How are karst landforms formed? Types of karst landforms.

More varied. The work of rivers takes place in dungeons, the depth of which reaches several kilometers.

underground relief- these are countless caves and abysses, mines and funnels. The waters flowing here in complete darkness rarely break through to the surface. Underground lakes are like black mirrors. They are full of secrets, cave pearls are hidden in them. This is such a peculiar world, the nature of which is still poorly understood. This is the world of stalagmites and stalactites. All this is called karst relief, or simply karst. The term "karst" comes from the name of the plateau Karst (Kras), which is located on one of the peninsulas in the Adriatic. The almost waterless plateau is replete with funnels, dry basins, dips, cracks, bottomless wells. - a complex of forms created by nature as a result of dissolution by water and precipitation of the dissolved material. Forms of karst relief range in size from a few centimeters (karr, holes, furrows, etc.) to many hundreds of meters and kilometers. Little is known about relief irregularities smaller than 1 cm.

Karst relief is usually formed in areas composed of water-soluble rocks. Most often they are limestones, dolomites, gypsums, anhydrites, marbles, saline clays and salt. Dissolution occurs at a high rate, which is why this group is even called karst rocks. But shales, sandstones, granites, quartzites, basalts, etc. are also subject to dissolution. Their dissolution rate is tens of thousands of times less than that of karst rocks.

Karst formation occurs because there are not only rocks and that can be dissolved, but also flowing waters and cracks in rocks. A person sees the later stages of karst formation, since observations of the migration of water along the thinnest cracks are impossible. The mechanisms of formation of karst relief in the first stages are most likely associated with the permeability of the rock. The most common forms of karst relief are funnels, saucers, mines, wells, karrs, valleys, fields, caves, boilers, dams and curtains, terraces, stalactites, stalagmites, etc.

Carry are usually formed on the surface of fractured limestones and dolomites by rainwater, the streams of which create gullies. Huge carr fields are located in, their depth reaches several meters. Karst sinkholes on the surface are more common. Their diameter is from 1 to 500 m, and the depth is from 0.5 to 45 m. Chains of funnels often merge, forming karst valleys.

In the Rhodopes (South) there are amazing creations of nature - rock bridges. They are huge arches thrown over large valleys, along the bottom of which a barely noticeable stream now flows. These are the remains of ancient underground valleys that crossed this part of the Rhodopes 1.5 million years ago. For many millennia, underground waters have dissolved marbles, destroyed the walls of caves and created a fantastic world of dungeons. Finally, the walls of the caves could not stand it and collapsed, pushing the bed of the underground river to the side. The height of the "wonderful bridges" reaches 30 m, and the width is 50 m. Here, in the niches of the former, the sites of an ancient man were discovered, stone axes, ceramics.

The Karst Plateau (territory and) is a rocky desert, striking in its dull appearance. There is no water and no greenery to be seen. Its surface is covered with cracks, pits, ruts and funnels. There are also rivers here, but they flow under the surface of the earth in dark and damp underground channels. In addition to lack of water, deep cracks, dips, bottomless wells await the traveler at every step. There are areas where funnels literally, like pockmarks, dug up the surface. Their number reaches 150 pieces per square kilometer. Red-brown clays with crushed stone, found at the bottom of the funnels, are the product of not only the chemical dissolution of limestones, but also the washout along the cracks of the karst massif, as well as dust brought by the wind.

Shafts and wells are narrow, almost vertical channels formed by the expansion of cracks. The diameter of the wells is different - from 0.3 to 350 m, the depth can reach 1300 m. Karst valleys, occupied by channels of both underground and surface rivers, are characterized by a sharply stepped longitudinal profile. Strange rivers appear from the cave, flow for several kilometers on the surface and again hide in the cave. These valleys are without floodplains, without terraces, without floods and floods. special kind karst are fields - closed or semi-closed basins. The areas of fields reach 500 - 600 km2, depth - hundreds of meters, width - 10 - 15 km. One of them - in the northwestern part of the Dinaric Highlands - covers an area of ​​380 km2. The axis of the basin coincides with the direction of the mountain ranges and the orientation of the folded structures. During periods of heavy rains, thin particles of soil are washed away and gradually all cracks are filled with water. This leads to the cessation of filtration, and atmospheric precipitation contributes to the silting of the basins.

