How are glaciers formed? Mountain glacier.

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glaciers, accumulations of ice that move slowly across the earth's surface. In some cases, ice movement stops and dead ice forms. Many glaciers advance some distance into oceans or large lakes and then form a calving front where icebergs break away. There are four main types of glaciers: continental ice sheets, ice caps, valley glaciers (alpine) and foothill glaciers (foot glaciers).

The best known are sheet glaciers, which can completely cover plateaus and mountain ranges. The largest is the Antarctic ice sheet with an area of more than 13 million km 2, which occupies almost the entire continent. Another sheet glacier is found in Greenland, where it even covers mountains and plateaus. The total area of this island is 2.23 million km 2, of which approx. 1.68 million km 2 is covered with ice. This estimate takes into account not only the area of the ice sheet itself, but also numerous outlet glaciers.

The term "ice cap" is sometimes used to refer to a small ice sheet, but it is more correct to refer to a relatively small mass of ice covering a high plateau or mountain range, from which valley glaciers radiate in different directions. A good example of an ice cap is the so-called. The Columbian Firn Plateau, located in Canada on the border of the provinces of Alberta and British Columbia (52° 30º N). Its area exceeds 466 km2, and large valley glaciers radiate from it to the east, south and west. One of them, the Athabasca Glacier, is easily accessible, as its lower end is only 15 km from the Banff-Jasper Highway, and in summer tourists can drive an all-terrain vehicle all over the glacier. Ice caps are found in Alaska north of Mount St. Elias and east of Russell Fjord.

Valley, or alpine, glaciers start from sheet glaciers, ice caps, and firn fields. The vast majority of modern valley glaciers originate in firn basins and occupy trough valleys, in the formation of which pre-glacial erosion could also take part. Under certain climatic conditions, valley glaciers are widespread in many mountainous regions of the world: in the Andes, the Alps, Alaska, the Rocky and Scandinavian mountains, the Himalayas and other mountains of Central Asia, and New Zealand. Even in Africa - in Uganda and Tanzania - there are a number of such glaciers. Many valley glaciers have tributary glaciers. So, at the Barnard Glacier in Alaska, there are at least eight of them.

Other varieties of mountain glaciers - cirque and hanging - in most cases are relics of a more extensive glaciation. They are found mainly in the upper reaches of the troughs, but sometimes they are located directly on the slopes of the mountains and are not connected with the underlying valleys, and the dimensions of many are slightly larger than the snowfields that feed them. Such glaciers are common in California, the Cascade Mountains (Washington State), and there are about fifty of them in the Glacier National Park (Montana State). All 15 glaciers The Colorados are classified as karts or hangings, and the largest of them, the Arapaho kar glacier in Boulder County, completely occupies the kar. The length of the glacier is only 1.2 km (and once it was about 8 km long), about the same width, and the maximum thickness is estimated at 90 m.

Piedmont glaciers are located at the foot of steep mountain slopes in wide valleys or on plains. Such a glacier may be formed due to the spreading of a valley glacier (an example is the Columbia Glacier in Alaska), but more often - as a result of the confluence at the foot of a mountain of two or more glaciers descending along the valleys. The Grand Plateau and Malaspina in Alaska are classic examples of this type of glacier. Piedmont glaciers are also found on the northeast coast of Greenland.

Characteristics of modern glaciers.

Glaciers vary greatly in size and shape. It is believed that the ice sheet covers approx. 75% of the area of Greenland and almost all of Antarctica. The area of ice caps ranges from several to many thousand square kilometers (for example, the area of the Penny ice cap on Baffin Island in Canada reaches 60 thousand km 2). The largest valley glacier in North America is the 116 km long western branch of the Hubbard Glacier in Alaska, while hundreds of hanging and cirque glaciers are less than 1.5 km long. The areas of foot glaciers range from 1–2 km 2 to 4.4 thousand km 2 (the Malaspina glacier descending into Yakutat Bay in Alaska). It is believed that glaciers cover 10% of the entire land area of the Earth, but this figure is probably too low.

The largest thickness of glaciers - 4330 m - was established near Baird Station (Antarctica). In central Greenland, the thickness of ice reaches 3200 m. Judging by the associated relief, it can be assumed that the thickness of some ice caps and valley glaciers is much more than 300 m, while others measure only tens of meters.

The speed of movement of glaciers is usually very small - about a few meters per year, but there are also significant fluctuations here. After a number of years of heavy snowfall, in 1937 the tip of the Black Rapids Glacier in Alaska moved at a speed of 32 meters per day for 150 days. However, such a rapid movement is not typical for glaciers. In contrast, the Taku Glacier in Alaska has been advancing at an average rate of 106 m/yr for 52 years. Many small cirque and hanging glaciers move even more slowly (for example, the Arapahoe glacier mentioned above moves only 6.3 m annually).

Ice in the body of a valley glacier moves unevenly—fastest on the surface and in the axial part, and much slower along the sides and near the bed, apparently due to increased friction and high saturation of detrital material in the bottom and marginal parts of the glacier.

All large glaciers are dotted with numerous cracks, including open ones. Their dimensions depend on the parameters of the glacier itself. There are cracks up to 60 m deep and tens of meters long. They can be either longitudinal, i.e. parallel to the direction of movement, and transverse, running across this direction. Transverse cracks are much more numerous. Less common are radial fissures found in spreading piedmont glaciers and marginal fissures confined to the ends of valley glaciers. Longitudinal, radial and edge cracks, apparently, were formed due to stresses resulting from friction or ice spreading. Transverse cracks are probably the result of ice moving over an uneven bed. A special type of fissures, the bergschrund, is typical of kars confined to the upper reaches of valley glaciers. These are large cracks that occur when a glacier exits a firn basin.

If glaciers descend into large lakes or seas, iceberg calving occurs along the cracks. Fissures also contribute to the melting and evaporation of glacial ice and play an important role in the formation of kams, basins and other landforms in the marginal zones of large glaciers.

The ice of sheet glaciers and ice caps is usually clean, coarse-grained, and blue in color. This is also true for large valley glaciers, with the exception of their ends, which usually contain layers saturated with rock fragments and alternating with layers of pure ice. Such stratification is due to the fact that in winter, snow falls on top of the dust and debris accumulated in summer that fell onto the ice from the sides of the valley.

On the sides of many valley glaciers there are lateral moraines - elongated ridges of irregular shape, composed of sand, gravel and boulders. Under the influence of erosion processes and slope washout in summer and avalanches in winter, a large amount of various detrital material enters the glacier from the steep sides of the valley, and a moraine is formed from these stones and fine earth. On large valley glaciers that receive tributary glaciers, a median moraine is formed, moving near the axial part of the glacier. These elongated narrow ridges, composed of clastic material, used to be lateral moraines of tributary glaciers. Coronation Glacier in Baffin Island has at least seven median moraines.

In winter, the surface of the glaciers is relatively flat, as snow levels out all the irregularities, but in summer they significantly diversify the relief. In addition to the fissures and moraines described above, valley glaciers are often deeply dissected by flows of melted glacial waters. Strong winds carrying ice crystals break and furrow the surface of ice caps and ice caps. If large boulders protect the underlying ice from melting, while the ice around has already melted, ice mushrooms (or pedestals) form. Such forms, crowned with large boulders and stones, sometimes reach a height of several meters.

Piedmont glaciers are characterized by uneven and peculiar character of the surface. Their tributaries may deposit an indiscriminate mixture of lateral, median, and terminal moraines, among which blocks of dead ice occur. In places where large ice blocks thaw, deep depressions of irregular shape appear, many of which are occupied by lakes. A forest has grown on the powerful moraine of the Malaspina glacier, covering a block of dead ice 300 m thick. A few years ago, within this massif, the ice began to move again, as a result of which sections of the forest began to shift.

In outcrops along the edges of glaciers, large shear zones are often seen, where some blocks of ice are pushed over others. These zones are thrusts, and there are several ways of their formation. First, if one of the sections of the bottom layer of the glacier is oversaturated with clastic material, then its movement stops, and the newly incoming ice moves towards it. Secondly, the upper and inner layers of the valley glacier move towards the bottom and lateral layers, as they move faster. In addition, when two glaciers merge, one can move faster than the other, and then an overthrust also occurs. The Baudouin Glacier in northern Greenland and many of the Svalbard glaciers have spectacular thrust outcrops.

At the ends or edges of many glaciers, tunnels are often observed, cut by subglacial and intraglacial meltwater flows (sometimes with the participation of rainwater) that rush through the tunnels during the ablation season. When the water level drops, the tunnels become available for exploration and provide a unique opportunity to study the internal structure of glaciers. Significant tunnels have been developed in the Mendenhall glaciers in Alaska, Asulcan in British Columbia (Canada) and Rhone (Switzerland).

