Ice ages, or the Great Glaciations, played an extremely important role in the formation of the nature of the Earth and, in particular, the North. They are associated with sea level fluctuations, which formed sea terraces, the formation of troughs, the appearance of permafrost, and many other features of the Arctic nature.
The influence of the cooling went far beyond the glaciers: the climates were sharply different from the modern ones, and the temperatures of the sea waters were much lower. The area of permafrost, or permafrost, was up to 27 million square kilometers (20% of the land area!), And floating ice occupied about half of the World Ocean. If the Earth was visited by intelligent beings at this time, it would certainly have received the name Ice Planet.
Such geography was characteristic of the Earth at least four times only during the Quaternary period of its existence, and over the past two million years, researchers have counted up to 17 glaciations. At the same time, the last ice age was not the most grandiose: about 100 thousand years ago, ice bound up to 45 million square kilometers of land. The interglacial situation on Earth, similar to the modern one, turns out to be a purely temporary state. After all, the Earth's glaciations lasted for about 100 thousand years each, and the intervals of warming between them lasted less than 20 thousand years. Even in a rather warm present time, glaciers occupy about 11% of the land area - almost 15 million square kilometers. Permafrost stretches across North America and Eurasia in a wide belt. In winter, in the Arctic Ocean, about 12 million square kilometers, and in the oceans around Antarctica, more than 20 million square kilometers are bound by floating ice.
Why do ice ages begin on Earth? In order for the planet to begin glaciation, two conditions are necessary. A global (i.e., covering most of the Earth) cooling should occur - such that snow becomes one of the main types of precipitation and that, having fallen in winter, it does not have time to melt over the summer. And besides, there should be a lot of precipitation - enough to ensure the growth of glaciers. Both conditions seem simple. But what causes the cold snap? There may be several reasons, and we do not know which of them determined the onset of this or that glaciation. Maybe several reasons worked at once. Possible reasons for the glaciation of the Earth are as follows.
Continents, being parts of lithospheric plates, move along the Earth's surface like rafts on water. Finding themselves in the polar or subpolar regions (like modern Antarctica), the continents find themselves in conditions favorable for the formation of an ice sheet. There is little rainfall here, but the temperature is low enough that it falls mainly in the form of snow and does not melt in summer. The displacements of the geographic poles could lead to the displacements of natural zones, respectively, the continent could get into polar conditions without moving - they themselves "came" to it.
With violent mountain building, significant land masses can appear above the snow line (i.e., such an altitude, upon reaching which the temperature becomes so low that the accumulation of snow and ice prevails over their melting and evaporation). At the same time, mountain glaciers are formed, the temperature becomes even lower. Cooling goes beyond the mountains, glaciers of the foothills appear. The temperature drops even lower, the glaciers grow and the glaciation of the Earth begins.
Indeed, during the period from the Pliocene to the middle of the Pleistocene, the Alps rose more than two thousand meters, the Himalayas - three thousand meters.
The climate and, in particular, average air temperatures are influenced by the composition of the atmosphere (greenhouse effect). The influence of dustiness in the atmosphere (for example, volcanic ash or dust raised by a meteorite impact) is also possible. The dust reflects sunlight and the temperature drops.
The oceans affect the climate in many ways. One of them is the storage of heat and its redistribution over the planet by ocean currents. The movements of the continents can lead to the fact that the inflow of warm waters into the circumpolar regions will decrease so much that they will become very cold. Something like this happened when the Bering Strait, which connects the Arctic Ocean with the Pacific, became almost closed (and there were periods when it was completely closed and when it was wide open). Therefore, mixing of water in the Arctic Ocean is difficult, and almost all of it is covered with ice.
Cooling can be associated with a decrease in the amount of solar heat coming to the Earth. The reasons for this, perhaps, are associated with fluctuations in solar activity or with fluctuations in the spatial relationship of the Earth and the Sun. Known are the calculations of the Yugoslav geophysicist M. Milankovic, who in the 1920s analyzed the changes in solar radiation depending on changes in the Earth-Sun system. The cycles of such changes roughly coincide with the cyclicity of glaciations. To date, this hypothesis is the most substantiated.
Each ice age was accompanied by characteristic processes. Continental ice sheets grew in high and temperate latitudes. Mountain glaciers grew all over the planet. Ice shelves appeared in the polar regions. Floating ice was widespread - in high latitudes with moving ice floes and icebergs in the vast waters of the World Ocean. Permafrost territories increased in high and temperate latitudes, outside the glaciers.
The atmospheric circulation changed - temperature drops increased in temperate latitudes, storms in the oceans became more frequent, and the inner parts of the continents in the tropics dried up. The circulation of oceanic waters was also rebuilt - the currents stopped or deviated due to the growth of ice sheets. The sea level sharply fluctuated (up to 250 m), since the growth and destruction of ice sheets were accompanied by the withdrawal and return of water to the World Ocean. In connection with these fluctuations, sea terraces appeared and are preserved in the relief - surfaces formed by the sea surf on ancient coastlines. At present, they may be higher or lower than the modern coast (depending on whether the ocean level was higher or lower than the modern one during the period of their formation).
Finally, there were tremendous changes in the position and size of the plant belts and corresponding shifts in the placement of animals.
The most recent cooling period was the Little Ice Age, recorded in the history of Western Europe, the Far East and other regions. It began around the 11th century, culminated about 200 years ago, and is gradually weakening. In Iceland and Greenland, the period from 800 to 1000 AD was characterized by a warm, dry climate. Then the climate deteriorated sharply, and for four hundred years the Viking settlements in Greenland fell into complete desolation due to the intensifying cold weather and the cessation of contact with the outside world. The passage of ships off the coast of Greenland has become impossible due to the removal of sea ice from the Arctic. In Scandinavia and a number of other regions, the Little Ice Age was manifested by extremely harsh winters, glacier movements and frequent crop failures.
What happened to the inhabitants of the northern regions of the Earth during the glaciers and the interglacials that separated them? The expansion and melting of ice sheets affects all living organisms.
Near the equator, climate changes were not particularly great, and many animals (elephants, giraffes, hippos, rhinos) survived the ice ages quite calmly. In the polar regions, the changes were very sharp. The temperature dropped, there was not enough water (there was plenty of ice and snow, but plants and animals also need liquid water), vast territories were occupied by ice. And in order to survive, the inhabitants of the North had to go south. But it is curious that in high latitudes areas of refuge remained, i.e. areas where the possibility of survival remained.
A decisive role in the survival of the northern species was probably played by the vast ice-free territory that existed during the maximum glaciation 18 thousand years ago in the Canadian Arctic, Alaska and adjacent regions. This area is known as Beringia. Recall that the maximum glaciation is the time when huge amounts of water were bound in glaciers, and therefore the level of the World Ocean dropped dramatically, and the shelves (and in the Arctic Ocean they are extremely large) were drained.
However, ice-free areas like Beringia and southern regions could not save everyone. And about 10 thousand years ago, not only many species, but also genera of animals and plants (for example, mammoths - Elephas and mastodons - Mastodon) became extinct.
It is possible, however, that this extinction was associated not only with changes in the landscape sphere, but also with the appearance of man here. Perhaps it was hunting that played a decisive role in the life and death of many inhabitants of the polar regions.
Australia is washed by the warm waters of the Indian and Pacific Oceans with high surface temperatures (+ 24 ° C in summer, about + 20 ° C in winter). These temperature conditions are conducive to coral growth. That is why along the northeastern coast of the mainland for more than 2 thousand km stretches Great Barrier Reef.
Research History Brief... Scientists of antiquity (K. Ptolemy and others) supposedly spoke about the existence of a large continent in the southern hemisphere. The first appearance of Europeans off the coast of Australia dates back to the era of the great geographical discoveries. In 1605 a Dutch navigator Willem Jansson penetrated the coast of the Gulf of Carpentaria. In 1606 the Spaniard Torros sailed by the strait, which separates the island of New Guinea from the mainland. In 1643 a Dutch navigator Abel Tasman circled the mainland from the south, where he met a large island, later named after him - about. Tasmania.
However, the Spaniards and the Dutch kept their territorial discoveries in deep secrecy for a long time. Only in 1770 was the famous English navigator discovered the east coast of Australia James Cook. Shortly thereafter, the city of Sydney was founded by the British on the southeast coast of the mainland. Initially, the attention of Europeans in Australia was attracted by the good pastures, which were used for raising livestock, especially sheep. Since the end of the 18th century. the colonization of Australia by the British began, its development and study. The entire 19th century was on the mainland a century of travel and geographical discoveries. In the 70s. XIX century. an outstanding Russian traveler and ethnographer lived and worked in Australia and New Guinea N.N. Miklukho Maclay.