Karst caves are deep underground. They are very diverse in size and configuration, which is explained not only by the occurrence of karst rocks, but also by a certain stage of their development. In caves, among the numerous forms of karst associated with the accumulation of dissolved matter, stalactites and stalagmites are mainly known. Lime icicles - stalactites - reach a height of several meters and a thickness of 1.5 - 5 m. In the process of growth of stalactites in the water, the content of CaCO3 decreases. Precipitated calcium carbonate cements the clastic material and forms carbonate deposits. Stalagmites - limestone pillars and cones - grow from the bottom up and reach a height of 15 - 20 m. All this happens very slowly. It is estimated that the 19 m high stalagmite in Carlsbad Cave took about 50 million years to form. Sinter forms of karst relief include dams blocking underground passages. Behind such dams there are lakes. But the age of the dams is younger than the stalagmites - 9 - 10 thousand years. Under the influence of warm, humid monsoons, limestone rocks undergo karst formation, as a result of which many bizarre landscapes arise: either steep cliffs rise above the abyss, then deep caves gape in the mountains, or stone bridges are thrown across the rivers. All this is called tower karst. In some areas, where limestone rocks have been destroyed, rounded valleys with a flat bottom have formed. In such valleys, at the same distance from each other, cone-shaped limestone hills rise, and at their foot stepped fields are located like an amphitheater, which makes each hill look like a giant castle with fortress walls and watchtowers. Sometimes small hills with sharp peaks are visible in the valleys, resembling huge haystacks from a distance. Karst valleys, as a rule, are very wide, and limestone blocks are often found in the middle of them.

In the warm and humid conditions of the tropics, the karst relief takes on bizarre forms. Dome-shaped hills and ridges, towers, sharp cones, karst plains stand out. The systems of rounded domes are dissected by gorges that arose along tectonic cracks. The periphery of the domes is framed by tower karst. Karst basins and plains are separated by jagged ridges and deep hollows. Fragments of limestone that have fallen from the slopes of towers or domes are quickly destroyed.

Dense vegetation covering the slopes contributes to the activity of acidic waters different composition. Therefore, as a rule, there is no accumulation of debris at the foot of karst hills or small mountains. Weathering turns them into sand and clay, which are quickly carried away by jets of water during rainy periods. The greatest intensity of karst processes is in wet areas, and the least - in dry areas.

Flowing water dissolves not only carbonate and saline, but also silicate rocks, in which this process proceeds a thousand times slower. Sandstones, granites, shales and other crystalline rocks are dissolved. River water flowing through such rocks in the humid tropics contains a lot of soluble silica. Landforms associated with silicate karst are diverse. On to South America dips, wells, mines, funnels are observed in quartzites. Even a system of caves about 2 km long with horizontal passages and deep wells was found in quartzites on the Guaiquinima plateau.

Giant mines with a diameter of 350 m and a depth of more than 500 m are observed on the Roraima plateau, composed of ancient quartzites. Based on the analysis of quartzites, which contain silicate karst, it can be concluded that dissolution of both quartz grains and silicate cement occurs here. Moreover, the process should not stop for tens and hundreds of millions of years.

Forms of silicate karst are formed as a result of both the dissolution of rocks and their biochemical weathering.

Karst is a set of processes and phenomena associated with the activity of water and is expressed in the dissolution of rocks and the formation of voids in them, as well as peculiar landforms that arise in areas composed of rocks that are relatively easily soluble in water - gypsum, limestone, marble, dolomite and rock salt.

The karst relief differs significantly in temperate and tropical latitudes. In temperate latitudes, karst processes depend on the depth of groundwater, which is the basis of denudation for karst. On this basis, shallow and deep karst are distinguished. Small karst is characterized by fast pace development, but less rugged terrain. Deep karst takes longer to develop, but at the same time deep depressions on the surface and numerous caves are formed.

According to the location of karst forms, surface and deep (underground) karst are distinguished. In turn, surface karst, depending on the exposure on the surface of karst rocks, is divided into two types: open (bare, Mediterranean), when karst rocks lie directly on the surface, inherent in mountainous areas where bedrock exposure is better; and covered (Eastern European), when karst rocks lie at some depth under loose non-karst deposits.

Surface forms of karst include karrs (shratts), funnels, hollows (ridge), fields.

Carry - a complex of narrow furrows 1-2 m deep, separated from each other by sharp ridges. Karr - forms of microrelief, which are formed due to the dissolution and mechanical destruction of rock cracks by surface water.

Funnels are widespread in conditions of both bare and covered karst, both in the interfluves and along the bottoms of the gullies. These are rounded, usually cone-shaped depressions of different sizes (up to tens, rarely hundreds of meters in diameter) and different depths (from a few meters to tens of meters). Small flat-bottomed funnels are called saucers. When connecting many funnels due to the destruction of the jumpers between them, extensive closed depressions are formed - hollows, or ridges. They usually have steep, scalloped slopes, uneven bottoms, and large dimensions: kilometers long, hundreds of meters wide, and a few tens of meters deep.

The largest karst forms - the lias resemble a graben in miniature. These are vast oblong closed depressions with an area of ​​more than 200-300 km, a depth of hundreds of meters, with steep slopes, with hills-outliers on the bottom, with streams and even villages. The largest fields are Lebanese with an area of ​​379 km2 in Bosnia, Popovo - 180 km2 in Herzegovina. Apparently, they are formed at the confluence of basins along the lines of tectonic faults, i.e., they are predetermined by tectonics.

Underground forms of karst - wells, mines, abysses, caves.

Karst wells are formed as a result of the collapse of the roof over an underground abyss. The wells are cylindrical in shape and up to 20 m wide and deep.