Formation of 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.

movement of glaciers

observed in nature, differs markedly from the flow of liquid or viscous substances (for example, resins). In reality, it is more like the fluidity of metals or rocks along numerous tiny slip planes along the planes of the crystal lattice or along cleavage (cleavage planes) parallel to the base of hexagonal ice crystals. MINERALS AND MINERALOGY) . The reasons for the movement of glaciers are not fully established. Many theories have been put forward about this, but none of them is accepted by glaciologists as the only true one, and there are probably several interrelated reasons. Gravity is an important factor, but by no means the only one. Otherwise, glaciers would move faster in winter when they carry an additional load in the form of snow. However, they actually move faster in the summer. The melting and refreezing of ice crystals in a glacier may also contribute to movement due to the expansion forces resulting from these processes. Melt water, falling deep into the cracks and freezing there, expands, which can speed up the movement of the glacier in summer. In addition, meltwater near the bed and sides of the glacier reduces friction and thus promotes movement.

Regardless of the causes that drive glaciers, its nature and results have some interesting implications. In many moraines there are glacial boulders that are well polished only on one side, and deep shading is sometimes visible on the polished surface, oriented only in one direction. All this indicates that when the glacier moved along the rock bed, the boulders were firmly clamped in one position. It happens that boulders are carried by glaciers up the slope. Along the eastern ledge of the Rocky Mountains in Prov. Alberta (Canada) has boulders that have been moved more than 1000 km to the west and are currently 1250 m above the point of separation. Whether the bottom layers of the glacier, moving west and up to the foot of the Rocky Mountains, were frozen to the bed, is not yet clear. It is more likely that repeated shearing occurred, complicated by overthrusts. According to most glaciologists, in the frontal zone, the glacier surface always has a slope in the direction of ice movement. If this is true, then in this example the thickness of the ice sheet exceeded 1250 m for 1100 km to the east, when its edge reached the foot of the Rocky Mountains. It is possible that it reached 3000 m.

Melting and retreat of glaciers.

The thickness of glaciers increases due to the accumulation of snow and decreases under the influence of several processes that glaciologists unite under the general term "ablation". This includes melting, evaporation, sublimation (sublimation) and deflation (wind erosion) of ice, as well as iceberg calving. Both accumulation and ablation require very specific climatic conditions. Heavy snowfalls in winter and cold, cloudy summers contribute to the growth of glaciers, while winters with little snow and warm, sunny summers have the opposite effect.

With the exception of iceberg calving, melting is the most significant component of ablation. The retreat of the end of the glacier occurs both as a result of its melting and, more importantly, a general decrease in the thickness of the ice. The melting of the marginal parts of valley glaciers under the influence of direct solar radiation and heat radiated by the sides of the valley also makes a significant contribution to the degradation of the glacier. Paradoxically, even during the retreat, the glaciers continue to move forward. Thus, a glacier can move 30 m in a year and retreat 60 m. As a result, the length of the glacier decreases, although it continues to move forward. Accumulation and ablation are almost never in perfect balance, so there are constant fluctuations in the size of glaciers.

Iceberg calving is a special type of ablation. In summer, small icebergs can be seen floating peacefully on mountain lakes located at the ends of valley glaciers, and huge icebergs that have broken off from the glaciers of Greenland, Svalbard, Alaska and Antarctica are a sight to inspire awe. The Columbia Glacier in Alaska enters the Pacific Ocean with a front 1.6 km wide and 110 m high. It slowly slides into the ocean. Under the action of the lifting force of water, in the presence of large cracks, huge blocks of ice break off and float away, at least two-thirds submerged in water. In Antarctica, the edge of the famous Ross Ice Shelf borders the ocean for 240 km, forming a ledge 45 m high. Huge icebergs form here. In Greenland, the outlet glaciers also produce many very large icebergs, which are carried by cold currents into the Atlantic Ocean, where they become a threat to ships.

Pleistocene Ice Age.

The Pleistocene epoch of the Quaternary period of the Cenozoic era began about 1 million years ago. At the beginning of this era, large glaciers began to grow in Labrador and Quebec (the Laurentian ice sheet), in Greenland, on the British Isles, in Scandinavia, Siberia, Patagonia and Antarctica. According to some glaciologists, a large center of glaciation was also located west of Hudson Bay. The third center of glaciation, called the Cordillera, was located in the center of British Columbia. Iceland was completely covered in ice. The Alps, the Caucasus and the mountains of New Zealand were also important centers of glaciation. Numerous valley glaciers have formed in the mountains of Alaska, the Cascades (Washington and Oregon), the Sierra Nevada (California), and the Rocky Mountains of Canada and the United States. A similar mountain-valley glaciation spread in the Andes and in the high mountains of Central Asia. The sheet glacier, which began to form in Labrador, then moved south to the state of New Jersey - more than 2400 km from its place of origin, completely covering the mountains of New England and the state of New York. Glacial growth also occurred in Europe and Siberia, but the British Isles were never completely covered with ice. The duration of the first Pleistocene glaciation is unknown. Probably, it was at least 50 thousand years old, and maybe twice as much. Then came a long period, during which most of the land covered with glaciers was freed from ice.

There were three other similar glaciations during the Pleistocene in North America, Europe, and North Asia. The most recent of them in North America and Europe occurred during the last 30 thousand years, where the ice finally melted approx. 10 thousand years ago. In general terms, the synchronism of the four Pleistocene glaciations of North America and Europe has been established.

The spread of glaciation in the Pleistocene.

In North America, during the maximum glaciation, ice sheets covered an area of more than 12.5 million square meters. km, i.e. more than half of the entire surface of the continent. In Europe, the Scandinavian ice sheet extended over an area exceeding 4 million km2. It blocked the North Sea and connected with the ice sheet of the British Isles. The glaciers that formed in the Ural Mountains also grew and extended into the foothill regions. There is an assumption that during the Middle Pleistocene glaciation they connected with the Scandinavian ice sheet. Ice sheets occupied vast areas in the mountainous regions of Siberia. In the Pleistocene, the ice sheets of Greenland and Antarctica probably had a much larger area and thickness (mainly in Antarctica) than modern ones.

In addition to these large centers of glaciation, there were many small local centers, for example, in the Pyrenees and Vosges, the Apennines, the mountains of Corsica, Patagonia (east of the southern Andes).

During the maximum development of the Pleistocene glaciation, over half of the area of North America was covered with ice. On the territory of the United States, the southern limit of the ice sheet follows approximately from Long Island (New York) to the north-central part of the state of New Jersey and northeast Pennsylvania almost to the southwestern border of the state. New York. From here it heads to the southwestern border of the Ohio state, then along the Ohio River into southern Indiana, then turns north into south central Indiana, and then southwest to the Mississippi River, while the southern part of the state of Illinois remains outside areas of glaciation. The glaciation boundary passes near the Mississippi and Missouri rivers to the city of Kansas City, then through the eastern part of Kansas, the eastern part of Nebraska, the central part of South Dakota, the southwestern part of North Dakota to Montana a little south of the Missouri River. From here, the southern limit of the ice sheet turns west to the foothills of the Rocky Mountains in northern Montana.

An area of 26,000 km 2 , covering northwestern Illinois, northeastern Iowa, and southwestern Wisconsin, has long been distinguished as "boulderless". It was assumed that it was never covered by Pleistocene glaciers. In fact, the Wisconsin ice sheet did not extend there. It is possible that ice entered there during earlier glaciations, but the traces of their presence were erased under the influence of erosion processes.

North of the United States, the ice sheet extended into Canada to the Arctic Ocean. Greenland, Newfoundland and Nova Scotia were covered in ice in the northeast. In the Cordillera, ice caps occupied southern Alaska, the plateaus and coast ranges of British Columbia, and the northern third of Washington State. In short, except for the western regions of central Alaska and its extreme north, all of North America north of the line described above was occupied by ice in the Pleistocene.

Consequences of the Pleistocene glaciation.

Under the influence of a huge glacial load, the earth's crust turned out to be bent. After the degradation of the last glaciation, the area that was covered with the thickest layer of ice west of Hudson Bay and northeast Quebec rose faster than that located at the southern edge of the ice sheet. It is estimated that the area of the northern shore of Lake Superior is currently rising at a rate of 49.8 cm per century, and the area located west of Hudson Bay will rise by another 240 m before the end of the compensatory isostasy. A similar uplift occurs in the Baltic region in Europe.

Pleistocene ice was formed at the expense of ocean water, and therefore, during the maximum development of glaciation, the greatest decrease in the level of the World Ocean also occurred. The magnitude of this decrease is a controversial issue, but geologists and oceanologists unanimously admit that the level of the World Ocean has dropped by more than 90 m. 90 m

Fluctuations in the level of the World Ocean influenced the development of the rivers flowing into it. Under normal conditions, rivers cannot deepen their valleys much below sea level, but when it decreases, river valleys lengthen and deepen. Probably, the flooded valley of the Hudson River, stretching on the shelf for more than 130 km and ending at depths of approx. 70 m, formed during one or more major glaciations.

