Glaciations in the history of the earth. “The Age of the Great Glaciations” is one of the mysteries of the Earth. Did you like the material? subscribe to our email newsletter

In the late Paleozoic, along with areas of warm tropical climate, there were also polar zones. The widespread development of continental glaciers in the late Paleozoic (middle, late Carboniferous) has been reliably established in southern Africa, Australia, India, South America, and Antarctica. Moreover, by the characteristic strokes, grooves, scratches that glaciers leave on rocks during their movement, by the peculiarities of the location of moraine deposits, it is possible to restore the direction of movement of Late Paleozoic glaciers. It is believed that there were several glaciation centers where glaciers originated and from where they began their movement.

In some cases, it seems as if the centers of glaciation were located outside the modern continents. So in South Africa, near the city of Durban, the ice moved from the direction of the modern Indian Ocean. This speaks in favor of the existence of a single supercontinent Gondwana in the late Paleozoic. In this case, the center of glaciation could be located in Antarctica, immediately adjacent to southern Africa. True, there are other opinions. French geologist Fourmarier believes, for example, that the hypothetical center of glaciation, from where glaciers advanced onto the area of ​​the city of Durban, is currently separated from Africa by a deep fault and hidden under the waters of the Indian Ocean.

The glaciation of the late Paleozoic was enormous. Judging by the thickness of the accumulated moraines (up to 300-600 meters), it can be assumed that the central regions of Gondwana in the Carboniferous were covered with an ice shell, the thickness of which could reach 5-6 km. Periodically, glaciers partially melted. In such periods, interlayers of ribbon clays appear in the strata of chaotic moraine deposits. Many scientists see the reasons for the Late Paleozoic glaciation in a different arrangement of the poles ( South Pole, for example, was located in southern Africa), in a different circulation of air masses and in the relatively high hypsometric position of Gondwana above sea level (it is known that the higher we rise, the colder it becomes; on average, per 1000 meters of rise, the temperature drops by 3-5° WITH).

Basically, the tropics then passed along the northern and northeastern shores of the sublatitudinal Tethys Ocean, covering modern areas of Europe, partially Central Asia, western North America, northern Africa, northern and western South America. The dots in the figure show areas of glaciation. They were located in the center of Gondwana. The area of ​​Late Paleozoic glaciation was unusually large. This raised doubts about the possibility of the existence of such grandiose glaciers. Some scientists even believe that there would not be enough water on Earth to form such huge glacial masses. They do not reject the existence of glaciers, but it is assumed that their sizes were much more modest. One thing is certain: in the late Paleozoic there was a clearly defined climatic zonation. The polar climate zones gave way to a temperate climate zone, which in turn turned into a tropical zone.

By studying modern glaciers in the mountains and on continents, establishing the features of their structure, mechanism of movement, destructive and accumulative work, it is possible to identify the presence of glaciations in the geological history of the Earth, using the famous expression of Charles Lyell: “The present is the key to the past.”

18-20 thousand years ago, the appearance of the Earth’s surface in the Northern Hemisphere was completely different from what it is today. Vast spaces of North America, Europe, Greenland, and the Arctic Ocean were occupied by gigantic ice sheets with a maximum thickness in their center of up to 3 km, and the total volume of ice exceeded 100 million km" 1. This was the last major glaciation, which advanced on the Russian Plain almost to latitude of Moscow, and in North America - south of the Great Lakes. Since then, glaciers began to retreat, and now the ice of the last glaciation is preserved only in Greenland and on a number of islands in the Canadian Arctic. In the last 10 thousand years, called the Holocene, the final collapse of the ice caps and Their rapid melting occurred about 8 thousand years ago, when the climate was warmer than today. This period corresponded to the “climatic optimum.” Somewhere between 8 thousand and 5 thousand years ago, the climate became even warmer, and in Africa more humid. But between 5 thousand and 3500 years ago there was a strong cooling and in some places new glaciers appeared, which made it possible to identify even a “small glacial period" It is this that the existing glaciers in the Caucasus, the Alps, the Pamirs, the Rocky Mountains of North America, etc. belong to.

All these events have occurred since the end of the maximum advance of glaciers over the past 18 thousand years. But in the Quaternary period, starting from about 2 million years ago, at least four glacial, or cryogenic, eras are reliably distinguished, traces of which were found in Eurasia and North America. At the beginning of the 20th century. German geologists A. PenkomiE. Brückner substantiated four major glaciations in the Alps: Günz (Late Pliocene), Mindel (Early Pleistocene), Riess (Middle Pleistocene) and Würm (Late Pleistocene) with two stages of glacial advance or with two independent glaciations. Subsequently, when traces of ancient glaciations were identified in other places, although they were given local names, they were always compared with the Alps. Through the work of many Russian geologists, traces of at least four glaciations, in the most general form comparable to the Alpine ones, have been established on the Russian Plain. The picture is the same in North America. Studying the core of ocean sediments and ice from the Antarctic cover for the ratio of the content of light - IO and heavy - 18 0 isotopes of oxygen, as an indicator of changes in climate and water temperature in the oceans, made it possible to identify the same cold climatic intervals within the same age boundaries , as in the Alps or on the Russian Plain. This proved the global nature of climate change during the Quaternary period and the approximate synchronicity of glaciations in North America and Eurasia. However, ocean stratigraphy, i.e., the study of layers of ocean sediments, now provides more accurate data that differs from classical continental data, into which they are trying to “squeeze” ideas that have already become familiar.

On the Russian Plain, the maximum advance of glaciers is established in the early stage (Dnieper) of the Middle Quaternary glaciation or in the Don, the tongues of which descended along the Dnieper valley to Dnepropetrovsk, and along the Don valley south of Voronezh. The second (Moscow) stage of the Middle Pleistocene glaciation reached areas south of Minsk and Moscow. All other glaciations had terminal moraine ridges to the north (Fig. 12.17). The boundaries of glaciations in Western and Eastern Siberia, where, of course, the traces of the last glaciation are better expressed in the form of extended winding terminal moraine ridges and ridges. A huge amount of ice took water from the ocean, the level of which dropped from 100 to 140 m in the late Pleistocene. The presence of giant ice sheets in the Pan-Arctic region is questioned by some geologists, which forces them to look for new factual data confirming or refuting the classical scheme.

Rice. 12.17. Scheme of the boundaries of the distribution of Moscow glaciation (according to I. N. Chuklenkova). 1-8 - options for drawing boundaries (finite-moraine ridges), according to various authors. 9 - boundary of the Valdai glaciation

The ice sheets of the last glaciation, together with the Pan-Arctic glacier, according to M. G. Grosswald, created an insurmountable obstacle for rivers flowing in a northern direction, for example, the Northern Dvina, Mezen, Pechora, Irtysh, Ob, Yenisei, etc. (Fig. 12.18) . As a result, huge subglacial lakes arose in front of the front of the cover glacier, which were looking for ways to drain in a southerly direction (Fig. 12.19). And such paths in the form of well-preserved ridge-hollow relief, oriented in the sublatitudinal direction, were found in many places in Western Siberia, the Aral Sea region and

Northern Caspian region. At times there were catastrophic outbursts of these periglacial lakes, and also, possibly, of lakes from under the “warm” type of ice sheets. Wide, flat-bottomed drainage basins, for example in an ancient river on the site of modern Manych lakes in the Ciscaucasia, passed up to 1000 km 3 of water per year. This flow rate varied greatly between seasons. As ice sheets began to melt and retreat, many of the glacial meltwater drainage basins were inherited by river systems. It should be emphasized the close connection between the formation, advance and melting of ice sheets with fluctuations in ocean level, which very sensitively responded to the “selection” and entry of water into it due to the growth or melting of glaciers.