Mines are narrow, deep (hundreds of meters) canals-pipes. Their trunks can be straight, broken, curved. They are formed as a result of the expansion of channels-fractures, and are often laid at the intersection of several fracture systems.

Combinations of natural mines with horizontal and inclined caves are commonly referred to as karst chasms. The deepest karst abyss in the world is Jean-Bernard with a depth of 1535 m in the Savoy Alps of France.

Caves - cavities of various shapes and sizes inside rocks, opening onto the earth's surface with one or more holes. The formation of caves is associated with the intense dissolving power of water in rock fissures. Expanding them, water creates a complex system of channels.

According to the structural conditions, two classes of modern karst are distinguished: flat and mountainous. Within these classes, depending on the geological structure, the history of the development of the territory, karst and related landforms are divided into a number. According to the composition of rocks, carbonate, sulfate, halide (salt) and transitional types of karst between them (carbonate-sulfate, etc.) are distinguished. Subtypes are distinguished within lithological types, for example, limestone, Cretaceous,

dolomitic, etc. Based on whether karst is currently developing on the surface or under the cover of any sediments, in the first case, naked, or Mediterranean, karst is distinguished, and in the second - covered, or East European (Russian), karst.

By age, karst is divided into modern (developing) and ancient (not developing), or fossil. All presented classes and types of karst are developed in all climatic zones the globe. They are also widely distributed on the territory of the Russian Plain, where eight karst regions are distinguished, including a number of provinces and districts with various types of karst. The map shows that most of the Russian Plain has developed carbonate karst, predominantly limestone. Cretaceous karst is developed on a smaller area and mainly in the southern regions. Despite the diversity of karst types, all of them are characterized by the same or similar landforms.

Karstom called phenomena that occur in soluble rocks (limestone, dolomite, gypsum, less often salt, chalk) under the combined action of surface and mainly groundwater. The phenomena of karst formation lead to the emergence of special landforms: carr, sinkholes, wells, mines, karst basins, fields, etc.
Conditions for the formation of karst forms: 1) the presence of soluble rocks; 2) the presence of cracks that make these rocks permeable; 3) a slight slope of the surface, allowing water not only to drain, but also to seep; 4) significant thickness of karst rocks; 5) their elevated position or the low position of the groundwater level, which ensures the vertical circulation of water in the rocks; 6). enough, but not too much water.
When karst rocks are on the surface, the karst is called open (Mediterranean); if these rocks are covered by other "rocks that do not karst, karst is called covered(Central European).
Carry(shratts) - deep furrows on the exposed surface of karst rocks, separated by narrow, often sharp ridges. The karrs are arranged in rows parallel to each other, or represent complex branching labyrinths. The depth of the karrs ranges from a few centimeters to 2 m.
The formation of this form of karst relief is caused by the chemical and mechanical action of rain water, melting snow, the sea (in the surf zone) on the surface of soluble rocks. The dissolution proceeds intensively in depressions through which water flows.
The shape and size of carr depend on the chemical composition and nature of rock fracturing, as well as on climate. Carr is best expressed in pure limestones in the dry subtropics. Under these conditions, the furrows and ridges are more or less symmetrical and have approximately the same dimensions.
Accumulations of carr form impenetrable carr fields. Over time, the surface covered with karr changes: the cracks widen, the ridges collapse, and heaps of limestone blocks appear, very typical for areas of developed open karst. Carr surfaces are almost always devoid of vegetation.
sinkholes characteristic of both open and covered karst (Fig. 109). This is the most typical and widespread form of karst relief. There are funnels of surface dissolution and failure, as well as funnels of "sucking".