Glaciation has affected the change in the direction of the flow of many rivers. In preglacial times, the Missouri River flowed from eastern Montana north into Canada. The North Saskatchewan River once flowed east across Alberta, but subsequently turned sharply north. As a result of the Pleistocene glaciation, inland seas and lakes were formed, and the area of those that already existed increased. Due to the influx of melted glacial waters and heavy rainfall, Lake. Bonneville in Utah, of which the Great Salt Lake is a relic. The maximum area of the lake Bonneville exceeded 50 thousand km2, and the depth reached 300 m. The Caspian and Aral seas (essentially large lakes) had much larger areas in the Pleistocene. Apparently, in Würm (Wisconsin), the water level in the Dead Sea was more than 430 m higher than the modern one.

Valley glaciers in the Pleistocene were much more numerous and larger than they are now. There were hundreds of glaciers in Colorado (now 15). The largest modern glacier in Colorado, the Arapahoe, is 1.2 km long, and in the Pleistocene, the Durango Glacier in the San Juan Mountains in southwestern Colorado was 64 km long. Glaciation also developed in the Alps, Andes, Himalayas, Sierra Nevada and other large mountain systems of the globe. Along with valley glaciers, there were also many ice caps. This has been proven, in particular, for the coastal ranges of British Columbia and the United States. In the south of Montana, in the Bartus Mountains, there was a large ice cap. In addition, in the Pleistocene, glaciers existed on the Aleutian Islands and Hawaii (Mauna Kea), in the Hidaka Mountains (Japan), on the South Island of New Zealand, on Tasmania, in Morocco and the mountainous regions of Uganda and Kenya , in Turkey, Iran, Svalbard and Franz Josef Land. In some of these areas, glaciers are still common today, but, as in the western United States, they were much larger in the Pleistocene.

GLACIER RELIEF

Exaration relief created by sheet glaciers.

Possessing considerable thickness and weight, the glaciers produced a powerful exaration work. In many localities, they destroyed the entire soil cover and partially underlying loose deposits and cut deep hollows and furrows in bedrock. In central Quebec, these hollows are occupied by numerous elongated shallow lakes. Glacial furrows can be traced along the Canadian Transcontinental Highway and near the city of Sudbury (prov. Ontario). The mountains of New York and New England were flattened and prepared, and the pre-glacial valleys that existed there were widened and deepened by ice flows. Glaciers have also expanded the basins of the five Great Lakes of the United States and Canada, and rock surfaces have been polished and hatched.

Glacial-accumulative relief created by sheet glaciers.

Ice sheets, including Laurentian and Scandinavian, covered an area of at least 16 million km 2, and, in addition, thousands of square kilometers were covered with mountain glaciers. During the degradation of glaciation, all the detrital material eroded and displaced in the body of the glacier was deposited where the ice melted. Thus, vast areas were found to be strewn with boulders and rubble and covered with finer-grained glacial deposits. A long time ago, boulders of unusual composition were found scattered over the surface of the British Isles. At first it was assumed that they were brought by ocean currents. However, their glacial origin was later recognized. Glacial deposits began to be subdivided into moraine and sorted sediments. Deposited moraines (sometimes referred to as tills) include boulders, rubble, sand, sandy loam, loam, and clay. Perhaps the predominance of one of these components, but most often the moraine is an unsorted mixture of two or more components, and sometimes all fractions are found. Sorted sediments are formed under the influence of melted glacial waters and compose outwash water-glacial plains, valley sands, kams and ozes ( see below), and also fill the basins of lakes of glacial origin. Some characteristic landforms of the glaciation areas are considered below.

main moraines.

The word "moraine" was first applied to the ridges and hills, composed of boulders and fine earth, and found at the ends of glaciers in the French Alps. The composition of the main moraines is dominated by the material of deposited moraines, and their surface is a rugged plain with small hills and ridges of various shapes and sizes, and with numerous small basins filled with lakes and swamps. The thickness of the main moraines varies widely depending on the amount of material brought by the ice.

The main moraines occupy vast areas in the USA, Canada, the British Isles, Poland, Finland, northern Germany and Russia. The surroundings of Pontiac (Michigan) and Waterloo (Wisconsin) are characterized by landscapes of the main moraine. Thousands of small lakes dot the surface of major moraines in Manitoba and Ontario (Canada), Minnesota (USA), Finland and Poland.

terminal moraines

form powerful wide belts along the edge of the sheet glacier. They are represented by ridges or more or less isolated hills up to several tens of meters thick, up to several kilometers wide and, in most cases, many kilometers long. Often the edge of the sheet glacier was not even, but was divided into quite distinctly distinct lobes. The position of the glacier edge is reconstructed from terminal moraines. Probably, during the deposition of these moraines, the edge of the glacier was almost in a stationary (stationary) state for a long time. At the same time, not one ridge was formed, but a whole complex of ridges, hills and basins, which noticeably rises above the surface of adjacent main moraines. In most cases, the terminal moraines, which are part of the complex, testify to repeated small movements of the glacier edge. Melt water from retreating glaciers has eroded these moraines in many places, as evidenced by observations in central Alberta and north of Regina in the Hart Mountains of Saskatchewan. In the United States, such examples are found along the southern boundary of the ice sheet.

Drumlins

- elongated hills, shaped like a spoon, turned upside down with a convex side up. These forms are composed of deposited moraine material and in some (but not all) cases have a bedrock core. Drumlins are usually found in large groups - several dozen or even hundreds. Most of these landforms are 900–2000 m long, 180–460 m wide and 15–45 m high. Boulders on their surface are often oriented with long axes in the direction of ice movement, which was carried out from a steep slope to a gentle one. Apparently, drumlins were formed when the lower layers of ice lost their mobility due to overloading with clastic material and were overlapped by moving upper layers, which processed the material of the deposited moraine and created the characteristic forms of drumlins. Such forms are widespread in the landscapes of the main moraines in the regions of the ice cover.

outwash plains

composed of material brought by flows of melted glacial waters, and usually adjoin the outer edge of the terminal moraines. These coarsely graded deposits consist of sand, pebbles, clay and boulders (the maximum size of which depended on the transport capacity of the flows). Outwash fields are usually widespread along the outer edge of terminal moraines, but there are exceptions. Illustrative examples of sanders are found west of the Altmont Moraine in central Alberta, near the cities of Barrington (Illinois) and Plainfield (New Jersey), as well as on Long Island and the Cape Cod Peninsula. The outwash plains of the central United States, especially along the Illinois and Mississippi rivers, contained vast amounts of silty material, which was subsequently picked up and carried by strong winds and eventually redeposited as loess.

Oz

- these are long narrow winding ridges, composed mainly of sorted sediments, ranging in length from several meters to several kilometers and up to 45 m high. Ozes were formed as a result of the activity of subglacial meltwater flows, which worked out tunnels in ice and deposited sediments there. Osses are found wherever ice sheets existed. Hundreds of such forms are found both east and west of Hudson Bay.

Kama

- these are small steep hills and short ridges of irregular shape, composed of sorted sediments. They probably formed in different ways. Some were deposited near terminal moraines by streams flowing from intraglacial fissures or subglacial tunnels. These kames often coalesce into broad fields of poorly sorted sediments called stone terraces. Others appear to have been formed by the melting of large blocks of dead ice at the end of the glacier. The resulting basins were filled with deposits of melt water flows, and after the complete melting of ice, kames formed there, slightly rising above the surface of the main moraine. Kamas are found in all areas of ice cover.

depressions

often found on the surface of the main moraine. This is the result of melting blocks of ice. At present, in humid areas they can be occupied by lakes or swamps, while in semi-arid and even in many humid areas they are dry. Such depressions are found in combination with small steep hills. Hollows and hills are typical landforms of the main moraine. Hundreds of these forms are found in northern Illinois, Wisconsin, Minnesota, and Manitoba.

Lacustrine-glacial plains

occupy the bottoms of former lakes. In the Pleistocene, numerous lakes of glacial origin arose, which were then drained. Streams of melted glacial waters brought detrital material to these lakes, which was sorted there. The ancient near-glacial lake Agassiz with an area of 285 thousand square meters. km, located in Saskatchewan and Manitoba, North Dakota and Minnesota, was fed by numerous streams starting from the edge of the ice sheet. At present, the vast bottom of the lake, covering an area of several thousand square kilometers, is a dry surface composed of interbedded sands and clays.

Exaration relief created by valley glaciers.

Unlike ice sheets, which produce streamlined shapes and smooth the surfaces through which they move, mountain glaciers, on the contrary, transform the topography of mountains and plateaus in such a way that they make it more contrasting and create the characteristic landforms discussed below.

U-shaped valleys (troughs).

Large glaciers, carrying large boulders and sand in their bases and marginal parts, are powerful agents of exaration. They widen the bottoms and steepen the sides of the valleys along which they move. This forms a U-shaped transverse profile of the valleys.

Hanging valleys.

In many areas, large valley glaciers received small tributary glaciers. The first of them deepened their valleys much more than shallow glaciers. After the melting of the ice, the ends of the valleys of the tributary glaciers were, as it were, suspended above the bottoms of the main valleys. Thus, hanging valleys arose. Such typical valleys and picturesque waterfalls were formed in Yosemite Valley (State of California) and Glacier National Park (State of Montana) at the junction of side valleys with the main ones.