Rice. 12.18. The maximum extent of the ice cover was 20 thousand years ago (Early Valdai glaciation). The arrows show the movement of ice. Points - periglacial lakes (according to M. G. Grosswald)

Modern calculations made by I. D. Danilov show that at the end of the Late Pleistocene, during the last maximum glaciation, the area occupied by ice in the Northern Hemisphere did not exceed 6 million km 2, and the volume of ice - 7-8 million km 3. while underground glaciation (permafrost) covered an area of ​​up to 45 million km 2 with a volume of more than 1 million km 3 of ice. In both hemispheres

Rice. 12.19. Finite-moraine belts, directions of ice movement and glacial

dammed lakes of the European part of the USSR in the era of the last glaciation (according to Kh. Arslanov, A. Lavrov and L. Potapenko). It is clearly visible that the ice came from the Barents and Kara seas: 1 - the boundaries of glaciation, the maximum stage of retreat; 2 - directions of ice movement; 3 - dammed lakes; 4 - melt water discharge channels (spillways); 5 - radiocarbon dating points of glacial (a) and lake (b) sediments. The numbers show ancient lake levels

the volume of floating ice was 45-50 million km 3 . It is quite natural that the Great Quaternary glaciations, whatever their size, left many more traces than more ancient ones. Nevertheless, several rather long epochs have been established in the history of the Earth, during which cooling and the development of glaciers were noted (Fig. 12.20). The features used to reconstruct the glaciers are similar. This is the development of tillites (ancient compacted and metamorphosed moraines), tilloids (formations resembling moraines), erratic boulders with a typical glacial

billion years YARCHN	- TO? -

Rice. 12.20. Major cryogenic (glacial) epochs in Earth's history (black)

Traces of the most ancient glaciation are recorded in sediments early Proterozoic in Canada, on the Baltic Shield (2.5-2 billion years), and the duration of the interval of 400 million years, within which presumably glacial deposits are found, is noteworthy. A younger ice age is recorded in Late Riphean layers And Venda(0.9-0.63 billion years) on the Russian plate, in Canada, the USA, Scotland and Norway, in the Northern Urals and in other regions. It is difficult to identify areas of distribution of glaciers and reconstruct their morphology and volume.

In the early Paleozoic ( Ordovician-Silurian) in the interval of 0.46-0.42 billion years, traces of glaciation were established in West Africa, in the Sahara, possibly

hatching, sheep's foreheads and curly rocks, ribbon clays and other clearly glacial or fluvioglacial (fluvioglacial) deposits.

but, in Argentina, Brazil, South West Africa, Western Europe, North America.

Sediments of obvious glacial origin belong to the time interval of 0.35-0.23 billion years, which corresponds to the Carboniferous and Permian times of the late Paleozoic. This was the time of the existence of the huge supercontinent Pangea II, when South and North America, Africa and Eurasia, Antarctica, Australia and Hindustan were welded together, and between Eurasia and Gondwana (southern continents) the Tethys Ocean existed. The areas of distribution of glaciers at this time do not need comment. Apparently, there was a large ice sheet or series of ice sheets in high latitudes, spreading radially from the center. The great Late Paleozoic glaciation is quite well studied and documented.

And finally, the Cenozoic cryogenic period (38 million years - now), lasting much longer than the well-studied Great Quaternary glaciations. The beginning of this period dates back to the interval 38-25 million years ago, i.e., to the late Oligocene, when the first glaciers appeared in Antarctica, primarily in the Transantarctic Mountains and the Gamburtsev Mountains. The global ice sheet formed in the early Miocene (25-20 million years ago). In the Middle Miocene (15 million years ago), the Greenland Glacier apparently formed, and a general cooling and a sharp deterioration in the climatic situation are clearly recorded from the turn of 700 thousand years. Perhaps this time determines the beginning of the Quaternary Ice Age, and its last major event was glaciation, which began about 25 thousand years ago and last reached a maximum 18 thousand years ago, after which the rapid degradation of the ice sheet began, retreating at a speed of up to 5 km in year.

One of the mysteries of the Earth, along with the emergence of Life on it and the extinction of dinosaurs at the end of the Cretaceous period, is - Great Glaciations.

It is believed that glaciations repeat on Earth regularly every 180-200 million years. Traces of glaciations are known in sediments that are billions and hundreds of millions of years old - in the Cambrian, Carboniferous, Triassic-Permian. That they could be is “said” by the so-called tillites, breeds very similar to moraine the latter, more precisely last glaciations. These are the remains of ancient glacial deposits, consisting of a clayey mass with inclusions of large and small boulders scratched by movement (hatched).

Separate layers tillites, found even in equatorial Africa, can reach thickness of tens and even hundreds of meters!

Signs of glaciations were found on different continents - in Australia, South America, Africa and India, which is used by scientists for reconstruction of paleocontinents and is often cited as confirmation plate tectonics theories.

Traces of ancient glaciations indicate that glaciations on a continental scale- this is not a random phenomenon at all, it is natural a natural phenomenon, arising under certain conditions.

The last of the ice ages began almost million years ago, in Quaternary time, or the Quaternary period, the Pleistocene and was marked by the extensive spread of glaciers - The Great Glaciation of the Earth.

Under thick, many-kilometer-long covers of ice were the northern part of the North American continent - the North American Ice Sheet, which reached a thickness of up to 3.5 km and extended to approximately 38° north latitude and a significant part of Europe, on which (an ice sheet with a thickness of up to 2.5-3 km) . On the territory of Russia, the glacier descended in two huge tongues along the ancient valleys of the Dnieper and Don.

Partial glaciation also covered Siberia - there was mainly the so-called “mountain-valley glaciation”, when glaciers did not cover the entire area with a thick cover, but were only in the mountains and foothill valleys, which is associated with the sharply continental climate and low temperatures in Eastern Siberia . But almost all of Western Siberia, due to the fact that the rivers were dammed and their flow into the Arctic Ocean stopped, found itself under water, and was a huge sea-lake.

In the Southern Hemisphere, the entire Antarctic continent was under ice, as it is now.

During the period of maximum expansion of the Quaternary glaciation, glaciers covered over 40 million km 2–about a quarter of the entire surface of the continents.

Having reached their greatest development about 250 thousand years ago, the Quaternary glaciers of the Northern Hemisphere began to gradually shrink as the glaciation period was not continuous throughout the Quaternary period.

There is geological, paleobotanical and other evidence that glaciers disappeared several times, giving way to epochs interglacial when the climate was even warmer than today. However, the warm eras were replaced by cold snaps again, and the glaciers spread again.

We now live, apparently, at the end of the fourth epoch of the Quaternary glaciation.

But in Antarctica, glaciation arose millions of years before the time when glaciers appeared in North America and Europe. In addition to the climatic conditions, this was facilitated by the high continent that had existed here for a long time. By the way, now, due to the fact that the thickness of the Antarctic glacier is enormous, the continental bed of the “ice continent” is in some places below sea level...