Surface dissolution funnels are formed in areas of open karst as a result of the dissolution of the walls of cracks that cut the surface. In shape, they are saucer-shaped and cone-shaped. Saucer-shaped depressions of the surface arise when the walls of numerous small cracks dissolve. When the walls of a deep crack dissolve, a cone-shaped funnel is formed with a slope steepness of 30-45°. At the bottom of such a funnel there is a ponor - a hole through which water flows into it.
Failed funnels- the result of the collapse of the roof of underground caves - they have steep, steep slopes, at the bottom - a heap of blocks of collapsed rocks. Over time, if the collapse is suspended, the slopes of the funnel become more gentle.
Funnels "sucking" common in areas of covered karst. They are formed when sandy-clay particles are washed out by water flowing into the ponor from surface insoluble rocks. If the washed out particles clog the ponor, funnel growth slows down or stops altogether. Externally, seepage funnels resemble cone-shaped dissolution funnels. Their slopes are usually covered with vegetation.
Karst funnels, when the ponor is blocked or when the groundwater level rises, can become a place of accumulation of water and turn into temporary or permanent karst lakes.
With the expansion of large cracks in karst rocks, karst wells and mines appear.
Karst wells- depressions of a cylindrical shape, reaching a depth of tens of meters. The width of a karst well is usually not less than its depth. They are formed as a result of the collapse of the arches of the underground cavity.
natural mines they look like a pipe with bends and expansions, descending to a great depth from the surface (the deepest karst mine near Trieste is 523 m). Rivers can disappear in karst wells and mines.
Vast closed basins found in karst areas are called fields. Polya occupy an area of ​​up to several hundred square kilometers (for example, the Lebanese field in Western Bosnia - 379 sq. km). The flat bottom of the fields is limited by ledges several hundred meters high. At the bottom, lined with sediment, limestone mountains can rise - remnants, rivers flow. When flooded with water, the fields turn into permanent or temporary lakes.
The formation of fields can be caused not only by the process of karst formation, but also by tectonic processes, as well as the removal of insoluble rocks occurring among limestones.
river valleys in karst areas, they usually result from the collapse of tunnel vaults over underground rivers. They can be classified as canyons. In some places, when the vaults collapse, karst bridges appear.
In karst rocks, along with special forms of surface relief, various underground cavities are created - caves. They occur mainly in limestone, gypsum and rock salt strata as a result of crack expansion under the action of groundwater. Watercourses often flow in growing caves, lakes are located. When groundwater flows down the cracks, the caves dry up and stop growing. If water seeps into the cave from above, droplets of which evaporate from the ceiling and floor of the cave, sinter formations of carbonic lime appear, gradually filling the cave. Stalactites hang from the ceiling in the form of giant icicles, and stalagmites rise from the floor to meet them. When they meet, they merge into columns. In the humid air of a cave (with a river or lake), sinter formations are not created.
Karst caves reach especially large sizes in thick limestone strata deformed by tectonics.
The Hellock Cave (Switzerland, Alps) is the largest of all known caves. Its length (without side branches) is 78 km. Mammoth Cave has a length of 74 km, without branches - 48 km. In Russia, the Kungur cave is interesting. It is formed in gypsum, which occurs among layers of limestone and dolomite. The complex labyrinth of the most branching explored galleries of the cave stretches for 4-5 km. The cave has several floors. There are more than 30 lakes of various sizes at the bottom of the cave. The area of ​​the largest of them is about 200 square meters. m, depth - 4-6 m. The Kungur cave belongs to the type of cold (ice) caves.
The air of cold (ice) caves has a low temperature throughout the year due to the fact that it communicates with the outside air through an opening (entrance) located in the upper part of the cave. In winter, cold heavy air fills the cave, in summer it remains in it and does not have time to warm up. Moisture that gets into the cave freezes, forming ice.
In contrast to cold caves in warm caves, the entrance is located at the bottom. The cold air that fills the cave in winter flows out of it in summer, giving way to rising warm air. In such caves, archaeologists often find the remains of the sites of ancient people.
Caves with two entrances - upper and lower - are called through (wind). The air temperature inside such caves is close to the temperature of the outside air.
Stages of development of karst relief. In the initial stage of development of the karst relief (young karst), groundwater is deep. The rocks on the surface are almost devoid of cracks and weakly pass water. There are surface streams. On the surface of the exposed karst, karrs appear, funnels, wells appear. As cracks widen and their number increases, seepage increases, but some water still remains on the surface.
Leaked water accumulates above the water-resistant layer (the layer may be water-resistant temporarily, until it is dissected by cracks), forming separate streams.
In the stage of maturity, the process of karsting proceeds from below and from above. Dips appear on the surface, funnels merge into depressions, fields appear. Almost all water from the surface goes down along the cracks, the vertical circulation of water leads to the formation of caves. Groundwater forms a continuous network of watercourses.
In the stage of old age, the forms of karst relief lose their definiteness; Funnels flatten, fields expand, sparingly soluble weathering products accumulate on the surface, clogging ponors. The destroyed surface is reduced to the level of groundwater, so the vertical circulation of water is replaced by a horizontal one, and a normal river network is developed. Rivers flow slowly, swamps form. Raising the surface or lowering the level of groundwater can revive the processes of karst formation and renewal of the relief.
Karst phenomena are primarily due to the presence of soluble rocks, therefore they occur at different latitudes. Soluble rocks occupy about 34% of the land surface, and even if we take into account that the karst relief is far from being developed over the entire area, its wide distribution is beyond doubt. The karst relief is widely developed along the coast of the Adriatic Sea (from the Karst plateau to Greece), in the Alps, in the Crimea, on the Black Sea coast of the Caucasus, in the Urals, in the Onega region, in many regions of Siberia and Central Asia, in Jamaica, in North America (states Kentucky and Tennessee, in the Northern Yucatan, in the interior of Florida), in China, Australia, etc.
Karst regions are distinguished not only by a special relief, they are characterized by a general originality of physical and geographical conditions, associated primarily with a special regime of waters.
The ruggedness of karst regions, the poverty of the surface with water make these regions unsuitable for economic use.

On the surface, karst forms are represented carrami, gutters And ditches, ponors, funnels different types, depressions, hollows, blind valleys(Fig. 8.1).