Circuses and karts.

Cirques are bowl-shaped recesses or amphitheaters that are located in the upper parts of the troughs in all mountains where large valley glaciers have ever existed. They were formed as a result of the expanding action of water frozen in the cracks of rocks and the removal of the formed large detrital material by glaciers moving under the influence of gravity. Cirques appear below the firn line, especially near the bergschrunds, when the glacier leaves the firn field. During the processes of expansion of cracks during freezing of water and gouging, these forms grow in depth and width. Their upper reaches cut into the slope of the mountain on which they are located. Many circuses have steep sides several tens of meters high. The bottoms of cirques are also characterized by lake baths worked out by glaciers.

In cases where such forms do not have a direct connection with the underlying troughs, they are called kars. Outwardly, it seems that the punishments are suspended on the slopes of the mountains.

Karovy stairs.

At least two caravans located in the same valley are called caravan stairs. Usually, the carts are separated by steep ledges, which, articulated with the flattened bottoms of the carts, like steps, form cyclopean (nested) stairs. On the slopes of the Front Range in Colorado, there are many distinct caravan stairs.

Carlings

- peaked forms, formed during the development of three or more kars on opposite sides of one mountain. Carlings often have a regular pyramidal shape. A classic example is the Matterhorn on the border between Switzerland and Italy. However, picturesque carlings are found in almost all high mountains where valley glaciers existed.

Aretas

- These are jagged ridges resembling a saw blade or knife blade. They form where two kara, growing on opposite slopes of a ridge, come close to each other. Aretes also appear where two parallel glaciers have destroyed the separating mountain barrier to such an extent that only a narrow ridge remains of it.

passes

- these are jumpers in the crests of mountain ranges, formed during the retreat of the rear walls of two caravans that developed on opposite slopes.

Nunataks

- These are rocky outcrops surrounded by glacial ice. They separate valley glaciers and lobes of ice caps or sheets. There are well-defined nunataks on the Franz Josef Glacier and some other glaciers in New Zealand, as well as in the peripheral parts of the Greenland Ice Sheet.

fjords

are found on all the coasts of mountainous countries, where valley glaciers once descended into the ocean. Typical fjords are trough valleys partially submerged by the sea with a U-shaped transverse profile. Glacier approx. 900 m can move into the sea and continue to deepen its valley until it reaches a depth of approx. 800 m. The deepest fjords include the Sognefjord Bay (1308 m) in Norway and the Messier (1287 m) and Baker (1244) straits in southern Chile.

While it is fairly certain that most fjords are deep-cut troughs that were flooded after glacier melt, the origin of each fjord can only be determined by taking into account the history of glaciation in the valley, bedrock conditions, the presence of faults, and the extent of coastal subsidence. Thus, while most fjords are deep troughs, many coastal areas, like the coast of British Columbia, have experienced subsidence as a result of crustal movements, which in some cases contributed to their flooding. Picturesque fjords are typical of British Columbia, Norway, southern Chile and the South Island of New Zealand.

Exaration baths (digging baths)

Exaration baths (ploughing baths) are developed by valley glaciers in bedrock at the base of steep slopes in places where the valley bottoms are composed of highly fractured rocks. Usually the area of these baths is approx. 2.5 sq. km, and the depth is approx. 15 m, although many of them are smaller. Exaration baths are often confined to the bottoms of cars.

Lamb foreheads

- These are small rounded hills and uplands, composed of dense bedrock, which have been well polished by glaciers. Their slopes are asymmetrical: the slope facing downstream of the glacier is slightly steeper. Often on the surface of these forms there is a glacial streak, and the streaks are oriented in the direction of ice movement.

Accumulative relief created by valley glaciers.

Terminal and lateral moraines

- the most characteristic glacial-accumulative forms. As a rule, they are located at the mouths of the troughs, but can also be found in any place that the glacier has occupied, both within the valley and outside it. Both types of moraines were formed as a result of the melting of ice, followed by the unloading of detrital material transported both on the surface of the glacier and inside it. Lateral moraines usually represent long narrow ridges. End moraines can also be ridge-shaped, often thick accumulations of large fragments of bedrock, rubble, sand and clay, deposited at the end of the glacier for a long time, when the rates of advance and melt were approximately balanced. The height of the moraine testifies to the thickness of the glacier that formed it. Often the two lateral moraines join to form one horseshoe-shaped terminal moraine, the sides of which extend up the valley. Where the glacier did not occupy the entire bottom of the valley, the lateral moraine could form at some distance from its sides, but approximately parallel to them, leaving a second long and narrow valley between the moraine ridge and the bedrock slope of the valley. Both lateral and terminal moraines have inclusions of huge boulders (or blocks) weighing up to several tons, broken out of the sides of the valley as a result of freezing water in rock crevices.

recessionary moraines

formed when the rate of glacier melting exceeded the rate of its advance. They form a small-hilly relief with many small depressions of irregular shape.

valley sanders

are accumulative formations composed of coarsely sorted detrital material from bedrock. They are similar to the outwash plains of ice sheet regions, since they were created by flows of glacial melt waters, but they are located within the valleys below the terminal or recessive moraine. Valley sanders can be observed near the ends of the Norris Glaciers in Alaska and the Athabasca Glaciers in Alberta.

Lakes of glacial origin

sometimes they occupy exaration baths (for example, kar lakes located in kars), but much more often such lakes are located behind moraine ridges. Similar lakes abound in all areas of mountain-valley glaciation; many of them give a special charm to the heavily rugged mountain landscapes surrounding them. They are used for the construction of hydroelectric power plants, irrigation and urban water supply. However, they are also valued for their scenic beauty and recreational value. Many of the most beautiful lakes in the world are of this type.

THE PROBLEM OF THE ICE AGES

In the history of the Earth, major glaciations have repeatedly occurred. In Precambrian time (over 570 million years ago) - probably in the Proterozoic (the youngest of the two divisions of the Precambrian) - part of Utah, northern Michigan and Massachusetts, and part of China were glaciated. It is not known whether the glaciation of all these areas developed simultaneously, although there is clear evidence in the Proterozoic rocks that glaciation was synchronous in Utah and Michigan. In the Late Proterozoic rocks of Michigan and in the rocks of the Cottonwood Series of Utah, horizons of tillites (compacted or lithified moraine) were found. During the Late Pennsylvanian and Permian times - perhaps between 290 million and 225 million years ago - large areas of Brazil, Africa, India and Australia were covered by ice caps or ice sheets. Oddly enough, all these areas are located at low latitudes - from 40 ° N.S. up to 40°S Synchronous glaciation also occurred in Mexico. Less reliable evidence of the glaciation of North America in the Devonian and Mississippian times (from about 395 million to 305 million years ago). Evidence of glaciation in the Eocene (from 65 million to 38 million years ago) was found in the San Juan Mountains (Colorado). If we add to this list the Pleistocene ice age and modern glaciation, which occupies almost 10% of the land, it becomes obvious that glaciations in the history of the Earth were normal phenomena.

Causes of Ice Ages.

The cause or causes of the ice ages are inextricably linked to the broader problems of global climate change that have taken place throughout the history of the earth. Significant changes in geological and biological settings occurred from time to time. The plant remains that make up the thick coal seams of Antarctica, of course, accumulated in climatic conditions different from those of today. Now magnolias do not grow in Greenland, but they are found in a fossil state. Fossil remains of the arctic fox are known from France, far to the south of the current range of this animal. During one of the Pleistocene interglacials, mammoths moved as far north as Alaska. The province of Alberta and the Northwest Territories of Canada were covered by seas in the Devonian, in which there were many large coral reefs. Coral polyps develop well only at water temperatures above 21 ° C, i.e. significantly higher than the current average annual temperature in northern Alberta.

It should be borne in mind that the beginning of all great glaciations is determined by two important factors. First, for thousands of years, the annual course of precipitation should be dominated by heavy and prolonged snowfalls. Secondly, in areas with such a precipitation regime, temperatures should be so low that summer snowmelt is minimized, and firn fields increase from year to year until glaciers begin to form. Abundant accumulation of snow should prevail in the balance of glaciers throughout the entire epoch of glaciation, since if ablation exceeds accumulation, glaciation will decline. Obviously, for each ice age it is necessary to find out the reasons for its beginning and end.

Pole migration hypothesis.

Many scientists believed that the Earth's axis of rotation changes its position from time to time, which leads to a corresponding shift in climatic zones. So, for example, if the North Pole were on the Labrador Peninsula, arctic conditions would prevail there. However, the forces that could cause such a change are not known either inside the Earth or outside it. According to astronomical data, the poles can migrate as little as 21º in latitude (which is about 37 km) from the central position.

The carbon dioxide hypothesis.

