Conditions for the formation and feeding of glaciers. types of glaciers. Conditions for the formation of glaciers. Types of glaciers Glacier formation process school knowledge

Glaciers are termed stable accumulations of ice on the earth's surface. They appear only above the snow line, although the glacier may descend below it during the course of dynamics. Ice in large masses acquires plasticity and is able to flow. The magnitude of the slope and the thickness of the ice are the most important conditions for its movement. The speed of glacier movement can vary from a few centimeters to several tens of meters per day. Since both the slope of the surface and the very possibility of ice accumulation are most favorable in the mountains, the formation of modern moving glaciers in all zones, except for the polar one, is possible only in conditions of high mountain relief.

The glacier is fed by solid atmospheric precipitation falling on its surface, the transfer of snow by the wind, the collapse of snow from the slopes and the condensation of air vapor on the surface of the glacier.

According to the conditions of the balance of the solid phase of water (i.e. snow, firn, ice), the glacier can be divided into accumulation zone and zone ablation. Ablation called the consumption of ice through melting and evaporation. Ablation leads to a decrease in the thickness of the marginal part of the glacier. The intensity of ablation is directly dependent on air temperature. Temperature fluctuations cause ablation fluctuations, so the position of the glacier edge does not remain constant. Slight changes in the position of the edge of the glacier are called oscillation.

Distinguish two main types of glaciers: mountain(or runoff glaciers) and integumentary (spreading glaciers). The former occupy predominantly negative relief elements in the mountains. The movement of ice in them occurs mainly under the influence of gravity - down the slope. Cover glaciers can cover areas of millions of square kilometers, burying even mountainous terrain under them, and in general have a convex surface shape. The ice in them spreads from the center (where the maximum power is observed) to the periphery. Floating ice shelves sometimes serve as continuations of ice sheets, partially resting on the seabed (they are distributed mainly in Antarctica). transitionalfrom the mountain to the cover are reticulated and foothill types of glaciation. The grid type of glaciation (Spitsbergen archipelago) is characterized by a network of through glacial valleys with ice domes in watershed areas, alternating with single rocks protruding from under the ice and steep ridges in the form nunataks.

The foothill type of glaciation (Alaska) is now rare and only in areas with abundant snow supply (Alaska, the Saint Elias Mountains). Glaciers of this type descend along isolated mountain valleys to the foothill plain, where they merge into a single ice lobe (Malyaspin glacier).

Cover glaciation is characteristic of the Arctic and Antarctic climatic zones. The largest areas of ice sheets occupy in Antarctica and Greenland. Of the total area of ​​modern ice sheets (14.4 million km 2), 85.3% falls on the land cover of Antarctica, 12.1% is the cover of Greenland and 2.6% is distributed between the small ice sheets of the northern part of the Canadian archipelago, Iceland, Svalbard and other islands of the Arctic basin. The maximum thickness (up to 4 km or more) is reached by the ice sheet of Antarctica in its central part. At the edge, the thickness of the glacier is reduced, and separate sections of the stone bed protrude here. Such exits in Antarctica are called "oases"(Banger oasis in the vicinity of the Soviet Antarctic station "Mirny").

The sheet glaciers of Greenland and Antarctica drain into the sea through depressions in the coastal relief. Such ice flows are called outlet glaciers. When the ends of outlet and shelf glaciers break off, huge blocks of floating ice are formed - icebergs. Icebergs, carried by sea currents, move to lower latitudes and gradually melt. In the process of melting, the clastic material contained in them is released and deposited on the seabed. This circumstance should be taken into account in paleogeographic reconstructions: the presence of coarse clastic material at great depths is not yet proof that this section of the seabed was once located in the coastal strip of the sea.

All types of modern glaciers occupy over 16 million km 2, or about 11% of the land surface. The total volume of ice and eternal snow is estimated at 27-30 million km 3 . It is estimated that the complete melting of glaciers and snow masses could raise the level of the World Ocean by about 60 m. The largest ice sheet is the Antarctic. Its area is approximately 13.5 million km2. The Greenland Glacier occupies 1.7 million km 2 of the 2.2 million km 2 of the entire surface of the island. In the USSR, there are about 28,000 glaciers in the arctic and mountain regions with a total area of ​​more than 75,000 km 2 .

