The most common surface landforms of karst areas. Karst landforms

Karst process is a process of dissolution rocks surface and groundwater. Geomorphological forms that are formed as a result of this process are called karst forms. Development map 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 arise in easily soluble rocks, practically devoid of insoluble impurities. Select 1) lime karst, 2)karst in gypsum-bearing and salt-bearing rocks, and also 3) pseudokarst, or “clayey” karst, in carbonate clayey rocks.

And although rock salt and gypsum have greater solubility than limestones and dolomites; gypsum and salt karst are relatively underdeveloped due to the insignificant distribution of these rocks, especially their outcrops on the daytime 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 karst landscapes appear that occupy vast spaces, 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 fracturing contributes to the development of karst forms. 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 stagnation of surface water and accumulation of snow. The base of erosion of groundwater and surface rivers should be located low enough, providing the greatest depth of karstization.

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

With a large slope and significant flow rates, 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 recharge determine the development of circulation zones in the karsting massif. Usually highlighted three circulation zones:

1) the upper one covers the rock thickness from its outcrop to the groundwater table. This zone of aeration or vertical circulation. Free gravitational movement of water prevails here, occurring periodically during rains or melting snow;

2) average - zone of periodically complete saturation. Here there are sharp fluctuations in the groundwater level associated with the periodic supply of water from the surface. The water circulation here is close to horizontal

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

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

4 Climatic factor. Favorable conditions for the development of karst are created by frequent rainfalls, which remove all sediment 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, etc. The solubility of limestones increases due to relatively high temperatures and surface heating of the rocks in the summer. All these favorable conditions with the release of easily soluble rocks to the surface lead to the formation bare, open or Mediterranean karst with varied karst topography. If karst develops in depressed conditions (soluble rocks are covered by slightly soluble rocks), this closed, or Central European, karst.

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

Surface forms of karst relief

Rain and melt water, flowing over the surface of the limestone, separates the walls of the cracks. As a result, a microrelief is formed Carrs or Shratts.

1. Carry , or shratts 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 fall. With a complex system of fractures, the karries are located incorrectly: they branch and intersect again. The depth of the furrows can reach 2 m. Karrs can also form in coastal strip when exposed to sea surf on karst rocks. Spaces covered with karrahs are called carr fields. When limestone dissolves, an insoluble part always remains, represented by red or brown clayey material. This eluvial material, accumulating on the surface of the rock, forms a kind of weathering crust, characteristic of karst areas, called terra rossa (red earth). The cessation of karr formation is associated with the accumulation of terra rossa and complete cementation of cracks. Consequently, fracturing is one of the conditions for carr formation.

2. With intense vertical circulation of water, the process of dissolution of karst rocks leads to the formation disgrace - channels that absorb surface water and discharge it into the depths of the karst massif. The size and shape of ponoras are different; on the surface, ponoras are expressed by 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 ponora in the process of further dissolution leads to the formation sinkholes various sizes and shapes. In areas of closed karst, there are saucer-shaped forms with a width approximately 10 times greater than the depth, and gentle (up to 10-12 0) slopes, and funnel-shaped ones, with steep, sometimes sheer walls. According to the method of education they are distinguished karst And suffosion-karst (or suction funnels). The merging of individual sinkholes leads to the formation of larger 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 across the surface of the karst massif, or concentrated along lines determined by the direction of underground flow or the occurrence of karst rocks. Landforms can transform into one another. Thus, a karst saucer, as a result of deepening, and a karst well, as a result of flattening the slopes, can turn into a karst funnel. With the 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 it reaches a depth of 637 m. The general direction of the mines is vertical, but individual sections of the mines can be almost horizontal or inclined. Landforms similar to natural mines, but smaller in size, are called natural wells .

Regular, or superficial, funnels, merging, form blind ravines or forms of bizarre outlines, called uvala . Uvalas up to 700 m in diameter at depths of up to 30 m are known. Uvalas are, as it were, transitional forms to even larger karst forms - fields- extensive karst depressions, usually flat-bottomed and with steep walls, several kilometers, and sometimes tens of kilometers in diameter. The area of ​​Popova Polja in Yugoslavia (western Herzegovina) is approximately 180 km 2 . Sometimes a watercourse flows along the flat bottom of a field, which in most cases appears from one wall of the field and disappears into 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 karst and non-karst rocks) and erosion, i.e. field formation is a complex, long-term polygenic process.

Rivers and valleys of karst areas

Surface watercourses of karst areas by hydrological regime and morphology river valleys I.S. Shchukin is divided into five types:

1. Episodic rivers, their valleys do not leave the aeration zone, i.e. shallowly embedded. Therefore, water appears in these valleys only during heavy rains or rapid spring snowmelt, when the pores in the riverbed do not have time to drain all the water deeper.

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 sides.

3. Constantly flowing rivers, the valleys of which are cut 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 close 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 sac-shaped. There are valleys that do not have a mouth, i.e. they do not open into another valley or body of water, but end in a dead end - blind valleys. Semi-blind valleys are also closed at the end, but the ledge into which the watercourse “rests” is low, and during floods the water overflows over it. The lower part of such rivers is a shallowly incised hollow, dry for most of the year.

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

5. Underground, or cave, rivers flowing through a system of underground galleries. They either begin outside the karst massif or originate within its boundaries. Sometimes they come to the surface in the form of powerful Vaucluse springs (Vaucluse is a constant source with a large flow rate, named after the Vaucluse spring, 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- these are diverse underground cavities that form in karst areas and have 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 entrance holes. With one entrance hole at the opposite end, it (the cave) will end in a system of narrow cracks and passages, or collapse or sinter formations that clog it - this blind caves. Caves with exits on both sides - walkable caves.

In caves, sinter forms form on the bottoms, walls and vaults. Narrow and long icicles hang from the ceiling of the cave stalactites. More powerful and shorter ones rise up from the bottom of the cave to meet them. stalagmites. Growing together, these forms form sinter columns. Sinter forms do not form in every cave. Ice accumulates in some caves, these 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 Crimea), and secondly, the favorable configuration of the cave, while the entrance to the cave should be vertical.

The hypsometric position of the caves through which rivers flow is in close connection with the height of the bottoms of the valleys draining the karst massif. With tectonic uplift of the area, the valleys deepen, while the mouths of cave rivers dry out, turn into dry caves, and at the level of the new erosion base, a new system of horizontal galleries is formed. Arises storey karst Human tools, bone remains of animals (ancient), remains of fire pits, etc. are found in the caves, which makes it possible to date the tier of the 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).

During negative tectonic movements, karst cavities descend (sometimes to a depth of several hundred and even 1000 m), fill with water and sediments and turn into buried karst.

Zonal and climatic types of karst

Karst process- This is a denudation process, so it occurs differently in different climatic zones. Bare (or open) karst is typical of areas with a Mediterranean subtropical climate. Karst processes along with favorable geological structure The climate here is conducive. In moderate climatic zone karst processes also develop quite intensively, but this zone is characterized mainly by closed karst, karst formations here are associated with underground leaching, and surface forms are caused by failures and subsidence of the loose cover above underground karst cavities (suction craters).

In conditions of a tropical humid climate, karst began to be studied relatively recently. If karst in temperate regions is characterized by a landscape of more or less single-height plateaus with numerous negative relief forms, then tropical karst is characterized by the development of positive relief forms in the form of towers or cones rising above a certain average level - the basal surface. During the development of tropical karst, depressions arise, dividing the entire karst massif into separate elevations. 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 hills until they are completely destroyed. Eventually, leveled karst-denudation surfaces are formed.

Based on the morphology of positive relief elements, tropical karst is divided into: domed, tower, conical, basin. 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 determined by local geological conditions.

