The concept of spreading, subduction and collision; their places of manifestation. Collision of lithospheric plates
Lithosphere can be called unique shell our planet. It consists of the earth's crust and the upper segment of the mantle. The structure of the lithosphere includes more or less stable areas - platforms, as well as unstable (seismically active areas).
According to the theory describing the drift of lithospheric plates, the earth's crust is not quite a solid "shell" covers the bowels of our planet. It consists of exorbitantly sized parts called lithospheric plates . They, like ice floes in the ocean, slowly move through the viscous mantle. This process leads to the appearance of joints and "chasms" between the plates. With different mutual types of impact of plates, a completely different kind of relief can arise.
Consequences These processes are the emergence of the deepest depressions (in places of movement in different directions) or mountain systems, such as mountain ranges (in places of "meeting"). The result of the collision of continental plates is the formation of folded mountains, with impacts of oceanic plates with the earth's crust - volcanoes and mountains. If there was a "meeting" of oceanic plates, then the result is subaqueous volcanoes and mountain ranges located in the depths of the oceans, which are better known as "mid-oceanic".
Now let's move on from the theoretical to the practical part.
Confirm In practice, this argument is possible if you just look at:
tectonic a map (if it is easier to explain - a map on which the relative position of the plates of the lithosphere is indicated);
physical(a map showing the location of the relief, water resources and others on a general scale);
topographic(More attention is paid to the state earth's surface than on the physical one).
After the inspection, you need to compare what you see. border areas at the edges of lithospheric plates are called seismic belts, within which often located volcanoes, often earth tremors happen. If we are talking about the deep-sea trench, the shaking of the earth's surface under a layer of water is fraught with such a devastating consequence as tsunami- a huge ocean wave. It is the consequences of subaqueous tremors or ejection of lava by volcanoes).
According to modern theories of lithospheric plates the entire lithosphere is divided into separate blocks by narrow and active zones - deep faults - moving in the plastic layer of the upper mantle relative to each other at a speed of 2-3 cm per year. These blocks are called lithospheric plates.
A feature of lithospheric plates is their rigidity and ability, in the absence of external influences, to maintain their shape and structure unchanged for a long time.
Lithospheric plates are mobile. Their movement along the surface of the asthenosphere occurs under the influence of convective currents in the mantle. Separate lithospheric plates can diverge, approach or slide relative to each other. In the first case, tension zones with cracks along the plate boundaries appear between the plates, in the second case, compression zones accompanied by thrusting of one plate onto another (thrust - obduction; underthrust - subduction), in the third case - shear zones - faults along which sliding of neighboring plates occurs. .
At the convergence of continental plates, they collide, forming mountain belts. This is how the Himalaya mountain system arose, for example, on the border of the Eurasian and Indo-Australian plates (Fig. 1).
Rice. 1. Collision of continental lithospheric plates
When the continental and oceanic plates interact, the plate with the oceanic crust moves under the plate with the continental crust (Fig. 2).
Rice. 2. Collision of continental and oceanic lithospheric plates
As a result of the collision of continental and oceanic lithospheric plates, deep-sea trenches and island arcs are formed.
The divergence of lithospheric plates and the formation of an oceanic type of earth's crust as a result of this is shown in Fig. 3.
The axial zones of mid-ocean ridges are characterized by rifts(from English. rift- crevice, crack, fault) - a large linear tectonic structure of the earth's crust with a length of hundreds, thousands, a width of tens, and sometimes hundreds of kilometers, formed mainly during horizontal stretching of the crust (Fig. 4). Very large rifts are called rift belts, zones or systems.
Since the lithospheric plate is a single plate, each of its faults is a source seismic activity and volcanism. These sources are concentrated within relatively narrow zones, along which mutual displacements and frictions of adjacent plates occur. These zones are called seismic belts. Reefs, mid-ocean ridges and deep-sea trenches are mobile areas of the Earth and are located at the boundaries of lithospheric plates. This indicates that the process of formation of the earth's crust in these zones is currently very intensive.
Rice. 3. Divergence of lithospheric plates in the zone among the nano-oceanic ridge
Rice. 4. Scheme of rift formation
Most of the faults of the lithospheric plates are at the bottom of the oceans, where the earth's crust is thinner, but they are also found on land. The largest fault on land is located in eastern Africa. It stretched for 4000 km. The width of this fault is 80-120 km.
At present, seven largest plates can be distinguished (Fig. 5). Of these, the largest in area is the Pacific, which consists entirely of oceanic lithosphere. As a rule, the Nazca plate is also referred to as large, which is several times smaller in size than each of the seven largest ones. At the same time, scientists suggest that in fact the Nazca plate is much larger than we see it on the map (see Fig. 5), since a significant part of it went under the neighboring plates. This plate also consists only of oceanic lithosphere.
Rice. 5. Earth's lithospheric plates
An example of a plate that includes both continental and oceanic lithosphere is, for example, the Indo-Australian lithospheric plate. The Arabian Plate consists almost entirely of the continental lithosphere.
The theory of lithospheric plates is important. First of all, it can explain why mountains are located in some places on the Earth, and plains in others. With the help of the theory of lithospheric plates, it is possible to explain and predict catastrophic phenomena occurring at the boundaries of plates.
Rice. 6. The outlines of the continents really seem compatible
Continental drift theory
The theory of lithospheric plates originates from the theory of continental drift. Back in the 19th century many geographers noted that when looking at a map, one can see that the coasts of Africa and South America when approached, they seem compatible (Fig. 6).
The emergence of the hypothesis of the movement of the continents is associated with the name of the German scientist Alfred Wegener(1880-1930) (Fig. 7), who most fully developed this idea.
Wegener wrote: "In 1910, the idea of moving the continents first occurred to me ... when I was struck by the similarity of the outlines of the coasts on both sides of the Atlantic Ocean." He suggested that in the early Paleozoic on Earth there were two major mainland— Laurasia and Gondwana.
Laurasia was the northern mainland, which included the territories of modern Europe, Asia without India and North America. southern mainland- Gondwana united the modern territories of South America, Africa, Antarctica, Australia and Hindustan.
Between Gondwana and Laurasia was the first sea - Tethys, like a huge bay. The rest of the Earth's space was occupied by the Panthalassa ocean.