Geological structure, relief and minerals... In the geological past, the main part of the continent was, together with Africa, an integral part of the Gondwana continent, from which Australia separated by the end of the Mesozoic. The basis of the modern continent is the Precambrian Australian Platform - part of the Indo-Australian lithospheric plate. The crystalline basement of the platform comes to the surface in the north, west and in the central regions of the mainland, forming shields. In the rest of the territory, the platform basement is covered by sedimentary rocks of both continental and marine origin. On the eastern edge of the continent, a mountainous region of Paleozoic (mainly Hercynian) folding is adjoined to the Australian Platform.
In the modern relief of Australia, stand out: West Australian Highlands, Central Lowlands and East Australian Mountains.
In the relief of the West Australian Plateau plateaus and elevated denudation plains alternate; in some regions, the latest tectonic movements have created revived block mountains. The Central Lowland is located between the Gulf of Carpentaria in the north and the Indian Ocean in the south. It is composed of deep sea and river sediments. The height of the Central Lowland does not exceed 100 m, and in the area of Lake Eyre there is a depression, which lies 12 m below sea level. The relief of the East Australian Mountains is based on the Great Dividing Range (average height 800-1000 m) and the Australian Alps (maximum height 2228 m - Kostsyushko). The mountains in the east of the continent, formed in the Paleozoic, were later severely destroyed, and in the era of alpine folding, they were broken by faults and uplifted. Now these are low ridges with characteristic domed peaks. The mountain ranges are separated by hollows, in some places the cones of ancient extinct volcanoes have been preserved. However, Australia - the only continent on which there are no active volcanoes and there is no modern glaciation in the mountains.
Australia is rich in minerals... The Australian platform, like South Africa, contains large reserves of gold, platinum, uranium, iron, copper, lead-zinc ores and tin. Deposits of phosphorites, bituminous and brown coal, oil and natural gas are confined to the sedimentary strata of the platform. Many minerals are located at shallow depths, and they are mined in an open way.
In terms of reserves of iron ores and ores of non-ferrous metals (bauxite, lead, zinc, nickel), as well as uranium, Australia occupies a leading position in the world. It has become a major supplier of mineral raw materials to the world market.
Climate... Australia is the driest continent on the planet. Only 1/3 of its territory receives sufficient or excessive moisture. In general, the continent receives five times less rainfall than Africa.
The climatic conditions of Australia depend primarily on the characteristics of its geographical position on both sides of the southern tropic. In addition to geographical latitude, the climate of the continent is influenced by the peculiarities of atmospheric circulation, relief, weak indented coastline and ocean currents, as well as the great extent of the continent from west to east.
Most of Australia is dominated by trade winds. But their influence on the climate of the eastern mountainous and western lowland parts of the continent manifests itself in different ways. In the extreme south, the climate formation is influenced by the influence of the westerly winds of temperate latitudes during the cold period of the year. The north of the mainland is influenced by the northwestern equatorial monsoons.
The shallow indented coastline and the mountainous barrier in the east of the mainland significantly weaken the influence of the surrounding oceanic waters on the climate of the inland (tropical) parts of Australia. Therefore, the climate of the most extended part of the continent from west to east is surprisingly dry and continental.
Mainland Australia is located in three climatic zones: subequatorial, tropical and subtropical.
In the subequatorial belt is the northern edge of the mainland up to about 20 ° S latitude. The northwestern equatorial monsoons penetrate to these latitudes in the summer of the southern hemisphere (December-February).
In the tropical zone (between 20 ° and 30 ° S) in Australia, two types of climate are formed: tropical humid - in the east and tropical dry - in the west. The region of humid tropical climate occupies the eastern coast of the mainland. Southeast trade winds blow here all year round. They pass over the warm East Australian Current, are saturated with moisture and bring abundant rainfall to the eastern slopes of the Great Dividing Range (1000-1500 mm per year). The area of dry tropical climate covers the western and central regions of the belt. Dry tropical air masses dominate here all year round. In summer, air temperatures in the deserts of Western Australia rise above + 30 ° С, in winter they stay within +10 ... + 15 ° С. Precipitation is only about 100-300 mm, they fall irregularly, sporadically.
In the subtropical zone (south of 30 ° S), there are three types of climate: subtropical humid - in the southeast, subtropical continental - north of the coast of the Great Australian Bay, subtropical Mediterranean - in the southwest of the belt. These types of climate differ mainly in the annual amount of precipitation and their regime. So, in the area of a subtropical humid climate, precipitation falls throughout the year (1000-2000 mm and more); January temperatures are about + 22 ° С, in July - + 6 ° С. The subtropical continental climate is characterized by low precipitation (300-400 mm per year) and rather sharp annual and daily temperature fluctuations. The subtropical Mediterranean climate in Australia is characterized by dry and hot summers, cool and rainy winters, with an annual rainfall of 500-600 mm.
The island of Tasmania, in addition to the northern part, lies already in the temperate zone of the southern hemisphere. There the westerly winds prevail all year round, bringing a lot of precipitation. Therefore, the climate in Tasmania is humid, with cool summers and relatively warm winters.
Inland waters... Australia is poor in surface waters, which is associated with the dominance of a dry tropical and subtropical climate on the mainland, the absence of high mountains with snow and glaciers. Australia has few rivers and lakes about 60% of the mainland has no flow into the ocean... No other continent has such a relatively large area of internal flow.
For the main part of the continent, especially for its inland desert and semi-desert regions, temporary drains are characteristic - screams... Water appears in them only after rare rains and for a short time. The rest of the mainland rivers belong to the basins of the Indian and Pacific Oceans. The rivers of the Indian Ocean basin are short, shallow, and often dry up during the dry season. The Pacific Ocean basin includes rivers flowing from the eastern slopes of the Great Dividing Range. These rivers are full-flowing throughout the year, as there is a lot of rainfall; short and rapids. Most of the rivers of the mainland are fed mainly by rain, and in the Australian Alps, they are mixed.
Australia's most significant river system is the Murray River with its tributary Darling... Murray (length - 2570 km) originates in the Australian Alps, feeds not only on rain, but also partly on snow. In summer, the river is full-flowing, during the rainy season it often overflows its banks, in winter it grows shallow. The main tributary of the Murray is the Darling, Australia's longest river (2,740 km). But this river is shallow. The water level varies greatly depending on the seasons of the year (up to 8 m above low water). During the dry season, Darling does not always bring its waters to Murray and breaks up into separate bodies of water.
There are about 800 lakes in Australia. Most of them relic lakes, the basins of which were formed in more humid geological epochs. Many of the modern lakes of Australia (Torrance, From, Amadies, etc.) are dry basins filled with loose clayey-saline silt, covered with a crust of salt or gypsum. They fill with water only after rare rainstorms that fall in Western Australia once over several years.
The largest lake in Australia - the closed-drain salt lake Eyre... It lies in a depression 12 m below sea level. In the dry season, Lake Eyre splits into many separate bodies of water, and during the period of heavy rains it turns into an immense body of water with an area of about 15 thousand km 2.
Against the background of a sparse hydrographic network and an almost complete absence of freshwater lakes, it strikes Australia's amazing wealth of groundwater... The area of all artesian basins occupies 1/3 of the mainland. More than 15 artesian basins are confined to the basement syneclises of the platform between the plateaus of Western Australia and the Great Dividing Range. The depth of the groundwater is from 100 to 2100 m. Sometimes (for example, in the area of Lake Eyre), groundwater comes to the surface under natural pressure in the form of mineral springs. The largest underground water storage facility in Australia - Great Artesian Basin in the Central Lowland - covers an area of 1,736 thousand km 2.
Natural areas. Australia differs from other continents of the globe in antiquity and unique originality of flora and fauna... They were formed under conditions of long-term isolation of the continent (since the Cretaceous). Among the plants, endemics make up 75% of the species. The most characteristic representatives of the flora of Australia are eucalyptus (more than 600 species), acacia (490 species) and casuarina (25 species). Among the eucalyptus trees, there are giants reaching 150 m in height, as well as shrub forms. Araucaria, Proteanaceae, southern beeches, tree ferns, palms and a number of other plants indicate the presence in the past of land connections with other continents (South America, Africa, Southeast Asia).