Karr is a variety of shallow excavations, formed mainly by the leaching of limestone by surface atmospheric waters. N. A. Gvozdetsky, one of the experts on karst, identified the following types of karrs: alveolar, tubular, furrowed, grooved, fissured, and a number of others (Fig. 8.2 and Fig. 16 on a color insert). All these forms have a depth of up to 20 cm, rarely the span of the relief reaches 1–2 m. Rel-

ef with grooved carr resembles a washboard, and areas of development of numerous carr are called carr fields.

Gutters and ditches are more extended and deeper areas of karst leaching of the limestone surface, inheriting surface cracks and reaching a depth of 5 m.

Ponors are narrow holes, inclined or vertical, that appear at the intersections of cracks during the further development of the process of dissolution and leaching. These channels serve as a drain for surface water and direct it deep into the rock mass.

Karst funnels are subdivided into: 1) funnels of surface leaching-, 2) failure-, 3) suction vortices (corrosion-suffusion, according to N. A. Gvozdetsky). The first type of funnels resembles a funnel from a projectile or bomb explosion (Fig. 8.3). They are formed due to the rock leached from the surface. Usually in the center of such a funnel there is a ponor-channel, through which water leaves. The diameter of the funnels is usually up to 50 m, rarely more, and the depth is 5-20 m. The sinkholes are associated with the collapse of the roof above the cavity, worked out by the waters at a certain depth. Corrosion-suffosion funnels occur when karsting limestones are covered by a layer of sandy deposits and the latter are washed into the underlying karst cavities. At the same time,

deposits into ponors and a funnel of suction or leaching is formed. Suffusion processes are widespread in nature.

Saucers and depressions are small, small sinkholes. If funnels of different genetic types merge several pieces together, then a karst basin is formed with a number of depressions at the bottom. Sometimes the bottom of the basins can be flat.

The fields are quite large, hundreds of meters in diameter, irregular shape depressions formed by the confluence of a number of basins and funnels. including failures.

Karst wells and mines are channels that go almost vertically into limestone massifs for tens and hundreds of meters with a diameter of several meters. They are formed by leaching through cracks, sometimes by surface water flows that erode limestone. Mines are called vertical cavities with a depth of more than 20 m, and less - wells. If the mines are connected to each other, as well as to sub-horizontal passages and caves, then karst abysses are formed, reaching a depth of 1000 m or more.

Blind valleys are small rivers flowing in karst areas, having a source, but suddenly ending at some funnel or ponora, where all the water goes. Sometimes the valleys are half-blind, when the water of the river suddenly goes underground, and then, after a few kilometers, reappears, as happens in the Western Crimea near Sevastopol. The river Suuksu, starting on the slopes of the mountains, suddenly disappears, and then only its dry valley with pebbles continues. After 10-12 km, the river reappears in the form of a powerful source and already like a river. Chernaya flows into the Sevastopol Bay. It should be noted that such blind and semi-blind valleys are widely developed in places where karst rocks are distributed - in the Urals, in Bashkiria, in the Leningrad, Smolensk, Nizhny Novgorod regions, in the Crimea and the Caucasus.

In some areas European plain lakes are known that suddenly disappear and then reappear. The fact is that these lakes are located in karst basins or funnels. The ponors present in them are clogged with silt, and then the water in the lakes holds. But if such a “plug” is washed out, then the water also goes into the ponor and deeper into the karst cavities.

Karst caves appear different ways: by dissolution, leaching and erosion; by collapse, opening and subsequent erosion of tectonic cracks. Groundwater, flowing through cracks or tectonic fragmented zones, gradually dissolves and leaches limestones or dolomites. In this way, cave cavities are formed, often multi-storey and complex, when individual large caves - “halls” - are connected to other narrow channels, crevices, often with streams flowing through them.

Large cave complexes are formed for a long time - tens and hundreds of thousands of years. Many important paleontological and archaeological finds have been made in the caves, which make it possible to date the upper floors of the caves to an older age than the lower ones. The development of caves is closely related to fluctuations in the level of the groundwater table and the local basis of erosion, such as a river, as well as tectonic movements. When the groundwater table is lowered, the already developed cave cavities are drained, and the process of dissolution and leaching passes to a lower level. This may continue several times according to the stages of the river's intrusion and fluctuations in the groundwater level. In the area of ​​permafrost rocks, sinter forms consisting of ice are developed in caves.

At the bottom of the caves, reddish clay deposits, the so-called "terra-rossa", or "red earth", are often found, which are an insoluble part of carbonate rocks enriched in iron and aluminum oxides. However, the most impressive feature of a number of karst caves are stalactites and stalagmites - bizarre sinter formations that create a unique appearance of cave halls (Fig. 8.4). The thing is that the water dripping from the ceiling of the caves is saturated with CO gas, due to the dissolution of carbonate rocks, and in addition, it is saturated with calcium bicarbonate - Ca (HCO) 9. It happens as a reaction

CaC0 3 + C0 2 + H 2 0 ^ Ca (HC0 3) 2.