Pseudokarst processes and forms. Along with real karst, there are phenomena and forms that are externally similar to karst, but are based on completely different reasons than those that lead to the formation of karst forms. This clay 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 failures are formed, filling real karst. Such pronounced formations are called clay karst. Thermokarst forms in permafrost conditions. Various collapse and subsidence forms are also observed here, but they are associated with the melting of buried ice.

Pseudokarst phenomena also include the ability of rocks to quickly and significantly compact when wetted. These rocks include loess and saline soils. As a result, pseudokarst saucers and, less commonly, sinkholes are formed.

Under the term "karst" understand the totality of specific landforms and features of land and underground hydrography, characteristic of some areas composed of soluble rocks, such as rock salt, gypsum, limestone, dolomite, etc.

The essence of karst processes consists in the dissolution of rock by atmospheric, melted, underground, and in some cases sea ​​waters.

According to the composition of karst rocks, karst is: halide, sulfate, carbonate.

And although rock salt and gypsum have greater solubility than limestones and dolomites, gypsum (sulfate) and salt (halide) karst relatively little developed due to the insignificant distribution of these rocks, especially their outcrops on the surface. Under normal conditions, limestones and dolomites are characterized by low solubility, but they are much more widespread than gypsum or rock salt. Therefore, it is the most studied and most widespread limestone karst.

The main condition for solubility limestone - a sufficient amount of dissolved CO 2 in water. Then the water becomes chemically aggressive and vigorously attacks carbonate rocks.

Other important conditions determining the development of karst include: a) relief; b) purity and power of limestones; V) rock structure; G) climate; d) fracturing karst rocks.

Depending on whether karst rocks extend to earth's surface or they are covered on top by non-karst deposits, distinguish bare and covered karst. Bare karst is most often characteristic of mountainous areas, where denudation processes are most intense, while covered karst is characteristic of plains.

The greatest variety of relief forms and the greatest activity of karst processes are usually characteristic of bare karst.

In the karst massif there are three floors (zones), different in hydrogeological terms.

The upper one, called the aeration zone, It is located from the surface to the groundwater level and is characterized by vertical circulation. The free gravitational movement of water, characteristic of the upper zone, is observed during periods of rainfall and snow melting. The main surface forms appear in the upper zone.

The middle zone is periodically completely saturated characterized by horizontal or slightly inclined movements of water within the boundaries of the highest and lowest levels of the groundwater table. This is an area of ​​active formation of karst caves.

Lower zone- constant complete saturation - extends up to the aquifer and is characterized by horizontal circulation. She nourishes karst rivers and large permanent springs.

Surface forms of karst.

1. On a young massif of calcareous rocks, recently exposed from under sea level, under the influence of the corrosive activity of rain and melt water penetrating into cracks in the aeration zone, a combination of specific open meso- and microforms appears:

carrs, or shratts, represented by a labyrinth of narrow sharp ridges and the same narrow furrows separating them, up to 0.5 - 1 meter deep;

carr fields;

blasphemy, those. more or less wide slots that serve as drainage channels for surface water;

rounded depressions and dips, united under the general name valleys;

most typical sinkholes, reaching a diameter of 20 - 50 meters, and a depth from several to a few tens of meters. The slopes of the craters are usually steep, bare, and the bottom is dry.

deep (up to several tens of meters) vertical depressions such as wells.

2. Further development of karst relief is directed along the line of surface denudation and the formation of surface watercourses through the opening of groundwater. In the carr fields the stable ridges turn to the outskirts. Insoluble sediment of limestone accumulates in depressions - red clay (terra rossa ) .

Mountain karst at this stage is characterized by the development of deep vertical channels - karst abysses, or mines, the depth of which reaches several hundred meters.

3. The transition to the stage of maturity of flat bare karst is expressed in the expansion of funnels, connecting them with each other, turning wells into funnel-shaped depressions. As a result of the merger, wide depressions of bizarre outlines are formed, called uvala. The bottom of the ridge does not yet have a permanent watercourse, but the accumulation terra rossa promotes the formation of temporary reservoirs fed by rain and snow waters.

The most typical forms of mature karst are considered fields. These are vast depressions stretching for many kilometers with steep slopes and flat bottoms, with permanent watercourses or chains of lakes fed by groundwater.

Rivers and valleys of karst areas.

Among the few surface watercourses of karst areas, five types are distinguished according to the hydrological regime and morphology of river valleys:

Occasional rivers whose valleys do not leave the aeration zone. Water appears in such shallowly incised valleys only during heavy rainfalls or rapid spring snowmelt.

Constantly flowing rivers whose valley bottoms lie above the groundwater level of the karst massif.

Constantly flowing rivers, the valleys of which are cut down to the groundwater level. They mainly feed on these species.

Rivers that cut not only through the entire thickness of the karst rock, but also deepened into the underlying water-resistant rocks.

Underground, or cave, rivers flowing through a system of underground galleries.

Lakes of karst areas They are divided into temporary, the bottom of which does not reach the groundwater level, and permanent, with a predominance of underground nutrition. The basins are usually round in plan, the slopes are steep, and the depths are significant, especially if the lake is located in a collapsed basin. Karst lakes are characterized by significant and rapid level fluctuations.

Caves of karst areas

Caves are a variety of underground cavities that form in karst areas and have one or more exits to the surface. The location of the caves and their topography are determined by the location of the systems of cracks that penetrate the karst rock and the hydrogeological features of the karst areas.

In many caves, sinter forms form on the bottoms, walls or vaults. Narrow and long stalactites, consisting of calcite and usually having a concentric structure in cross-section, hang from the ceiling of the cave in the form of icicles. More massive and shorter forms called stalagmites rise from the bottom of the cave towards the stalactites. Often stalactites and stalagmites collapse and form sinter columns (stalagmata).

The karst process is primarily a denudation process, so it occurs differently in different climate zones. In areas with a Mediterranean subtropical climate, karst processes are favored not only by the geological structure, but also by the climate. Shower nature of precipitation and the presence dry season contribute to the intense impact of rainwater on the surface of limestone rocks and the relatively slow accumulation of eluvium.

Forms of lowland karst in temperate latitudes: gently sloping saucer-shaped depressions at the bottom of which water accumulates or forms lowland swamp; Often there are deep karst funnels and even sinkholes such as wells. Their bottom is lined with weathering products and lakes are formed, in the nutrition of which the waters of the underground karst massif play a significant role.

In humid hot tropical climates The development of karst has specific features. The young stage is characterized by a predominance positive landforms in the form of cones, towers, which are raised high above the base of erosion, the so-called basal surface. Based on morphological differences, dome-shaped, tower-shaped, conical and basin-shaped tropical karst is distinguished.

Karst processes develop in rocks soluble by natural surface and groundwater: limestone, dolomite, gypsum, anhydrite, rock and potassium salts.

The basis of the process is chemical dissolution process breeds and leaching process, i.e. dissolution and removal of some part of the rocks. Waters of different composition dissolve rocks in different ways. Waters saturated with carbon dioxide are especially aggressive towards carbonate rocks, and gypsum is more dissolved in brackish waters.

Karst is understood not only as a process, but also as a result, i.e. formation of specific forms of dissolution. The term itself karst comes from the name of the calcareous plateau in the Slovenian Alps, where karst landforms are most pronounced. Karst develops wherever there are outcrops of carbonate rocks on the surface: in the Mountainous Crimea, on the coast of the Adriatic Sea, in the Caucasus, the Urals, in Central Asia and in many other places around the world. If karst forms are visible on the surface, then they speak of open karst , and if they are covered by the thickness of some other deposits, then - oh closed karst . The latter is more likely to develop in flat platform areas, while the former is more likely to develop in mountainous areas.