The fauna of Australia is exceptionally unique... The fauna of the mainland has a pronounced relict character. Endemics make up 90% of the total animals in Australia. Only here the most primitive mammals (platypus and echidna) survived. The greatest variety of species was given by marsupials: giant kangaroos (up to 3 m high) and dwarf (up to 30 cm in size); koala - marsupial bear, wombats - remind our hamsters; marsupial predators and rodents, insectivorous and herbivorous marsupials. Birds are also peculiar in Australia: parrots, emu, black swans, cassowaries, weed chickens, lyrebirds and brightly colored birds of paradise. Crocodiles and turtles are found in the waters of Northern Australia. In dry savannas and deserts, there are many lizards, poisonous snakes; mosquitoes and other insects. The local fauna of Australia, which had been developing in isolation for a long time, turned out to be easily injured and could not compete with the settlers who came with humans. The dingo dog ran wild and became a dangerous predator. Rabbits, foxes, rats, sparrows, starlings brought here from England multiplied rapidly. Many Australian animal species have become extremely rare or completely disappeared, like the marsupial wolf of Tasmania. Currently, 27 species of animals and 18 species of birds are under the threat of extinction. Australia is well aware of the uniqueness and significant vulnerability of local nature. This is probably why the Australian Union now has more than 1000 protected areas (national parks, reserves, state parks), which occupy more than 3% of the country's territory.
In Australia, as in Africa, the natural zoning of the landscape is well expressed. v. This is facilitated by the flat relief of the continent and the absence of well-defined orographic boundaries on it. Natural zones are gradually changing when moving from north to south as temperatures, regime and amount of precipitation change.
Australia ranks first among the continents in terms of the relative area of deserts and semi-deserts and the last in terms of forest area.... However, only 2% of Australia's forests are of industrial importance.
The central and western regions of Australia within the tropical belt are occupied by deserts and semi-deserts with sparse vegetation of hard grasses and shrubby forms of eucalyptus and acacias (scrub)... In deserts, special primitive soils are formed, often colored red.
Equatorial, subequatorial and tropical rainforests are represented in small areas in the far north of the mainland and along the eastern windward slopes of the Great Dividing Range. In these forests, palms, ficuses, laurels, tree ferns intertwined with lianas grow predominantly on red ferralite soils; the forests of the eastern part are dominated by eucalyptus trees.
The subequatorial climatic zone corresponds mainly to savannas and woodlands (from eucalyptus, acacias and casuarinas). Red-brown and red-brown soils are formed under the canopy of light eucalyptus forests and in savannas.
Within the subtropical zone in the southeast and southwest of the mainland, special natural complexes are formed. In humid subtropical forests in the southeast of the continent, eucalyptus forests grow on red and yellow soils, and evergreen southern beeches grow in the southern part of this zone. In the southwest of the mainland there is a zone of hard-leaved evergreen forests and shrubs of typical Australian species on brown soils.
All areas convenient for farming in Australia's natural zones are occupied by fields and plantations of crops imported from Europe and other parts of the world. Along with cereals, vines, cotton, corn, rice, many vegetables and fruit trees are well acclimatized here.
Population and political map... Australia is home to about 16 million people. The modern population of the mainland consists of two groups - Aboriginal Australians and Anglo-Australians, immigrants from Europe, speaking English.
Aborigines came to Australia about 40 thousand years ago from Southeast Asia. They have dark brown skin color, wavy black hair. Scientists attribute the Aboriginal Australians to the Australian branch of the equatorial race. Before the arrival of Europeans, the indigenous inhabitants of the mainland led a nomadic lifestyle, were engaged in hunting and gathering, did not engage in either agriculture or cattle breeding, i.e. were at the level of the Stone Age. By the way, the aborigines of Australia invented a unique military and hunting weapon - boomerang, which, in the event of a miss, returns back to the hunter.
The colonization of the mainland by Europeans was accompanied by the ruthless extermination of the indigenous population. By the time of the arrival of the colonialists, there were about 300 thousand indigenous people. Now there are about 50 thousand of them left. The Tasmanians were completely destroyed. With the development of sheep breeding, Europeans pushed the indigenous people into arid regions in the northern, central and western parts of the mainland. For a long time, the aborigines lived on reservations and were disenfranchised. Now they mainly work as laborers and shepherds on livestock farms, and also live on the outskirts of large cities. Some of the natives continue to lead a semi-nomadic lifestyle.
The average population density in Australia is about 2 people. by 1 km 2. The distribution of the population on the territory of the mainland is determined by the history of its development by Europeans and natural conditions. The coastal areas in the east and southwest of the continent have population densities 10 times or more higher than the average population density. The interior regions of the mainland are almost deserted. The bulk of the population lives in cities. Moreover, 2/3 of the population is in large cities. There are over 6 million people in Sydney and Melbourne alone.
The Australian Union is the only state in the world that occupies the territory of the whole mainland., as well as the island of Tasmania and a number of other small islands. The Australian Union belongs to the group of developed capitalist countries. It is an economically highly developed state, the formation of the economy of which was facilitated by both historical and favorable natural factors.
Physico-geographical zoning... According to the peculiarities of natural conditions (differences in relief, climate, vegetation) on the mainland, three natural areas - North; Western and Central; Eastern Australia.
Northern australia occupies the subequatorial climatic zone. The southern border is drawn at 20 ° S latitude. This area is dominated by plateaus and lowlands; in the west and east, small areas are occupied by low mountains. It is hot here throughout the year, with a long rainy period. The region is crossed by many short rivers flowing mainly to the north. A significant part of the region's territory is occupied by a zone of savannas and woodlands on red and red-brown soils. Among the tall grasses are eucalyptus, acacias, casuarines and bottle trees. In Northern Australia, both savannah and forest animals are found. For savannas, ostrich emu, kangaroo, wombats are typical. In drier places, the echidna is found, the peculiar appearance of the area is given by the bizarre structures of termites. The forests are characterized by lyrebirds, parrots, and the koala marsupial. There are many crocodiles in the rivers. During the rains, large flocks of birds gather near the flooded reservoirs.
The vast expanses of Northern Australia are almost deserted, although the subsoil contains significant reserves of minerals, and the natural conditions are favorable for tropical agriculture. This area preserved, in the main, the pristine appearance of nature in Australia and is considered most often as an example of a brief description of one of the natural areas of the mainland.
Western and Central Australia- an area of predominant distribution of tropical deserts and semi-deserts. Only small areas in the south-west are occupied by subtropical forests, consisting mainly of eucalyptus trees. There is almost no vegetation on the stony placers of the Western Australian highlands and on the mobile sandy ridges of the Central Lowland. In contrast to Africa, there are no oases in the deserts of Australia. One of the driest and most barren places in the region and throughout Australia is the vicinity of the lake. Eyre (got the figurative name "the dead heart of Australia").
Eastern australia includes the Great Dividing Range, the Australian Alps and the east coast of the mainland. The main part of the region is influenced by the southeastern trade winds, which bring 1000-2000 mm of precipitation from the ocean per year. Eastern Australia is the most wooded area on the mainland. However, it is densely populated, so its nature has been greatly changed by man. A significant part of the land is plowed up, especially in the southeastern part of Eastern Australia, the most favorable climatic conditions for the life of the population and for farming and cattle breeding.
Oceania
Oceania is the name for islands and archipelagos of islands lying in the central and southwestern Pacific Ocean to the north and northeast of Australia between 28 ° N latitude. and 53 ° S; 130 ° East and 105 ° W. This island world includes almost 7 thousand islands. The total area of the island land of Oceania is about 1.3 million km 2. This is only 2% of the Pacific Ocean area.
Geographical position, size and relief of the islands closely related to their origin. According to the genesis, the islands of Oceania belong to four main types: continental, volcanic, biogenic and geosynclinal, which arise in the contact zones of the lithospheric plate - island arcs.
Mainland islands- the most significant in terms of area (New Guinea, New Zealand). Mountain ranges on them are combined with vast low-lying plains and plateaus. Hawaiian Islands are a typical example of islands volcanic origin... Coral reefs and atolls have biogenic origin... Atolls are flat, low ring-shaped islands with a lagoon in the middle that communicates with the ocean. Such are, for example, the islands of Central Polynesia (the Tuamotu archipelago is the most grandiose cluster of atolls in the world). Geosynclinal island arcs lie in the western part of Oceania. The relief of this type of islands is a combination of mountains and plains. Such, for example, is the island of New Caledonia, stretched for more than 400 km.
Minerals Oceania is determined by the origin and geological structure of the islands. Thus, New Caledonia is characterized by rich deposits of nickel, chromite, and a number of other metals. Coal, bauxite and oil are mined in New Guinea. Phosphorite deposits have been discovered on the atoll islands.