Unlike the ancient ice sheets of the Northern Hemisphere, which disappeared and then reappeared, the Antarctic ice sheet has changed little in its size. The maximum glaciation of Antarctica was only one and a half times larger than the modern one in volume, and not much larger in area.

Now about the hypotheses... There are hundreds, if not thousands, of hypotheses about why glaciations occur, and whether there were any at all!

The following main ones are usually put forward: scientific hypotheses:

• Volcanic eruptions leading to a decrease in the transparency of the atmosphere and cooling throughout the Earth;
• Epochs of orogenesis (mountain building);
• Reducing the amount of carbon dioxide in the atmosphere, which reduces the “greenhouse effect” and leads to cooling;
• Cyclicity of solar activity;
• Changes in the position of the Earth relative to the Sun.

But, nevertheless, the causes of glaciations have not been fully elucidated!

It is assumed, for example, that glaciation begins when, with increasing distance between the Earth and the Sun, around which it rotates in a slightly elongated orbit, the number of solar heat, received by our planet, i.e. glaciation occurs when the Earth passes the point of its orbit that is farthest from the Sun.

However, astronomers believe that changes in the amount of solar radiation hitting the Earth alone are not enough to trigger an ice age. Apparently, fluctuations in the activity of the Sun itself also matter, which is a periodic, cyclical process, and changes every 11-12 years, with a cyclicity of 2-3 years and 5-6 years. And the largest cycles of activity, as established by the Soviet geographer A.V. Shnitnikov - approximately 1800-2000 years old.

There is also a hypothesis that the emergence of glaciers is associated with certain areas of the Universe through which our planet passes. solar system, moving with the entire Galaxy, either filled with gas or “clouds” of cosmic dust. And it is likely that “cosmic winter” on Earth occurs when the globe is at the point furthest from the center of our Galaxy, where there are accumulations of “cosmic dust” and gas.

It should be noted that usually before epochs of cooling there are always epochs of warming, and there is, for example, a hypothesis that the Arctic Ocean, due to warming, at times is completely freed from ice (by the way, this is still happening), and there is increased evaporation from the surface of the ocean , streams of moist air are directed to the polar regions of America and Eurasia, and snow falls over the cold surface of the Earth, which does not have time to melt during the short and cold summer. This is how ice sheets appear on continents.

But when, as a result of the transformation of part of the water into ice, the level of the World Ocean drops by tens of meters, the warm Atlantic Ocean ceases to communicate with the Arctic Ocean, and it gradually becomes covered with ice again, evaporation from its surface abruptly stops, less and less snow falls on the continents and less, the “feeding” of the glaciers deteriorates, and the ice sheets begin to melt, and the level of the World Ocean rises again. And again the Arctic Ocean connects with the Atlantic, and again the ice cover began to gradually disappear, i.e. the development cycle of the next glaciation begins anew.

Yes, all these hypotheses quite possible, but so far none of them can be confirmed by serious scientific facts.

Therefore, one of the main, fundamental hypotheses is climate change on the Earth itself, which is associated with the above-mentioned hypotheses.

But it is quite possible that glaciation processes are associated with combined influence of various natural factors, which could act together and replace each other, and the important thing is that, having begun, glaciations, like a “wound clock,” already develop independently, according to their own laws, sometimes even “ignoring” some climatic conditions and patterns.

And the ice age that began in the Northern Hemisphere about 1 million years back, not finished yet, and we, as already mentioned, live in a warmer period of time, in interglacial.

Throughout the era of the Great Glaciations of the Earth, the ice either retreated or advanced again. On the territory of both America and Europe there were, apparently, four global ice ages, between which there were relatively warm periods.

But the complete retreat of the ice occurred only about 20 - 25 thousand years ago, but in some areas the ice lingered even longer. The glacier retreated from the area of ​​modern St. Petersburg only 16 thousand years ago, and in some places in the North small remnants of ancient glaciation have survived to this day.

Let us note that modern glaciers cannot be compared with the ancient glaciation of our planet - they occupy only about 15 million square meters. km, i.e. less than one-thirtieth of the earth's surface.

How can one determine whether there was this place Is the Earth glaciated or not? This is usually quite easy to determine by the peculiar forms of geographical relief and rocks.

In the fields and forests of Russia there are often large accumulations of huge boulders, pebbles, blocks, sands and clays. They usually lie directly on the surface, but they can also be seen in the cliffs of ravines and on the slopes of river valleys.

By the way, one of the first who tried to explain how these deposits were formed was the outstanding geographer and anarchist theorist, Prince Peter Alekseevich Kropotkin. In his work “Research on the Ice Age” (1876), he argued that the territory of Russia was once covered by huge ice fields.

If we look at the physical-geographical map of European Russia, then we can notice some patterns in the location of hills, hills, basins and valleys of large rivers. So, for example, the Leningrad and Novgorod regions from the south and east are, as it were, limited Valdai Upland shaped like an arc. This is exactly the line where in the distant past a huge glacier, advancing from the north, stopped.

To the southeast of the Valdai Upland is the slightly winding Smolensk-Moscow Upland, stretching from Smolensk to Pereslavl-Zalessky. This is another of the boundaries of the distribution of cover glaciers.

Numerous hilly, winding hills are also visible on the West Siberian Plain - "manes" also evidence of the activity of ancient glaciers, or rather glacial waters. Many traces of stopping moving glaciers flowing down the mountain slopes into large basins were discovered in Central and Eastern Siberia.

It is difficult to imagine ice several kilometers thick on the site of current cities, rivers and lakes, but, nevertheless, the glacial plateaus were not inferior in height to the Urals, the Carpathians or the Scandinavian mountains. These gigantic and, moreover, moving masses of ice influenced the entire natural environment - topography, landscapes, river flow, soils, vegetation and wildlife.

It should be noted that on the territory of Europe and the European part of Russia, practically no rocks have been preserved from the geological eras preceding the Quaternary period - Paleogene (66-25 million years) and Neogene (25-1.8 million years), they were completely eroded and redeposited during the Quaternary period, or as it is often called, Pleistocene.

Glaciers originated and moved from Scandinavia, the Kola Peninsula, the Polar Urals (Pai-Khoi) and the islands of the Arctic Ocean. And almost all the geological deposits that we see on the territory of Moscow are moraine, or rather moraine loams, sands of various origins(aquaglacial, lake, river), huge boulders, as well as cover loams - all this is evidence of the powerful influence of the glacier.

On the territory of Moscow, traces of three glaciations can be identified (although there are many more of them - different researchers identify from 5 to several dozen periods of ice advances and retreats):

• Oka (about 1 million years ago),
• Dnieper (about 300 thousand years ago),
• Moscow (about 150 thousand years ago).

Valdai the glacier (disappeared only 10 - 12 thousand years ago) “did not reach Moscow”, and the deposits of this period are characterized by hydroglacial (fluvio-glacial) deposits - mainly the sands of the Meshchera Lowland.

And the names of the glaciers themselves correspond to the names of those places to which the glaciers reached - the Oka, Dnieper and Don, the Moscow River, Valdai, etc.

Since the thickness of the glaciers reached almost 3 km, one can imagine what colossal work he performed! Some hills and hills on the territory of Moscow and the Moscow region are thick (up to 100 meters!) deposits that were “brought” by the glacier.