Karst forms. On the surface, karst forms are represented by karrs, gutters and ditches, ponors, funnels of various types, depressions, basins, blind valleys (Fig. 8.1.1).

Carry- these are various shallow excavations formed mainly by the leaching of limestone by surface atmospheric waters; The following types of carr were identified:

· hole,

· tubular,

· grooved,

· grooved,

· cracked and a number of others.

All these forms have a depth of 5-20 - 5-0 cm, rarely the relief reaches 1-2 m. The most typical are grooved quarries, represented by parallel grooves, separated by sharp ridges. The relief with grooved karrs resembles a washboard, and areas where numerous karrs develop are called carr fields.

Gutters and ditches They represent more extended and deeper areas of karst leaching of the surface of limestone, inheriting surface cracks and reaching depths of up to 5 m.

Ponory– narrow holes, inclined or vertical, that appear at the intersections of cracks with the further development of the dissolution and leaching process. These channels serve as a drain for surface water and direct it deep into the mountain range.

Rice. 8.1.1. Karst landforms: 1 – karrs, 2 – funnels, 3 – fields, 4 – wells, 5 – mines, 6 – disappearing rivers, 7 – sinkholes, 8 – gorge, 9 – cave, 10 – stalactites, 11 – stalagmites, 12 - “terra rossa”, 13 – cave lake

Sinkholes are divided into:

1. surface leaching funnels (resembles a crater from the explosion of a shell or bomb; they are formed due to rock leached from the surface; usually in the center of such a crater there is a pore channel through which water flows out; the diameter of the craters is usually up to 50 m, rarely more, and the depth is 5-20 m );

2. sinkholes (associated with the collapse of the vault above a cavity excavated by water at a certain depth);

3. suction funnels (=corrosion-suffusion sinkholes occur when karst limestones are covered by a layer of sandy sediments and the latter are washed into the underlying karst cavities. In this case, sediments are carried away from the sand layer into the pit and a suction or washout funnel is formed).

Saucers and basins are small, small sinkholes. If funnels of different genetic types merge several pieces together, then

is formed karst basin with a series of indentations at the bottom. Sometimes the bottom of the basins can be flat.

Polia are quite large, hundreds of meters in diameter, irregular shape depressions formed by the merger of a number of basins and craters (including failures).

Karst wells and mines- these are channels that go almost vertically into the calcareous massifs for tens and hundreds of meters with a diameter of a few meters. They are formed by leaching along cracks, sometimes by surface water flows that erode limestones. Mines vertical cavities with a depth of over 20 m are called, and less - wells. If the mines are connected with each other, as well as with subhorizontal passages and caves, then karsts are formed abyss reaching depths of 1000 meters or more.

Blind Valleys They are small rivers flowing in karst areas, having a source, but suddenly ending at some funnel or ponor, where all the water goes. Sometimes valleys are half-blind, when the water of a river suddenly goes underground, and then, after a few kilometers, appears again (found in Western Crimea).

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

Karst caves arise in various ways: by dissolution, leaching and erosion; by collapse, opening and subsequent erosion of tectonic cracks. Groundwater flows through cracks or tectonic fractured zones, gradually dissolving and leaching limestones or dolomites. Thus, cave cavities are formed, often multi-story and complex, when individual large caves - “halls” - are connected to other narrow channels, crevices, and often with streams flowing through them. Large cave complexes take a long time to form – 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, for example, a river, as well as tectonic movements. When the groundwater table decreases, already mined out cave cavities are drained and the process of dissolution and leaching moves to a lower level. This can continue several times in accordance with the stages of river incision and fluctuations in groundwater levels. In the area of ​​permafrost rocks in caves, sinter forms consisting of ice are developed.

At the bottom of caves there are often reddish clay deposits, the so-called. “terra rossa” or “red earth”, which is an insoluble part of carbonate rocks, enriched in oxides of iron and aluminum. However, the most impressive feature of a number of karst caves are stalactites and stalagmites– bizarre sinter formations that create the unique appearance of cave halls. The thing is that the water that always drips from the ceiling of the caves is saturated with CO2 gas, due to the dissolution of carbonate rocks, and, in addition, it is also saturated with calcium bicarbonate - Ca (HCO3)2. This happens through the reaction CaCO3 + CO2 + H2O → Ca(HCO3)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 bicarbonate again turns into CaCO3, which is deposited both on the ceiling of the cave (stalactite) and on the bottom (stalagmite). First of all, sagging appears on the floor of the cave, similar to stearine floating from a candle. This is the so-called gurs. Then stalagmites with a wide base appear on the gours, and even later resembling a stick or pillar.

Much later, stlactites begin 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 bizarre shapes are formed. There are beautiful multi-tiered caves in the Crimean mountains, where they were formed in thick strata of Upper Jurassic limestone; in the Czech Republic, Slovenia, the Urals, the Caucasus and other places.

Until now 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 (Latin “suffosio” - digging). They arise when the process of washing out karst cavities begins from the thickness of sediments overlying karst forms. Gradually, a funnel forms in place of this thickness, and even lower - cavities into which these deposits can fall (Fig. 8.1.3).

Karst forms develop wherever karst rocks are present - limestones, dolomites, gypsum, anhydrites, rock salts.

Cryogenic landforms

Landscapes of the permafrost zone are characterized by special, unique forms of relief, caused by the processes of repeated freezing and thawing of the layer. It is this circumstance that leads to the formation of frost cracks and various polygonal forms of relief, heaving, thermokarst, kurum formation, soil flow, ground, slush, etc. Let's consider these forms of cryogenic relief.

1. Frost cracking of rocks is widespread in the permafrost zone. The formation of cracks in frozen rock is due to the emergence of stresses in it during cooling and compression. In the same way, columnar cracks form in basaltic lavas or cracks in drying takyrs. The mechanism is the same. The difference is that frost cracks can occur multiple times in the same place. In areas with a well-defined continental or maritime climate, the soil appears to be broken up by systems of perpendicular cracks in such a way that a polygonal, quadrangular or other structure becomes clearly visible on the ground. The sizes of these polygons can vary from a few tens of cm to 20-30 cm.

The formation of frost cracks inevitably leads to polygonal vein structures or PZhS various types. The most important of them seem to be re-weed ice - PZHL, most widely developed in the northern regions of the permafrost zone (Fig. 1)

Rice. 1. The structure of the ice complex of the Kolyma Lowland near Duvan Yar (compiled under the direction of T.N. Kaplina): 1 – ice veins(repeated ice wedges); 2 – silts with strong bends of layers at contacts with ice veins; 3 – the same, without deformations at the contacts; 4 - 6 – buried silts (4), cover layer (5) and peat (6); 7 – sands; 8 – peat; 9 – melted ice veins; 10 – remains of ancient wood; 11 – absolute age of sediments according to radiocarbon, year

PZhL - are formed either after the formation of frozen rocks and then they are called epigenetic, or simultaneously with them – syngenetic.

Epigenetic PZHL arise in permafrost deposits above which there is an active layer (Fig. 2, A). A frost crack that appears in winter fills with water when the active layer thaws in summer. The resulting ice expands the crack in winter, it fills again with water, and the whole process repeats in winter. This will happen many times, and the ice wedge in the frozen rocks will expand, and the ice in the active layer will melt in the summer. All this leads to the formation of ice veins, and the annual, thin layers of newly formed ice make it possible to determine how long this ice vein has been growing.

Syngenetic AFLs grow simultaneously with the sedimentation of sandy-loamy and peat deposits on accumulative relief elements. Every year new sediments accumulate, which undergo frost cracking and the ice vein seems to grow upward, resembling cones nested inside each other (Fig. 2, B). Syngenetic PZHL are usually the largest and most powerful, reaching a height of 60 m and a width of 6-8 m.