Oceania islands climate determined by the geographical location of the territory and the softening influence of the ocean. The main archipelagos of the islands lie in the equatorial, subequatorial and tropical zones of the Northern and Southern Hemispheres. Only New Zealand and the surrounding islands are located in the subtropical and temperate zones. Average monthly temperatures of the warmest month range from + 25 ° C in the north to + 16 ° in the south; the coldest - from + 16 ° in the north to + 5 ° С in the south. The Marshall, Caroline and Mariana Islands, as well as New Guinea, lie in a strip where the temperature is around + 26 ° C all year round. The softening influence of the ocean affects the slight fluctuations in temperature over the seasons of the year and during the day. There is a lot of precipitation in Oceania, on average 3000-4000 mm. They are especially abundant in the western part of Oceania, where mountains of mainland islands stand in the way of trade winds from the ocean. However, one of the wettest places on Earth is in the Hawaiian Islands, where upwind slopes of volcanoes receive up to 12,500 mm of precipitation per year.
Species composition flora and fauna poor and peculiar due to the remoteness and isolation of the islands of Oceania from the rest of the land. The large islands of Oceania are covered mainly by evergreen moist forests (on the windward slopes) or savannas. Here, among the trees, ficuses, pandanuses, bamboos, casuarins prevail. There are many valuable tree species and plants useful for humans: coconut and sago palms, bread and melon trees, rubber plants, bananas and mangoes. There are many endemic species in the forests of New Zealand: special types of tree ferns, pines (cowrie pine is one of the world's giant trees), cabbage tree, New Zealand flax, etc.
The fauna is also peculiar. It is richer and more diverse on the islands closer to Australia. So, in New Guinea, echidna and tree kangaroo are common, crocodiles are found in rivers. In New Zealand, there is not a flying, but a running kiwi bird. Among the land animals on the islands of Oceania, there are almost no mammals, there have never been predators, there are no poisonous snakes. The coastal waters and lagoons of the islands are unusually rich in various forms of life.
Europeans brought livestock (cows, pigs, horses) to Oceania, as well as a number of cosmopolitan animals from other parts of the world. Rats have bred on the islands, cats have run wild; goats and rabbits have destroyed much of the vegetation on many islands, which has led to soil cover being washed away. Irrational use of land, deforestation, pollution of coastal waters, the transformation of some islands into military test sites for nuclear weapons upset the natural balance on the islands of Oceania.
Population Oceania , constituting about 10 million people, represented by indigenous people, settlers and a mixed population. In New Guinea and adjacent islands live Papuans belonging to the equatorial race. The indigenous population of New Zealand ( Maori) and other islands of Oceania belongs to a special Polynesian group of peoples occupying an intermediate position between the three main races of mankind. These peoples have lighter skin and wavy hair than the Papuans. It is still not entirely clear where and in what ways the Polynesians settled the main archipelagos of the islands of Oceania many millennia ago. The migrant population is immigrants from Europe, Asia and America. So, Anglo-New Zealanders make up 3/4 of the population of this country, and the indigenous people - Maori - only 9%. However, on other islands in Oceania, Aboriginal people (as opposed to Australia) make up the majority of the population.
The inhabitants of Oceania are traditionally engaged in agriculture and fishing. In New Zealand, immigrants from Europe raise sheep and cattle; meat, wool and butter are the main export products.
Political Map Oceania was formed as a result of the capture of the islands by European and American colonialists in the 19th and 20th centuries. Three decades ago, there was only one independent state in Oceania - New Zealand. Now there are more than ten politically independent countries: Fiji, Western Samoa, the Kingdom of Tonga and others. The Hawaiian Islands are part of the United States as a separate state. But many of the islands of Oceania are still colonies.
Zoning Oceania To a certain extent, conventionally and historically, it is carried out taking into account not only the peculiarities of natural conditions, but also the ethnographic characteristics of the indigenous population. Usually Oceania is divided into Melanesia, Polynesia, Micronesia and New Zealand.
Melanesia(from the Greek melas - black and nesos - island) includes archipelagos from New Guinea in the west to the Fiji Islands in the east, i.e. a territory with a predominantly Papuan population. Polynesia(“Many islands”) includes islands in the central and southern Pacific Ocean east of 177 ° E. The largest archipelago of Polynesia is Hawaiian Islands consisting of 24 islands. Micronesia consists of many (more than 1500!) small islands in the western part of the Pacific Ocean north of the equator (Mariana, Marshalov, Caroline Islands, etc.). In a special area of Oceania stands out New Zealand... And not only in terms of natural and ethnographic conditions, but also taking into account the level of economic development throughout Oceania.
Antarctica
Geographical location, size of the territory and nature of the coastline... Geographers distinguish between the concepts of "Antarctica" and "Antarctica". The name "Antarctica" comes from the Greek words "anti" - against, "arktikos" - northern, ie lying against the northern polar region of the Earth - the Arctic. Antarctica includes the mainland Antarctica with adjacent islands and the southern polar waters of the Atlantic, Indian and Pacific oceans to the zone of the so-called Antarctic convergence, where cold Antarctic waters converge with relatively warm waters of temperate latitudes. This zone occupies an intermediate position between the northern boundary of the appearance of icebergs and the edge of sea ice during the period of their maximum spread. On average, it lies about 53 ° 05 "S.
Antarctic area within the specified limits, including the mainland Antarctica, is approximately 52.5 million km 2.
Antarctica- the mainland, almost entirely located inside the Antarctic Circle. His area of about 14 million km 2, which is about twice the area of Australia. The geometrical center of the continent, called the Pole of Relative Inaccessibility, is located at 84 ° S, in relatively close proximity to the South Pole.
Coastline, the length of which is more than 30 thousand km, it is poorly indented. The mainland shores almost along their entire length are glacial cliffs up to several tens of meters high. From the side of the Pacific and Atlantic oceans, the marginal seas of Weddell, Bellingshausen, Amundsen, Ross protrude into the coast of the mainland. Large areas of the marginal seas are covered ice shelves, which are an extension of the continental ice shell. A narrow Antarctic Peninsula protrudes towards South America, protruding a few degrees north of the Antarctic Circle.
Brief information from the history of discovery and research... The hypothesis of the existence of Antarctica is associated with the name of the ancient Greek geographer and astronomer K. Ptolemy who lived in the 1st-2nd centuries. ad. Then the assumption was born that the ratio of land and sea areas in the Northern and Southern Hemispheres should be approximately the same. For many centuries, this hypothesis has not been confirmed.
Glaciers Are mobile ice accumulations of atmospheric origin on the land surface (Glaciers, along with underground ice, are part of cryospheres- spheres of ice and cold. The term "cryo-sphere" was proposed by the Polish scientist A. Dobrovolsky in the 1920s. XX century The selection of the cryosphere as an independent integral natural shell of the Earth in recent decades has found more and more recognition among scientists.). Currently, glaciers cover an area of 16.3 million km 2, which is almost 11% of the land. The total volume of the Earth's ice sheet is estimated at 30 million km 3, which is equivalent to 27 million km 3 of water. Most of the ice is concentrated in Antarctica (about 90%) and Greenland (almost 10%), while the remaining glacial regions account for less than 1%. Every year 1.8% of the entire ice sheet appears and disappears on Earth. The change in its volume plays an important role in the fluctuation of global water exchange on the Earth's surface. The melting of all glaciers on Earth could lead to a rise in the current level of the World Ocean by 75 m. The distribution of glaciers across latitudes and continents can be seen from Tables 12 and 13.
Table 12
Distribution of glaciers in latitudes (according to V.M.Kotlyakov)
Table 13
The area and volume of modern continental glaciation(according to V.M.Kotlyakov)
Glaciers are formed in the polar regions and in the mountains, where the air temperature is negative all year round and the annual amount of snow exceeds its consumption for melting and evaporation,
i.e. ablation. The tropospheric layer, within which a constant positive balance of solid atmospheric precipitation is possible, i.e., the arrival of snow is greater than its consumption for melting, is called chionosphere(Greek. chion- snow and sphaira- ball). The Chionosphere surrounds the Earth in the form of a continuous irregularly shaped shell with a thickness of up to 10 km. It has upper and lower snow boundaries at which the solid precipitation balance is zero. The upper boundary of the chionosphere passes near the tropopause. The zero balance of solid precipitation on it is due to the negligible humidity of the air and, therefore, a very small amount of snow, which evaporates even at low air temperatures prevailing there. The upper snow border cannot be seen, since not a single mountain on Earth reaches this level. The mountain peaks above this line would be snowless.
The lower boundary of the chionosphere, also with a zero balance of solid precipitation, is imprinted on the earth's surface in the form of a strip, which is usually called climatic snow boundary. Its height depends primarily on the distribution of heat on the Earth: in the polar regions, it is at sea level, to low equatorial-tropical latitudes it rises into the mountains up to 5-6 km (Fig. 101). The amount of precipitation also affects the height of the snow line. Therefore, it rises above all not above the equator, but in tropical latitudes - 5.5–6 km, which is associated not only with high temperatures, but also with dry air and low precipitation. At the equator, where there is more precipitation, the snow boundary lies at an altitude of 4.5 km.
