a thesis paper on the topic of "Is it true that our higher Alps run wild for a number of years? " And marginalized further a sought was "a Unpartheyische compilation of several years of observations on the partially advancing and retreat of glaciers in the transverse valleys, through setting and disappearance of the same on the heights; Exploration and determination of the recognizable here and there through the advanced rock debris deeper former boundaries of different glacier " ..

Excellent 1822 it was a work of Ignaz Venetz that closed because of the distribution of moraines and boulders that once large parts of Europe were glaciated. However, he took to convince only the ear of Jean de Charpentier, in turn recited 1834 Venetz ' thesis in Lucerne and managed to Louis Agassiz. The rhetorically gifted Agassiz, the intensive studies for operation in the following years to glaciology, finally succeeded in further enforce areas as a general doctrine, the former glaciation.

In northern Germany the first evidence for glaciation of Scandinavia have been collected from 1820 to 1840. However, they could not bring down the old school of thought. It was not until 1875 sat down, due to the findings of the Swedish geologist Otto Torell, who showed clear glacial striations in Rüdersdorf, the icing theory in Northern Germany by.

Archeology

In the accumulation area of a glacier is snow turns to glacial ice, while organic and inorganic objects are included. Over time, the ice flows downhill and so the objects move into the ablation zone where the glacier ice thaws. During the year the ice melt is in the month of September in the northern hemisphere at its highest, so that at this time most likely archaeological finds can be made. In addition to this wandering ice there are a few depressions, where keeps ice for a long time stationary, the thaw now because of global warming. The advantage of this stationary ice is that the resulting during the flow of a glacier forces attributable to the enclosed items. So found at Schneidejoch, a mountain pass in the Bernese Alps, from different eras finds from previous pass -goers. The famous glacier mummy Ötzi in turn was in a 40 m long, 2.5-3 m deep and 5-8 m wide stony basin, over which a glacier than 5300 years away moved without changing the ice in the trough.

Climate Archive

The ice of the glacier can be used for research into the climate history of the earth. These ice cores are taken and analyzed. For the Greenland Ice Core Project were drilled to a depth of 3029 meters, where the ice reaches an age of more than 200,000 years, and in the European Project for Ice Coring in Antarctica could even 900,000 years old ice are drilled.

Another firm with which glaciers in conjunction climate archive is glacier wood. These are remnants of trees that were trapped in the ice for centuries and where the annual rings can be evaluated.

Dangers of glacier

The dangers posed by glaciers are classified according to their causes into the following categories:

Dangers of length and geometry changes: Through changes in geometry structures, which are located directly on the edge of the glacier can be at risk. After glacial retreat exposed moraines and rock walls may be unstable, so that it comes to landslides and crashes.
Dangers of glacier floods: glacier flood are not usually precipitation -related but arise when drained by the glacier dammed lakes or in the ice mass stored hidden pockets of water suddenly. These outbreaks often cause devastating tidal waves, which cause great damage in the valley. In Iceland they are called outbreaks glacier run.
Dangers of glaciers and ice falls: For hanging glaciers there are regular large ice seracs. This triggered avalanches and ice falls can be a threat to settlements and infrastructure, and on impact with the sea by means of the displacement pressure of the water masses dangerous tidal waves that run along the seabed, so-called trigger tsunamis.
Crevasses make especially for tourists is a threat that should not be underestimated in any way. Especially often too little people abseil at glacier crossings adjacent to each other or too close together. Crevasses can be very deep and are partially covered by snow overlay (so-called snow bridges ), so they are not visible.

Find out more about glaciers

Size and behavior

Currently, 15 million km ² of the surface of solid earth are covered by glacial ice. This represents around 10 % of all land areas. During the last glacial period, there were 32% of the land surface.

The largest glaciers in the world (without ice ) is the Lambert Glacier ( Antarctica ).
The largest non- polar mountain glaciers in the world, with 4275 km ² area of the Malaspina (Alaska).
The longest other than polar valley glaciers of the Earth is the Fedchenko Glacier in the Pamirs in Tajikistan with 77 km length
The largest area of European glacier is 8,200 km ² of Austfonna ( Svalbard / Norway).
It is followed by 8,100 sq km area of the largest plateau glacier in Iceland, the Vatnajökull. With up to 900 m thick he is the volume of the largest European glacier.
Europe's largest mainland glacier is about 500 km ² of Jostedalsbreen (Norway).
The largest and longest Alpine glacier is the Aletsch Glacier ( 117.6 km ² / 23.6 km long).
The largest of the five glaciers in Germany is the Northern Schneeferner on the Zugspitze.
The largest glacier in Austria is the Pasterze am Großglockner.
The largest and longest glacier in the Caucasus is the Besengi in Besengi wall in the Besengi region.
The largest glacier in the tropical climate zone is the Quelccaya in Peru.
The largest glacier in South America is the Campo de Hielo Sur in Chile.

The Glacier des Bossons on Mont Blanc dropping down to about 1,400 m above sea level.

Alpine glaciers move at up to 150 m per year.
Himalayan glaciers to flow up to 1,500 m in the year, ie up to 4 m per day.
The outlet glaciers of Greenland move up to 10 km per year, or up to about 30 meters a day. The Jakobshavn Isbræ on Greenland's west coast is considered the largest glacier with the permanent speed, surge glaciers can flow even faster and cover more than 100 m per day but during the active phase.

Near the equator:

The equatorial glaciers are located next to the volcano Cayambe (Ecuador).
The equator next glacier, which calves even into the sea, the Ventisquero San Rafael, part of the Campo de Hielo Norte ( Chile ) near the 47th latitude south is ( exactly: 46.689 ° S, 73.848 ° W 46689-73848 corresponds to the northern hemisphere about the location of Bolzano ).

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