Rice. 2. Scheme of epigenetic (A) and syngenetic (B) growth of re-veined ice (according to B.A. Dostovalov): I-IV – successive stages of growth of wedges, a-d – elementary ice wedges formed annually, Δh – thickness of accumulated ice 1 year of layer during syngenesis, h and c are the height and width of the elementary vein, m is the total width of the wedge

If the ice veins melt, then the vacated space is filled with various soils, i.e. secondary formations called pseudomorphoses on re-wed ice. They are especially widely developed where permafrost existed in the geological past. Similar pseudomorphoses are developed in central Europe, Ukraine, Mongolia, China and other places (Fig. 3).

Rice. 13.6.3. Pseudomorphoses on re-vegetated ice: 1 - soil-vegetative layer and humified rocks, 2 - heavy loams, 3 - sandy loams, 4 - peat, 5 - sand and gravel, 6 - layering of rocks and small faults.

The melting of large re-veined ice wedges leads to the emergence of thawing basins, between which rise cone-shaped mounds called baijerakhs(Fig. 4) . These are the rocks that were previously located between the ice wedges. The height of baijerakhs is 2-5 meters and if there are many of them, a peculiar relief appears, similar to numerous termite mounds.

In addition to PZHL, there are so-called originally ground veins, which occur when a crack is filled with water-saturated soil, which flows or crumbles from the walls of the crack. It is as if a vein is formed from the rock.

Sand veins are formed in exactly the same way, only sand blown by the winds in a dry, very cold climate gets into the frost cracks. In some cases, they form sand-ice veins, which are in Yakutia, in Western Siberia penetrate deeper than the active layer.

Polygonal relief forms of the permafrost zone include, in addition to those described above, spots-medallions, polygonal-roller relief forms: stone polygons and baijerakhs.

Medallion spots range in size from 0.2-0.3 to 1-2 m, are delimited from each other by frost cracks and form a characteristic surface resembling giant scales (Fig. 5).

Rice. 4. Formation of baijerakhs: 1 – re-veined ice, 2 – melting of ice and formation of baijerakhs in the form of earthen cone-shaped mounds

Penetration of frost cracks occurs to the base of the active layer. When freezing begins, which occurs faster on the sides of the crack, excess pressure is created in the center of the structure and still thawed clayey or sandy-loamy soil can break through the thin frozen surface crust of the active layer and fill some area in the form of a liquid mass (Fig. 6). A mud spot forms, bounded by a polygonal network of cracks (Fig. 7). This process can be repeated many times and herbaceous vegetation often appears along the edges of medallion spots. Medallion spots form various morphosculptures of landscapes (Fig. 8). Sometimes the border and centerpiece are on the same level; in another case, the border is lowered and the center of the medallion is raised; in the third, the curb is raised and the center is lowered. All varieties are determined by the nature of the movement of the liquefied soil mass (Fig. 9).

In the active layer, frost sorting of clastic material occurs, the main factors of which are frost heaving and the formation of a polygonal system of frost cracks. It is most effective in the upper part of the active layer, when large stone material is pushed to the edges of polygonal structures, and the center is occupied by fine earth. Buckling or freezing of stone fragments occurs because freezing occurs underneath them earlier and ice lenses are formed that lift the fragments. In the summer, when the active layer thaws, the place of the ice lens is occupied by liquid soil, as a result of which the fragment cannot sink again, and in winter the process is repeated and the fragment rises again until it reaches the surface. Piles dug only into the active layer bulge in the same way.

The process of uneven freezing in a polygonal network of frost cracks leads, as already mentioned, to an increase in pressure inside a single polygon, under the influence of which the liquefied soil that breaks through to the top moves to the sides the stones frozen out to the surface, which form stone polygons(Fig. 10) or stone polygons - areas with thin material in the center and stone fragments along the edges (Fig. 11).

Rice. 6. Scheme of water migration and sorting of clastic material in loose rock (left)

Rice. 7. Scheme of formation of ground spots: 1 – crack in the seasonally frozen layer; soil: 2 – seasonally frozen, 3 – permafrost, 4 – thawed.

The entire process is controlled by repeated freezing and thawing of the active layer.

Rice. 8. Stone strips (a), stone rings (b), stone polygons (c)

Rice. 9. Basic morphological types medallion spots: I – flat or slightly convex, II – convex on hummock pedestals, III – flat or concave. 1 – loam or sandy loam, 2 – humified soil, 3 – peat

Thermokarst

A change in the thermal regime in the surface part of the permafrost zone leads to the thawing of individual sections of the soil, the thawing of segregation and wedge ice and, as a consequence, to subsidence of the soil and the emergence of specific forms of thermokarst, negative relief. These are small depressions, funnel-shaped depressions, rounded basins, usually occupied by lakes or already drained and called Alasami in Yakutia, and in Western Siberia - Khasyreys. Alases can be tens of kilometers in diameter and 30-40 m deep, and lake-marsh deposits form in their bottom (Fig. 1).

Thermokarst relief is especially widely developed on alluvial accumulative plains in the Arctic and subarctic zones, where thawing basins are most often occupied by lakes, the water in which, accumulating heat, itself contributes to the further thawing of frozen soil, up to the formation of sub-lake blind taliks. In the southern regions of the permafrost zone, manifestations of modern thermokarst disappear.

Rice. 1. Scheme of successive stages (I - IV) of the development of the alas relief (according to P.A. Solovyov): 1 - loam in the primary occurrence, 2 - loam and deposits of the ice complex, displaced during the development of thermokarst, 3 - ice complex, 4 - sediments , underlying the ice complex, 5 – lacustrine and lacustrine-swampy alas deposits, 6 – deposits performing pseudomorphoses along recurrent ice wedges,

7 – injection and segregation ice, 8 – permafrost surface, 9 – primary surface, 10 – lake waters

Frozen rocks are extremely sensitive to any, even the most insignificant, technogenic disturbance of the natural thermal regime.

The construction of roads, oil and gas pipelines, deforestation, even a tractor mark immediately leads to change thermal equilibrium, increasing thawing and the development of thermokarst begin, which is very difficult to combat.

Frost heaving processes are associated with the formation of ice and an increase in the volume of rock in the active layer, composed of fine rocks and peat bogs.

Individual perennial heaving mounds reach a height of 15-20 m and a diameter of up to 100 m, but more often less.

Segregation heaving mounds can be seasonal or perennial. They form when moisture rushes toward the freezing front, forming schlers of ice, causing the volume to increase and the surface to rise. This process can occur annually. In winter, snow is blown away from the perennial heaving mound that has arisen, which causes an increase in the depth of freezing and “additional” migration of moisture, leading to intense ice formation and, accordingly, the growth of the mound. Such a process can continue for hundreds of years and subsequently the swelling mound “dies,” as it were, passing into a relict state.

Perennial injection mounds of heaving or bulgunnyakh (pingo) arise due to the freezing of taliks, which are often located under lakes and oxbow lakes of rivers, in particular, after the drainage of thermokarst lakes, alas, etc. When a thermokarst lake is drained, the thawed rocks underneath begin to freeze and increasing pressure squeezes the thawed soil upward, lifting the frozen crust formed above it. A swelling mound is formed, which subsequently grows, because thawed soil freezes more and more due to the release of segregated ice. And finally, instead of a talik, an ice lens is formed, located inside a mound or bulgunnyakh. The sizes of bulgunnyakhs reach up to 200 m in diameter and 30-60 m in height (Fig. 2).

Hydrolaccoliths are formed during the intrusion of pressure supra-permafrost and sub-permafrost waters into thawed soil in places where groundwater is discharged, and during freezing an ice lens is also formed, lying in accordance with the host rocks, which rise above the ice to form mounds.