The real height of the snow boundary is also influenced by the insolation exposure of the slopes. On the slopes of the solar exposure, it is 300 - 500 m higher than on the shady slopes of the same ridge. It is also important to take into account the wind exposure: the windward slopes receive more precipitation than the leeward slopes, therefore the snow boundary lies lower on them. Moreover, if the mountains are high, then on their leeward slopes the phene effect is of a certain importance: the air there is both warmer and drier. Within individual mountainous countries, the snow line rises from the outskirts to the inner parts due to an increase in air dryness and a decrease in precipitation.
In a specific area, in addition to climate, the configuration of the snow boundary is influenced by the orographic features of the slopes.
In negative landforms, snow may persist slightly below the climatic snow boundary, and on steep slopes it may not exist even above this boundary. Therefore, the actual snow boundary in mountains is a function of climate and relief and, in essence, is oroclimatic boundary.
Rice. 101. Height of the snow line at different latitudes; section along the South American and North American Cordilleras (according to V.VV. Kotlyakov)
Within the chionosphere, as a result of compaction and recrystallization, snow first turns into firn- granular porous opaque ice, and then into dense transparent bluish glacial ice. The mass of 1 m 3 of freshly fallen snow is 60–80 kg, mature firn - 500–600 kg, glacier ice - 800–900 kg. The density of ice is about 0.9 g / cm 3. It takes decades to turn snow into ice, and millennia in the harsh climate of Antarctica.
Of the properties of ice, the most important is its fluidity, which increases upon reaching a temperature close to the melting point (–1–2 ° С) and high pressure. The second property of ice associated with the first is its traffic. In the mountains, it occurs along the slope of the bed under the influence of gravity, on the plains - in accordance with the slope of the glacier surface. Since the under-ice bed is uneven, cracks-ruptures hundreds of meters long and 20–30 m deep appear in the glacier, and different parts of the glacier - bottom, middle, surface, lateral - move at different speeds depending on the friction force. The speed of movement of glaciers is several centimeters per day, sometimes it can reach meters per day. Ice moves faster in summer and daytime, slower in winter and at night. The third property of ice is the ability of its pieces to freezing (rejection), leading to the disappearance of cracks.
Glaciers can "advance" and "retreat" due to climate change and fluctuations. In the geological past, such fluctuations on a huge scale led to the alternation of glacial and interglacial eras. Paleogeographic reconstructions of the last glacial stage indicate that continental ice sheets occupied 30% of the world's area, including the temperate latitudes of Eurasia and North America, while the Antarctic and Greenland ice sheets significantly increased their thickness and size (Fig. 102). Currently, due to climate warming, there is a slow retreat of glaciers. Glaciers are sensitive indicators of climate change. They, like giant refrigerators, reliably store meteorological information.
According to the appearance and nature of movement, glaciers are divided into two main types - continental (integumentary) and mountain. The former occupy about 98% of the area of modern glaciation, the latter - about 1.5%.
Cover glaciers- these are, first of all, the huge ice sheets of Antarctica (area 13.979 million km 2, average thickness of the ice sheet 1720 m, maximum - 4300 m) (Fig. 103) and Greenland (respectively 1.8 million km 2, 2300 m, 3400 m).
The glaciation of Antarctica, according to modern data, began to take shape 25 million years ago, and 7 million years ago, the glacier area was maximum, 1.8 times more than the modern one. The Greenland ice sheet already existed about 10 million years ago. The cover glaciers have a flat-convex shape that does not depend on the subglacial relief. The accumulation of snow occurs in the center, due to snow and sublimation of water vapor on the surface of the glacier, consumption - on the outskirts. The movement (flow) of ice is "radial" - from the central part to the periphery, regardless of the under-ice bed, where mainly mechanical unloading takes place by breaking off the ends of the afloat glaciers. On the surface of glaciers, ice is consumed by ablation.
It was found that the Greenland glacier is frozen to the base (except for the southern tip) and its lower layers are frozen to the surface of the rocky bed, where the temperature is –10… –13 ° С.
In Antarctica, the relationship between ice sheet and rocks is more complex. It has been established that in its central part under ice 3 - 4 km thick there are subglacial lakes. According to V.M.Kotlyakov, their nature can be twofold: either they are associated with the melting of ice due to intraterrestrial heat, or they were formed due to the frictional heat arising during the movement of the glacier. The central part of the glacier is surrounded by a closed belt, where the rocks are frozen to a depth of 500 m. Along the periphery of the Antarctic ice sheet, there is an annular zone, which is characterized by the melting of ice at the base due to the heat of the movement of the glacier.
102. Antarctic ice sheet during the last ice maximum 17-21 thousand years ago (according to RK Klige and others) The ice thickness is shown within the continent, and around it - the area of distribution of ice shelves and sea ice
Mountain glaciers have incommensurably smaller sizes, a very diverse shape, depending on the shape of their containers. The movement of mountain glaciers is determined by the slope of the bed and is linear, the speed of movement is higher than that of the ice sheets. Mountain glaciers are divided into three groups: glaciers peaks(flat and conical tops), slope glaciers(inclined, curved and hanging) and valley glaciers(simple valley glacier - Alpine type and complex valley glacier - Himalayan type). Mountain glaciers have a well-defined recharge area (firn basin), transit area and melting area. It feeds on snow, partly due to sublimation of water vapor, avalanches and snowstorm transport. In the melting area, glacial tongues descend into the zone of alpine meadows and forests, where the ice not only melts intensively, but also "evaporates", and also breaks off into the abyss. The world's largest valley glacier is considered to be the Lambert Glacier in East Antarctica, 450 km long and 30–120 km wide. It originates in the northern part of the International Geophysical Year Valley and flows into the Aymery Ice Shelf. The longest glaciers in the mountains are in Alaska: the Bering Glacier (203 km) - in the Chugach Ridge and the Hubbard Glacier (112 km) - in the St. Elijah Mountains.
An intermediate position between mountain and cover glaciers is mountain-cover glaciers: glaciers of the foothills (foothills) and glaciers of the plateau, which were identified by V.M.Kotlyakov as a special type. Foothill glaciers are formed from several streams with different feeding areas, which merge at the foothills of the mountains on the foothill plains into a single "glacial delta". Such, for example, is the Malyaspin Glacier (area 2200 km2) on the southern coast of Alaska. They are characteristic of subpolar and polar mountainous countries with heavy snowfalls and a low-lying snow border (700–800 m).
Glaciers of the plateau otherwise, "mesh glaciation" occurs due to the fact that glaciers, due to abundant supply, overwhelm intermountain valleys, flow over the lower parts of the ridges and merge with each other. As a result, a continuous field of ice is formed with chains of "islands" in place of ridges. Isolated rocky peaks protruding above the surface of the glacier are called nunatakami(for example, on the Svalbard archipelago). Nunataks are also very typical for the marginal parts of the ice sheets of Antarctica and Greenland.
Rice. 103. Antarctic ice sheet (according to V. Ye. Khain)
Glaciers, as a consequence of climatic conditions, themselves have a huge impact on the Earth's climate, especially the ice sheets of Antarctica and Greenland. The huge icy continent of Antarctica, where the baric maximum is maintained all year round, from which freezing winds blow to temperate latitudes, is one of the main reasons that the southern hemisphere of the Earth is colder than the northern one. Thanks to the Greenland Ice Sheet and the East Greenland Cold Current, the Icelandic baric minimum exists all year round, while its analogue, the Aleutian minimum, located far from the ice sheets, is pronounced only in winter. Iceland's glaciation is also explained by the influence of the Greenland Ice Sheet through the circulation of the atmosphere and water (East Greenland Cold Current).
The high albedo of snow-glacial surfaces (80 - 90%) in low cloud weather conditions a negative annual radiation balance on the ice plateaus, which is reflected in the radiation balance of the globe. In the summer season, such a large amount of heat is consumed for melting snow and ice and for evaporation that the air temperature remains below zero in the polar regions. Therefore, in general, ice sheets significantly affect the energy of the atmosphere.
A large amount of fresh water is conserved in the glaciers. According to calculations, the total glacial runoff entering the World Ocean is about 3850 km 3 per year, which is equivalent to half of the entire modern world drainage area. It is formed mainly as a result of icebergs breaking off (76%), surface melting of glaciers (12.6%) and their bottom melting (11.4%). According to RK Klige, every year as a result of glacial runoff, about 2.8 thousand km 3 of water flows into the ocean from the Antarctic continent, about 0.7 km 3 from Greenland, and about 0.4 km 3 from the Arctic islands. Mountain glaciers consume water to feed rivers. For the arid regions of the world, glacial feeding of rivers is of great economic importance. In recent years, the idea of transporting Antarctica icebergs with the help of powerful sea tugs to the regions of "thirst" - Arabia, Africa, Australia, California, has arisen. all the way, and especially in the places of delivery.