Carbon dioxide CO 2 in the atmosphere acts like a warm blanket to trap the Earth's radiated heat close to the Earth's surface, and any significant reduction in CO 2 in the air will cause the Earth's temperature to drop. This reduction can be caused, for example, by unusually active rock weathering. CO 2 combines with water in the atmosphere and soil to form carbon dioxide, which is a very reactive chemical compound. It easily reacts with the most common elements in rocks, such as sodium, potassium, calcium, magnesium and iron. If significant land uplift occurs, fresh rock surfaces are subject to erosion and denudation. During the weathering of these rocks, a large amount of carbon dioxide will be extracted from the atmosphere. As a result, the temperature of the land will drop, and the ice age will begin. When, after a long time, carbon dioxide absorbed by the oceans returns to the atmosphere, the ice age will come to an end. The carbon dioxide hypothesis is applicable, in particular, to explain the development of the Late Paleozoic and Pleistocene glaciations, which were preceded by land uplift and mountain building. This hypothesis has been objected to on the grounds that the air contains much more CO 2 than is required for the formation of a heat-insulating cover. In addition, it did not explain the recurrence of glaciations in the Pleistocene.

Hypothesis of diastrophism (movements of the earth's crust).

Significant land uplifts have repeatedly occurred in the history of the Earth. In general, the air temperature over land decreases by about 1.8°C for every 90 m rise. Thus, if the area located west of Hudson Bay were to rise by only 300 m, firn fields would begin to form there. In reality, the mountains rose many hundreds of meters, which turned out to be sufficient for the formation of valley glaciers there. In addition, the growth of mountains changes the circulation of moisture-bearing air masses. The Cascade Mountains in western North America intercept incoming air masses from the Pacific Ocean, resulting in heavy precipitation on the windward slope, and much less liquid and solid precipitation to the east of them. The uplift of ocean floors can, in turn, change the circulation of ocean waters and also cause climate change. For example, it is believed that there was once a land bridge between South America and Africa, which could prevent the penetration of warm water into the South Atlantic, and Antarctic ice could have a cooling effect on this water area and adjacent land areas. Such conditions are put forward as a possible cause of the glaciation of Brazil and Central Africa in the Late Paleozoic. It is not known whether only tectonic movements could be the cause of glaciation, in any case, they could greatly contribute to its development.

Hypothesis of volcanic dust.

Volcanic eruptions are accompanied by the release of a huge amount of dust into the atmosphere. For example, as a result of the eruption of the Krakatau volcano in 1883, approx. 1.5 km 3 of the smallest particles of volcanogenic products. All this dust was carried around the globe, and therefore, for three years, New Englanders watched unusually bright sunsets. After violent volcanic eruptions in Alaska, the Earth for some time received less heat from the Sun than usual. Volcanic dust absorbed, reflected and scattered back into the atmosphere more solar heat than usual. Obviously, volcanic activity, widespread on Earth for millennia, could significantly lower air temperatures and cause the onset of glaciation. Such outbreaks of volcanic activity have happened in the past. During the formation of the Rocky Mountains, New Mexico, Colorado, Wyoming, and southern Montana experienced many very violent volcanic eruptions. Volcanic activity began in the Late Cretaceous and was very intense until about 10 million years ago. The influence of volcanism on the Pleistocene glaciation is problematic, but it is possible that it played an important role. In addition, such volcanoes of the young Cascades as Hood, Rainier, St. Helens, Shasta, emitted a large amount of dust into the atmosphere. Along with the movements of the earth's crust, these ejecta could also significantly contribute to the onset of glaciation.

Continental drift hypothesis.

According to this hypothesis, all modern continents and the largest islands were once part of the single mainland Pangea, washed by the oceans. The consolidation of the continents into such a single land mass could explain the development of the Late Paleozoic glaciation of South America, Africa, India and Australia. The territories covered by this glaciation were probably located much to the north or south of their present position. The continents began to separate in the Cretaceous, and reached their present position about 10 thousand years ago. If this hypothesis is correct, then it helps to a large extent to explain the ancient glaciation of areas currently located in low latitudes. During the glaciation, these regions must have been located at high latitudes, and subsequently they took their present positions. However, the continental drift hypothesis does not provide an explanation for the multiple Pleistocene glaciations.

The Ewing–Donne hypothesis.

One of the attempts to explain the causes of the Pleistocene Ice Age belongs to M. Ewing and W. Donn, geophysicists who have made a significant contribution to the study of the topography of the ocean floor. They believe that in pre-Pleistocene times, the Pacific Ocean occupied the northern polar regions and therefore it was much warmer there than it is now. The Arctic land areas were then located in the northern part of the Pacific Ocean. Then, as a result of the drift of the continents, North America, Siberia and the Arctic Ocean took their current position. Thanks to the Gulf Stream, which came from the Atlantic, the waters of the Arctic Ocean at that time were warm and evaporated intensively, which contributed to heavy snowfalls in North America, Europe and Siberia. Thus, the Pleistocene glaciation began in these areas. It stopped due to the fact that as a result of the growth of glaciers, the level of the World Ocean dropped by about 90 m, and the Gulf Stream was eventually unable to overcome the high underwater ridges that separate the basins of the Arctic and Atlantic oceans. Deprived of the influx of warm Atlantic waters, the Arctic Ocean froze, and the source of moisture that feeds the glaciers dried up. According to the Ewing and Donn hypothesis, a new glaciation awaits us. Indeed, between 1850 and 1950 most of the world's glaciers retreated. This means that the level of the World Ocean has risen. Ice in the Arctic has also been melting over the past 60 years. If ever the Arctic ice completely melts and the waters of the Arctic Ocean again experience the warming effect of the Gulf Stream, which can overcome the underwater ridges, there will be a source of moisture for evaporation, which will lead to heavy snowfalls and the formation of glaciation along the periphery of the Arctic Ocean.

Hypothesis of the circulation of oceanic waters.

There are many currents in the oceans, both warm and cold, which have a significant impact on the climate of the continents. The Gulf Stream is one of the wonderful warm currents that washes the northern coast of South America, passes through the Caribbean Sea and the Gulf of Mexico and crosses the North Atlantic, having a warming effect on Western Europe. The warm Brazilian Current moves south along the coast of Brazil, and the Kuroshio Current, which originates in the tropics, follows north along the Japanese Islands, passes into the latitudinal North Pacific Current and, a few hundred kilometers from the coast of North America, is divided into the Alaska and California currents . There are also warm currents in the South Pacific and the Indian Ocean. The most powerful cold currents are sent from the Arctic Ocean to the Pacific through the Bering Strait and into the Atlantic Ocean through the straits along the eastern and western coasts of Greenland. One of them - the Labrador Current - cools the coast of New England and brings fog there. Cold waters also enter the southern oceans from the Antarctic in the form of particularly powerful currents moving north almost to the equator along the western coasts of Chile and Peru. The strong subsurface countercurrent of the Gulf Stream carries its cold waters south into the North Atlantic.

It is currently believed that the Isthmus of Panama sank several tens of meters. In this case, there would be no Gulf Stream, and the warm Atlantic waters would be sent by trade winds to the Pacific Ocean. The waters of the North Atlantic would be much colder, as, indeed, the climate of the countries of Western Europe, which in the past received heat from the Gulf Stream. There were many legends about the "lost mainland" Atlantis, once located between Europe and North America. Studies of the Mid-Atlantic Ridge in the area from Iceland to 20°N. geophysical methods and with the selection and analysis of bottom samples showed that once there really was land. If this is true, then the climate of all Western Europe was much colder than at present. All these examples show the direction in which the circulation of oceanic waters has changed.

Hypothesis of changes in solar radiation.

As a result of a long study of sunspots, which are strong plasma ejections in the solar atmosphere, it was found that there are very significant annual and longer cycles of changes in solar radiation. Solar activity peaks approximately every 11, 33, and 99 years, when the Sun radiates more heat, which leads to more powerful circulation of the Earth's atmosphere, accompanied by more clouds and more abundant precipitation. Due to the high cloud cover that blocks the sun's rays, the land surface receives less heat than usual. These short cycles could not stimulate the development of glaciation, but based on the analysis of their consequences, it was suggested that there may be very long cycles, perhaps on the order of thousands of years, when the radiation was higher or lower than usual.

Based on these ideas, the English meteorologist J. Simpson put forward a hypothesis explaining the multiplicity of the Pleistocene glaciation. He illustrated with curves the development of two full cycles of above-normal solar radiation. Once the radiation reached the middle of its first cycle (as in the short cycles of sunspot activity), the increase in heat contributed to the activation of atmospheric processes, including increased evaporation, increased solid precipitation, and the onset of the first glaciation. During the radiation peak, the Earth warmed up to such an extent that the glaciers melted and the interglacial began. As soon as the radiation dropped, conditions arose similar to those of the first glaciation. Thus began the second glaciation. It ended with the onset of such a phase of the radiation cycle, during which there was a weakening of the atmospheric circulation. At the same time, evaporation and the amount of solid precipitation decreased, and glaciers retreated due to a decrease in snow accumulation. Thus began the second interglacial. The repetition of the radiation cycle made it possible to single out two more glaciations and the interglacial period separating them.