This water, dripping from the ceiling, loses part of the carbon dioxide, as a result of which the reaction shifts to the left and the bicarbonate again passes into CaCO 3, which is deposited both on the ceiling of the cave (stalactite) and on the bottom (stalagmite). First of all, streaks appear on the floor of the cave, similar to melted candle wax. These are the so-called gurus. Then stalagmites with a wide base appear on the gouras, and even later - resembling a stick or a pillar. Much later, stalactites began to form on the ceiling of the cave, very similar to ordinary icicles. After some time, stalactites and stalagmites can close together, and then columns of a bizarre shape are formed. There are beautiful multi-tiered caves in the Crimean mountains, where they were formed in thick limestone strata of the Upper Jurassic; in the Czech Republic, Slovenia, the Urals, the Caucasus and elsewhere.

So far, we have been talking about open karst. However, in many areas, especially platform ones, where closed karst is developed, there are

so-called suffusion funnels. They arise in the case when the process of leaching into karst cavities begins from the thickness of sediments overlying karst forms. Gradually, a funnel forms in place of this thickness, and even lower - cavities where these deposits can fall (Fig. 8.5).

Karst forms develop wherever there are karst rocks - limestone, dolomite, gypsum, anhydrite, rock salt. Covered karst is widely developed within the Russian Plate, since Carboniferous and Devonian limestones are everywhere overlain by moraine and fluvioglacial Quaternary deposits. There is also ancient karst, for example, near Moscow, where in karst forms on the surface of carboniferous limestones pockets of clayey Upper Jura occur. During the Permian, Triassic, Early and Middle Jurassic, this area was dry land and intensive karst formation took place on it.

Gypsum karst is developed on the northern slopes of the Ufimsky plateau in Bashkiria, where Lower Permian red-colored rocks with interlayers of gypsum and dolomites are common. Karst basins there have depths of up to 100 m and a diameter of up to several kilometers. Gypsum karst caves in Transnistria are 142.5 km long (Optimisticheskaya Cave), ranking second in the world. The famous Kungur "ice" cave in the Perm region in the Urals has a length of 5.6 km and was formed in gypsum and anhydrite of the Kungurian stage of the Lower Permian. It is famous for its 150-160 m long grottoes with ice ceilings on the vaults and floor.

Karst process is the process of dissolution of rocks by surface and ground waters. The geomorphological forms that form as a result of this process are called karst forms. The development of the map is determined geological, orographic, hydrogeological and climatic conditions.

1. Among geological conditions is of great importance composition of rocks and nature of fracturing. The largest and most pronounced forms of karst relief occur in easily soluble rocks, practically devoid of insoluble impurities. Allocate 1) calcareous karst, 2)karst in gypsum and saline rocks, and also 3) pseudokarst, or "clay" karst, in carbonate clay rocks.

And although rock salt and gypsum are more soluble than limestone and dolomite, gypsum and salt karst is relatively little developed due to the insignificant distribution of these rocks, especially their outcrops on the day surface. Limestones and dolomites under normal conditions are characterized by low solubility, but under certain physical and geographical conditions, the chemical aggressiveness of water in limestone areas can increase significantly, and under favorable geological conditions, expressive and vast karst landscapes appear, confined specifically to limestones. The main condition for the solubility of limestone is a sufficient amount of CO 2 in water, then it becomes aggressive and dissolves carbonate rocks. In addition to carbon dioxide, limestones are dissolved by humic and sulfuric acids.

An important factor facilitating the development of karst forms is fracturing. But very narrow ones less than 1 mm in size do not contribute to karst formation. In active cracks larger than 1 mm, water circulates and expands them. This is how the development of karst forms begins.

2. Orographic conditions . The most favorable for karst formation are open spaces composed of easily soluble rocks, without steep slopes, but with small depressions for surface water stagnation and snow accumulation. The basis of erosion of groundwater and surface rivers should be low enough to provide the greatest depth of karst.

3. Hydrogeological conditions . If the flow of groundwater has a slight slope, low speeds, then the nature of its movement approaches laminar, contributing to dissolution.

With a large slope and significant flow velocities, the nature of the movement corresponds to turbulent, and along with the processes of karst formation, suffusion- mechanical destruction and removal of insoluble particles. The depth of groundwater, the thickness of the aquifer and the conditions of its supply determine the development of circulation zones in the karst massif. Usually allocated three circulation zones:

1) the upper one covers the rock mass from its exit to the surface to the groundwater table. This aeration or vertical circulation zone. The free gravitational movement of water prevails here, occurring periodically during rains or snowmelt;

2) average - zone of intermittent saturation. There are sharp fluctuations in the level of groundwater associated with the periodic flow of water from the surface. The circulation of water here is close to horizontal.

3). The boundaries of this zone are the highest and lowest levels of the groundwater table;

4) lower zone - permanent full saturation zone. Its upper boundary is the lowest level of the groundwater table, the lower one is the aquifer. The circulation here is predominantly horizontal. On the outskirts of the karst region, this zone gives rise to rivers, karst springs, through which groundwater is discharged to the surface.