The best known are, for example Klinsko-Dmitrovskaya moraine ridge, individual hills on the territory of Moscow ( Sparrow Hills and Teplostanskaya Upland). Huge boulders weighing up to several tons (for example, the Maiden Stone in Kolomenskoye) are also the result of the glacier.

Glaciers smoothed out the unevenness of the relief: they destroyed hills and ridges, and with the resulting rock fragments they filled depressions - river valleys and lake basins, transporting huge masses of stone fragments over a distance of more than 2 thousand km.

However, huge masses of ice (given its colossal thickness) put so much pressure on the underlying rocks that even the strongest of them could not stand it and collapsed.

Their fragments were frozen into the body of the moving glacier and, like sandpaper, for tens of thousands of years they scratched rocks composed of granites, gneisses, sandstones and other rocks, creating depressions in them. Numerous glacial grooves, “scars” and glacial polishing on granite rocks, as well as long hollows in earth's crust, subsequently occupied by lakes and swamps. An example is the countless depressions of the lakes of Karelia and the Kola Peninsula.

But the glaciers did not plow up all the rocks on their way. The destruction was mainly carried out in those areas where the ice sheets originated, grew, reached a thickness of more than 3 km and from where they began to move. The main center of glaciation in Europe was Fennoscandia, which included the Scandinavian mountains, the plateaus of the Kola Peninsula, as well as the plateaus and plains of Finland and Karelia.

Along the way, the ice became saturated with fragments of destroyed rocks, and they gradually accumulated both inside the glacier and under it. When the ice melted, masses of debris, sand and clay remained on the surface. This process was especially active when the movement of the glacier stopped and the melting of its fragments began.

At the edge of glaciers, as a rule, water flows arose, moving along the surface of the ice, in the body of the glacier and under the ice thickness. Gradually they merged, forming entire rivers, which over thousands of years formed narrow valleys and washed away a lot of debris.

As already mentioned, the forms of glacial relief are very diverse. For moraine plains characterized by many ridges and shafts, marking places where moving ice stops, and the main form of relief among them is shafts of terminal moraines, usually these are low arched ridges composed of sand and clay mixed with boulders and pebbles. The depressions between the ridges are often occupied by lakes. Sometimes among the moraine plains you can see outcasts- blocks hundreds of meters in size and weighing tens of tons, giant pieces of the glacier bed, transported by it over enormous distances.

Glaciers often blocked river flows and near such “dams” huge lakes arose, filling depressions in river valleys and depressions, which often changed the direction of river flow. And although such lakes existed for a relatively short time (from a thousand to three thousand years), at their bottom they managed to accumulate lacustrine clays, layered sediments, by counting the layers of which, one can clearly distinguish the periods of winter and summer, as well as how many years these sediments have accumulated.

In the era of the last Valdai glaciation arose Upper Volga periglacial lakes(Mologo-Sheksninskoye, Tverskoye, Verkhne-Molozhskoye, etc.). At first their waters flowed to the southwest, but with the retreat of the glacier they were able to flow to the north. Traces of Mologo-Sheksninsky Lake remain in the form of terraces and shorelines at an altitude of about 100 m.

There are very numerous traces of ancient glaciers in the mountains of Siberia, the Urals, Far East. As a result of ancient glaciation, 135-280 thousand years ago, sharp mountain peaks - “gendarmes” - appeared in Altai, the Sayans, the Baikal region and Transbaikalia, on the Stanovoi Highlands. The so-called “net type of glaciation” prevailed here, i.e. If you could look from a bird's eye view, you would be able to see how ice-free plateaus and mountain peaks rise against the backdrop of glaciers.

It should be noted that during the ice ages, quite large ice massifs were located on part of the territory of Siberia, for example on archipelago Severnaya Zemlya, in the Byrranga mountains (Taimyr Peninsula), as well as on the Putorana plateau in northern Siberia.

Extensive mountain-valley glaciation was 270-310 thousand years ago Verkhoyansk Range, Okhotsk-Kolyma Plateau and Chukotka Mountains. These areas are considered centers of glaciations in Siberia.

Traces of these glaciations are numerous bowl-shaped depressions of mountain peaks - circuses or punishments, huge moraine ridges and lake plains in place of melted ice.

In the mountains, as well as on the plains, lakes arose near ice dams, periodically the lakes overflowed, and gigantic masses of water through low watersheds rushed with incredible speed into neighboring valleys, crashing into them and forming huge canyons and gorges. For example, in Altai, in the Chuya-Kurai depression, “giant ripples”, “drilling boilers”, gorges and canyons, huge outlier boulders, “dry waterfalls” and other traces of water flows escaping from ancient lakes “only” are still preserved. just” 12-14 thousand years ago.

“Invading” the plains of Northern Eurasia from the north, the ice sheets either penetrated far to the south along relief depressions, or stopped at some obstacles, for example, hills.

It is probably not yet possible to accurately determine which of the glaciations was the “greatest,” however, it is known, for example, that the Valdai glacier was sharply smaller in area than the Dnieper glacier.

The landscapes at the boundaries of the cover glaciers also differed. Thus, during the Oka glaciation era (500-400 thousand years ago), to the south of them there was a strip of Arctic deserts about 700 km wide - from the Carpathians in the west to the Verkhoyansk Range in the east. Even further, 400-450 km to the south, stretched cold forest-steppe, where only such unpretentious trees as larches, birches and pines could grow. And only at the latitude of the Northern Black Sea region and Eastern Kazakhstan did comparatively warm steppes and semi-deserts begin.

During the era of the Dnieper glaciation, glaciers were significantly larger. Along the edge of the ice sheet stretched the tundra-steppe (dry tundra) with a very harsh climate. The average annual temperature was approaching minus 6°C (for comparison: in the Moscow region the average annual temperature is currently about +2.5°C).

The open space of the tundra, where there was little snow in winter and there were severe frosts, cracked, forming the so-called “permafrost polygons,” which in plan resemble a wedge in shape. They are called “ice wedges,” and in Siberia they often reach a height of ten meters! Traces of these “ice wedges” in ancient glacial deposits “speak” of a harsh climate. Traces of permafrost, or cryogenic effects, are also noticeable in sands; these are often disturbed, as if “torn” layers, often with a high content of iron minerals.

Fluvio-glacial deposits with traces of cryogenic impact

The last “Great Glaciation” has been studied for more than 100 years. Many decades of hard work by outstanding researchers went into collecting data on its distribution on the plains and in the mountains, mapping end-moraine complexes and traces of glacial-dammed lakes, glacial scars, drumlins, and areas of “hilly moraine.”

True, there are also researchers who generally deny ancient glaciations and consider the glacial theory to be erroneous. In their opinion, there was no glaciation at all, but there was a “cold sea on which icebergs floated,” and all glacial deposits are just bottom sediments of this shallow sea!

Other researchers, “recognizing the general validity of the theory of glaciations,” nevertheless doubt the correctness of the conclusion about the grandiose scale of glaciations of the past, and they are especially distrustful of the conclusion about ice sheets that overlapped the polar continental shelves; they believe that there were “small ice caps of the Arctic archipelagos”, “bare tundra” or “cold seas”, and in North America, where the largest “Laurentian ice sheet” in the Northern Hemisphere has long been restored, there were only “groups of glaciers merged at the bases of the domes”.