Various heaving processes in the surface part of the permafrost zone are extremely widespread and have various forms of manifestation.

Heaving structures create great difficulties during construction in areas where permafrost occurs.

Rice. 2. Bulgunyakh section. Leno-Amga interfluve. Central Yakutia (according to P.A. Solovyov): 1 – sandy loam, 2 – loam, 3 – sand, 4 – ice, 5 – upper boundary of frozen rocks, 6 – core boundary with the release of a lens of pure ice, 7 – aquifer pressure

Rice. 3. Section of a heaving mound in the river valley. Khantaiki (according to G.S. Konstantinova): 1 – ice schlierens up to 20 - 25 cm thick, 2 – peat, 3 – loam, 4 – clay, 5 – sand, 6 – upper surface of permafrost

Naledi. In winter, in areas of permafrost, many rivers freeze to the bottom in some places. The water that is still in certain sections of the channel and in the river alluvium seeks a way out and breaks out onto the ice, spreading over it in a thin layer. This can be repeated many times and, in the end, a thickness of ice is formed, with a thickness of a few meters and an area of ​​tens and hundreds of km2. River water dams stop growing by January, while groundwater dams, inter-permafrost and sub-permafrost water dams grow until spring and do not have time to melt in the summer, forming large ice masses - Taryn. The largest aufees are known in the Momo-Selennyakh depression, in the area of ​​the Chersky ridge, for example, Momsky Ulakhan-Taryn, with an area of ​​more than 100 km2 and a thickness of up to 6 m. If the natural paths of water movement are disrupted, then aufees will appear where there were none before It was also possible to interfere with the construction of bridges, roads, etc. Therefore, special anti-ice measures are being implemented.

Thus, there are aufeis of river, supra-permafrost and sub-permafrost waters. Sometimes water cannot rise to the surface for various reasons, for example, if it gets into the space between permafrost rocks and frozen seasonally thawed layers. Then it freezes and turns into an ice lens, which, increasing in volume, lifts the roof, forming hydrolaccolith or underground ice. Such aufees can be annual or perennial, especially where there is a continuous discharge of groundwater. The thickness of the ice core in this case can reach 10 m. But it usually lies shallow, only 2-3 m from the surface.

Cryogenic landforms associated with gravitational processes. Gravity processes on slopes, especially steep ones, under conditions of seasonal thawing of cover formations lead to the development of solifluction, kurums, and landslides.

Solifluction(Latin “solum” - soil, “fluxus” - flow) is the slow viscoplastic flow of loose sediments that occurs in the summer above the roof of permafrost. The intensity of solifluction development is directly related to the steepness of the slopes, because As the steepness of the slopes increases, the current becomes stronger (Fig. 1).

Rice. 1 Scheme of the movement of particles and debris in the active layer on the slope - the process of solifluction: 1 - active layer; 2 – permafrost

The process of solifluction depends on the depth of seasonal thawing of rocks, the slope of the relief, the nature of the turf and the composition of sediments. Most often, thawing, silty loams and sandy loams and schlieren ice content are subject to visco-plastic sliding. In case integumentary solifluction, soil flow occurs slowly and evenly on slopes with a steepness of less than 15°. There are no sinter forms.

Differential solifluction appears on the slopes in the form of terraces, slides, tongues, stripes and other forms. This happens because the speed of soil displacement in different places is different (Fig. 2).

Rice. 2. Solifluction mudslides: 1 – fine earth, 2 – rock fragments “flowing” along the slope, 3 – active layer of the substrate, 4 – clayey rock

Rapid solifluction or raftings occur on slopes up to 25°, when ice-saturated soils and rocks thaw. This usually happens at the beginning of summer, during the period of rapid thawing of the soil. The speed of movement of such drifts reaches several meters per minute.

Kurums, stone fields, rivers or streams usually consist of crushed stone-block material of rocks and are developed on slopes up to 40°. The processes of kurum formation are caused by seasonal and daily temperature fluctuations, which either expand or contract the size of the fragments, thereby promoting the gradual movement of blocks down the slope. Stone fragments are gradually frozen out of fine-earth material, the flow of which, when thawing, also moves downward fragments, forming large fields or streams. They allow water to pass through well, and in the spring, char ice forms underneath them in still cooled rocks. During the warm summer months, it can melt and waterlog thin dispersed rocks, which begin to slowly slide down the slope, carrying debris with them. Kurums move downslope at a rate of only a few cm per year. In principle, kurums are closely related to solifluction processes.

Economic activity in the permafrost zone. The permafrost zone occupies more than half of the territory of Russia and is precisely in places rich in minerals - oil, gas, coal, and various ores. The development of these territories is of enormous importance for our country.

The areas where permafrost occurs are very sensitive to any natural or man-made interventions. The high ice content of permafrost and the thermal equilibrium, ready to shift from the slightest changes, determine the unstable behavior of permafrost. Any increase in temperature immediately increases the depth of seasonal thawing, the ice turns into water, which flows away, the soil becomes compacted and subsides. This phenomenon, called thermokarst, accompanies construction done without taking into account the rules provided for permafrost. And they consist, first of all, in maintaining the frozen state of the soil. It follows that under each building there must be a ventilated underground, and the piles on which it stands must be driven into frozen rocks below the layer of seasonal thawing (Fig. 1).

By preserving permafrost without disturbing their thermal equilibrium, it is possible to prevent thermal settlement of the soil, and then of the structure, which may simply collapse after some time. To prevent it from starting to melt, the soil is sometimes even specially frozen using a cooling system.

Rice. 1. Construction in the permafrost zone. The houses stand on concrete piles driven into permafrost, below the active layer: 1 - holes for air circulation, 2 - active layer, 3 - permafrost

Pile foundations are now the main method of construction in the permafrost zone, although they are also built on fill soils. Cities located in the permafrost zone include Yakutsk, Norilsk, Bilibino Nuclear Power Plant, Anadyr and other cities. At one time, the pile foundation was first tested during the construction of the Yakutsk Central Thermal Power Plant, a facility that generates a large amount of heat. Her ventilated underground reaches almost 2 meters. This structure was built in 1937 and has been operating without deformation since then.

Particularly difficult is the installation of utilities in the cryolithozone - heating pipelines, sewerage, and regular water supply. We must keep this in mind.

That the permafrost rocks on which construction is carried out have different properties, which need to be taken into account. The science of frozen soils is extremely complex, interesting and necessary. Even a standard 6 m high pillar cannot be dug into a thawed layer without it bulging out of this layer after some time, just as stones bulge out of it. And it rises because, being dug into the active layer, when the layer begins to freeze from the surface, with an increase in the volume of the water-saturated layer, it will be slightly pulled up by the soil frozen to it.

Naturally, a cavity forms under the pillar, which is immediately filled with liquefied soil, which will subsequently also freeze, increasing its volume. And this is repeated from year to year, several cm at a time, and finally the pillar will collapse, being completely bulged out of the ground (Fig. 2).

Rice. 2. Diagram showing the successive stages (I - IV) of the bulging of a column from a layer of summer thawing soils composed of wet loose rocks: 1 - thawed part of the seasonally thawed layer; 2 – permafrost thickness; 3 – frozen part of the summer thawing layer; 4 – cavity under the melted pillar, filled with liquefied soil; 5 – the same, filled with frozen icy soil; 6 – the same, filled with compacted soil

In general, soil heaving in the area of ​​permafrost development is a disaster that causes enormous damage to the entire economy of the north. Deformed embankments of railways and highways, gas and oil pipelines, airfields, cable communication lines, water and heating pipelines and many other structures experience uneven soil heaving.

Enormous problems arise with the excavation of mine workings and mines in coal-bearing regions, in Vorkuta, for example, where all underground structures are heat sources, and the temperature of permafrost is about 0°C.