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Modern glaciers cover an area of over 16 million square kilometers, which is 11% of the total land area of the planet. They contain about two-thirds of the world's fresh water reserves. Glaciers contain over 25 million cubic meters of ice. The force of gravity shapes them, giving the appearance of streams, domes or slabs.
The conditions for the formation of glaciers - low temperatures and a large amount of solid atmospheric precipitation - develop in high latitudes and in the summit parts of the mountains. Glaciers are formed as a result of long-term accumulation of snow, its settling, compaction and transformation first into firn (granular opaque ice), and then into glacier ice (dense, transparent, bluish). Moreover, these magical changes occur both at low temperatures - through recrystallization, pressure of the upper layers and a decrease in porosity, and at zero temperature - due to melting and re-freezing of melt water in the snow column.
Three zones are conventionally distinguished in the structure of the glacier. In the upper part there is a recharge (accumulation) area, where ice masses accumulate. In the lower part - the area of discharge (ablation), where melting, evaporation and mechanical destruction of the glacier take place. The middle part is the feeding boundary, where a certain equilibrium of the ice mass is observed. Excess ice moves from the accumulation zone to the melting zone and makes up for the losses.
Pulsating glaciers
In the case of the predominance of the glacier supply over the ice discharge, its edge moves forward, the glacier advances. In the opposite scenario, it retreats. If a long equilibrium period sets in, the edge of the glacier takes a stationary position. However, it was recently discovered that, in addition to the described processes associated with the balance of ice reserves, some glaciers experience rapid movements under the influence of some kind of internal processes - possibly a change in the state of the bed or redistribution of ice within the massif, not related to a change in its total mass. Such glaciers were called pulsating. They are extremely dangerous due to their unpredictability and volatility. No weather and atmospheric processes that would provoke this phenomenon have not been recorded. So in 2002, the pulsating Kolka glacier (pictured) became the culprit for the disaster that claimed human lives, when huge masses of ice and soil slid into the Karmadon Basin, filling it completely.
Glaciers are mobile formations. Ice creeps at a speed of several meters to 200 kilometers per year. In the mountains, the glacier moves at a speed of 100 - 300 meters per year, polar glaciers (Greenland, Antarctica) - 10 - 130 meters per year.
How do cover glaciers differ from mountain ones?
Driving faster in summer and daytime. Chunks of ice are capable of freezing, overgrowing cracks.
On land, glaciers are continental and mountainous, afloat and at the bottom of the sea - shelf ones.
Ice sheets
Antarctica is an example of a continental glacier. Its thickness is 4 kilometers with an average thickness of 1.5 kilometers. Continental (cover) glaciers make up 98.5% of the entire area of modern glaciation. They are shaped like domes or shields, which has led to the name ice sheets. Ice in such formations moves from the center to the periphery. On the edges of the glacier there are so-called “calving zones” where icebergs break away from it. Winds and currents sweep away huge chunks of ice that are stranded or plummeted into the ocean, sometimes causing tsunamis.
Separate branches are distinguished within a single cover, with the direction of movement to the outskirts. The largest of these is the Bidmore Glacier, which flows down from the Victoria Mountains and is 180 kilometers long and up to 20 kilometers wide. At the edges of the Antarctic ice sheet are glaciers, the ends of which are floating in the sea. Such glaciers are called offshore... The largest of these on this continent is the Ross Glacier.
Mountain glaciers
Mountain glaciers can be located at any latitude, for example, the glacier at the top of Kilimanjaro, the highest mountain in Africa. It is located at an altitude of over 4.5 thousand meters. Glaciers of this type are smaller but more diverse. They are located on the tops of mountains, occupy valleys and depressions on the slopes of the mountains. The largest mountain glaciers are located in Alaska, the Himalayas (pictured), the Hindu Kush, the Pamirs and the Tien Shan. Mountain glaciers are divided into glaciers of peaks, slopes and valleys. Between mountain and cover (continental) land glaciers, mountain-cover glaciers occupy an intermediate position. Some of them are formed at the confluence at the foot of the expanding branches of mountain glaciers, others - when a mountain glacier flows over the pass, forming a continuous stream.
There are large reserves of fresh water in mountain glaciers. They are often the source of mountain rivers. For areas of mountain glaciers, avalanches are characteristic. They unload ice areas. Avalanches are avalanches of snow sliding off mountain slopes. In this respect, any slopes with steepness exceeding 15 degrees are dangerous. The reasons for the descent can be different - a loose layer lying on already compacted snow, an increase in temperature in the lower layer as a result of pressure, thaw. The most frequent avalanches are in the Alps, Cordilleras, in the Caucasus.
For all the severity of natural conditions, glaciers are the keepers of not only cold and water, but also life. On them (just imagine!) Live the simplest algae (snow Chlamydomonas) and cyanobacteria (blue-green algae). They were first described by the Russian botanist Ivan Vladimirovich Palibin (1872 - 1949) back in 1903 on Franz Josef Land. Tiny settlers living and breeding in ice actively use sunlight in the process of photosynthesis. It is cyanobacteria that rise above all into the glacier zone. The universality of each organism, which is inherent in blue-green, allows them not to depend on the external environment. Deterioration of living conditions serves as a stimulus for their development. At one time, they created the conditions for the life of higher organisms on the planet, but at the same time they did not give way, retained their significance as the last inviolable reserve of Life, as its extreme protective border.
Distinctive features of cover and mountain glaciers
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| Cover glaciers | Mountain glaciers |
| They cover the earth's surface, regardless of the relief forms, in the form of ice caps and shields, under which all the relief irregularities are hidden. Occupy 98% of the entire area of glaciation on Earth. The movement of ice occurs from the center of the dome to the outskirts (from the center to the periphery). Ice has tremendous power. Examples: ice of Antarctica, Greenland. The feeding area is the accumulation of ice that did not have time to melt. | Mountain peaks occupy mountain peaks, various depressions on their slopes and valleys. Significantly smaller integumentary in size, characterized by great diversity. The movement of ice occurs along the slope of the valley (due to the slope of the underlying Surface). Example: Fedchenko glacier in the Pamirs, Himalayas.
Runoff (ablation) area - ice destruction due to melting, mechanical chipping. |
The thickness of the Antarctic ice reaches 4 km. If these ice suddenly melted, the level of the World Ocean would rise by 70 m!
The glacier has the area of nutrition and runoff ... The movement of the glacier occurs as a result of deformations caused by gravity.
Glaciers protect the Earth from overheating and are the largest reserves of fresh water.
Using glaciers to obtain fresh water is a difficult scientific and technical problem. Transporting icebergs to the shores of drylands is one of the possible ways to use the reserves of glacial fresh water. Another way is to artificially create conditions that will cause rapid melting of ice on Earth. But the rise of water in the world's oceans will destroy coastal cities and vast fertile lowlands; it is difficult to predict how the Earth's climate will change. Even minor changes in the Earth's climate - a decrease in air temperature, for example, by several degrees - can cause the onset of glaciers.
In the geological past, there are three glaciations of the Quaternary : Oka, Dnieper and Valdai... Glaciers covered the entire north and northwest of the European part of our country and a significant part of Siberia. The glaciation center was located on Scandinavian mountains, from there the glacier moved in the south, south-west, south-east and north-west directions. The most extensive glaciation was Dnieper, at which the tongues of the glacier reached Kremenchug and the mouth of the river Bears... During the era of maximum glaciation, glaciers covered up to 30% of the land area.
Modern glaciation of the Earth- Antarctica with adjacent islands (the total area of glaciation is 12,230 thousand km2), the Arctic (2073 thousand km2), North America (75 thousand km2), South America (22 thousand km2), Asia (120 thousand km2), Europe (10 thousand km2), Africa (0.05 thousand km), New Zealand and New Guinea (1 thousand km2). The whole Earth is about 14,531.05 thousand km.
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Glaciers, continental and mountain glaciers. Height of the snow line at different latitudes
In polar countries at sea level, and in temperate and hot zones in high mountains, the hydrosphere is represented by snow and ice. The shell of the Earth, which contains perennial snow and ice, is called chionosphere ... It was first identified by MV Lomonosov under the name of the frosty atmosphere. The term "chionosphere" was introduced in 1939 by S. V. Kalesnik.
The chionosphere is formed as a result of the interaction of the three main shells of the Earth: a) the hydrosphere, which supplies moisture for the formation of snow and ice, b) the atmosphere, transporting this moisture and storing it in the solid phase, c) the lithosphere, on the surface of which the formation of a snow shell is possible. The Chionosphere is intermittent - it appears only where there are conditions for snow accumulation.