For Northern Eurasia, these researchers recognize only the Scandinavian ice sheet and isolated “ice caps” of the Polar Urals, Taimyr and the Putorana Plateau, and in the mountains of temperate latitudes and Siberia - only valley glaciers.

And some scientists, on the contrary, are “reconstructing” “giant ice sheets” in Siberia, which are not inferior in size and structure to the Antarctic.

As we have already noted, in the Southern Hemisphere, the Antarctic ice sheet extended over the entire continent, including its underwater margins, in particular the areas of the Ross and Weddell seas.

The maximum height of the Antarctic ice sheet was 4 km, i.e. was close to modern (now about 3.5 km), the ice area increased to almost 17 million square kilometers, and the total volume of ice reached 35-36 million cubic kilometers.

Two more large ice sheets were in South America and New Zealand.

The Patagonian Ice Sheet was located in the Patagonian Andes, their foothills and on the adjacent continental shelf. Today it is reminded of by the picturesque fjord topography of the Chilean coast and the residual ice sheets of the Andes.

"South Alpine complex" of New Zealand– was a smaller copy of Patagonian. It had the same shape and extended onto the shelf in the same way; on the coast it developed a system of similar fjords.

In the Northern Hemisphere, during periods of maximum glaciation, we would see huge Arctic ice sheet resulting from the merger North American and Eurasian covers into a single glacial system, Moreover, an important role was played by floating ice shelves, especially the Central Arctic, which covered the entire deep-water part of the Arctic Ocean.

The largest elements of the Arctic ice sheet were the Laurentian Shield of North America and the Kara Shield of Arctic Eurasia, they were shaped like giant flat-convex domes. The center of the first of them was located over the southwestern part of Hudson Bay, the peak rose to a height of more than 3 km, and its eastern edge extended to the outer edge of the continental shelf.

The Kara ice sheet occupied the entire area of ​​the modern Barents and Kara seas, its center lay over the Kara Sea, and the southern marginal zone covered the entire north of the Russian Plain, Western and Central Siberia.

From other elements of the Arctic cover special attention deserves East Siberian Ice Sheet, which spread on the shelves of the Laptev, East Siberian and Chukchi seas and was larger than the Greenland ice sheet. He left traces in the form of large glaciodislocations New Siberian Islands and Tiksi region, are also associated with it grandiose glacial-erosive forms of Wrangel Island and the Chukotka Peninsula.

So, the last ice sheet of the Northern Hemisphere consisted of more than a dozen large ice sheets and many smaller ones, as well as the ice shelves that united them, floating in the deep ocean.

The periods of time during which glaciers disappeared, or were reduced by 80-90%, are called interglacials. Landscapes freed from ice in a relatively warm climate were transformed: the tundra retreated to the northern coast of Eurasia, and the taiga and deciduous forests, forest-steppes and steppes occupied a position close to the modern one.

Thus, over the past million years, the nature of Northern Eurasia and North America has repeatedly changed its appearance.

Boulders, crushed stone and sand, frozen into the bottom layers of a moving glacier, acting as a giant “file”, smoothed, polished, scratched granites and gneisses, and under the ice, peculiar layers of boulder loams and sands were formed, characterized by high density associated with the influence of glacial load - main, or bottom moraine.

Since the size of the glacier is determined balance between the amount of snow that falls on it annually, which turns into firn, and then into ice, and what does not have time to melt and evaporate during the warm seasons, then with climate warming, the edges of the glaciers retreat to new, “equilibrium boundaries.” The end parts of the glacial tongues stop moving and gradually melt, and boulders, sand and loam included in the ice are released, forming a shaft that follows the contours of the glacier - terminal moraine; the other part of the clastic material (mainly sand and clay particles) is carried away by meltwater flows and deposited around in the form fluvioglacial sandy plains (Zandrov).

Similar flows also operate deep in glaciers, filling cracks and intraglacial caverns with fluvioglacial material. After the melting of glacial tongues with such filled voids on the earth's surface, chaotic piles of hills of various shapes and composition remain on top of the melted bottom moraine: ovoid (when viewed from above) drumlins, elongated, like railway embankments (along the axis of the glacier and perpendicular to the terminal moraines) oz And irregular shape kama.

All these forms of glacial landscape are very clearly represented in North America: the boundary of ancient glaciation here is marked by a terminal moraine ridge with heights of up to fifty meters, stretching across the entire continent from its eastern coast to the western. To the north of this “Great Glacial Wall” the glacial deposits are represented mainly by moraine, and to the south of it they are represented by a “cloak” of fluvioglacial sands and pebbles.

Just as four glacial epochs have been identified for the territory of the European part of Russia, four glacial epochs have also been identified for Central Europe, named after the corresponding Alpine rivers - Günz, Mindel, Riess and Würm, and in North America - Nebraska, Kansas, Illinois and Wisconsin glaciations.

Climate periglacial The areas (surrounding the glacier) were cold and dry, which is fully confirmed by paleontological data. In these landscapes a very specific fauna appears with a combination cryophilic (cold-loving) and xerophilic (dry-loving) plants – tundra-steppe.

Now similar natural areas, similar to periglacial ones, are preserved in the form of so-called relict steppes– islands among the taiga and forest-tundra landscapes, for example, the so-called alasy Yakutia, the southern slopes of the mountains of northeastern Siberia and Alaska, as well as the cold, dry highlands of Central Asia.

Tundra-steppe was different in that her the herbaceous layer was formed mainly not by mosses (as in the tundra), but by grasses, and it was here that it took shape cryophilic option herbaceous vegetation with a very high biomass of grazing ungulates and predators – the so-called “mammoth fauna”.

In its composition, various types of animals were intricately mixed, both characteristic of tundra – reindeer, caribou, muskox, lemmings, For steppes - saiga, horse, camel, bison, gophers, and mammoths and woolly rhinoceroses, saber-toothed tiger - Smilodon, and giant hyena.

It should be noted that many climate changes have been repeated, as it were, “in miniature” within the memory of mankind. These are the so-called “Little Ice Ages” and “Interglacials”.

For example, during the so-called “Little Ice Age” from 1450 to 1850, glaciers advanced everywhere, and their sizes exceeded modern ones (snow cover appeared, for example, in the mountains of Ethiopia, where there is none now).

And in the period preceding the Little Ice Age Atlantic optimum(900-1300) glaciers, on the contrary, shrank, and the climate was noticeably milder than the present one. Let us remember that it was during these times that the Vikings called Greenland the “Green Land”, and even settled it, and also reached the coast of North America and the island of Newfoundland in their boats. And the Novgorod Ushkuin merchants traveled along the “Northern Sea Route” to the Gulf of Ob, founding the city of Mangazeya there.

And the last retreat of glaciers, which began over 10 thousand years ago, is well remembered by people, hence the legends about the Great Flood, as a huge amount of meltwater rushed down to the south, rains and floods became frequent.

In the distant past, the growth of glaciers occurred in eras with lower air temperatures and increased humidity; the same conditions developed in the last centuries of the last era, and in the middle of the last millennium.

And about 2.5 thousand years ago, a significant cooling of the climate began, the Arctic islands were covered with glaciers, in the Mediterranean and Black Sea countries at the turn of the era the climate was colder and wetter than now.