About 200 million years ago, Gondwana and Laurasia were united into a single continent - Pangea (Pan - universal, Ge - earth) (Fig. 8).
Rice. 8. The existence of a single mainland Pangea (white - land, dots - shallow sea)
Approximately 180 million years ago, the mainland of Pangea again began to be divided into constituent parts, which mixed up on the surface of our planet. Separation took place in the following way: first, Laurasia and Gondwana reappeared, then Laurasia split, and then Gondwana also split. Due to the split and divergence of parts of Pangea, oceans were formed. The young oceans can be considered the Atlantic and Indian; old - Quiet. Northern Arctic Ocean became isolated with an increase in land mass in the Northern Hemisphere.
Rice. 9. Location and directions of continental drift in Cretaceous 180 million years ago
A. Wegener found a lot of evidence for the existence of a single continent of the Earth. Particularly convincing seemed to him the existence in Africa and South America of the remains of ancient animals - leafosaurs. These were reptiles, similar to small hippos, that lived only in freshwater reservoirs. So, to swim huge distances on the salty sea water they couldn't. Similar evidence he found in the plant world.
Interest in the hypothesis of the movement of the continents in the 30s of the XX century. decreased slightly, but in the 60s it revived again, when, as a result of studies of relief and geology ocean floor data were obtained indicating the processes of expansion (spreading) of the oceanic crust and "diving" of some parts of the crust under others (subduction).
Global Relief- this is a set of irregularities of the land, the bottom of the oceans and seas on the territory of the entire the globe. The global relief includes the largest forms of the earth's surface: continents (continental protrusions) and oceans ( ocean trenches). There are six continents, they are located in the North and southern hemispheres(Australia, Africa, Antarctica, Eurasia, South America, North America). Four oceans (Pacific, Atlantic, Indian, Arctic) form the World Ocean.
Some scientists also distinguish the fifth Southern Ocean, washing Antarctica. Its northern boundary passes within the limits of parallels from 57 to 48 ° S. sh.
The geographical patterns of the Earth's relief as part of the geographic shell are expressed in the peculiar arrangement of the continents and oceans on the planet. On the globe, the features of the Earth's relief are clearly visible: North hemisphere stands out as continental, and the South - as oceanic. The Eastern Hemisphere is more land, and the Western - mostly bodies of water. Most of the continents are wedge-shaped, narrowing towards the south.
A. Wegener's hypothesis
There are several hypotheses and theories about the formation of the Earth's relief, including the development of its largest forms - continents and oceans. The German scientist A. Wegener put forward a hypothesis (scientific assumption) of continental drift. It consisted in the fact that in the geological past there was a single supercontinent Pangea on Earth, surrounded by the waters of the Panthalassa ocean. About 200 million years ago, Pangea split into two continents - Laurasia (it formed most of Eurasia, North America, Greenland) and Gondwana (formed South America, Africa, Antarctica, Australia, the Hindustan and Arabian peninsulas), separated by the Tethys ocean (Fig. 3). The continents gradually diverged in different directions and took on modern shapes.
Theory of lithospheric plates
Later, scientists found out that A. Wegener's hypothesis justified itself only partially. She failed to explain the mechanism and causes of vertical movements in the lithosphere. New views on the origin of continents and oceans arose and developed. In the early 60s of the XX century, with the advent of new data on the structure of the oceans, scientists came to the conclusion that there are lithospheric plates that are involved in movement. Lithospheric plates are stable blocks of the earth's crust, separated by mobile areas and giant faults, slowly moving along the plastic layer in the upper mantle. Lithospheric plates include the oceanic and continental crust and the uppermost part of the mantle.
The largest lithospheric plates are the Eurasian, Indo-Australian, North American, South American, African, Antarctic, Pacific. Mid-ocean ridges and deep-sea trenches are the boundaries of lithospheric plates and major landforms of the Earth.
Plates lie on the asthenosphere and slide over it. Asthenosphere- a plastic layer of the upper mantle of reduced hardness, strength and viscosity (under the continents at a depth of 100-150 km, under the oceans - about 50 km).
The forces that cause plates to slide along the asthenosphere are formed under the action of internal forces arising in the outer core of the Earth and during the rotation of the Earth around its axis. The most important reason for sliding is the accumulation of heat in the bowels of the Earth during the decay of radioactive elements.
The most significant horizontal movements of lithospheric plates. Plates move on average at a speed of up to 5 cm per year: they collide, diverge or slide one relative to the other.
At the point of collision of lithospheric plates, global folded belts are formed, which are a system of mountain formations between two platforms.
If two lithospheric plates approach the continental crust, then their edges, together with the sedimentary rocks accumulated on them, are crushed into folds and mountains are formed. So, for example, the Alpine-Himalayan mountain belt at the junction of the Indo-Australian and Eurasian lithospheric plates (Fig. 4a).
If the lithospheric plates, one of which has a more powerful continental crust, and the other a less powerful oceanic crust, approach each other, then the oceanic plate seems to “dives” under the continental one. This is due to the fact that the oceanic plate has a greater density, and as it is heavier, it sinks. In the deep layers of the mantle, the oceanic plate is melting again. In this case, deep-water trenches appear, and on land, mountains (see Fig. 4b).
Nearly everything happens in these places. natural disasters associated with the internal forces of the Earth. Off the coast of South America are the deep-water Peruvian and Chilean trenches, and the highlands of the Andes, stretching along the coast, are replete with active and extinct volcanoes.
In the case of thrusting of the oceanic crust on another oceanic crust the edge of one slab rises somewhat, forming an island arc, while the other subsides, forming troughs. So in the Pacific Ocean the Aleutian Islands and the trench framing them, the Kuril Islands and the Kuril-Kamchatka Trench, the Japanese Islands, the Mariana Islands and the trench were formed, in the Atlantic - the Antilles and the Puerto Rico Trench.
In places where the plates diverge, faults appear in the lithosphere, forming deep depressions in the relief - rifts. Molten magma rises, lava erupts along fractures and gradually cools (see Fig. 4c). In places of breaks at the bottom of the ocean, the earth's crust builds up and renews itself. An example is the mid-ocean ridge - the region of divergence of lithospheric plates, located at the bottom of the Atlantic Ocean.