It should be borne in mind that two successive solar radiation cycles could last 500 thousand years or more. The interglacial regime by no means means the complete absence of glaciers on Earth, although it is associated with a significant reduction in their number. If Simpson's hypothesis is correct, then it perfectly explains the history of the Pleistocene glaciations, but there is no evidence of such a periodicity for the pre-Pleistocene glaciations. Therefore, either it should be assumed that the regime of solar activity has changed throughout the geological history of the Earth, or it is necessary to continue the search for the causes of the occurrence of ice ages. It is likely that this occurs due to the combined action of several factors.

Literature:

Kalesnik S.V. Essays on glaciology. M., 1963
Dyson D.L. In a world of ice. L., 1966
Tronov M.V. Glaciers and climate. L., 1966
Glaciological dictionary. M., 1984
Dolgushin L.D., Osipova G.B. Glaciers. M., 1989
Kotlyakov V.M. World of snow and ice. M., 1994

Predominantly solid precipitation, located mainly on land, in motion and existing for a long time.
Source: Encyclopedia for children Avanta +, v. 4. Geology, ed. 2, 2002.

Glaciers- moving natural accumulations of ice of atmospheric origin on the earth's surface; are formed in those areas where solid atmospheric precipitation is deposited more than it melts and evaporates. Within the glaciers, areas of nutrition and ablation are distinguished. Glaciers are divided into terrestrial ice sheets, shelf and mountain. The total area of modern glaciers is about 16.3 million km 2 (10.9% of the land area), the total volume of ice is about 30 million km 3.
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Source: TSB

Glaciers- accumulations of ice that move slowly on the earth's surface. These are natural masses of crystalline ice (in the upper part - firn), formed on the surface of the Earth as a result of the accumulation and subsequent transformation of solid atmospheric precipitation (snow). In some cases, ice movement stops and dead ice forms. Many glaciers advance some distance into oceans or large lakes and then form a calving front where icebergs break away. There are four main types of glaciers: continental ice sheets, ice caps, valley glaciers (alpine) and foothill glaciers (foot glaciers).
The best known are sheet glaciers, which can completely cover plateaus and mountain ranges. The largest is the Antarctic ice sheet with an area of more than 13 million km. 2, which occupies almost the entire mainland. Another sheet glacier is found in Greenland, where it even covers mountains and plateaus. The total area of this island is 2.23 million km. 2, of which approx. 1.68 million km. 2 is covered with ice. This estimate takes into account not only the area of the ice sheet itself, but also numerous outlet glaciers.

The term "ice cap" is sometimes used to refer to a small ice sheet, but it is more correct to refer to a relatively small mass of ice covering a high plateau or mountain range, from which valley glaciers radiate in different directions. A good example of an ice cap is the so-called. The Columbian Firn Plateau, located in Canada on the border of the provinces of Alberta and British Columbia (52°30ºN). Its area exceeds 466 km2, and large valley glaciers radiate from it to the east, south and west. One of them - the Athabasca Glacier - is easily accessible, since its lower end is only 15 km away. from the Banff-Jasper motorway, and in the summer, tourists can ride an all-terrain vehicle all over the glacier. Ice caps are found in Alaska north of Mount St. Elias and east of Russell Fjord.

Valley, or alpine, glaciers start from sheet glaciers, ice caps and firn fields. The vast majority of modern valley glaciers originate in firn basins and occupy trough valleys, in the formation of which pre-glacial erosion could also take part. Under certain climatic conditions, valley glaciers are widespread in many mountainous regions of the world: in the Andes, the Alps, Alaska, the Rocky and Scandinavian mountains, the Himalayas and other mountains of Central Asia, and New Zealand. Even in Africa - in Uganda and Tanzania - there are a number of such glaciers. Many valley glaciers have tributary glaciers. So, at the Barnard Glacier in Alaska, there are at least eight of them.

Other varieties of mountain glaciers - car and hanging - in most cases are relics of a more extensive glaciation. They are found mainly in the upper reaches of the troughs, but sometimes they are located directly on the slopes of the mountains and are not connected with the underlying valleys, and the dimensions of many are slightly larger than the snowfields that feed them. Such glaciers are common in California, the Cascade Mountains (Washington State), and there are about fifty of them in the Glacier National Park (Montana State). All 15 glaciers The Colorados are classified as karts or hangings, and the largest of them, the Arapaho kar glacier in Boulder County, completely occupies the kar. The length of the glacier is only 1.2 km (and once it was about 8 km long), about the same width, and the maximum thickness is estimated at 90 m.

There are different classifications of glaciers. Most of them are morphological or morphological-dynamic, used mainly in compiling catalogs of glaciers. Similar schemes exist in the World Glacier Watch Service (WGMS) and the new Glacier Cataloging Project (GLIMS). In addition, there are geophysical classifications of glaciers according to their thermal regime and hydrothermal state.

Glacier structure

A glacier is a mass of natural terrestrial ice, predominantly of atmospheric origin, which has independent movement as a result of deformations caused by gravity.
The snow limit/snow line is the altitude above which the accumulation of solid atmospheric precipitation prevails over their melting and evaporation. This is an important boundary level that determines the existence of glaciers. The height of the snow boundary is determined by: atmospheric circulation, which determines the amount of precipitation in a given area; radiation conditions, air temperature, which determine the proportion of solid precipitation and the intensity of snow and ice melting; the absolute and relative height of mountain structures, the dissection of the relief and the orientation of mountain ranges relative to the direction of moisture-carrying air flows. There are several varieties of the snow boundary: climatic (theoretical, "level 365"), seasonal, local (true), orographic, firn line.
The main characteristics of glaciers are: area, length, altitude position, thickness, volume, mass of the glacier, surface and bed characteristics, temperature regime.

Main parts of the glacier

Each glacier consists of recharge and discharge areas separated by a recharge boundary. In the first of them, the feeding area (firn region, firn basin) the accumulation of solid atmospheric precipitation (accumulation) is greater than their consumption for melting, evaporation, and removal of snow by the wind. In the second - the area of flow (the area of ablation, glacial tongue), the flow of ice is greater than the income.
Accumulation on glaciers consists of solid precipitation falling from the atmosphere in the form of snow, grains, hail, and freezing rain; increasing precipitation formed on the surface of snow and ice in the form of frost and ice; blizzard blowing snow and avalanches from overlying slopes. The main source of snow accumulation on glaciers is solid atmospheric precipitation associated mainly with cyclonic activity.

Glacial tongue with lake

Ablation(from the Latin “ablatio” - taking away, demolition) - a decrease in the mass of a glacier by melting, evaporation, ice collapses, blowing snow away by the wind, breaking off icebergs (for glaciers in the high latitudes of the Arctic and Antarctic). The main role in the ablation of mountain glaciers belongs to the melting of snow and ice under the influence of solar radiation and the heat of atmospheric air. The role of evaporation is small. This type of ablation is called surface ablation. There are also internal and subglacial ablations caused by geothermal heat, the heat of water penetrating into the thickness of the glacier and under the glacier through cracks and glacial wells, as well as heat released as a result of the movement of the glacier and its friction against the bed. The role of internal and subglacial ablation is usually much less than that of surface ablation. The abelation zone is sometimes called the sink area or the discharge area.

The ratio of the inflow and outflow of the mass of snow and ice on the glacier over a certain time is called the mass balance of the glacier. The increase in the mass of snow and ice from the previous summer surface to a maximum at the end of winter is the winter mass balance, and the decrease in mass from the maximum to the end of the melting period is the summer mass balance. When glaciers melt and are washed away by surface water penetrating through cracks, glacial

A terrible memory - an antediluvian refrigerator, which had to be defrosted all the time. Sometimes it seemed that all the glaciers of the world were magically dumping their multi-ton ice deposits right into the freezer of this monster.

Fortunately, now I have a normal refrigerator that requires a minimum of maintenance, so I only occasionally recall this method of glacier formation.

Glacier formation

Glaciers are huge ice masses. In nature, they are formed mainly from snow.

For their formation, only snow and constantly low temperatures are needed for many years. Then the snow cover does not melt, but grows, eventually compacting so that it turns into ice.

Glaciers are not static. They are constantly moving (under the force of their own weight). The movements of a large glacier change and deform the terrain.

In the history of the Earth, several ice ages are known - time periods when the temperature on the planet dropped, which contributed to the active growth of glaciers.

Traces of now non-existent are imprinted on the relief of many areas. This is especially noticeable in the Northern Hemisphere.

Where are glaciers located

Of course, in regions with constantly low temperatures: on the tops of mountains and in the polar regions - the Arctic and Antarctic.

A large glacier can cover an entire continent. This is what happened in Antarctica, for example. The mass of ice there is so huge that the mainland even sank a little under its weight.

It is interesting to observe the movement of mountain glaciers. They have distinct areas:

food area;
food (balance) boundary;
consumption area.

The feeding area is the upper part, where the snow that feeds the glacier constantly enters. Discharge area - where the glacier descends to the area with positive temperature and begins to melt. It is there that mountain rivers with a glacial type of food are born.

The boundary of equilibrium is the area where the flow and income are the same.