In the Alps in the 1st millennium BC. e. glaciers moved to lower levels, blocked mountain passes with ice and destroyed some high-lying villages. It was during this era that glaciers in the Caucasus sharply intensified and grew.

But by the end of the 1st millennium, climate warming began again, and mountain glaciers in the Alps, Caucasus, Scandinavia and Iceland retreated.

The climate began to change seriously again only in the 14th century; glaciers began to grow rapidly in Greenland, summer thawing of the soil became increasingly short-lived, and by the end of the century permafrost was firmly established here.

From the end of the 15th century, glaciers began to grow in many mountainous countries and polar regions, and after the relatively warm 16th century, harsh centuries began, which were called the “Little Ice Age”. In the south of Europe, severe and long winters often recurred; in 1621 and 1669, the Bosporus Strait froze, and in 1709, the Adriatic Sea froze off the coast. But the “Little Ice Age” ended in the second half of the 19th century and a relatively warm era began, which continues to this day.

Note that the warming of the 20th century is especially pronounced in the polar latitudes of the Northern Hemisphere, and fluctuations in glacial systems are characterized by the percentage of advancing, stationary and retreating glaciers.

For example, for the Alps there is data covering the entire past century. If the share of advancing alpine glaciers in the 40-50s of the 20th century was close to zero, then in the mid-60s of the 20th century about 30%, and at the end of the 70s of the 20th century, 65-70% of the surveyed glaciers were advancing here.

Their similar state indicates that the anthropogenic (technogenic) increase in the content of carbon dioxide, methane and other gases and aerosols in the atmosphere in the 20th century did not in any way affect the normal course of global atmospheric and glacial processes. However, at the end of the last, twentieth century, glaciers began to retreat everywhere in the mountains, and the ice of Greenland began to melt, which is associated with climate warming, and which especially intensified in the 1990s.

It is known that the currently increased man-made emissions of carbon dioxide, methane, freon and various aerosols into the atmosphere seem to help reduce solar radiation. In this regard, “voices” appeared, first from journalists, then from politicians, and then from scientists about the beginning of a “new ice age.” Environmentalists have “sounded the alarm”, fearing “the coming anthropogenic warming” due to the constant increase in carbon dioxide and other impurities in the atmosphere.

Yes, it is well known that an increase in CO 2 leads to an increase in the amount of retained heat and thereby increases the air temperature at the Earth’s surface, forming the notorious “greenhouse effect”.

Some other gases of technogenic origin have the same effect: freons, nitrogen oxides and sulfur oxides, methane, ammonia. But, nevertheless, not all carbon dioxide remains in the atmosphere: 50-60% of industrial CO 2 emissions end up in the ocean, where they are quickly absorbed by animals (corals in the first place), and of course they are also absorbed by plants–Let's remember the process of photosynthesis: plants absorb carbon dioxide and release oxygen! Those. the more carbon dioxide, the better, the higher the percentage of oxygen in the atmosphere! By the way, this already happened in the history of the Earth, in the Carboniferous period... Therefore, even a multiple increase in the concentration of CO 2 in the atmosphere cannot lead to the same multiple increase in temperature, since there is a certain natural regulation mechanism that sharply slows down the greenhouse effect at high concentrations of CO 2.

So all the numerous “scientific hypotheses” about “ greenhouse effect“,” “rising sea levels,” “changes in the Gulf Stream,” and naturally “the coming Apocalypse” are mostly imposed on us “from above,” by politicians, incompetent scientists, illiterate journalists or simply science swindlers. The more you intimidate the population, the easier it is to sell goods and manage...

But in fact, an ordinary natural process is taking place - one stage, one climatic epoch gives way to another, and there is nothing strange about it... But what is happening natural disasters, and that there are supposedly more of them - tornadoes, floods, etc. - just 100-200 years ago, vast areas of the Earth were simply uninhabited! And now there are more than 7 billion people, and they often live where floods and tornadoes are possible - along the banks of rivers and oceans, in the deserts of America! Moreover, let us remember that natural disasters have always existed, and even destroyed entire civilizations!

As for the opinions of scientists, which both politicians and journalists love to refer to... Back in 1983, American sociologists Randall Collins and Sal Restivo, in their famous article “Pirates and Politicians in Mathematics,” wrote openly: “...There is no immutable set of norms that guide the behavior of scientists. What remains constant is the activity of scientists (and related other types of intellectuals), aimed at acquiring wealth and fame, as well as gaining the ability to control the flow of ideas and impose their own ideas on others... The ideals of science do not predetermine scientific behavior, but arise from the struggle for individual success under various competition conditions...”

And a little more about science... Various large companies often provide grants to conduct so-called “ scientific research"in certain areas, but the question arises - how competent is the person conducting the research in this area? Why was he chosen out of hundreds of scientists?

And if a certain scientist, “a certain organization” orders, for example, “a certain research on the safety of nuclear energy,” then, it goes without saying that this scientist will be forced to “listen” to the customer, since he has “well-defined interests,” and it is understandable , that he will most likely “adjust” “his conclusions” to the customer, since the main question is already not a question of scientific research–and what does the customer want to receive, what is the result?. And if the customer's result won't suit, then this scientist won't invite you anymore, and not in any “serious project”, i.e. “monetary”, he will no longer participate, since they will invite another scientist, more “flexible”... Much, of course, depends on civic position, and professionalism, and reputation as a scientist... But let’s not forget how much scientists “get” in Russia... Yes, in the world, in Europe and the USA, a scientist lives mainly on grants... And any scientist also “wants to eat.”

In addition, the data and opinions of one scientist, albeit a major specialist in his field, are not a fact! But if the research is confirmed by some scientific groups, institutes, laboratories, etc. o only then can research be worthy of serious attention.

Unless, of course, these “groups”, “institutes” or “laboratories” were funded by the customer this study or project...

A.A. Kazdym,
Candidate of Geological and Mineralogical Sciences, member of MOIP

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The mountainous areas of South America, Africa and Australia were subject to glaciation. The snow line at that time ran in these areas several hundred meters lower than the modern one, and in some places the glaciers descended almost to the sea (New Zealand).
In South America, glaciation covered the Andes; in Africa, glaciers were noted in the Atlas Mountains, and in the equatorial part they descended from the slopes of the Kenya and Kilimanjaro volcanoes 270 m lower than now. There are no glaciers in the Australian Andes, and during glaciation they dropped to 1000 m above sea level.
The climate of the Southern Hemisphere was wetter and milder than the Northern Hemisphere.
NON-GLACIAL TERRITORIES
Even during maximum glaciation, more than 2/3 of the surface of the continents was devoid of ice cover. This vast non-glacial territory of the Earth, located within the modern temperate, subtropical, tropical and equatorial zones, was influenced global changes climate caused by the change of glacial and interglacial eras. This influence was most pronounced in the periglacial zone - the area located south of the edge of the ice cover. Here, during glaciation, loess and loess-like rocks were formed, and during interglacial periods, buried soils were formed. Alluvium of various ages accumulated in river valleys, and the water abundance of rivers underwent strong changes during glacial and interglacial eras. The alternation of these eras caused a shift in landscape zones, either to the south or to the north, for hundreds of kilometers.