Occupying vast land areas, glaciers play a very significant role in exogenous morphogenesis. The relief-forming role of glaciers especially increased during the epochs of glaciation, when, due to the cooling of the climate caused by a decrease in summer or average annual temperatures, the amount of solid precipitation increased. This led to a decrease (depression) of the snow boundary, accompanied by an increase in glaciation of mountainous countries and the formation of huge ice sheets on the plains of North America and Eurasia.

Depending on the ratio of the incoming and outgoing parts of the glacial balance, several phases are distinguished in the development of a glacier: advance, stationary position, and retreat. Each of these phases is associated with a certain complex of glacial landforms. In the advancing phase, active ice performs the main destructive work; in the stationary position of the glacier and during its retreat, a predominantly accumulative glacial relief is formed.

Glacial processes

And glacial landforms

Glacial relief-forming processes are due to the activity of ice. The condition for their development is glaciation - the long-term existence of masses of ice within a given area of ​​the earth's surface.

Ice- the most common rock on Earth. But glaciers are very unevenly distributed: 85.6% of them are in Antarctica, >11% in Greenland, and only 3.4% in the rest of the land (Alps, Caucasus, Central and Central Asia, Cordillera, Andes).

Glaciation is possible if the area is within the chionosphere. Chionosphere - layer of the atmosphere within which a constant positive balance of solid atmospheric precipitation is possible. Its lower boundary is uneven and, when crossing with land, forms snow line . The upper one is limited by a height of 8-10 km and passes where there is still enough moisture to turn it into ice or snow.

Distinguish two types of natural ice – water and snow . water ice formed when land or ocean water freezes snow ice - during the metamorphization of snow, which, as a result of repeated freezing and thawing, as well as pressure, acquires a coarse-grained structure, turns into firn, and later on in glacier ice.

Conditions for the formation and feeding of glaciers. Glacier types

Glaciers- stable in time accumulation of ice on the earth's surface. appear only above the snow line, but can also descend below it. Ice is plastic and able to flow. the most important conditions for its movement – slope and ice thickness. the formation of modern moving glaciers in all zones, except for the polar one, is possible only in conditions of high mountain relief.Glacier nutrition carried out by solid atmospheric precipitation. The glacier is divided into zones accumulation and ablation. Ablation – ice consumption through melting and evaporation leads to a decrease in the thickness of the marginal part of the glacier. Slight changes in the position of the edge of the glacier are called oscillation .

Distinguish the main t types of glaciers :

1) coverslipsor mainland

2) mountainglaciers, subdivided into:

valley, cirque, volcanic cones,

caldera, plateau and etc.

Along with the main types, there are:

ice shelves and glaciers at the foot of the mountains .

Allocate more norwegian type glaciers, which is ice caps (ice caps in English literature). They are are transitional from mountainous to continental covers of the polar countries. characteristic of subpolar oceanic countries with heavy snowfalls and are usually developed in flattened plateau-like summit surfaces of mountain ranges. They are found in the mountains of Norway and on the volcanic massifs of Iceland. The firn and ice covers look like a convex cap without protruding peaks and peaks. The ice slowly spreads in all directions from the center to the periphery, reaching the steep edges, with short and wide blades descends into the valleys.

Speaking of Norway, I would also like to dwell on fjords - ancient erosional valleys worked by the glacier and flooded by the sea during its retreat. Now it's narrow deep sea bays with high rocky shores. In cross section they have the shape of a trough (trough). Depth up to 1000 meters or more.

At present, there are only two continental ice sheets Greenland and Antarctica . Their characteristic features: a huge area of ​​ice (in Antarctica about 13.2 million km 2) and its colossal thickness (up to 4 km). The glacier has its maximum thickness in the central part, at the edge the thickness is reduced, and here separate protrusions of its stone bed are visible - oases . If the remnants are pronounced in relief, they are called nunataks . The sheet glaciers of Greenland and Antarctica drain into the sea through depressions in the coastal relief. Such streams are called outlet glaciers . The ice, having reached the water, floats up, breaks, resulting in the formation of huge blocks of floating ice - icebergs . Large masses of ice on the periphery of Antarctica lie on the shelf or are partially afloat: ice shelves .