The rift separates the North American and Eurasian plates in the north Atlantic Ocean and the African plate from the South American in the south. In the zone of axial mid-ocean ridges, rifts represent large linear tectonic structures of the earth's crust hundreds and thousands in length and tens and hundreds of kilometers in width. Due to the movement of plates, the outlines of the continents and the distances between them change.
Data from the International Space Orbital Station make it possible to calculate the location of the divergence of lithospheric plates. It helps to predict earthquakes and volcanic eruptions, other phenomena and processes on Earth.
Global folded belts, formed over a long time, continue to develop on Earth - the Pacific and Alpine-Himalayan. The first encircles the Pacific Ocean, forming the Pacific "Ring of Fire". It includes mountain ranges Cordillera, Andes, mountain systems of the Malay Archipelago, Japanese, Kuril Islands, Kamchatka Peninsula, Aleutian Islands.
The Alpine-Himalayan belt across Eurasia stretches from the Pyrenees in the west to the Malay Archipelago in the east (Pyrenees, Alps, Caucasus, Himalayas, etc.). Active mountain-building processes continue here, accompanied by volcanic eruptions.
The Alpine-Himalayan and Pacific fold belts are young mountains that have not been completely formed and have not had time to collapse. They are mostly composed of young sedimentary rocks. marine origin covering the ancient crystalline cores of the folds. Volcanic rocks overlap sedimentary ones or are embedded in their thickness. Deposits of iron and polymetallic ores, tin and tungsten are confined to the folded belts.
The global relief of the Earth includes the largest forms of the earth's surface: continents (continental protrusions) and oceans (ocean depressions). The northern hemisphere of the Earth stands out as a continental hemisphere, while the southern hemisphere is predominantly oceanic, the eastern hemisphere is mostly dry land, the western one is mainly water spaces.
Hello dear readers! Today I would like to talk about what are the main landforms. So let's get started?
Relief(French relief, from Latin relevo - I raise) is a set of uneven land, the bottom of the seas and oceans, different in contour, size, origin, age and history of development.
Consists of positive (convex) and negative (concave) shapes. The relief is formed mainly due to the long-term simultaneous influence of endogenous (internal) and exogenous (external) processes on the earth's surface.
The basic structure of the earth's relief is created by forces that lurk deep in the bowels of the Earth. From day to day, external processes act on it, relentlessly modifying it, cutting through deep valleys and smoothing mountains.
Geomorphology - it is the science of changes in the earth's relief. Geologists know that the old epithet "eternal mountains" is far from the truth.
Mountains (you can learn more about mountains and their types) are not eternal at all, even though the geological time of their formation and destruction can be measured in hundreds of millions of years.
In the mid 1700s began industrial Revolution. And since that moment, human activity has played an important role in the transformation of the face of the Earth, which sometimes leads to unexpected results.
The continents acquired their current place on the planet and appearance as a result of tectonics, that is, the movement of geological plates that form the solid outer shell of the Earth.
The movements that are most recent in time have occurred within the last 200 million years - this includes the connection of India with the rest of Asia (more on this part of the world) and the formation of the Atlantic Ocean depression.
Our planet has undergone many other changes throughout its history. The result of all these convergences and divergences of huge massifs, movements were numerous folds and faults of the earth's crust (more detailed information about the earth's crust), as well as powerful heaps of rocks from which mountain systems were formed.
I will give you 3 striking examples of recent mountain building or orogeny, as geologists call it. As a result of the collision of the European plate with the African one, the Alps arose. When Asia collided with India, the Himalayas rose to the skies.
The Andes pushed up the shift of the Antarctic Plate and the Nazca Plate, which together form part of the Pacific Trench, under the plate on which South America rests.
These mountain systems are all comparatively young. Their sharp outlines did not have time to mitigate those chemical and physical processes that continue to change the earth's appearance even today.
Earthquakes cause enormous damage and rarely have long-term effects. But on the other hand, volcanic activity injects fresh rocks into the earth's crust from the depths of the mantle, often significantly changing the habitual appearance of mountains.
Basic landforms.
Within the land, the earth's crust consists of a variety of tectonic structures, which are more or less separated from one another, and differ from adjacent areas. geological structure, composition, origin and age of rocks.
Each tectonic structure is characterized by a certain history of movements of the earth's crust, its intensity, regime, accumulation, manifestations of volcanism and other features.
The nature of the relief of the Earth's surface is closely related to these tectonic structures, and to the composition of the rocks that form them.
Therefore, the most important regions of the Earth with a homogeneous relief and a close history of their development - the so-called morphostructural regions - directly reflect the main tectonic structural elements earth's crust.
The processes on the earth's surface that affect the main landforms formed by internal, that is, endogenous processes, are also closely related to geological structures.
Individual parts large forms relief is formed by external, or exogenous, processes, weakening or strengthening the action of endogenous forces.
These details of large morphostructures are called morphosculptures. According to the scope of tectonic movements, according to their nature and activity, two groups of geological structures are distinguished: moving orogenic belts and persistent platforms.
They also differ in the thickness of the earth's crust, its structure and the history of geological development. Their relief is also not the same - these are different morphostructures.
Plain territories of various types with small relief amplitudes are characteristic of platforms. Plains distinguish high (Brazilian - 400-1000 m of absolute height, that is, heights above sea level, African) and low (Russian Plain - 100-200 m of absolute height, West Siberian Plain).
More than half of the entire land area is occupied by morphostructures of platform plains. Such plains are characterized by a complex relief, the forms of which were formed during the destruction of heights and the redeposition of materials from their destruction.
In large expanses of plains, as a rule, the same layers of rocks are exposed, and this causes the appearance of a homogeneous relief.
Among the platform plains, young and ancient sections are distinguished. Young platforms can sag and are more mobile. Ancient platforms are inherently rigid: they rise or fall as a single larger block.
4/5 of the surface of all land plains falls on a part of such platforms. On the plains, endogenous processes manifest themselves in the form of weak vertical tectonic movements. The diversity of their relief is associated with surface processes.
Tectonic movements also affect the nas: denudation, or destruction processes, predominate in the rising areas, and accumulation, or accumulation, in the areas that are decreasing.