Snow line and its height at different latitudes. The frosty atmosphere is found at high altitudes in the hot zone, decreases in temperate latitudes and descends to sea level in polar countries. Its polar compression is 5 km greater than that of solid Earth. The lower limit of the chionosphere was named snow line.
Snow line is called the height at which the annual arrival of solid atmospheric precipitation is equal to their annual consumption, or as much snow falls in a year as it melts. Below this limit, during the year less snow falls than it can melt, and its accumulation is impossible. Above the snow boundary, due to the temperature drop, the accumulation of snow exceeds its melting. Eternal snows accumulate here.
From a distance in the mountains, the snow line appears to be a comparatively regular line. In fact, it is very meandering: on gentle slopes, the thickness of the snow is significant, on steep slopes it lies in spots in depressions, and completely drifts off the rocks.
The height of the snow boundary and the intensity of glaciation depend on the geographical latitude, local climate, orography of the area, and self-development of glaciers.
Latitudinal differences in the heights of the snow boundary depend on the air temperature and the amount of precipitation. The lower the temperature and the more precipitation, the more favorable the conditions for snow accumulation and glaciation, the lower the snow boundary.
In the height of the snow boundary, the dissymmetry of the Earth relative to the equator is also manifested: outside the tropical belt in the northern hemisphere, as in the warmer one, it lies higher, and in the southern, colder one, it lies lower. On Franz Josef Land at 86 ° C, its heights range from 50 to 300 m; in the Arctic, only in the northeast of Greenland by 82 0 С - the snow line decreases to sea level, in the south it reaches it in the belt between 60 and 70 0 S. NS. The South Shetland Islands are always covered with snow.
Continental and mountain glaciation. The type of glaciation depends on the nature of the contact of the earth's crust with a frosty atmosphere. It happens mainland and mountain... The first glaciation occurs when a frosty atmosphere touches the continental surface (Antarctica), or a large island (Greenland). The second occurs when mountains enter a frosty atmosphere. There is a transitional type between the two types, characteristic of the Arctic islands. They have glaciers of both mountain type and ice domes with features of continental glaciation.
The relief of the mountains determines the possibility of snow accumulation and the existence of glaciers. The power of glaciation of mountainous countries depends on how high they rise into the hoinosphere. This height is expressed by the difference between the level of the snow line and the level of the mountain peaks. In the Alps, it is about 1000-1300 m, in the Himalayas - 3200 m.
In order for snow to accumulate and glaciers to form, the slopes must have a favorable relief for this: a gentle dip, horizontal platforms, small hollows. On narrow mountain ranges and steep slopes, conditions for glaciation are unfavorable.
During mountain glaciation, snow and ice accumulate in depressions and do not go beyond them. In continental conditions, the thickness of glaciation exceeds the possibilities of the relief, ice not only overwhelms all depressions, but also covers positive forms. Only individual rocks protrude from under the ice, called nunatakami .
The accumulation of snow in the mountains should be accompanied by the opposite process - the unloading of snow areas. It occurs in two ways: a) the fall of snow avalanches and b) the transformation of snow into ice and its current.
Avalanches they call the avalanches of snow sliding off the mountain slopes and carrying new snow masses along the way.
The immediate causes of collapses can be: 1) looseness of snow in the first time after its fall, 2) an increase in temperature in the lower horizons of snow with a slope, 3) the formation of melt water during a thaw, wetting the slopes.
Avalanches are extremely destructive. The impact power in them reaches 100 t / m 2. They sometimes lead to big disasters.
In those forms of mountainous relief from which snow does not fall, or in those areas where the entire relief is buried under the ice, snow accumulates and turns into firn, and then into glacial ice.
Firn is called coarse-grained packed and compacted snow, consisting of interconnected ice grains. Its density ranges from 0.4 to 0.7 g / cm 3. The firm layer is layered: each layer corresponds to snowfall and is separated from the other by a compacted crust. In the lower strata, firn passes into glacial, or glacial, ice of granular structure.
Ice formed under the thickness of snow and firn, possessing plasticity, flows down the relief in the form of a glacial tongue, glacier, or glacier.
The structure and movement of glaciers. Every glacier has power area and drain area... In the feeding area, which lies in the chionosphere, snow accumulates, becomes compacted, passes into firn and ice. In the runoff area, the glacier descends below the snow line; here its melting, or ablation, takes place. Most of the glacial tongue is an open glacial surface, the smaller part is covered with fragments of rocks, buried under them.
The largest mountain glacier in the CIS - Fedchenko glacier in the Pamirs. Its length is 71-77 km, the total area is 600-690 km 2; ice thickness in the middle part is 700-1000 m.
The longest of the mountain - Hubbard Glacier in Alaska; its length is 145 km, width in some places reaches 16 km. There is also Bering glacier 80 km long.
The ice thickness of mountain glaciers is quite significant. In the largest glacier in the Alps - Bolshoy Aletsch, the length of which is 26.8 km, it reaches 790 m. The thickness of the Icelandic glacier Vatna-Yokul 1036 m. Usually the thickness of mountain glaciers is about 200-400 m. The mainland ice of Antarctica and Greenland is incomparably grander.
The glaciers of most mountainous countries flow at speeds from 20 to 80 cm / day or 100-300 m / year, and only in the Himalayan glaciers the speed reaches 2-3, and sometimes 7 m / day.
The movement of ice generates stresses in its body, which lead to the formation of cracks - transverse, longitudinal and lateral. The melting of glaciers under the influence of sunlight, rain and wind leads to the appearance of potholes and pits on the surface of the glacier.
Contemporary glaciation on the Earth's surface. The area covered with eternal ice makes up about 11% of the land surface. There is eternal snow and ice in all climatic zones, but in different quantities.
Hot Belt. In Africa, only the highest peaks rise to the chionosphere - Kenya, Kilimanjaro. Glaciers do not descend below 4500 m. Small glaciers are found in the mountains of New Guinea.
There is one crater glacier on the North Island of New Zealand; on the South Island, the glaciation is already quite extensive. There are no glaciers in Australia.
In the tropical Andes, there are ice caps only on peaks higher than 6000 m. Under the equator, the snow line descends to 4800 m. All the peaks lying above have snow and glaciers.
In Mexico, only Orizaba and Popocatepetl reach the chionosphere.
The Himalayas are an area of powerful glaciation. This is due to the enormous height of the mountain system and its location on the path of the sea monsoon. The snow line lies high - at 4500-5500 m. The area of glaciation is over 33000 km 2.
Temperate zone. Iceland, thanks to its oceanic subpolar climate and relief with volcanic cones, is favorable for glaciation. Glaciers cover 11% of its territory. Glacier domes predominate, there are outlet, mountain-peak and tar glaciers.
The Scandinavian mountains lie in the path of cyclones. The climate and relief are favorable for glaciation. The snow boundary lies at an altitude of 700-1900 m. The area of glaciation is 5000 km 2. Plateau ice caps predominate; valley glaciers (Scandinavian type) flow from them.
In the polar Urals, the low altitude of the mountains and the continental climate are not favorable for glaciation. The total area of glaciers is 25 km 2. Small tar glaciers prevail.
In the mountains of North-Eastern Siberia, there are 540 small glaciers with a total area of about 500 km 2. The largest glaciation area is located on the Suntar-Khayata ridge. There are small glaciers in the Byrranga mountains, in the Verkhoyansk and Chersky ridges.
What is the difference between cover glaciers and mountain glaciers?
In the Koryak Upland there are about 280 glaciers with a total area of 200 km 2; the snow boundary drops to 500 m.
Kamchatka is rich in precipitation, so its mountain ranges are heavily glaciated, the total area of which is over 800 km 2. The snow border runs at altitudes from 1000 to 3000 m.
Alaska is one of the most significant areas of modern glaciation. The reason is the humid cool climate and mountainous terrain. Depending on the amount of precipitation, the snow line rises from 300 to 2400 m. The total area of glaciers is 52000 km 2. Some reach the sea. The longest glacier on Earth is located here - Hubbard on Mount Logan, 145 km long.
The Alps are the most typical mountainous country with valley glaciers, the birthplace of glaciology. The snow boundary is located at an altitude of 2500-3300 m, the number of glaciers is about 1200, the area of glaciation is 3600 km 2. The centers of glaciation are the main peaks of the Alps.
The Caucasus is a country of powerful glaciation. There are 2,200 glaciers in the Greater Caucasus with a total area of 1,780 km 2. The height of the snow boundary is about 3000 m. Glaciers are summit, valley and tar. Glaciers centers - Elbrus, Kazbek and other peaks.