The activity of continental and insular glaciers is also quite noticeable. Their melting can be judged by the rise in the level of the World Ocean.

1. these are huge blocks of ice crawling along the earth's surface;

2. natural masses of ice moving along the earth's surface, formed as a result of many years of accumulation, compaction and recrystallization of snow. A glacier standing still is called "dead" ice.

The total area of modern glaciers is about 16.3 million km2. Glaciers occupy about 11% of the land area, and their total volume reaches 30 million km 3. Naturally, glaciers can exist only where low air temperatures are steadily observed and a lot of snow falls. Usually these are subpolar or high mountain regions. Glaciers can be in the form of a stream, a dome (shield) or a floating plate (in the case when they slide into a reservoir). The parts of glaciers that break off and float on the sea are called icebergs. All large glaciers are dotted with numerous cracks, including open ones. Their dimensions depend on the parameters of the glacier itself. There are cracks up to 60 m deep and tens of meters long. They can be either longitudinal, i.e. parallel to the direction of movement, and transverse, running across this direction. Transverse cracks are much more numerous. Less common are radial fissures found in spreading piedmont glaciers and marginal fissures confined to the ends of valley glaciers. Longitudinal, radial and edge cracks were formed due to stresses resulting from friction or ice spreading. Transverse cracks are probably the result of ice moving over an uneven bed. The ice of sheet glaciers and ice caps is usually clean, coarse-grained, and blue in color. This is also true for large valley glaciers, with the exception of their ends, which usually contain layers saturated with rock fragments and alternating with layers of pure ice.

Glacier types

There are mountain-valley glaciers (since they are associated with mountainous terrain, occupying valleys with a characteristic trough-shaped transverse profile, the so-called troughs), cover and shelf glaciers.

Mountain-valley glaciers, among which there are hanging, cirque, and transitional glaciers, are distributed almost everywhere, from Kilimanjaro in Africa and the glittering crests of the Andes in South America to the peaks of the Himalayas, the Hindu Kush, the Pamirs and the Tien Shan. The largest of the mountain glaciers is the Fedchenko Glacier. In Russia, the largest mountain glaciers are concentrated in the Caucasus. However, their area rarely exceeds 30 km2, and their length is 10 km. Valley, or alpine, glaciers start from sheet glaciers, ice caps, and firn fields. The vast majority of modern valley glaciers originate in firn basins and occupy trough valleys, in the formation of which pre-glacial erosion could also take part. Under certain climatic conditions, valley glaciers are widespread in many mountainous regions of the world: in the Andes, the Alps, Alaska, the Rocky and Scandinavian mountains, the Himalayas and other mountains of Central Asia, and New Zealand. Even in Africa - in Uganda and Tanzania - there are a number of such glaciers. Many valley glaciers have tributary glaciers.

The ice sheet of Antarctica can be attributed to the sheet glaciers, if it is considered as a single sheet glacier. Within a single cover, separate ice flows are distinguished, directed from the center of the mainland to the periphery. The largest among them is the Bidmore Glacier (length 200 km, width up to 40 km). The ice caps of the Arctic are much smaller in size.

Ice shelves are floating extensions of continental ice sheets. The largest of these is the Ross Ice Shelf.

On rare occasions, ice shelves are formed by the accumulation of snow on sea ice and by the cementation of iceberg clusters by snow and ice. They are typical for areas with a low relative to sea level position of the food boundary.

Glacier formation

Near glaciers, areas of nutrition (accumulation) and ablation are distinguished. In the first of them, snow turns into firn, and then into ice, and there is an increase in the mass of ice transported to the ablation region, where this mass decreases as a result of melting, chipping, evaporation, and blowing of snow by the wind. Freshly fallen snow consists of fine crystals, many of which have a delicate 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. 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 vary in size. If they have an area of less than 0.1 km 2, then they are called small. The largest ones can reach many million km2. For example, the ice sheet of Antarctica reaches almost 14 million km 2, and its maximum thickness exceeds 4.7 km.

Large icebergs can serve as an indirect indicator of the gigantic size of glaciers. The collision with an iceberg was the cause of the greatest maritime disaster of the 20th century. - The sinking of the Titanic. The largest icebergs, having a length of 170 km and a volume of up to 5 thousand km 3, are found near Antarctica. The mass of glaciers changes over time, mainly due to climate change. In the geological past, there have been times when glaciers occupied a much larger area than now.

Glacier movement

The speed of movement of glaciers is usually low, averaging from several tens to several hundred meters per year. But there are cases of very fast movement of glaciers. One of the fastest is the Greenland glacier Jakobshavn, which flows into Disko Bay. Its speed exceeds 7 km per year. Pulsating glaciers are very mobile. In their life, periods of relative rest, lasting from 10 to 50–100 years, alternate with periods of short, rapid movements, or pulsations, during which the speed of the glacier can be 100–120 m/day, and the tongue of the glacier can move 10– 15 km. This is often fraught with catastrophic consequences - ice landslides, snow avalanches, outbursts of dammed lakes, floods and mudflows. The movements of the Pamir Medvezhiy glacier in 1963 and 1973, which fortunately did not lead to natural disasters, became widely known.

The speed of glacier movement is not constant, it can differ significantly for different areas and change depending on the season of the year and in accordance with long-term cycles of glacier fluctuations.

Role of glaciers

Glaciers influence the climate, create specific glacial landforms and unique beauty and severity of nival-glacial alpine landscapes. They serve as "pantries" of fresh water, in which almost 69% of the world's reserves of fresh water are concentrated. The melting of glaciers forms a significant part of the river flow in mountainous areas, especially in summer, when water is most needed for irrigating crops. For example, in Central Asia, where glaciers occupy only 5% of the area, their share in river runoff is 20% per year, and 50% in summer.

There are projects for the forced melting of glaciers, for example, by blackening their surface with coal dust, in order to obtain more water. However, the direct and indirect consequences (including environmental ones) of such projects are still unclear. There is a danger of irreversible degradation of glaciers.

Water supply projects for arid regions and countries, such as Saudi Arabia, seem more realistic, through the transportation and subsequent use of iceberg melt water.

The hydrological role of glaciers is to redistribute the runoff of atmospheric precipitation within the year and to smooth out fluctuations in the annual flow of rivers. For the water management practice of Russia, the glaciers and snowfields of mountainous regions, which determine the water content of mountain rivers, are of particular interest.

Modern glaciation

The main area of modern glaciation (more than 56 thousand km 2) is located on the Arctic islands, which is explained by their position in high latitudes, which determines the formation of a cold climate. The lower boundary of the nival zone here descends almost to sea level. Glaciation is concentrated mainly in the western and central regions, where more precipitation falls. The islands are characterized by cover and mountain cover (network) glaciation, represented by ice sheets and domes with outlet glaciers. The most extensive ice sheet is located on the Northern Island of Novaya Zemlya. Its length along the watershed is 413 km, and its maximum width reaches 95 km (Dolgushin L.D., Osipova G.B., 1989). Ushakov Island, lying between Franz Josef Land and Severnaya Zemlya, is a continuous ice dome, the edges of which break off to the sea with ice walls ranging in height from several meters to 20–30 m, and on Victoria Island, located west of Franz Josef Land, it is free from ice is only a small section of the beach with an area of about 100 m 2 .

As you move eastward, more and more of the islands remain ice-free. Thus, the islands of the Franz Josef Land archipelago are almost entirely covered with glaciers, on the New Siberian Islands glaciation is typical only for the northernmost group of De Long Islands, and on Wrangel Island there is no ice cover - only snowflakes and small glaciers are found here. Most of the snow-ice formations are perennial snowfields with cores of infiltration ice.

The thickness of the ice sheets of the Arctic islands reaches 100–300 m, and the water reserve in them approaches 15 thousand km 3, which is almost four times the annual flow of all Russian rivers.

The glaciation of the mountainous regions of Russia, both in terms of area and volume of ice, is significantly inferior to the cover glaciation of the Arctic islands. Mountain glaciation is typical for the highest mountains of the country - the Caucasus, Altai, Kamchatka, mountains of the North-East, but also occurs in low mountain ranges of the northern part of the territory, where the snow border lies low (Khibiny, the northern part of the Urals, the Byrranga, Putorana, Kharaulakh mountains ), as well as in the area of Matochkina Shara on the Northern and Southern islands of Novaya Zemlya.

Many mountain glaciers lie below the climatic snow limit, or "365 level," at which snow remains on a horizontal underlying surface for all 365 days of the year. The existence of glaciers below the climatic snow limit becomes possible due to the concentration of large masses of snow in negative landforms (often in deep ancient kars) of leeward slopes as a result of snowstorm transport and avalanches. The difference between the climatic and the actual snow limit is usually measured in hundreds of meters, but in Kamchatka it exceeds 1500 m. The area of mountain glaciation in Russia is slightly more than 3.5 thousand km 2. The most widespread are cirque, cirque-valley and valley glaciers. Most of the glaciers and areas of glaciation are confined to the slopes of the northern points, which is due not so much to the conditions of snow accumulation, but also to greater shading from the sun's rays (insolation conditions).