FROM climatic features areas are closely related external, or exogenous, processes - the work of the wind (eolian processes), erosion flowing waters(erosion), the solvent action of groundwater (more about groundwater) (karst), rainwater flushing (deluvial processes) and others.
The relief of mountainous countries corresponds to orogenic belts. Mountainous countries occupy more than a third of the land area. As a rule, the relief of these countries is complex, strongly dissected and with large height amplitudes.
Different types of mountain relief depend on the rocks that make them up, on the height of the mountains, on the modern features of the nature of the area and on geological history.
In mountainous countries with complex terrain, individual ridges, mountain ranges and various intermountain depressions stand out. Mountains are formed by bent and inclined rock layers.
Strongly bent into folds, crumpled rocks alternate with igneous crystalline rocks in which there is no foliation (basalt, liparite, granite, andesite, etc.).
Mountains arose in places on the earth's surface that were subjected to intense tectonic uplift. This process was accompanied by the collapse of layers of sedimentary rocks. They were torn, cracked, bent, compacted.
From the bowels of the Earth, magma rose through the gaps, which cooled down at a depth or poured out to the surface. Earthquakes happened repeatedly.
The formation of large landforms - lowlands, plains, mountain ranges - is primarily associated with deep geological processes that have shaped the earth's surface throughout geological history.
During various exogenous processes, numerous and diverse sculptural or small landforms are formed - terraces, river valleys, karst abysses, etc ...
For the practical activities of people has a very great importance the study of large landforms of the Earth, their dynamics and various processes that change the surface of the Earth.
Weathering of rocks.
The earth's crust is made up of rocks. Softer substances, which are called soils, are also formed from them.
A process called weathering is the main process that changes the appearance of rocks. It occurs under the influence of atmospheric processes.
There are 2 forms of weathering: chemical, in which it decomposes, and mechanical, in which it crumbles into pieces.
Rocks are formed under high pressure. As a result of cooling, deep in the bowels of the Earth, molten magma forms volcanic rocks. And at the bottom of the seas, sedimentary rocks are formed from rock fragments, organic remains and silt deposits.
The impact of the weather.
Often in rocks there are multilayer horizontal stratifications and cracks. They eventually rise to the surface of the earth, where the pressure is much lower. The stone expands as the pressure decreases, and all cracks in it, respectively.
The stone is easily exposed to weather factors due to naturally formed cracks, layers and joints. For example, water that has frozen in a crack expands, pushing its edges apart. This process is called frost wedging.
The action of plant roots that grow in cracks and, like wedges, push them apart, can be called mechanical weathering.
With the mediation of water, chemical weathering occurs. Water, flowing over the surface or soaking into the rock, brings chemicals into it. For example, the oxygen in water reacts with the iron contained in the rock.
Carbon dioxide absorbed from the air is present in rainwater. It forms carbonic acid. This weak acid dissolves limestone. With its help, a characteristic karst relief is formed, which got its name from the area in Yugoslavia, as well as huge labyrinths of underground caves.
Water dissolves many minerals. And minerals, in turn, react with rocks and decompose them. Atmospheric salts and acids also play an important role in this process.
Erosion.
Erosion is the destruction of rocks by ice, sea, water currents or wind. Of all the processes that change the earth's appearance, we know it best of all.
River erosion is a combination of chemical and mechanical processes. Water not only moves rocks, and even huge boulders, but, as we have seen, it dissolves their chemical components.
Rivers (more about rivers) erode floodplains, carrying soil far into the ocean. There it settles at the bottom, eventually turning into sedimentary rocks. The sea (about what the sea can) is constantly and tirelessly working on the alteration of the coastline. In some places it builds up something, and in others it cuts something off.
The wind carries small particles, like sand, over incredibly long distances. For example, in southern England, the wind brings, from time to time, sand from the Sahara, covering the roofs of houses and cars with a thin layer of reddish dust.
The impact of gravity.
Gravity during landslides causes solid rocks to slide down the slope, changing the terrain. As a result of weathering, fragments of rocks are formed, which make up the bulk of the landslide. Water acts as a lubricant, reducing friction between particles.
Landslides sometimes move slowly, but sometimes they move at a speed of 100 m/sec or more. A creep is the slowest landslide. Such a landslide crawls only a few centimeters per year. And only after a few years, when trees, fences and walls bend under the pressure of the bearing earth, it will be possible to notice it.
A mudflow or mudflow can cause clay or soil (more on soil) to become oversaturated with water. It happens that for years the earth is held firmly in place, but a small tremor is enough to bring it down the slope.
In a number of recent disasters, such as the eruption of Mount Pinatubo in the Philippines in June 1991, the main cause of death and destruction was mud flows, which flooded many houses to the very roof.
Avalanches (rock, snow, or both) result in similar disasters. A landslide or mudslide is the most common form of landslide.
On the steep bank, which is washed away by the river, where a layer of soil has broken away from the base, traces of a landslide can sometimes be seen. A large landslide can lead to significant changes in the relief.
Rockfalls are not uncommon on steep rocky slopes, in deep gorges or mountains, especially in those places where destroyed or soft rocks predominate.
The mass that has slid down forms a gentle slope at the foot of the mountain. Many mountain slopes are covered with long tongues of rubble talus.
Ice Ages.
Centuries-old climatic fluctuations also led to significant changes in the earth's relief.
In the icy polar caps, during the last ice age, huge masses of water were bound. The northern cap extended far into the south of North America and the European continent.
Ice covered about 30% of the land on Earth (for comparison, today it is only 10%). Sea levels during the Ice Age (more information on the Ice Age) were about 80 meters lower than they are today.
The ice melted, and this led to colossal changes in the relief of the Earth's surface. For example, to these: between Alaska and Siberia, the Bering Strait appeared, Great Britain and Ireland turned out to be islands that are separated from all of Europe, the land area between New Guinea and Australia went under water.
Glaciers.
In the ice-covered subpolar regions and in the highlands of the planet, there are glaciers (more about glaciers) - ice rivers. The glaciers of Antarctica and Greenland annually dump huge masses of ice into the ocean (about what an ocean is), forming icebergs that pose a danger to navigation.
During the ice age, glaciers played a major role in giving the topography of the northern regions of the Earth a familiar look to us.
Crawling with a giant plane along the earth's surface, they carved out the hollows of the valleys and cut off the mountains.