Tien Shan is a mountainous country with powerful glaciation, the area of which is over 10 thousand sq.
km 2. Glaciation nodes are Pobeda Peak, Khan-Tengri, Trans-Ili Alatau, Zeravshan Range and other peaks.
The area of glaciation is over 10 thousand km 2. More than 60% of the Pamir area lies above the snow line, which is located at an altitude of about 5000 m. Here is the longest in the CIS Chersky glacier.
In the Sayan Mountains, glaciation is weak, occupying only 40%.
On the Karakorum, the total area of glaciation is 17800 km 2. The snow boundary lies very high - 5000-6000 m. The largest glacier is 75 km long; it is the largest in Eurasia.
All high ridges in Tibet and on its outskirts - Kunlun, Trans-Himalayas, inner Tibet - carry eternal snow and ice. Their area is over 32,000 km 2. The snow border lies high, about 6000 m.
The southern part of Chile and Tierra del Fuego receive a lot of precipitation, have significant glaciation. The snow border runs at an altitude of 600-900 m. Many glaciers reach the sea.
In the Lesser Caucasus, there are glaciers on Ararat, Alagez and Zangezur ridge. Small glaciers also occur on some peaks of the mountains of Asia Minor and Iran.
Cold belts. This is the kingdom of eternal snow and ice, ice zones of the Earth. On the Arctic islands, the snow border lies above sea level. Therefore, their coasts are free of ice. Glaciation decreases towards the Bering Strait with decreasing precipitation.
In Greenland, ice occupies 1,700 thousand km 2, i.e. 83%. The island is covered with a huge ice sheet, consisting of two or three interlocking domes. Its length is 2400 km, thickness is 1500-3400 m. The highest point of the ice plateau is 3157 m. By outlet glaciers, ice flows into the sea and forms icebergs.
Svalbard is favorable for glaciation. Ice covers 90% of its territory. Shields and ice fields, glaciers of the Svalbard type prevail, there are shelf and outlet ones.
Franz Josef Land is 87% ice covered. Glaciation is mainly cover, continental type.
On Novaya Zemlya, valley glaciers appear near Matochkin ball. On Severnaya Zemlya, glaciation is cover, it occupies 45% of the archipelago area.
To the west of the North Atlantic Current and towards the eastern Arctic, the continentality of the climate is increasing and glaciation is weakening. The Canadian islands are 35-50% ice-covered.
In Antarctica, the border of the chionosphere goes down to sea level, so the whole of Antarctica is a continuous area of snow accumulation. Ice covers the entire mainland, adjacent islands and overflows into the sea in the form of shelf and floating glaciers. The average ice thickness is 1720 m. More than 90% of all ice on the planet's land is concentrated here. There are two centers of glaciation: one on the mainland East Antarctica, the other on the West.
Table 7 - Distribution of glaciation by parts of the world (according to S. V. Kalesnik)
Total: 15708251
Glacier types
There are two main types of glaciers: mountainous and continental ice sheets. They differ significantly in size, morphology, feeding and runoff conditions. The type of transitional glaciers is also distinguished.
Mountain glaciers. Among the glaciers of this type, the most fully formed are valley, or alpine glaciers.
They have a rather large feeding area, in which snow accumulates and turns into firn, and then into ice. This area is usually confined to the converging upper reaches of mountain rivers. Alpine glaciers have a well-defined drainage valley. The glacial tongue emerging from the feeding area spreads along the already developed erosional or tectonic-erosion gorge, which has a V-shaped transverse profile. As a result of the influence of the glacier, the valley acquires U-shaped outlines of the transverse profile, due to which it received the name trog(from it. Trog - trough). The bottom of the troughs is very uneven; along with depressions in places of occurrence of relatively soft rocks, there are protrusions of harder rocks that form steps.
Widespread tar glaciers, half-circus-shaped and worked out on steep slopes. (The karite-like, armchair-like depression cut into the upper part of the slopes of the mountains. The walls of the kara are steep, often sheer, the bottom is gently sloping, concave, occupied by the pan glacier.
What is the difference between mountain glaciers and ice sheets?
Circus is a concave relief form of various origins: 1) glacial circus - a depression in the mountains in the form of an amphitheater, closing the upper end of the glacial valley (trough) and containing firn and ice, which feed the valley glaciers; 2) landslide circus - a hollow in the form of an amphitheater, formed on steep slopes, at the base of which there are plastic rocks that cause the development landslides).
When the circus is overflowing with firn and ice, a glacial tongue is formed, emerging onto the slope along an erosional depression. Such a glacier is called hanging, since it does not reach the base of the slope.
Mountain glaciers are represented not only by tar, hanging and alpine ones. Large volcanoes form ice caps, covering the tops of volcanic cones, located above the snow line, from where the glacier in separate tongues descends along radially diverging erosion gorges. An example is the glaciers of Elbrus, Kazbek and Ararat in the Caucasus, the lower border of which is located at an altitude of about 4250 m.
Transitional glaciers. Sometimes valley glaciers go out onto the foothill plain, forming wide glacial fields.
Such glaciers are called foothill, they belong to the transitional type between mountain and cover types. They are available in Svalbard, Franz Josef Land, Novaya Zemlya, on the Pacific coast of Alaska.
The transitional type also includes plateau glaciers, covering the leveled surfaces of ancient mountains over an area of hundreds of square kilometers. On the outskirts of the plateaus, they slide into valleys in the form of tongues.
Covering glaciers. They got their name because they are not confined to certain landforms, but cover the entire surface of the large polar islands and even one continent - Antarctica. Glaciers of this type include ice caps, ice sheets and shields.
Ice caps are located on low elevations among flat relief. Their area is measured in thousands of square kilometers.
Ice sheets even more extensive. They cover all landforms, reflecting them on their surface.
Ice sheets have significant power and for this reason completely hide the subglacial relief.
A special group of ice sheets is formed by ice shelves, located partly on land, partly in the sea.
Separate blocks of covers, breaking off, turn into icebergs. Such glaciers are found mainly on the coasts of Antarctica and Greenland.
Olympics grade 11.
3. Indicate the landforms for which winter temperature inversions are characteristic:
a) mountain tops; b) flat plains;
c) intermontane basins; d) plateaus.
4. What mineral is called rock crystal?
a) aquamarine; b) diamond;
c) quartz; d) opal.
5. City of India called "Indian Hollywood":
a) Mumbai; b) Calcutta;
c) New Delhi; d) Chennai.
6. Which country is a monarchy:
a) Vietnam; b) Moldova;
c) Tonga; d) Finland.
7. Is it a continent that lacks modern glaciation?
a) Australia; b) Eurasia;
c) Africa; d) South America.
8. The only Hispanic country in Africa:
a) Cameroon; b) Angola;
c) Equatorial Guinea; d) Tunisia.
9. New Zealand is the world's leading producer of:
a) cotton; b) wood;
c) dairy products; d) sugar cane.
11. In which country the capital is not the largest city in terms of population:
a) Great Britain; b) Morocco;
c) Poland; d) Peru.
12. The youngest state in Oceania?
a) Palau; b) Tonga;
c) Fiji; d) Tuvalu.
13. The capital of this African state is named after one of the presidents of the United States.
Independence was obtained in the middle of the 19th century. The official language is English.
a) Nigeria; b) Ghana;
c) Liberia; d) Senegal.
14. Country of tobacco, rum, sugarcane and nickel?
a) Costa Rica; b) Guatemala;
c) Jamaica; d) Cuba.
15. Country of the world, which Russia is inferior in the production of fur skins:
a) Denmark; b) Canada;
To China; d) USA.
Exercise 1
Here is a brief description of unique natural objects included in the ratings of unique natural objects ("Miracles of Russia")
1. The water edge in the lake is 21 m below sea level, and its salinity is 370 ‰
2. The largest swamp in the world.
3. Officially the lowest recorded temperature is -67.7 ° C (in 1933).
4. The second largest bay in the world.
5. One of the largest gypsum and ice caves in the world.
6. Geological formations and the national natural park of the same name, on the banks of the river, which has the largest delta in Russia.
7. Two-headed peak, which is the highest point of the mountainous country and part of the world.
8. A World Natural Heritage Site, within which the Ukok Plateau and Lake Teletskoye are located.
9. An island located in two hemispheres.
Determine which objects are referred to in these descriptions. Place their names in the table next to the names of major natural areas. Find analogs of these objects from the list below and enter them into the table. In the last column, write the natural areas where these analogs are located.Ubsunur Basin, Shulgan-Tash, Belukha, Commander Islands, Ust-Shchugor, Western Caucasus, Curonian Spit, Manpupuner, Polesie.
Which of the "Miracles" listed in the table is experiencing the greatest anthropogenic load? Explain the answer.