In terms of glaciation area among the mountains of Russia, the first place is occupied by the Caucasus (994 km 2). It is followed by Altai (910 km 2) and Kamchatka (874 km 2). Less significant glaciation is typical for the Koryak highlands, the Suntar-Khayat and Chersky ranges. Glaciation of other mountainous regions is small. The largest glaciers in Russia are the Bogdanovich glacier (area 37.8 km2, length 17.1 km) in the Klyuchevskaya group of volcanoes in Kamchatka and the Bezengi glacier (area 36.2 km2, length 17.6 km) in the Terek basin in the Caucasus. Glaciers are sensitive to climate fluctuations. In the XVIII - early XIX centuries. began a period of general reduction of glaciers, which continues to this day. At present, most scientists believe that traces of three glacial epochs in the Pleistocene can be traced on the territory of Russia: Mindel (or Oka) - early Pleistocene; Risskoy (Dnieper with the Moscow stage) - middle Pleistocene; Würm (Valdai) – Late Pleistocene (see Fig. 1).

Rice. 1. Ancient glaciations (according to the Atlas of the USSR, 1983)

It is known that glaciers are such accumulations of ice that slowly move along the earth's surface. Sometimes the movement stops and a dead cluster forms. Some blocks are capable of passing many tens, hundreds of kilometers across the oceans, seas, inland.

There are several types of glaciers: continental-type covers, ice caps, valley glaciers, foothills. Cover formations occupy about two percent of the area of ice formations, and the rest are continental species.

Glacier formation

What are glaciers and where do they occur? There are many factors that influence the formation of a glacier. Although this is a long process, it depends on the relief and climate whether the surface of the Earth will be covered with ice formation or not.

So what is a glacier and what does it take to form it? For it to begin to form, certain conditions are necessary:

The temperature should be negative throughout the year.
Precipitation should be in the form of snow.
A glacier can form at high altitude: as you know, the higher up the mountain, the colder it is.
The formation of ice is influenced by the shape of the relief. For example, glaciers can appear on plains, islands, plateaus, plateaus.

There are formations that can hardly be called mountain glaciers - they cover an entire continent. These are the ice of Antarctica and Greenland, the thickness of which reaches four kilometers. In Antarctica there are mountains, bays, pits and valleys - all covered with a thick layer of ice. And the island of Greenland is a huge glacier that covers the earth.

Scientists have proven that glaciers such as the Antarctic have existed on Earth for over 800,000 years. Although there is an assumption that the ice covered the continent millions of years ago, but so far, scientists have established that the ice here is 800 thousand years old. But even this date suggests that there has been no life in this part of the planet for many millennia.

Glacier classification

There are several classifications of glaciers, among which the main one is the division according to the morphological type, namely, depending on the shape of the glacier. There are cirque, hanging, valley types of boulders. In some areas of ice, several varieties are located at once. For example, you can find hanging and valley varieties.

It is possible to globally divide all accumulations by morphological type into mountain glaciers, cover, transitional ones. The latter are a cross between cover and mountain.

mountain views

Mountain varieties have a variety of forms. Like all types of ice accumulations, this type tends to move: the movement is determined by the slope of the relief and is linear. If we compare this type of formations with integumentary ones in terms of speed, then mountain ones are much faster.

Mountain glaciers have a strongly pronounced area of feeding, transit and melting. The mineral is nourished by snow and water vapor, avalanches, and snow transport during a snowstorm. When moving, ice often descends into the melting zone: alpine forests, meadows. In these territories, the cluster breaks off and can fall into the abyss, intensively begins to melt.

The largest mountain formation is considered to be the Lambert Glacier, located in East Antarctica, with a length of 450 kilometers. It originates in the north in the International Geophysical Year valley and enters the Amery Shelf. Another long glaciers are formations in Alaska - these are Bering and Hubbard.

Mountain cover varieties

We have considered in general what glaciers are. When defining the concept of a mountain cover type, one immediately wants to pay attention to the fact that this is a formation of a mixed type. They were first identified as a separate species by V. Kotlyarov. The glacial formations of the foothills consist of several streams with different types of food. At the foot of the mountains, in the zone of foothills, they merge into a single delta. A representative of such formation is the Malaspina Glacier, located in southern Alaska.

plateau glaciers

When intermountain valleys overflow, at the moments of flow over low ridges, plateau glaciers are formed. And what are glaciers in geography? The definition of the concept of "plateau" is as follows - it is nothing more than a huge chain of islands that merge with each other and arise in place of the ridges.

Formations in the form of a plateau are found on the edges of Antarctica, Greenland.

Sheet glaciers

Integumentary species are represented by the huge shields of Antarctica, whose area reaches fourteen thousand square kilometers, and the formations of Greenland, whose area is 1.8 million km2. These glaciers have a flat-convex shape, independent of the relief. The formations are fed by snow and water vapor present on the surface of the glacier.

Cover glaciers move: they are characterized by radial movement, from the center to the periphery, which does not depend on the subglacial bed, where the breaking off of the ends mainly occurs. The detached parts remain afloat.

Scientists have long been trying to figure out what glaciers are and how they form. As a result of the study, it was possible to establish that the Greenland formation was frozen to the very foundation, and the lower layers were frozen with a rocky bed. In Antarctica, the connection between the platforms and the earth's surface is more complex. Scientists managed to establish that there are lakes in the central part of the formations under the ice. They are located at a depth of three or more kilometers. According to the famous scientist V. Kotlyarov, the nature of these lakes can be twofold: they can influence the melting of ice due to the internal heat. The theory of the emergence of lakes as a result of friction of glaciers on the surface of the earth during their movement is not excluded.

Classification of glaciers according to Alman

The Swedish scientist Alman proposed three classes of division of all existing world formations:

temperate glaciers. In another way, he called them thermal formations, in which the entire thickness, except for the upper layers, has a melting point.
Polar ice. These species are not subject to melting processes.
Subpolar. They are characterized by melting processes in the summer.

Avsyuk's classification

Our compatriot proposed another version of the classification. Avsyuk believes that it is most correct to divide glaciers according to the type of temperature distribution in the thickness of the formations. According to this principle, there are:

Dry polar species. At times when the temperature in the thickness is below that at which crystallized water melts, dry polar species are formed. Avsyuk refers to such formations on the territory of Greenland, Antarctica, on the mountains of Asia with a height of more than 6 thousand meters, where it is always cold, and even colder in the thickness of the ice than outside.
Wet polar view. In this form, in the summer, the temperature rises above zero degrees, and melting processes begin.
Wet cold glacier. It is characterized by temperatures above the average annual air temperatures, although they are both negative. Melting of ice is noted only on the surface, even at sub-zero temperatures.
Nautical. It is characterized by a temperature at zero in the region of the active layer.
Warm ice. Such species are located in the mountains, namely in Central Asia, on the Canadian archipelago.

Dynamic classification

When considering the topic "What are glaciers and what are they like," another question immediately arises: "Is there a division of formations according to the type of movement?" Yes, such a classification exists, and it was proposed by Shumsky, a Soviet glaciologist. This division is based on the main forces that cause the movement of formations: the spreading force and the runoff force. The latter is due to the curvature of the bed and the slope, and the spreading force is due to the sliding process. According to these forces, glaciers are usually divided into runoff blocks, which are also called mountain blocks: in them, the flow force reaches one hundred percent. Spreading formations are represented by ice caps and shields. They do not have any obstacles, so this species can spread in all directions.

The largest glaciers on our planet

It has already been said above what glaciers are in geography and how they are classified. Now it is worth mentioning the most famous glaciers in the world.

In the first place in terms of size is the Lambert Glacier, located in East Antarctica. It was found in 1956. According to preliminary estimates, the length of the formation is about 400 miles, and the width is more than 50 kilometers. This is about ten percent of the area of the entire ice formation.

The largest glacier in the Svalbard archipelago is Austfonna. In terms of size, it ranks first among all existing formations of the Old World - the area of \u200b\u200bice is more than 8200 square kilometers.

In Iceland, there is a glacier, the size of which is one hundred square kilometers smaller - Vatnaekul.

South America also has a glacier, more specifically the Patagonian Ice Sheet located in Chile and Argentina. Its area is more than fifteen thousand square kilometers. Huge streams of water depart from the glacier, which created the lake.

At the foot of Mount St. Elias in Alaska, there is another giant - Malaspina. Its area is 4200 sq. km. But the longest formation of ice located outside the polar zone is Fedchenko, located in Tajikistan. It is located at an altitude of six thousand kilometers above sea level. The glacier is so large that its tributaries exceed the size of the most powerful glaciers in Europe.

There is also an ice mass in Australia - these are Pastors. It is considered the largest formation in this country.

There are many different glaciers in the world, located in various parts of the world, including on warm continents. Many of them have a height of at least three thousand kilometers, and there are objects that are melting at an accelerated pace. It would seem that ice of this size should be only at the poles, but it is on every continent of the world, including in warm countries. Such a scatter of formations indicates the movement of ice and the fact that once the Earth was completely different.