To the south, in the area of ​​modern subtropics, wet (pluvial) and dry (arid or interpluvial) climates successively changed. During glacial epochs (pluvials), the boundaries of climatic zones shifted to the south; during interglacial periods (arids), the climate and the position of the boundaries of climatic zones were close to modern ones. During the glaciation era, the subtropical climate region experienced changes of various types (climatic, geological, hydrographic, etc.) and turned into a pluvial belt that had nothing in common with the modern subtropics. The Quaternary history of the pluvial belt of the Northern Hemisphere is quite well studied in Eurasia, North America and North Africa. Lakes were especially widespread within the pluvial belt, some of which have survived to this day. During the Quaternary period, large changes occurred in the size of these lakes, the nature of sedimentation in them, and the composition of the rocks. The genetic types of Quaternary deposits, their area distribution, weathering processes, denudation, etc. were subject to change.
In the subtropical zone of Eurasia, as in North America, numerous ancient lakes are known; the contours of their former boundaries and traces of ancient watercourses have been preserved. Ancient lakes include the Dead Sea, a lake in the Middle East whose water surface is currently 400 m below sea level. During the pluvial epochs of the Pleistocene, the level of the Dead Sea reached ocean level twice, which was caused by an increase in humidity and a decrease in evaporation due to a decrease in average temperature.
Of great interest is the well-restored Pleistocene history of the world's largest endorheic lake - the Caspian Sea, the southern part of which is located in the subtropical zone. In the Pleistocene, the Caspian Sea experienced significant transgressions and regressions. During the period of the largest transgressions, the area of ​​the Caspian Sea expanded almost twice, and its level increased by almost 100 m. In the Pleistocene, the Caspian Sea was a giant isolated lake, which was not affected by changes in the level of the World Ocean and the Black Sea. Fluctuations in its level were associated with changes in the water balance: an increase in the influx of water from land due to the melting of the cover glacier of Europe and the mountain glaciers of the Caucasus and a decrease in evaporation from the surface of the Caspian Sea led to transgressions, and a decrease in water influx and an increase in evaporation led to regressions. In the late Pleistocene, during the Valdai glaciation, little water entered the Caspian Sea due to the melting of the glacier and transgressions were associated mainly with a decrease in evaporation from the surface of the lake-sea. In general, it was not glacial runoff, but evaporation that had a significant impact on changes in the level of not only the Caspian Sea, but all other pluvial lakes in Eurasia and North America.
A mass of drainless lakes of pluvial origin are located in the subtropics of Central Asia - in Central Asia, Mongolia, and China. In area they are inferior to the Great Lakes of North America! ", but still very large and have the same origin. In Central Asia, these huge reservoirs of water are located at different levels, often at significant altitudes (in the Mongolian Altai). The lowest point is 759 m has the largest lake in Mongolia, Uvsu-Nur, with an area of ​​3350 km2, and the mountain lake North Azin Issyk-Kul is located at an altitude of 1608 m.

Pluvial and arid eras are traced in North Africa, located in the subtropical zone. They are installed in Morocco on the High and Small Atlas mountains, on plateaus and in foothill plains over a huge range of altitudes from 100 to 3100 m above sea level. Five pluvial epochs were noted, coinciding with climate humidification. The lake is of pluvial origin. Chad. During the Valdai glaciation, the level of this lake rose by 120 m and the surface increased 16 times, from 20,000 km2 (the area of ​​modern Lake Chad) to 330,000 km2 (three quarters of the Caspian Sea). The northern part of the vast Koro-Toro basin, in which the lake is located. Chad, is currently dry.

In Africa, as in the entire equatorial belt of the globe, modern glaciers can only exist on the tops of the highest mountain structures. Here, only three mountain ranges rising above 5000 m bear modern glaciers and bear traces of more extensive glaciation in the past.

These are the Pleistocene-Holocene volcanic structures of Kilimanjaro (5895 m) and Kenya (5199 m) on the eastern flank of the East African Rift Zone and the Rwenzori mountain range with Margaret Peak (5109 m) - a horst rise at the intersection of the Edward George and Albert grabens, composed of Precambrian gneisses.

All three named mountain ranges are located near the equator, not far from each other. Therefore, the climatic conditions for the existence of glaciers on them are similar.

A common feature of the climate is the division of the year into two wet and two dry periods, with slight fluctuations in temperature conditions throughout the year.
Dry periods occur in January - February and July - October, and wet periods occur in March - June and November - December.
Wet periods with predominant cloudy weather are periods of predominant accumulation of snow in the glacial zone, and dry periods with little cloudiness are periods of predominant ice ablation. This is reflected in the stratigraphy of the firn strata.

Thus, in the firn region of the Lewis Glacier (Kenya), the layered structure of firn was traced over a number of years in boreholes and in a 20-meter crack. Each pack of layers consisted of layers of dense firn with ice layers and layers of dirty ice separating them. Each layer of dirty ice corresponds to an ablation period, and each layer of clean ice corresponds to an accumulation period. A similar alternation of clean and contaminated ice was also noted in the section of the firn strata on the Elena glacier (Rwenzori).

The bulk of the sediment that feeds the glaciers is brought by the southeast trade wind from the Indian Ocean. South-westerly winds, bringing moisture from the Atlantic Ocean, are less important. The main factor in glacier ablation is solar radiation. Its share accounts for about 90%, and turbulent heat exchange only 10% of the total energy consumption for melting and evaporation of ice. In this regard, changes in cloudiness and shading by slopes play a greater role in glacier ablation than fluctuations in temperature conditions.

The modern snow line rises highest on Kilimanjaro - up to 4800 - 5200 m, on Kenya it is at an altitude of 4680-4750 m, and on Rwenzori - at 4570 - 4750 m. The difference in the height of the snow line is apparently associated with less cloudiness and less rainfall in the glacial zone on Kilimanjaro compared to Kenya and Rwenzori.

According to observations on Rwenzori, the maximum precipitation falls below the snow line, at an altitude of 3300 m, where it reaches 2300 mm per year. At the level of the snow line, about 2000 mm falls, and at an altitude of 5000 m, the annual precipitation drops to 1150 mm. Kilimanjaro receives less precipitation than Rwenzori, and its amount decreases more rapidly with altitude. According to observations over 5 years (1945-1949), the average annual precipitation decreased from 1800 mm at an altitude of 2850 m to 180 mm at an altitude of 4300 m and to 70 mm at 5800 m.

Thus, firn areas of glaciers receive very poor nutrition, which does not compensate for the loss of snow and ice due to melting and evaporation. The material balance of glaciers is currently negative and has been negative all the time since the end of the last century. It is reasonable to assume that if climatic conditions do not change, the glaciers of Kilimanjaro, Kenya and Rwenzori will cease to exist over the next century.

Kilimanjaro Glaciers

Kilimanjaro (3°05′ S, 37° 22′ E) is the largest volcanic massif in Africa with a diameter of about 100 km, formed by three merged volcanoes: Mawenzi (5183 m), Shira (4005 m) and Kibo (5895 m). Volcano Kibo is the youngest and highest, and only it has modern glaciers. At the top of Mawenzi, migratory snow patches periodically form.