Under the weight of glaciers, old mountains, such as those in the north of Scotland, have lost their sharpness and height.
Glaciers in many places have completely cut off many meters of rock layers that have accumulated over millions of years.
The glacier, as it moves, captures, in the so-called accumulation area, a lot of rock fragments.
Not only stones get there, but also water in the form of snow, which turns into ice and forms the body of the glacier.
Glacial deposits.
Having passed the border of the snow cover on the mountain slope, the glacier shifts to the ablation zone, that is, gradual melting and erosion. The glacier, closer to the end of this zone, begins to leave dragged rock deposits on the ground. They are called moraines.
The place where the glacier finally melts and turns into an ordinary river is often designated as the terminal moraine.
Those places where long-vanished glaciers ended their existence can be found along such moraines.
Glaciers, like rivers, have a main channel and tributaries. The glacial tributary flows into the main channel from the side valley, which is laid by it.
Usually its bottom is located above the bottom of the main channel. The glaciers, which have completely melted, leave behind the main valley in the shape of the letter U, as well as several side ones, from where picturesque waterfalls rush down.
In the Alps you can often find such landscapes. clue driving force The glacier lies in the presence of so-called erratic boulders. These are separate fragments of rock, different from the rocks of the ice bed.
Lakes (more information about lakes) from a geological point of view are short-lived landforms. Over time, they are filled with sediment from the rivers that flow into them, their banks are destroyed and the water leaves.
Glaciers have formed countless lakes in North America, Europe (you can learn more about this part of the world) and Asia, carving hollows in rocks, or blocking valleys with terminal moraines. There are a great many glacial lakes in Finland and Canada.
For example, other lakes, such as Crater Lake in Oregon (USA) (more about this country), are formed in the craters of extinct volcanoes as they fill with water.
Siberian Baikal and the Dead Sea, between Jordan and Israel, originated in deep cracks in the earth's crust that were formed by prehistoric earthquakes.
Anthropogenic landforms.
The labors of builders and engineers create new landforms. The Netherlands is a great example of this. The Dutch proudly say that with my own hands created their own country.
They were able to recapture about 40% of the territory from the sea, thanks to a powerful system of dams and canals. The need for hydroelectric power and fresh water forced people to build a considerable number of artificial lakes or reservoirs.
In the state of Nevada (USA) there is Lake Mead, it was formed as a result of the blocking of the Colorado River by the Hoover Dam dam.
After the construction of the high-altitude Aswan dam on the Nile, Lake Nasser appeared in 1968 (near the border of Sudan with Egypt).
The main task of this dam was the regular supply of water. Agriculture and regulation of annual floods.
From time immemorial, Egypt suffered from the fluctuations in the level of the Nile floods, and it was decided that a dam would help solve this centuries-old problem.
But on the other hand.
But the Aswan High Dam is a prime example that playing with nature is bad: it will not tolerate rash actions.
The problem is that this dam blocks the annual fresh silt that fertilized the farmland, and in fact, that shaped the Delta.
Now, silt is accumulating behind the wall of the Aswan Dam, and thus it threatens the existence of Lake Nasser. Significant changes can be expected in the Egyptian relief.
The appearance of the Earth is given new features by man-made railways and highways, with their undercut slopes and embankments, as well as mine heaps, which have long disfigured the landscape in some industrial countries.
Cutting down trees and other plants leads to erosion (their root system holds moving soils together).
It was these ill-conceived human actions that led, in the mid-1930s, to the emergence of the Dust Pile on the Great Plains, and today threaten disaster in the Amazon basin in South America.
Well, dear friends, that's all for now. But stay tuned for more articles soon. 😉 I hope that this article helped you figure out what landforms are.
Spreading, subduction - see 93
COLLISION - a collision of two continental plates, which, due to their relative ease, cannot sink under each other, but colliding form a mountain-fold belt with a very complex internal structure. This is how the Himalayan mountains were born.
No. 96. Geochronology. Methods for establishing the relative age of rocks.
1) Stratigraphic method: study of sedimentary rock formations, samples in marine or continental conditions;
2) Lithological method: comparison of rocks by their composition;
3) Paleontological method: the study of the fossilized remains of animals and plants that lived in past geol.epochs;
Based on 1) and 3), a stratigraphic scale was created. Scale ranks: eonoteme; erathema; system; departments; tiers and smaller subdivisions. Each rank corresponds to a geochronological subsection: eon; era; period; era; century.
No. 97. Age of the Earth. Methods for establishing the absolute age of rocks.
Potassium-argon - the study of the radioactive transformation of the potassium isotope with an atomic weight of 40. (K 40 + e \u003d Ar 40). Created by E.K. Gerling.
Rubidium-strontium - used for minerals and rocks; radioactive decay of Rb 87 and its transformation into Sr 87 .
Carbon - for young Anthropogenic deposits; radioactive decay C 14 ; during the life of plants, the radioactive naradioac. carbon is the same in them, after the death, decay occurs; know the half-life and the ratio in dead plants determine the age of the deposits.
Age of the Earth: using radiological methods, Polkanov and Gerling established the age of the oldest highly metamorphosed rocks - 3500 million years; Sobotovich determined the age of shales from the Okhotsk massif to be 4000 Ma; Maximum value the absolute age of stone meteorites is 4550-4600 million years (the Moon is also about this age).
№101. General characteristics of the Quaternary period.
The Quaternary period is the youngest stage in the geological history of the Earth (0.8 - 3.5 million years) that continues to the present day. It follows immediately after the Neogene.
Signs:
The emergence of man and his culture (the remains of culture give a chronological scale, the equivalent of which is not found in more ancient periods)
A sharp change in climate, the formation and latitudinal distribution of ice sheets over most of the northern hemisphere.
Deposits are developed everywhere (for example, Moscow State University stands on a moraine of glacial origin). All deposits are parent rocks for soil development. Serious study of deposits began in the 20-30s of the 20th century.
1825 - J. Denoyer singled out post-Tertiary deposits into an independent Quaternary system.
1839 - C. Lyell introduced the term "Pleistocene" to refer to deposits younger than the Pliocene.
1888 - approved official name"Quaternary period".
1919 - A.P. Pavlov proposed to replace the "Quaternary" with the "Anthropogenic".