The ongoing changes in climate and natural environment under the influence of man-made activities and subsequently natural causes can cause future generations a lot of trouble in areas where permafrost occurs.

Basic concepts about permafrost, distribution, thickness, types of underground ice, occurrence of the permafrost zone.

In areas of cold and moderately cold sharply continental climates, the surface layers of soil and soil are subject to freezing in winter and thawing in the summer months. Seasonally frozen soils appear. Certain patterns of freezing and thawing have been identified, the temperature conditions of these processes have been established, the behavior of soils and soils during periods of thawing and freezing, and the influence of soil composition and their moisture on these processes have been characterized. The top layer, subject to periodic freezing and thawing, is characterized by significant dynamism and is called the active layer. Under this layer, in large areas of Siberia, Alaska and Canada, there are permafrost rocks. In Russia they occupy about 60% of the area. The zone of distribution of permafrost rocks is called the frozen zone of the lithosphere, or cryolithozone.

The cryolithozone consists of frozen, frosty and chilled rocks. Frozen refers to rocks that contain ice and are characterized by negative temperatures. Frosty rocks differ from frozen rocks in that they lack water and ice. Such rocks are most often represented by igneous and metamorphic varieties, as well as dry sands and pebbles.

Cooled rocks also have a temperature below 0°C and are saturated with mineralized salty waters - cryopegs(Greek “krios” - cold, “pegi” - salty waters).

Spreading. The permafrost zone in a wide ring covers the space around the Arctic Ocean and in general occupies about 25% of the entire land area (Fig. 1) and 64% of the territory of Russia. Permafrost rocks exist in the form of “islands” and in the summit areas of high mountain ranges in the Alps, the Caucasus, the Tien Shan and Pamirs, the Himalayas and other places, occupying a total of 3 million km 2.

A large area of ​​alpine permafrost (2 million km 2) covers the Tien Shan, Pamir and Himalayas, reaching 27° N in the south. Thanks to the harsh winters in Russia, almost the entire uppermost layer of the earth’s crust outside the permafrost zone freezes to a depth of a few meters. In the summer it thaws, and in the winter it becomes frozen again.

The distribution of the permafrost zone is such that in the southern regions it is located as separate islands among thawed rocks. The frozen rocks are 10-25 m thick and occur in the form of lenses. To the north there is a zone of non-continuous frozen rocks up to 100 m thick, in which there is a lot taliks- areas of unfrozen rocks. To the north, usually, the permafrost zone occupies the entire space, and its thickness increases to 1000-1500 m.

The thickness of “permafrost” varies over a very wide range from the first meters along the southern edge of its distribution, to 1000 m and even 1500 m.

Origin of the permafrost zone

There is no doubt that the emergence of the permafrost zone in the Northern Hemisphere as a whole is associated with repeated glaciations that covered vast areas in the last 2 million years. The cryolithozone is formed not only in space, but also in time. From previous chapters it is known that freezing of the upper part of the earth’s crust occurred more than once in geological history. But then, of course, the rocks thawed, in some places retaining only vague traces of former freezing.

Within Russia, it has been established that approximately 2 million years ago, i.e. in the late Pliocene, the cryolithozone already existed within the New Siberian Islands, the Yana-Indigirka and Kolyma lowlands. But at certain moments in subsequent geological history it disappeared and reappeared. Having arisen somewhere around 650,000 years ago, it was already preserved, because Ice ages followed one after another.

It would seem that where there were more powerful glaciers and where they persisted the longest, the maximum thickness of the permafrost zone should be expected there. However, the picture is more complex. Just in those places where there were glaciers, the thickness of the permafrost zone was less than in those places where there was no ice. There, in severe winter conditions, rocks froze to great depths, all other things being equal. In a relict state, “permafrost” is now located under the bottom of the shelf seas of the northern coasts of Russia, despite the controversial existence of the Pan-Arctic ice sheet within their boundaries. If the shelves were not covered with ice, then under the conditions of a strong drop in sea level during the last glaciation they should have frozen to great depths.

Rice. 1. Geocryological map Northern Hemisphere. Permafrost zone: 1 – continuous, 2 – discontinuous, 3 – island

Thus, areas of continuous “permafrost” began to appear in the late Pliocene - 2 million years ago, but the continuous permafrost zone, which did not disappear subsequently, formed about 650,000 years ago, i.e. in the Early Pleistocene within the northern Siberian Platform. In the flat areas of the continents, the distribution of the permafrost zone is associated with latitudinal zonality, because the amount of solar radiation becomes less to the north, average annual temperatures decrease, and increases albedo– reflectivity of the Earth’s surface due to long-term preservation of snow cover. A snow field reflects up to 90% of solar radiation, while a plowed field only reflects 7-8%. In mountainous areas, high-altitude geocryological zoning is observed. It is possible that in the Pamir Mountains and the Himalayas the thickness of the permafrost zone increases to 3000 m. The thickness of the permafrost zone depends on many factors: latitude, landscape, relief, geological structure, structure and heat flow. For example, on the ancient Anabar massif of the Siberian Platform the thickness of the permafrost zone exceeds 1000 m, the heat flow in Precambrian structures is low - 15-25 mW/m2 and the geothermal gradient is very small. At the same time, the younger, epipaleozoic West Siberian plate is characterized by a higher heat flow - up to 50 mW/m2 and a geothermal gradient of up to 5 ° C per 100 m. Therefore, at the same latitudes, the thickness of the permafrost zone in Western Siberia is 2-3 times less and ranges from 300 to 400 m.

Structure of the cryolithozone. Within the permafrost zone, the top of permafrost always lies at a certain depth, which is determined by the thickness of the layer that thaws in summer. This layer is called seasonally thawed; it freezes completely. In the permafrost zone and on taliks in winter, a seasonally frozen layer is formed, which is underlain by unfrozen or thawed rocks. In summer, this layer completely thaws.

The depth of freezing or thawing is important and depends on the amount of solar radiation entering a given area in summer and winter. In the southern regions of Western Transbaikalia, thawing in summer can reach 4-6 meters, but nearby, depending on the relief and landscape, it does not exceed 0.5 m. In the far north, for example, on Franz Josef Land, only 10-20 cm thaws in summer soil. In the permafrost zone there are always areas where the seasonally thawed layer does not completely freeze in winter and areas where the seasonally frozen layer does not completely thaw in summer. Thawing of rocks begins immediately after the snow melts and its rate can reach several tens of cm per month. Even over a small, seemingly climatically homogeneous area, summer thawing occurs to different depths and at different speeds. It all depends on specific geological and geomorphological features, slope exposure, forest cover, etc. Seasonal thawing layers can freeze not only from above, but also from below, from the side of permafrost.

The layer of seasonal freezing and thawing is extremely important for construction, because... It is its power that determines the conditions in which the foundations of buildings are laid, piles are driven, etc. Therefore, detailed maps of seasonally thawed and seasonally frozen areas are compiled, in which phase transformations of water occur associated with the absorption or release of heat. A layer with seasonal changes in the thermal state of rocks reacts very quickly to any technogenic intervention, and negative processes can develop, which are then difficult to eliminate.

In different geological regions, the structure of the permafrost zone may differ. In some places only frozen rocks are developed. In other areas, for example, on ancient platforms, where the sedimentary cover covers the metamorphic basement, the first is represented by frozen rocks, and the second by frozen rocks. On the coasts of the seas of the Arctic Ocean, cooled rocks with cryopegs lie under frozen rocks, and the transition between them is gradual. The upper layer of frozen rocks is younger than the lower layer.