in the mountains the formation of glaciers begins with the stage of a snow patch or firn spot. in some areas, the snow accumulated during the winter does not have time to melt during the summer. Further, a new portion of snow accumulates here, gradually the mass turns into firn, and then into ice. A stable accumulation of ice causes frosty weathering of the rocks on which it lies, and the weathering products are carried out by melt water. Formed car – circus-shaped (armchair-shaped) recess with steep, sheer walls and a gently sloping, concave bottom. The glacier enters new stage of development – cirque glacier stage . Active penalties, i.e. karts occupied by glaciers are located somewhat above the snow line. The next stage of glacier development – valley ice formation . the mass of ice does not fit in the square and begins to slowly move down the slope along some erosive or tectonic form, developing and expanding it. The valley acquires a trough-like shape, called trog . If the snow boundary lies low, at the level of the foot of the mountains, the glacier enters the foothill plain and spreads at the foot. Such glaciers are called foot glaciers.

Glaciers exist wherever the rate of snow accumulation is much higher than the rate of ablation (melting and evaporation). The key to understanding the mechanism of glacier formation is the study of high mountain snowfields. Freshly fallen snow consists of thin tabular hexagonal crystals, many of which have a graceful lacy or lattice shape. Fluffy snowflakes that fall on perennial snowfields, as a result of melting and secondary freezing, turn into granular crystals of ice rock called firn. These grains can reach 3 mm or more in diameter. The firn layer resembles frozen gravel. Over time, as snow and firn accumulate, the lower layers of the latter are compacted and transformed into solid crystalline ice. Gradually, the thickness of the ice increases until the ice begins to move and a glacier is formed. The rate of such transformation of snow into a glacier depends mainly on how much the rate of snow accumulation exceeds the rate of its ablation.

Glaciers are formed by the accumulation of snow and its transformation (metamorphization) into ice. For a glacier to form, a cold and humid climate is required, in which the amount of snowfall is greater than or equal to the amount of snowmelt. Snow accumulation is possible only at negative average annual temperatures (alpine) and foothill glaciers (foot glaciers).

The line delimiting the zone within which the average annual amount of solid precipitation is equal to their loss is called the snow line. Glaciers form only above the snow line. The position of the snow line depends on the latitude of the area. In Greenland, it coincides with the zero mark, in the Caucasus 3000 m, in the Altai Range - 4800 m, in the Himalayas up to 6000 m. It also depends on the humidity of the climate. In the Alps, it passes at around 2600 m, in the Western Caucasus - 2700 m, in the Eastern Caucasus - 3800. Depending on the exposure of the slope, the amount of precipitation changes, and the position of the snow line also changes. So on the northern slopes of the Altai Range it passes at a level of 4000 m, on the southern slopes - 4800 m.

Within one mountain system, the snow line is lower on the front ridges. So, in the Tien Shan, on the front ranges, the snow line falls 600 meters lower than on the main ones. There are also exceptions to the rules. For example, in the Western Caucasus there is the Himsa glacier. It exists in the zone of positive average annual temperatures and is preserved only due to the large amount of snow falling on its surface. Humid air coming from the sea cools over the glacier and gives it water in the form of snow. In neighboring parts of the ridge, where there are no glaciers, such intense precipitation does not occur.

How is ice formed? Snow falls to the bottom of the valleys in the form of solid precipitation, or is carried there by avalanches. On the flat and concave parts of the slopes, snow can accumulate for many hundreds of years. Under the influence of the sun and wind, it is converted into firn. A snowflake is a radiant ice crystal. The sun and wind change the fallen snowflake, while it loses its stellar shape and turns into a grain. When the snow melts, water seeps into its thickness and freezes there. But at the same time, new crystals are not formed, but existing ones grow. Sublimation, the sublimation of snow, also plays a significant role here. The resulting water vapor condenses and freezes on the firn crystals. Firn is snow that has a granular structure and is over a year old. At a younger age, firn is usually called firn snow. Firn grains gradually grow, reaching a size of 5 to 100 millimeters.