Minerals of the period:
Construction Materials
precious metals
Iron-manganese nodules
№102.Climate change, the structure of the earth's crust in quaternary period.
Changing of the climate: during the Cenozoic, the climate worsened and became colder. At the beginning of the Neogene, Antarctica was covered with ice. The surface of the Earth was repeatedly covered with powerful glaciers. The last ice age ended 10-12 thousand years ago, the modern climate is interglacial. Compared to the Neogene, the temperature dropped by 8 degrees. IN this moment there is global warming against the background of global cooling (warming only against the background of the greenhouse effect).
Causes of climate change:
Extraterrestrial (solar activity)
Terrestrial (angle of inclination of the earth's axis; position in space; shape of the orbit)
Technogenic factors (emissions of gases and freons into the atmosphere)
Changing the structure of the earth's crust: The mountains have grown by 2-3 km. The platform plains were rising. The area of the seas and oceans has decreased. The relief contrast is 20 km. Rifts open (9 cm/year). High speed of fault movement (horizontal movements). There is a general rise of the land and the bowing of the oceans.
No. 103. Hypotheses about the causes of glaciation in the Quaternary period.
According to the summary of M. Schwarzbach (1955), various scientists prove that ice ages arose for the following reasons:
1. Due to harsh winters(Krol, Pilgrim).
2. Due to mild winters (Köppen).
3. Due to weakening intensity solar radiation(Dubois).
4. In connection with the increase in the intensity of solar radiation (Simpson).
5. Due to the weakening of the influence of the warm Gulf Stream (Wundt).
6. In connection with the strengthening of the influence of the warm Gulf Stream (Berman).
7. Due to increased volcanic activity (Huntington).
8. Due to the weakening of volcanic activity (Frech).
On the same principle, hypotheses about the causes of the cessation of ice ages are also constructed. Some scientists believe that the ice sheets disappeared due to climate warming and rising temperatures, while others (A.A. Velichko) - due to a cooling climate and a sharp drop in temperatures.
The theory of great glaciations occupies an honorable place among the predictors and popularizers of science. Many publications have appeared (especially in the west) in which the imminent onset of a new ice age is predicted. N. Calder in the book “The Time Machine and the Ice Threat” foreshadows the arrival of the Ice Age at any moment, since, in his opinion, in recent decades increased snowfall, a sure sign of the onset of glaciation. J. Gribbin in the book "Climate Threat" gives earthlings a certain respite. According to him, glaciers will cover Europe and North America not earlier than a few centuries later. Our Soviet Semyon Barrash postpones the ice threat for several millennia, but warns that the 400,000-year rhythm of global cataclysms he calculated is ending.
№104.Eustatic fluctuations in the level of oceans and seas in the Quaternary. Glacioisostasia.
Glaciation is associated with vertical movements of the earth's crust, caused by a violation of its isostatic equilibrium - glaciostasia. Under the weight of the ice, the crust sags (Antarctica is bent by more than 1 km - the uplift rate is 3 mm / year). Melting causes the earth's crust to rise. Such movements are typical for areas that were the main centers of ancient continental glaciations - the Scandinavian and Canadian shields. It is believed that today's movements do not yet compensate for the effect of previous glacial loads.
During the glaciation a sharp decline ocean level. The older the glaciation, the more powerful it is. During melting, sea and ocean levels rise. Over the past 100 years, the ocean level has risen by 12 cm. If all the ice melts, the ocean level will rise by 66 meters.
№105. Features of the development of the organic world in the Quaternary period.
The animal world was formed from the original fauna - hipparion, which lived in the Neogene (three-toed horse, gazelles, giraffes, Saber-toothed tiger, mastodons). Due to climate change, the fauna has changed a lot. Cold-resistant species (mammoth, reindeer, woolly rhinoceros) spread. The areas have also changed a lot. Holocene - modern - fauna is a depleted fauna of the Pleistocene.
Landscape zones have been formed. During the interglacials, the tundra almost disappeared, and the tropics expanded. Heat-loving plants disappeared in the glaciers. There is a lot of beech, hornbeam and yew in the Moscow deposits, which indicates that the area used to have a warmer climate.
№106.The main stages of human development in the Quaternary period.
First great apes(Romapithecus) appeared 8-14 million years ago in the Miocene. Australopithecus (southern monkeys) appeared 5 million years ago. 3 million years ago, the first representatives of the genus hominids appeared - a skilled man.
Fossil human remains are very rare. Much more common are traces of his activities, cultural remains.
Stages of development:
About 2 million years ago - the manufacture of stone tools. Epochs: Archeolithic, Paleolithic, Mesolithic, Neolithic.
13 thousand years ago - the appearance of "reasonable man."
13-9 thousand years ago - bow, arrows, hooks.
10-6 thousand years ago - the emergence of floriculture and agriculture.
5 thousand years ago - copper alloys.
3 years ago - "Bronze Age".
2 thousand years ago - "Iron Age".
№107. Influence of climatic and tectonic factors on the formation of Quaternary deposits.
Tectonics creates all landforms. Positive forms are areas of destruction. They supply Quaternary deposits to depressions. The uplifts are represented by high plateaus, ridges, and ridges. Depressions - intermountain and foothill depressions, basins. Seismic phenomena form seismic deposits (colluvial series - landslides, landslides, talus). The latest tectonics determines the energy of sedimentation and the distribution of areas of denudation and accumulation.
The climate distributes sediments over the surface of the earth. Determines the location of climatic zones. Vertical zonality is due to the fact that every kilometer the temperature drops by 5-6 degrees. The nature and rate of weathering and destruction of rocks of the ancient substrate, the method of transporting material, the conditions and mechanisms of its accumulation depend on the climate (in the polar climate, freezing of the upper part of the earth's crust and the formation zone of frozen rocks; in an arid climate, dry wind as a denudation agent - destroys and transfers material.).
№108. The Holocene is the youngest section of the Quaternary system. Climatic conditions and deposits.
The youngest section - the Holocene - has a duration of about 10 thousand years. It is indexed as Q4 and IV. The Holocene consists of one link - modern. fossil fauna refers to the modern complex.
Mining and fold systems Central Asia in Holocene time remain tectonic. The deformation of modern terraces and high seismicity testify to ongoing tectonic movements at the present time.