Types of underground ice. Frozen rocks are characterized by different contents of underground ice and the nature of its distribution in the rocks. Constitutional ice found in any permafrost. If the rock has high humidity, then the water, freezing and turning into ice, holds and cements its grains or their accumulations. Such ice-cement most widely developed. Ice, which cements dispersed rocks, increases their strength. Concept ice content of rock characterizes the amount of ice contained in it. If the rock is strong, rocky, then ice fills everything in it possible pores and cracks that formed naturally before the rock began to freeze.

If clayey rocks begin to freeze, then the moisture contained in them migrates to the freezing front, where layers are formed - schliers ice of varying thickness from fractions of a cm to 0.5 m. Such rocks are characterized by much greater ice content, and ice schlierens form different cryogenic textures - reticular, layered, lens-shaped, ataxitic, porphyritic, etc. Rocks containing ice schlierens lose their increased strength and give significant settlement.

Ice content usually increases in rocks up the section and decreases with depth. If water penetrates into frozen rocks from taliks or pressure sub-permafrost waters, then injection ice appears, the thickness and length of which reaches many tens of meters.

In the marginal areas of mountain-valley and cover glaciers, when they melt and retreat, individual ice masses are covered with moraines and landslides, and then a buried ice, which does not melt for a long time.

If the rock was formed before freezing began, then epigenetic ice, and if freezing occurs simultaneously with the formation of rock, then it is characterized syngenetic ice. Various types re-weed ice associated with these processes and will be discussed below.

Quite rare, but they do occur cave ice , lying in deep caves, for example, in the Kungur ice cave in the Urals.

Groundwater in the permafrost zone. The formation of permafrost rocks, which are aquicludes, greatly changed the conditions of water exchange between atmospheric and groundwater in the permafrost zone. Most of the fresh groundwater in the permafrost zone is confined to taliks.

Talikami or thawed zones are called strata of melted rocks that develop from the surface of the earth or under reservoirs and rivers and which continuously exist for more than ten years. If taliks are underlain by frozen rocks from below, then they are called supra-permafrost or non-through, and if taliks are only framed on the sides by frozen rocks, like walls, then they are called end-to-end. Taliks can also be interpermafrost And intrapermafrost in the form of lenses of “tunnels”, “pipes”, bounded on all sides by frozen rocks.

Groundwater of the permafrost zone in relation to frozen rocks - cryogenic aquitards is divided into: 1) supra-permafrost; 2) interpermafrost; 3) intrapermafrost and 4) sub-permafrost waters.

1. Supra-permafrost groundwater is divided into temporary waters of the active layer And permanent waters of non-through taliks.

Temporary waters exist only in summer, and their depth does not exceed the top of the frozen rocks. Waters are important for the processes of solifluction, the formation of kurums, mudslides, and rock heaving. Permanent waters are associated with non-through taliks above the roof of frozen rocks and they are responsible for the formation of hydrolaccoliths, heaving mounds, and ice dams.

2. Inter-permafrost waters are usually located between two layers of frozen rocks, for example, between the Holocene upper and relict, late Miocene, lower. These waters are most often not dynamically active.

3. Intra-permafrost waters, as their name suggests, exist inside the thickness of frozen rocks and are located in closed volumes, being confined to taliks in karst limestones.

4. Sub-permafrost waters circulate near the base of the permafrost, have positive temperatures, are sometimes weakly or highly mineralized and can be pressure or non-pressure, as well as contacting with frozen rock or non-contacting, i.e. separated by a layer of thawed rocks from frozen ones.

COURSE WORK

Karst and karst deposits

Annotation

The work is devoted to issues related to karst and karst deposits. It reveals the concept of karst. The main forms of karst relief, formation factors, reasons for the accumulation of mineral substances and their sources are described. The classification and methods of studying karst are outlined. Mineral resources of the karst facies are considered.

Introduction

Chapter 1. General information

1.1 Concept of karst

1.2 Karst forms

1.3 Classification of karst and the issue of its zoning

1.4 Karst research methodology

Chapter 2. Factors of karst formation

2.1 Chemical composition of rocks

2.2 Rock structure

2.3 Rock fracturing

2.4 Tectonic structures and thickness of karst rocks

2.5 Overburdens and terrain

2.6 Topographic surface slope steepness

2.7 Gravity

2.8 Underground rivers

Chapter 3. Reasons for the accumulation of minerals in karst facies

Chapter 4. Sources of matter in karst deposits

Chapter 5. Minerals of the karst facies area

5.1 Types of minerals

5.2 Ore minerals

5.3 Non-metallic minerals

Conclusion

References

Introduction

The topic of this course work is karst. I believe that every geologist should know about karst, since in the study of karst (karst science) various scientific directions. The most widely represented are geographical and geomorphological. At the same time, karst is the result of certain transformations of rocks. During these processes, rock-forming minerals are destroyed, substances are transported, and new formations are accumulated. Consequently, in the doctrine of karst there is a range of problems solved by geological sciences. A discussion of these problems based on extensive factual material is of scientific and practical interest. Karst also significantly affects the landscape features of the territory, its topography, runoff, groundwater, rivers and lakes, soil and vegetation cover, and economic activities of the population. In the karst areas there are fabulous underground cave palaces, richly decorated by nature.

Expand the concept of karst

Describe the main underground and surface karst landforms

Characterize the factors influencing the development of the karst process and the formation of karst landforms

Find the reasons for the accumulation of minerals in karst forms.

To study the sources of matter in karst deposits

Describe the minerals of the karst facies area

Chapter 1.General information

Karst concept

The karst process is a long-term process of dissolution and leaching of fractured soluble rocks by ground and surface waters. As a result of the activity of karst processes, they arise as negative forms relief on the earth's surface, as well as various cavities, channels, grottoes or caves at depth. The term “karst” comes from a corruption of the Austrian name for the Karst plateau in Slovenia, where these phenomena are pronounced and well studied by European researchers. Karst phenomena are extremely widespread. According to geological conditions, approximately a third of the world's land area has potential for their development.

There are several conditions necessary for the development of karst phenomena.

Firstly, this is the presence of rock soluble in natural waters, permeable to water due to fracturing or porosity.

Secondly, the presence of a solvent, i.e. water that is aggressive to rock.

Thirdly, the presence of conditions that ensure water exchange is the outflow of water saturated with a dissolved substance and a constant influx of fresh solvent. If the first condition is determined by the geological structure of the area, then the second and partly the third are closely related to the physical-geographical situation, the second to the soil-vegetation cover and climate, the third to geomorphological and hydrological conditions in addition to the geological structure and hydrogeological features.

Typically karst rocks are mono- and bimineral rocks - rock salt, gypsum, anhydrite, chalk, limestone, dolomite, limestone - dolomite rocks, varieties of marble, magnolite, carbonatite. The leading role in this list is played by carbonate rocks, both due to their wide distribution (about 15% of the land area) and due to the contrast in composition between them and loose sediments, which causes side interactions leading to further karstification.

The concept of dissolution (solubility) refers to chemical compounds, including minerals. There are two types of dissolution of a substance - congruent, when all its components are transferred into solution, and the reaction is reversible, and incongruent, when not all components of the substance pass into solution. In this case, a solid phase remains and the reaction is irreversible. Both types of dissolution occur in the hypergenesis zone, but congruent dissolution is characteristic of karstification, and incongruent dissolution is characteristic of crust formation and leaching metasomatism.

A distinction is made between open or bare karst, when soluble rocks come to the surface, and closed karst, when they lie deep underground and are covered from the surface by layers of insoluble rocks.

Surface karst forms include pits, ponors, karst niches, funnels, basins and fields, as well as wells and abysses.

Underground karst forms are represented by caves and channels.