In the late Pleistocene, a vast caldera more than 3 km in diameter formed at the top of Kibo, and above its flat bottom - a younger cone with an internal crater and a very recent outlet (the volcano was active in the Holocene, but is now in the solfatorium stage). The height of the ridge-shaped shaft surrounding the young crater ranges from 5800 to 5895 m. The outer slopes of the volcano are dissected by radial valleys, along some of them glaciers descend, most of which begin from the shaft surrounding the caldera at the top of the volcano. In the caldera itself, only scattered blocks of dead ice have survived from the once continuous ice cap.

There are a total of 11 glaciers on Kibo, the total area of ​​which, measured on a 1964 map (scale 1:25,000), is about 7 km². The largest glacier, Penka, 2.4 km long, descends along the western slope of the volcano without a clearly defined valley from 5800 to 4580 m. The upper edge of the Penka glacier, like other glaciers of the northwestern group, ends towards the crater with a vertical wall 30-40 m high Over half a century (from 1912 to 1959), the end of the glacier retreated from the terminal moraine with an ice core by about 500 m.

Along the northern side of the caldera, from the Penka glacier to the east and southeast, the Severny slope-type glacier stretches. Both the lower and upper edges of this glacier are sheer ice walls 30-40 m high. On the southern slope of Kibo, 4 glaciers descend steeply from general area accumulation, which in the upper reaches is also terminated by a vertical wall of ice that has retreated from the caldera rim. From this group of glaciers last years The Ratzel glacier became detached. Previously, these glaciers reached a steep cliff on the slope of the volcano and fell from it in avalanches, forming a revived glacier at the foot of the cliff, ending behind the shaft of the terminal moraine. Now they do not reach the cliff, and the power of the revived glacier has stopped. Inside the caldera, scattered blocks of ice 30-60 m thick stand apart from each other, their slopes are cut by deep hollows with pyramidal peaks between them.

The collapse of the single ice cap on the top of Kibo apparently began at the end of the last century. In 1889, the ice in the caldera was already divided into several large massifs. By 1957, some of them had completely disappeared, and the rest had significantly decreased in size. The process of collapse and retreat of the glaciers of Mount Kilimanjaro continues.

Glaciers of Kenya

Kenya (0°10′ S, 37°10′ E) is an extinct, heavily eroded volcano with alpine landforms, the second highest in Africa. The vast volcanic massif is crowned by sharp peaks, among which two main ones stand out: Batian, or Kenya (5199 m), and Nelion (5188 m).

In total, in 1978 there were 12 glaciers with a total area of ​​0.7 km². The largest of them, Lewis Glacier, descends along the south-southwestern slope of the volcano from Lenana Peak (4985 m) to an altitude of 4580 m and ends in a small periglacial lake. From 1926, when the size of the glacier was first measured, it continuously retreated at an average rate of about 10 m per year until 1974.

During this time, it became shorter by 395 m, and its end rose 130 m higher up the slope. The vacated bottom of the valley was occupied by a periglacial lake, which did not exist before 1934. After 1974, the retreat of the glacier stopped, and until 1978 it was stationary. In 1978, it was about 1 km long and 0.3 km² in area. The firn line passed at an altitude of 4750 m.

The second largest glacier - Tyndall - descends to the south from the peak of 4780 m and ends at an altitude of 4500 m. In 1926, the end of the glacier descended into the periglacial lake of the same name, but by 1958 it retreated from it by 130 m horizontally and by 50 m vertically. Subsequently, the retreat of the glacier stopped, and until 1978 the position of its end did not change. The height of the firn line is 4700 m.

The Caesar Glacier retreated by 250 m from 1929 to 1958. The Darwin Glacier, also located on the southern slope, has a very short tongue, but it also retreated by about 80 m. During the period under review, almost all glaciers in Kenya shrank, and only at the end of 70 's, this process slowed down and stopped on some glaciers. Detailed measurements showed that between 1963 and 1978. the total area of ​​glaciers in Kenya decreased by 18%, and from 1926 to 1978 - almost halved - from 1.2 to 0.7 km². Kenya's glaciers, like Kilimanjaro, are little active. The maximum measured speed of ice movement in the middle part of the Lewis Glacier was 4.6 m/year.

Rwenzori Glaciers

Rwenzori (Mountains of the Moon) is a highly dissected mountain range, a horst of Precambrian gneisses among the rocks of the volcanogenic complex, stretching from south-southwest to north-northeast for almost 120 km.

Glaciers are concentrated in the central group of the highest mountains located between 0°20′ and 0°26′ N. w. and 29°51′ and 29°56′ E. In total, there are 37 glaciers on Rwenzori with a total area of ​​about 5 km². The bulk of glaciers are located on the Stanley (Margarita Peak, 5109 m), Speke (4890 m) and Baker (4843 m) mountain ranges.

The central part of the Stanley massif, surrounded by high peaks, is occupied by a firn field, from which 7 glacial tongues descend in different directions - Margaret, East Stanley, Helena, West Helena, Moebius, West Stanley, Alexandra, and 7 more glaciers exist independently of the main firn field . The glaciated area of ​​the Stanley Massif is about 2 km². The height of the firn line on the Elena glacier is 4560 m.

Above 4650 m, a decrease in accumulation and an increase in ablation was noted due to a decrease in cloudiness and an increase in radiative melting and evaporation. Thus, the net accumulation in 1958 decreased from 1220 mm at an altitude of 4635 m to 860 mm at an altitude of 4920 m. In the stratigraphic section of the firn, an alternation of clean and contaminated layers was observed. The thickest contaminated layers are formed in January - February. Most glaciers are retreating. The West Stanley Glacier has been retreating continuously since 1932, and in just one decade, between 1940 and 1950, it became shorter by 245 m.

The top of the Speke massif is covered with a firn field 2.5 km long and up to 1.2 km wide, from which short blades of glacial tongues extend. According to observations in 1958-1961, the area of ​​accumulation area was doubled more area ablation areas, and the total area of ​​glaciation of the Speke massif was 1.6 km². The firn line ran at an altitude of 4570 m. Between 1950 and 1956. the ends of the glaciers retreated by 60-70 m.

The Vittorio Glacier is the largest on Rwenzori. It is wider than it is long, and extending from its lower edge are three short tongues, which have been slowly retreating during the last half century, like all the other glaciers of the Speke massif.

There are 6 small glaciers on the Baker Massif with a total area of ​​0.67 km². They do not have a common firn pool, but exist independently. These glaciers were first visited in 1906. At that time, the East and Middle Baker glaciers and the Moore Glacier shared a common firn basin, but by 1963 they separated, and now the Moore Glacier lies entirely below the firn line. If climatic conditions remained constant, it should have disappeared in 20-30 years. We don’t know what the state of the glacier is now, but several smaller glaciers that were observed at the beginning of the 20th century have disappeared.

Six small cirque glaciers with a total area of ​​0.26 km² are located on the Jesse massif. They all retreat. In the south of the massif from the city of Yolanda, several steep glacial tongues descended from the common firn basin in 1931. By 1959, this glacial massif had broken up into several parts, which continued to degrade in 1966.

In the southern part of Rwenzori, the summit of Luigi di Savoia (4626 m) was covered with a thin layer of ice in 1906. In 1932, at the source of the river. Kurugata, 5 small glaciers with signs of retreat were discovered. None of them ate firn fields. In 1960, the glaciated area of ​​this mountain decreased to 4 hectares.

Three isolated glaciers with a total area of ​​0.08 km² have been preserved in the northern part of the Rwenzori massif, on the city of Emin.