Lacustrine-marsh Holocene deposits form from the surface of low marshy terraces.
Eluvial-deluvial deposits are developed in the mountainous part of the region and on the denudation plains of western Kamchatka.
Bog Holocene deposits are developed on west coast Kamchatka, where they stretch in an almost continuous strip from 5 to 50 km wide along the coast of Okhotsk.
Lake-marsh Holocene deposits (overlap various rocks from the surface. They are represented mainly by peat various types, the thickness of which varies from 2 to 4 - 6 m and more. Alluvial Holocene deposits that make up terrace I and the floodplain are developed in the valleys of all rivers in the region.
Alluvial Holocene deposits are predominantly represented by sand-gravel-pebble material with a complex physical structure.
Late Pleistocene and Holocene deposits are represented by a wide range of genetic types characteristic of the temperate humid climate prevailing here at that time: alluvial, lacustrine, swampy, etc. The total thickness of the Quaternary deposits of the region varies from 3 to 80 m on the watersheds.
Alluvial-proluvial Pleistocene and Holocene deposits are common in the southern part of the depression. Alluvial and proluvial Holocene sediments are represented by gravel-pebble material with uneven-grained sand, less often sands with interlayers of sandy loam, loam, silt, and gravel.
Marine and alluvial-marine Upper Pleistocene and Holocene deposits are developed along the sea coast. The former form terraces up to 40 m high and parts of plains. Alluvial-marine deposits are developed in the estuarine parts of the most major rivers, forming accumulative plains, and are represented by intercalation of sands with pebbles, loams, clays and silts.
The most sensitive to any climatic changes during the removal of vegetable and soil cover sandy Holocene deposits.
In accordance with the general cooling that occurred after the thermal maximum, freezing of the upper part of the Holocene deposits that melted into the thermal maximum and newly formed occurs.
During the Holocene there were:
soil formation
Formation of floodplain alluvium, foothill proluvium.
In the middle Holocene (the warmest) the tundra almost disappeared.
The last interglacial (now) lasts 10 thousand years.
The water level in the Caspian Sea rises and it floods coastal buildings.
№109. Methods of stratigraphic division of Quaternary deposits.
For the dismemberment of four deposits by age, two groups of methods are used, giving relative and absolute age.
Regional stratigraphic units are a complex of rocks that reflect the features of sedimentation and the development of flora and fauna in a given area.
The main regional subdivision is the horizon (deposits sampled during one epoch or climate phase). Horizons have local names(geographic points where they were first identified), indices. In addition to horizons, there are suites, strata, layers, etc.
On geol.maps, quarter deposits are shown only where the thickness is hundreds of meters. These are the coasts of the seas, deltas of large rivers, depressions in the mountains. The color of deposits on the map is usually light gray, bluish-gray, as is customary in the common geochronological scale.
On maps of Quaternary deposits, the color reflects the genesis of the deposits. Glacial deposits - brown. Alluvial - green. Marine - blue. Eolian - yellow. Colluvial - red. Deluvial - orange. Chemogenic - gray. Volcanic - bright green.
Age is reflected by the intensity of the color - the younger, the lighter.
In addition to color, deposits have their own indices.
In addition to deposits, facies are marked on the maps. Facies are designated by initial letters from the Latin name.
№110. Methods for determining the relative age of Quaternary deposits and the conditions for their formation.
1) Climatographic:
Lithological-genetic method (alternation in the section of "cold" and "warm" deposits)
Cryological method (distinguishing traces of fossil permafrost in the section)
Pedological method (identification in the context of buried soils)
2) Paleontological:
Paleofaunistic method
Carpological method (plant seeds)
Palynological method (spores and pollen of plants)
diatom (algae residue)
3) Geomorphological (identification of even-aged landforms different origin)
4) Archaeological (fossil remains of a person and traces of his life)
№111. Methods for determining the absolute age of Quaternary deposits.
1) Varvochronological (calculation of annual clay layers determines the accumulation of lacustrine sediments)
2) Dendrochronological (calculation of annual rings of fossil wood in four deposits)
3) Lichenometric (based on the study of the growth rate of lichens on moraine boulders)
4) Radiological (radiocarbon, uranium-ion, potassium-argon - based on the radioactive decay of isotopes)
5) Paleomagnetic (based on the ability of minerals to retain the magnetization of the era in which they formed)
6) Thermoluminescent (based on the ability of minerals to "glow")
№112. Scheme of Quaternary stratigraphy for the European part of Russia.
| System (Period) | The Department. Subsection (epoch) | Subdivision. Chapter (Phase) | Link (It's time) | step (Thermochron. cryochron) |
| Quaternary Quaternary (Quarter or Quaternary) | Holocene ( Holocene) | - | - | - |
| Pleistocene ( Pleistocene) | Neopleistocene ( Neopleistocene) | top ( late) | fourth ( late cryogen) | |
| third ( late thermogen) | ||||
| second ( early cryogen) | ||||
| first ( early thermochron) | ||||
| the average ( average) | - | |||
| bottom ( early) | - | |||
| Eopleistocene ( Eopleistocene) | top ( late) | - | ||
| bottom ( early) | - |
| System | Subsection | Chapter | Link | step | Interregional correlation horizons. European part Russia (ISC Resolution, 2007) | Ural (Resolution MSC, 1995) | Western Siberia (Decree MSC, 2000) |
| Quaternary | Holocene | Shuvalovsky | Gorbunovsky | modern | |||
| Pleistocene | Neopleistocene | upper | Ostashkovsky | polar Ural | Sartan | ||
| Leningrad | Nevyansk | karginsky | |||||
| Kalinin | Hanmei | ermakovskiy | |||||
| Mezinsky | archer | Kazantsev | |||||
| the average | Moscow | leplinsky | tazovsky | ||||
| Gorkinsky | Nitsinsky | shirtinsky | |||||
| Dnieper | Vilgortovsky | Samarovsky | |||||
| Chekalinsky | sylwitz | Tobolsk | |||||
| Kaluga | |||||||
| Likhvinsky | |||||||
| bottom | Oksky | karpinsky | shaitanic | ||||
| muchkapi | Chernorechensky | ||||||
| Don | lozvinsky | ||||||
| okatovsky | Baturinsky | talagaykinsky | |||||
| Setunian | |||||||
| Krasikovsky | |||||||
| pokrovskiy | tynyinsky | ||||||
| Akulovsky | Sarykul | ||||||
| Eopleistocene | upper | krinitsky | chumlyaksky | Kochkovsky | |||
| lower | tolucheevsky | Uvelian |
№113. The concept of genetic types and facies of Quaternary deposits.