The older the firn, the deeper it lies, and the larger its grains. With the growth of grains, air is forced out of the firn, and it becomes denser. Finally, the grains grow together and form a homogeneous mass - white firn ice. We see something similar on the pavement in the spring, when the windshield wipers break off the ice from the pavements. But in cities, pedestrians turn fresh snow into ice in just a couple of days, while in nature this takes many years.

Ice is both brittle and ductile. The higher the temperature and pressure, the more plastic the ice. Due to plasticity, the lower layers of ice are squeezed out by the upper layers, and they begin to flow. Glacier ice crawls out from under the firn. Of course, the direction of its flow depends on the terrain. In order for the ice to start flowing over a flat surface, the weight of a sixty-meter thickness of ice is needed. However, if the slope of the valley is significant, the ice flows at a lower pressure. With a steepness of 40-45 °, only a two-meter thickness is enough for this.

The speed of ice flow is measured in centimeters per day, but in large glaciers it reaches 3-7 meters per day.

At the glacier, there is a feeding zone (firn basin), where the main masses of snow accumulate, and a runoff zone - the tongue of the glacier. The boundary between them is called the firn line.

As it flows down the valley, the ice melts and, finally, at a certain height, the amount of inflowing ice becomes equal to the amount of melting. Here the tongue of the glacier ends. If the amount of precipitation is constant, the glacier takes a stationary position. If it increases, the glacier advances until it comes back into balance.

As the climate warms and solid precipitation decreases, the equilibrium line rises up the valley. With a rapid retreat of the glacier, patches of ice at the ends of the tongue or near the coast, usually covered with a moraine cover, stop moving and separate from the glacier. Such ice is called dead. The ice under the moraine cover melts unevenly, forming funnels, lakes, and steep faults. Traffic in these areas requires special attention. Dead ice covered with thick debris is called buried ice.

The initial stage of a glacier is called a snowfield. When the snow-glacier masses reach such a thickness, they begin to noticeably move, they become real glaciers.

Merging, valley glaciers form a dendritic glacier, and dendritic glaciers, merging, form a network glacier system.

Glaciers called the time-stable accumulation of ice on the earth's surface. They can only appear above the snow boundary, although in the process of dynamics the glacier can also descend below it. Ice in large masses acquires plasticity and is able to flow. The magnitude of the slope and the thickness of the ice are the most important conditions for its movement. Since both the magnitude of the slope of the surface and the very possibility of ice accumulation are most favorable in the mountains, the formation of modern moving glaciers in all zones except the polar one is possible only in conditions of high mountain relief.

The glacier is fed by solid atmospheric precipitation falling on its surface, the transfer of snow by the wind, the collapse of snow from the slopes and the condensation of air vapor on the surface of the glacier.

According to the conditions of the balance of the solid phase of water (i.e., snow, ice firn), the glacier can be divided into an accumulation zone and an ablation zone. Ablation called the consumption of ice through melting and evaporation. Ablation leads to a decrease in the thickness of the marginal part of the glacier. The intensity of ablation is directly dependent on air temperature. Temperature fluctuations cause ablation fluctuations, so the position of the glacier edge does not remain constant. Slight changes in the position of the edge of the glacier are called oscillation.

First of all, they distinguish sheet glaciers, or mainland, and mountain glaciers. The latter are subdivided into a number of types - valley, cirque, volcanic cones, caldera, plateau, etc. Along with these main types, glaciers at the foot of the mountains and ice shelves can also be distinguished. Currently, there are only two detailed continental glaciers on Earth - these are the ice sheets of Greenland and Antarctica. Characteristic features of this type of glaciation are a huge area of ​​ice (the area of ​​glaciation in Antarctica is about 13.2 million square kilometers) and its colossal thickness - up to 4 km. The ice sheet reaches its maximum thickness in the central part. At the edge, the thickness of the glacier is reduced, and here individual ledges of its stone bed are visible. Such bedrock outcrops in Antarctica are called "oases" (Banger oasis in the vicinity of the Soviet Antarctic station "Mirny"). If the remnants are pronounced in relief, they are called nunataks.

The sheet glaciers of Greenland and Antarctica drain into the sea through the depressions they occupy in the coastal relief. Such ice flows are called outlet glaciers. The ice, having reached the water, floats up, breaks, resulting in the formation of huge blocks of floating ice - icebergs.