4 Climate factor. Favorable conditions for the development of karst are created by frequent downpours, which carry away all deposits from insoluble rocks, and the corrosive effect of slowly melting snow cover. This applies to the mountainous regions of the calcareous plateaus of the Crimea, the Caucasus, the Carpathians, the Alps, and others. The solubility of limestones increases due to relatively high temperatures and surface heating of rocks in summer. All these favorable conditions with the release of easily soluble rocks to the surface leads to the formation bare, open or mediterranean karst with varied karst topography. If karst develops under oppressed conditions (soluble rocks are covered by slightly soluble ones), this closed, or Central European, karst.

In the areas of karst formation, there are: 1) surface, 2) transitional and 3) underground karst.

Surface forms of karst relief

Rain and melt water, flowing down the surface of the limestone, separate the walls of the cracks. The result is a microrelief carr or schratt.

1. Carry , or shratty represent a system of ridges and ruts or furrows separating them, located almost parallel to each other, if the fall of the layers is clearly expressed and the fracturing of the rocks coincides with the direction of the fall. With a complex system of fracturing, the carres are located incorrectly: they branch out and intersect again. The depth of the furrows can reach 2 m. Karr can also be formed in the coastal strip under the influence of the sea surf on karst rocks. The spaces covered with carr are called carr fields. When limestone dissolves, an insoluble part always remains, represented by clay material of red or Brown. This eluvial material, accumulating on the surface of the rock, forms a kind of weathering crust, characteristic of karst regions, called terra rossa (red earth). The cessation of carr formation is associated with the accumulation of terra-rossa and complete cementation of fractures. Therefore, fracturing is one of the conditions for carr formation.

2. With intensive vertical circulation of water, the process of dissolution of karst rocks leads to the formation honor - canals that absorb surface waters and divert them into the depths of the karst massif. The size and shape of the ponors are different; on the surface, the ponors are expressed as gaping cracks or holes; in the depths, they begin a complex system of channels for the vertical circulation of water.

3. Expansion of the mouths of the ponor in the process of further dissolution leads to the formation sinkholes various sizes and shapes. Distinguished in areas of closed karst are saucer-shaped shapes with a width approximately 10 times greater than the depth, and gentle (up to 10-12 0) slopes, and funnel-shaped, with steep, sometimes sheer walls. According to the method of formation, they are distinguished karst And suffusion-karst (or suction funnels). The merging of individual sinkholes leads to the formation of more large forms -karst baths . The long-term development of this process contributes to the emergence of extensive depressions of rounded and elliptical outlines - karst basins .

Karst landforms can be randomly scattered over the surface of a karst massif, or be concentrated along lines determined by the direction of underground runoff or the occurrence of karst rocks. Landforms can change from one to another. So a karst saucer as a result of deepening, and a karst well as a result of flattening of the slopes can turn into a karst funnel. With continued dissolution of the walls of the ponor, the channel can become very large and turn into a natural well or natural mine, which can reach a depth of several tens to several hundred meters. For example, the depth of one of the mines in northern Italy near the city of Verona reaches a depth of 637 m. General direction the mines are vertical, but some sections of the mines can be almost horizontal or inclined. Landforms like natural mines, but smaller, are called natural wells .

Correct, or superficial, funnels, merging, form blind ravines or forms of bizarre outlines, called ridge . Ridges up to 700 m in diameter are known at depths up to 30 m. Ridges represent, as it were, transitional forms to even larger karst forms - polyam- extensive karst depressions, usually flat-bottomed and with steep walls, several kilometers, and sometimes tens of kilometers in diameter. The area of ​​Popov Polya in Yugoslavia (western Herzegovina) is approximately 180 km2. Sometimes a watercourse flows along the flat bottom of the field, which in most cases emerges from one wall of the field and hides in an underground gallery in the opposite wall. It is assumed that in the origin of the fields, leaching processes in combination with various factors were of primary importance: tectonic, lithological (the ratio of karsting and non-karsting rocks) and erosional, i.e. field formation is a complex long polygenic process.

Rivers and valleys of karst regions

According to the hydrological regime and morphology of river valleys, I.S. Shchukin subdivides the surface watercourses of karst regions into five types:

1. episodic rivers, their valleys do not leave the aeration zone, i.e. deeply embedded. Therefore, water in these valleys appears only during heavy rains or rapid spring snowmelt, when the ponors in the channel do not have time to divert all the water deep into.

2. constantly flowing rivers. The bottoms of the valleys of such rivers lie above the groundwater level of the karst massif. These are high-water rivers, they begin outside the karst region, within the karst rocks they lose water, but do not dry out completely. The valleys of such rivers are often narrow, deep canyons with steep sheer sides.

3. Constantly flowing rivers, the valleys of which are incised to the groundwater level which they mainly feed on. The morphology of their valleys is similar to type 2, but there are differences. Often the slopes of the valleys turn towards each other towards the source and merge in the form of a wall, at the base of which the river emerges from the grotto. Such valleys with a closed upper end are called bag-shaped. There are valleys that do not have a mouth, i.e. they do not open into another valley or reservoir, but end in a dead end - blind valleys. The semi-blind valleys are also closed at the end, but the ledge, against which the watercourse "rests", is low, and during the flood the water overflows through it. The lower part of such rivers is a shallow incised hollow, dry for most of the year.