The basis of the general class of quaternary deposits was created by A.P. Pavlov. According to Pavlov, the gen.type is deposits, form. as a result of the activities of geologists.agents. Pavlov introduced the types of deluvium and proluvium into the class.
E.V. Shantser proposed another definition: gen.type - scoop. sedimentary or volcanogenic accumulations, formed in the course of accumulation, the features of which determine the commonality of the main features of their structure as a pattern of combinations of certain sediments and rocks.
Gen.types are divided into facies (a complex of deposits of the same age of the same gen.type, differing in composition and formation conditions - G.F.Krashennikov).
Genetic types are understood as complexes of sedimentary formations that form close combinations, causally determined by the activity of a certain leading accumulation factor.
All continental Quaternary deposits are divided into two classes: weathering crusts and sedimentary deposits. The weathering crust class includes the eluvial series; the class of sedimentary deposits - five series: subaerial-phytogenic, slope, water, glacial and wind. Deposits of the underground-water series, including sedimentary deposits of caves and springs, play an insignificant role in the total Quaternary land cover.
№115. Quaternary formations of the eluvial series.
This series stands out as a special class of weathering crusts. The process of formation of eluvial formations is associated with the weathering of various rocks under the influence of physical, chemical and biogenic factors. Within the eluvial series, two genetic groups are distinguished: eluvium itself and soils.
Eluvium– topographically undisplaced products of bedrock alteration. Most often - loose formations located on the parent bedrocks, the destruction products of which are.
Eluvial formations are one of the main sources of initial material carried by various denudation agents.
Soils- a special genetic group of the eluvial series, which is the surface part of the weathering crusts. Of great importance is the complex combination of chemical decomposition of the mineral base of soils (the formation of soil eluvium) and the accumulation of humus, or humus.
Thus, the soil is a complex geobiological system that differs significantly from the subsoil zone.
Soils are divided into two subgroups:
automorphic (zonal)
- the most widely developed and formed under conditions when the position of the groundwater level and the height of their capillary rise is deeper than the lower boundary of the soil. hydromorphic (intrazonal)
- are confined mainly to various depressions. The main importance in their formation is the high near-surface position of the level of underground groundwater and zones of their capillary rise. Weathering products are not removed from the soil, and iron oxide compounds turn into ferrous ones.
№116. Genetic types of Quaternary deposits of the slope (colluvial) series.
Crash savings most pronounced in mountainous regions. They play a subordinate role in the complex of slope deposits of mountainous countries. Only at the foot of large ledges with actively developing faults are they developed over a significant area and have a large thickness.
Scree accumulations
are formed at the foot of mountain slopes as a result of periodic rolling of different-sized material, which is separated from the rocky slopes due to physical weathering.
Landslide accumulations ( delapsions) - these are displaced masses of rocks that make up the banks of rivers, lakes, seas. Landslide formation occurs under the influence of a complex of factors, one of which is the steepness of the slopes and the composition of the rocks that make them up.
Solifluction accumulations are formed as a result of a slow viscoplastic flow of loose highly waterlogged dispersed deposits on slopes with a steepness of 3-10 o. The most widely developed in the zone of distribution of permafrost rocks.
deluvium- deposits formed on slopes as a result of flat water runoff, which occurs periodically during precipitation precipitation and melting snow. Planar runoff occurs in the form of a thin veil or dense network of streams that carry material (mainly sandy-loamy) down the slope. At the bottom of the slope, the water flow slows down and the material begins to be deposited directly at the foot and in the adjacent part of the slope. Deluvial deposits form gently inclined concave plumes. The greatest thickness of deposits (5-10 m and more) is observed at the base of the slope, gradually decreasing up the slope and down towards the bottom of the valley.
№117. Genetic types of Quaternary deposits of water (aquatic) type.
Alluvium composes channels, floodplains and terraces above the floodplains of different levels.
Channel alluvium is represented by well-washed cross-bedded sands of various grain sizes, sometimes with gravel; coarser deposits usually lie at the base - basal erosion horizon.
Above the channel alluvium deposits are deposited floodplain alluvium that accumulates during floods.
Proluvius- sediments formed by land estuarine removal of various material by temporary streams and permanent rivers, especially widely developed at the foot of mountains in arid climate conditions. They compose powerful alluvial fans and piedmont wavy plumes formed from their confluence.
The composition of proluvial deposits varies from the top of the cone to its periphery from pebbles and boulders with sandy-argillaceous filler to fine and sorted sediments (sandy, sandy loamy), often in the marginal part - to loess-like sandy loams and loams.
Lacustrine deposits ( limnium).
Sedimentation in lakes depends on the climate, which determines their hydrological and hydrochemical regime. There are three types of lake sediments:
1 - terrigenous - formed due to the introduction of clastic material;
2 - chemogenic - due to the precipitation of salts and colloids dissolved in water;
3 - organogenic - formed due to various organisms.
№118. Quaternary deposits of the glacial (glacial) series.
The glacial series includes two paragenetically related groups of sediments: the glacial proper and the water-glacial (fluvioglacial).
A group of glacial deposits proper.
Main (bottom) moraine
according to Yu.A. Lavrushin, it is divided into monolithic and scaly.
^ Monolithic main moraine formed under the cover of a slowly moving glacier from material enclosed in the bottom parts of the ice.
^ Scaly main moraines arise as a result of the pressure of ice masses and the formation of internal chips. In this case, the bottom moraine moves along the line of internal spalls.
Ablation moraines are usually associated with the peripheral zones of glaciers during their degradation. Under these conditions, the material present inside the glacier or on its surface is exposed to the influence of moving glacial waters that carry out fine earth.
Marginal (terminal) moraines formed during a long stationary position of the edge of the glacier. In the marginal part of the glacier, the brought clastic material is loaded - bulk terminal moraine.