Large masses of ice on the periphery of Antarctica lie on the shelf or are partially afloat. This is ice shelves.

In the mountains, the formation of glaciers begins with the stage of a snow patch or firn spot. In some areas, the snow accumulated over the winter does not have time to melt over the summer. The following year, a new portion of snow accumulates here. The snow gradually turns into firn and then into ice. The presence of a stable accumulation of ice causes intense frost weathering of the rocks on which it lies, and melt water ensures the removal of weathering products. A circus-shaped (armchair-shaped) depression is gradually formed with steep, often sheer walls and a gently sloping, concave bottom - car 1 . The glacier is entering a new stage of development - the stage car glacier. Active karts, i.e., karts occupied by glaciers, are located slightly above the snow boundary. The next stage in the development of a glacier is the formation valley glacier. The mass of ice no longer fits in the square and begins to slowly descend down the slope. Ice usually uses some kind of erosional form as a runoff route, gradually developing and expanding it. The valley along which the glacier moves acquires a trough-like shape. Such

1 Corrie - Scottish. armchair. 186

glacier valley is called trog 1 .

If the snow boundary lies low, somewhere at the level of the foot of the mountains undergoing glaciation, the glacier enters the foothill plain and spreads at the foot. Glaciers in this stage of development are called foot glaciers. A typical foot glacier is the Malaspina Glacier in Alaska, formed as a result of the confluence of several valley glaciers at the foot of the mountains.

A glacier is called "a mass of ice, characterized by constant regular movement, located mainly on land, existing for a long time, having a certain shape and significant size, and formed due to the accumulation and recrystallization of various solid atmospheric precipitation" . From the above definition it is clear that glaciers can form only where the accumulation of large snow masses that persist for a long time is possible.

To turn into a mass of ice, snow must go through a series of transformations. In the first stage, the loose snow mass is gradually compacted and undergoes recrystallization, which is carried out by melting snow from the surface, penetration and subsequent freezing of the resulting water in the snow mass, as well as due to the sublimation of water vapor on snow crystals, by evaporation of small snowflakes and growth due to them. larger ice crystals. As a result of these processes, the snow acquires a granular structure and is called firn. With further growth and compaction, the firn grains freeze, but between them there are still separate pores with air bubbles, due to which the ice

is called bubbly. Subsequently, the air bubbles are removed and granular dense ice (glacial ice) is formed.

The movement of glaciers and the relief of their surface

From the area of ​​accumulation, ice, due to its inherent plasticity, being under the action of gravity of the accumulating new masses of firn and ice, under the pressure of water penetrating and freezing in cracks, moves to the place of melting. Melting begins below the snow line, but the location of the place of final melting of the glacier largely depends on the size of the glacier itself and on the microclimatic conditions of the territory along which the glacier moves. Because of this, the tongues of even neighboring glaciers can end at different heights. In the polar countries, large glaciers do not have time to melt on land, they descend into the sea, large masses of ice break off from their edge, which are carried away by sea currents. Such fragments of glaciers floating on the sea are called icebergs.

The speed of movement of glaciers is very different: from a few centimeters to 500 m in year. The movement of glaciers is uneven in their various parts. In mountain valley glaciers, the highest velocities are observed in their axial part, where the effect of friction against the coast and the bottom of the ice bed is less pronounced. Near the ice sheets of Antarctica, the highest speeds are observed where the accumulated masses of ice find an outlet to the sea (outflow glaciers). The uneven movement of the glacier is accompanied by the appearance of large stresses in its body and the formation of cracks. Numerous cracks also appear where the glacier moves along an uneven bed. The most typical for mountain glaciers are cracks that occur at the place where ice passes through rocky rapids - crossbars; icefalls form here. The transverse profiles of mountain valley glaciers depend to a large extent on the part of the glacier in which it is being studied. In the feeding area, the transverse profiles of the glacier surface have a concave shape, at the place where the glacier crosses the snow line, they are rectilinear, and in the melting area, they are convex. The latter is explained by the fact that in the area of ​​melting the edges of the glacier melt most quickly, where it is near the mountain slopes heated by the sun's rays.