4. Rivers that cut through the entire thickness of karst rocks and deepened into the underlying impermeable rocks. Naturally, they have a constant and ever-increasing water flow due to numerous springs at the contact of carbonate rocks with an aquiclude. The upper parts of the slopes of such valleys, composed of limestone, are usually steep, while the lower ones are gentle. Landslides and blocks of settling for the slopes of the valleys are characteristic.

5. Underground or cave rivers flowing through the system of underground galleries. They begin either outside the karst massif, or originate within it. Sometimes they come to the surface in the form of powerful vokluzny sources (vaucluse - a permanent source with a large debit, named after the Vaucluse source, first described in France).

transitional forms. These include karst cavities that combine surface and underground forms with vertical and inclined channels - ponors and natural wells.

Caves of karst areas

caves- it's varied underground cavities formed in karst areas and having one or more exits to the surface. Their formation is associated with the dissolving activity of water penetrating into cracks. When they expand, a complex system of channels is formed, and in the zone of horizontal circulation, where water produces the greatest dissolving effect, a main channel is formed. It gradually expands due to neighboring cracks, drawing water from neighboring channels. This is how an underwater river is formed.

The cave may have one or two entrances. With one inlet at the opposite end, it (the cave) will end with a system of narrow cracks and passages, or landslide or sinter formations that clog it - this blind caves. Caves with exits on both sides - passing caves.

In caves, on the bottoms, walls and vaults, sinter forms are formed. From the ceiling of the cave hang in the form of icicles, narrow and long stalactites. From the bottom of the cave, more powerful and shorter ones rise towards them. stalagmites. Growing together, these forms form sinter columns. Sinter forms are not formed in every cave. Ice accumulates in some caves, such caves are called icy or cold(Kungur ice cave). For the accumulation of ice and snow, firstly, appropriate climatic conditions(there are no ice caves in the tropics, but there are in the Crimea), and secondly, a favorable configuration of the cave, while the entrance to the cave should be vertical.

The hypsometric position of the caves through which the rivers flow is closely related to the height of the bottoms of the valleys draining the karst massif. During the tectonic uplift of the terrain, the valleys deepen, while the mouths of the cave rivers dry up, turn into dry caves, and at the level of a new basis of erosion, new system horizontal galleries. Arises storey karst. Human tools, bone remains of (ancient) animals, remains of fire pits, etc. are found in the caves, which makes it possible to date the tier of caves and the corresponding erosional mountain terraces on the slopes of ancient river valleys. A number of Paleolithic sites have been discovered in the Ural Mountains (Glukhaya and Medvezhya caves).

With negative tectonic movements, karst cavities sink (sometimes to a depth of several hundred or even 1000 m), are filled with water and sediments and turn into buried karst.

Zonal-climatic types of karst

Karst process- This is a denudation process, so it proceeds differently in different climatic zones. Bare (or open) karst is typical of areas with a Mediterranean subtropical climate. Along with the favorable geological structure, climate contributes to karst processes here. In the temperate climate zone, karst processes also develop quite intensively, but this zone is characterized by mostly closed karst, karst formations are associated here with underground leaching, and surface forms are due to failures and subsidence of loose cover above underground karst cavities (sucking funnels).

In a tropical humid climate, karst began to be studied relatively recently. If the karst of temperate regions is characterized by a landscape of more or less one-height plateaus with numerous negative landforms, then the tropical karst is characterized by the development of positive landforms in the form of towers or cones rising above a certain middle level - the basal surface. In the process of development of tropical karst, depressions appear, dividing the entire karst massif into separate hills. The depressions deepen to the level of the basal surface, and then this surface expands due to the reduction of the areas occupied by the elevations until they are completely destroyed. In the end, leveled karst-denudation surfaces are formed.

According to the morphology of positive relief elements, tropical karst is divided into: domed, tower, conical, hollow. According to I.S. Shchukin, these types are genetically related and most likely represent only different stages in the formation of the karst landscape or may be due to local geological conditions.

Pseudokarst processes and forms. Along with real karst, there are phenomena and forms that outwardly resemble karst, but are based on completely different reasons than those that lead to the formation of karst forms. This clayey karst and thermokarst. Clay karst characteristic of arid and semiarid regions composed of highly carbonate clays, loams and loess. The fracturing and porosity of these rocks brings these areas closer to the areas of typical karst development. Suffusion in carbonate or saline clays and loams leads to the formation of subsidence depressions - the so-called saucers. Under conditions of well-developed fracturing in such rocks, deep underground passages and dips are formed that fill real karst. Such pronounced formations are called clayey karst. Thermokarst is formed in permafrost conditions. Various collapse and subsidence forms are also observed here, but they are associated with the melting of buried ice.

Pseudo-karst phenomena also include the ability of rocks to quickly and significantly compact when wetted. These rocks include loess and saline soils. As a result, pseudo-karst saucers and, more rarely, funnels are formed.