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 form in those places where the snow accumulated over a long winter does not have time to melt in summer. The level below which all the snow accumulated in winter melts is called the snow line. This line can be seen in the mountains at the end of summer: it separates the upper dazzling white parts of the slopes from the dark, snowless lower ones. Most of the glaciers lie above the snow line, but the tongues of many of them descend even lower; sometimes they end in slopes covered with green forests, as can be seen in New Zealand.

The snow line in different parts of the globe lies at different heights, depending on the climate. It is highest in tropical regions - the hottest and driest on Earth, but drops somewhat towards the equator, where there is a lot of precipitation. As we approach the poles, the snow line passes lower and lower, descending in Antarctica to sea level.

Glaciers of the Greenland Shield (view from the plane).

The height of the snow line varies not only with latitude, but also with the longitude of the place. This is due to the fact that less precipitation falls in the depths of the continent, and the less precipitation, the higher the snow line lies. For example, in the Alps, located near the Atlantic Ocean, the snow line runs at an altitude of 2700 m above sea level; in the Caucasus - already at an altitude of 3500 m, in the mountains of Central Asia - at an altitude of 4500-5000 m, and in Tibet - above 6000 m.

One of the largest mountain glaciers is the Bernard Glacier in Alaska.

So are glaciers. They descend to sea level in Antarctica and in many places in the Arctic, lie relatively low in the mountains of the temperate zone adjacent to the ocean, and rise in the skies of the highest mountains on Earth, located in the depths of the continents and in the tropics.

This is how icebergs form from continental ice.

But not only the climate controls the glaciers. The influence of the ice itself on the climate is also great. Antarctica has a particularly great influence, where in winter the air temperature sometimes drops to -80 o, and huge masses of ice have a constant temperature from -30 to -50 o. This is a giant refrigerator of our planet, whose influence extends to the entire globe.

In the Arctic, the main source of cold is floating sea ice, as well as glaciers that cover many islands, including the largest island on Earth - Greenland. In both the Arctic and the Antarctic, ice reflects up to 80% of solar energy, and despite the fact that the Sun does not set below the horizon here throughout the summer, they still remain cold and melt very little.

Extensive ice masses near the poles are one of the main reasons for modern geographic zoning on Earth. Without these ices, the polar regions would become much warmer, and the Earth's climate would be milder and more even at all latitudes.

Facts from geological history suggest that this is exactly what the earth's climate was like several million years ago, when there were no glaciers on Earth.

The annual life cycle of a glacier consists of two parts: the influx of matter during the long winter and its outflow during the short summer. Glaciers “feed” on snow that falls on their surface during snowfalls and snowstorms or is brought by avalanches from the surrounding slopes.

In summer, when the air temperature rises above 0°, the snow on the surface of the glacier begins to melt and turns into firn, the transitional stage between snow and ice. Firn consists of separate melted grains of ice, which are firmly soldered to each other, but have not yet turned into a continuous ice layer.

A few more summer seasons pass, and the melt water, freezing in the firn, finally turns it into ice. In the upper reaches of the glacier, the snow accumulated during the winter does not have time to melt completely in the summer, and the glacial surface is covered with snow and firn all year round.

This is the feeding area of ​​the glacier. In its lower part, which is called the flow area, on the contrary, all the snow accumulated during the winter melts in the summer and in the warm season one can see bare ice on the surface.

These two regions of the glacier are separated by a firn line. In our time, on most mountain glaciers, the feeding area is not much larger than the discharge area, and often they are equal in area. The more severe the natural conditions, the larger the glacier feeding area and the smaller the area of ​​its discharge. On the ice sheet of Antarctica, where the air temperature even near the sea is so low that the snow hardly melts, the discharge area is 100 times smaller than the recharge area.

Thus, as a result, the ice sheet here descends into the sea and floating ice shelves are formed - huge ice plates 200-300 m thick, sheerly breaking off into the sea.

From glaciers ending in the sea, icebergs break off - blocks of ice, reaching a length and width of many kilometers. The largest iceberg was seen in the Southern Ocean in 1927 - its length was 167 km. Small icebergs, 1-2 km in size, are much more common in the sea, but they also pose a serious threat to navigation. It is known that in 1912, from a collision in the fog with an iceberg, the huge passenger ocean-going steamer Titanic sank in the Atlantic Ocean, making voyages between Europe and North America.

Icebergs found in the Arctic Ocean are called ice islands. They are much smaller than the Antarctic ones, but are convenient for landing aircraft. Therefore, almost all Soviet and American drifting research stations are located on the ice islands of the Arctic Ocean.

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, snow transport by the wind, snow fall from the slopes and air vapor condensation on the glacier surface.

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. it 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.

Presentation on the topic "Glaciers and icebergs" in geography in powerpoint format. This interesting presentation for schoolchildren tells about what glaciers are, how they form, what they are, what they matter. Presentation author: Dedukh Galina Vasilievna, teacher of geography.

Fragments from the presentation

How does snow turn into ice?

Glacier ice is formed from snow. If more snow falls than it has time to melt, it accumulates, becomes granular, riddled with pores, that is, it turns into firn, and later, under the influence of its own gravity, firn turns into ice.

What conditions are necessary for the formation of a glacier?

• The air temperature must be below 0°C throughout the year.
• There must be more snow than it can melt.

The snow line is the boundary above which snow does not melt, but accumulates to form a glacier.

Glacier structure

The glacier consists of two main parts:

• feeding area - here snow accumulates;
• flow area - snow melts.

Types of glaciers

• Mountain (glacier in the Alps);
• integumentary (glaciers of Antarctica, Greenland, Iceland).

What is a moraine?

Glaciers are plastic. Their tongues descend from the feeding area, sometimes well below the snow line. At the same time, they melt, forming streams and rivers. On the surface there are fragments of rocks brought by the glacier (sizes from grains of sand to large boulders), which are called moraine.

How are icebergs formed?

Icebergs off the coast of Antarctica reach gigantic sizes: 45 km wide, 170 km long and more than 200 m thick. Most of the iceberg (up to 90% of its volume) is under water.

Significance of glaciers

Glaciers give rise and nourishment to mountain rivers, they also serve as a source of drinking water.

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.