Karst processes not only create certain forms of relief, but also participate in the formation of peculiar deposits. On the surface and at the bottom of karst relief forms there are residual formations from dissolution - this is a non-carbonate, mainly aluminosilicate material remaining after dissolution. It is called terra rossa (red earth). On the surface and in the caves there are landslide accumulations - products of the collapse of the arches of karst cavities or from blocks rolling down the slopes of karst valleys and craters. The caves contain peculiar alluvial sediments formed by underground rivers. There are also travertines - sinter forms of calcareous tuff, as well as peculiar sinter forms - stalactites, growing from the roof of the cave downwards. Their thin weaves are often called stalactite curtains. Stalagmites grow upward from the bottom of the caves.

Karst forms

Landforms formed as a result of the karst process are divided into surface and underground.

surface forms of karst

Surface karst forms include karrs, gutters and ditches, funnels, saucers and depressions, basins, fields, and outcrops.

According to their genetic origin, karrs should be distinguished into forms that arose on the bare surface of soluble rock, and forms that formed under soil and vegetation cover with its subsequent removal. Punishments of the second type are found in many countries of the world.

Morphologically, quarries are divided into grooved, wall, hole, tubular (in the form of tube-shaped cylindrical depressions in gypsum) stones, quarries in the form of traces, grooved, meander, and fissures. Another type has been identified - structural quarries; on a steep limestone slope, quarries have been developed in chemically relatively pure limestone, separated by narrow ridges that correspond to highly siliceous layers.

According to their genesis, groove and fissure quarries are particularly distinguished. Grooved quarries are formed under the influence of only atmospheric precipitation, as a result of the first three phases of limestone dissolution, without the participation of the fourth phase, while other types of quarries are formed under the influence of all phases of dissolution: their formation also involves water enriched with biogenic carbon dioxide due to the contact of atmospheric precipitation and melt water with soil and vegetation cover.

(Figure 1) grooved carries

Fissure karries differ from others in the way they remove solute. If in most other types of karres it is carried out by surface runoff, then during the formation of fissure quarries, the removal of dissolved matter by underground route, through cracks, also participates.

Karst trenches and ditches (deeper and always with steep sides) develop along open tectonic cracks (often as a result of unloading on steep slopes) or along slope subsidence cracks, or “side thrust” cracks. They stretch for tens and hundreds of meters, and sometimes for several kilometers, reaching different widths and depths. They are closed at the ends and may have numerous depressions at the bottom. Rectilinear ditches in limestone, developed along vertical tectonic cracks, 2 ~ 4 m wide and up to 5 m deep in Yugoslavia are called bogaz.

There are three main genetic types among sinkholes:

Surface leaching funnels, or purely corrosion funnels. They are formed due to the removal of rock leached on the surface through underground channels in a dissolved state.

Failed funnels, or gravitational ones. Formed by the collapse of the roof of an underground cavity, which arose due to the leaching of karst rocks at depth and the removal of substances in a dissolved state

Suction funnels, or corrosion-suffusion funnels. They are formed by washing and subsidence of loose cover deposits into wells and cavities of the karst basement, carrying particles into underground channels and removing them through them in a agitated and suspended state.

(Figure 2)karst sinkhole.

Saucers and depressions are vaguely defined small funnels.

Basins. Funnels of all genetic types, merging with their edges, form double, triple and more complex baths and basins. There are two main types of basins - complex, which are formed by the merger of several large craters and have depressions at the bottom, and flat-bottomed basins. The following genetic types of basins are distinguished: surface leaching, failure, suction, and those created in combination with other processes, for example, erosion. Large surface leaching basins are often formed due to the corrosive action of meltwater from snow and firn patches. Many of these basins are a legacy of the periglacial conditions of the last Ice Age.

Polje is a vast closed depression with steep sides, a flat bottom, which has reached a temporary or permanent limiting level of karstization, with karst-type hydrography.

Polje arises as a result of the development and connection of karst basins formed from merged sinkholes.

By their origin, until recently, fields were divided into: 1) tectonic, 2) formed by underground mechanical removal of insoluble rock lying among karst limestones or in contact with them, 3) formed by the merger of a group of adjacent craters and basins (ridges) during their growth in the horizontal direction, 4) failure.

Large basins of purely tectonic origin (grabens, synclinal troughs) cannot be considered fields. When fields are formed, leaching and removal of dissolved matter through underground channels are required. Therefore, the first group should include tectonic-corrosive and tectonic-corrosion-erosive. This group includes the fields of Yugoslavia. Fields of the third type are usually small, irregularly lobed in plan. They are characteristic not only of carbonate, but also of gypsum karst, and are found even in platform conditions.

Remnant karst is a mature stage of dissection of an uplifted flat-topped limestone massif. The steepness of the slopes of the remains is due to the vertical fracturing of the limestones and the weakening of the slope flow due to their water permeability. Great value has limestone collapsing along cracks due to the undermining of the remains from below by waters that flood the plains at their base, or by groundwater lying at the base surface. Because of this, corrosion niches develop in the horizontal direction at the base of the remnants. The erosion of the remains from below by lateral corrosion of surface waters is facilitated by the accumulation of water-resistant sedimentary clays on the base surface. The distribution of relict remnant karst is consistent with the displacement of the equator during the geological history of the Earth. Since humid tropical climatic conditions have existed in low latitudes for more than one geological period, the remnant karst widespread there can be considered not only modern, but also ancient.

The transition from surface forms to grotto-type caves is represented by canopies and niches. They are often interesting from an archaeological point of view. Often these are surface formations that arose due to more intense leaching of individual layers or packs of layers by water flowing down a cliff, with a high level of biochemical weathering (under the influence of lower plants settling on periodically moistened surfaces). In river valleys and on seashores, river and sea waters play the main role in surface leaching. On sea ​​shores the dissolving effect of sea water is combined with abrasion.

In the process of formation of deeper niches, corrosion due to water seeping through cracks in the rock, and, in addition, the collapse of rock blocks due to the expansion of cracks due to leaching of their planes, become significant.

In limestone niches of subtropical and tropical regions, drip-drip formations are found. Stalactites merge to form curtains and draperies.

Natural bridges and arches most often arise when the ceiling of cave tunnels, and sometimes niches, collapses.

Under karst understand the process of leaching of rocks mainly by underground, partly surface and sea waters and the totality of specific denudation processes that arise as a result (corrosive) relief forms. In this case, water has a certain mechanical effect on the rocks, but the main thing is the removal of substances from the rock in a dissolved state. The name "karst" (from German. Ka^5^) comes from the proper name of the Karst plateau in the Dinaric mountains. Now it bears the Slovenian name Kras. Karst processes and landforms are widespread across the globe. Moreover, in extratropical latitudes, cave-in karst is developed, while in equatorial-tropical latitudes, convex remnant karst predominates.

The development of karst is facilitated by a number of conditions, primarily the presence of easily soluble rocks: either carbonate (limestone, dolomite, chalk, etc.) or non-carbonate (salt, gypsum). Gypsum has the highest solubility, but limestones are more widespread, so karst is associated primarily with limestones. In accordance with various karstic rocks, there are carbonate, gypsum And salt karst. The chemical purity of the rock is also important: the less insoluble residue it contains, the more significant the leaching. Karst is favored by the fracturing of rocks, which facilitates the conditions for water to penetrate into them. Rock fracturing is greater in the mountains than on the plains due to significant tectonic faults. The thickness of the karst strata is also important - with their great thickness, karst processes manifest themselves in all forms, including the formation of caves, while in thin ones they form only funnels, saucers and other small relief forms. The carbon dioxide content in water is of great importance, as a result of which it becomes chemically aggressive and increases the solubility of rocks tens of times. Small surface slopes are preferable, at which less water flows and more seeps into the ground. A sufficient, but not excessive amount of precipitation is necessary, since the low position of the groundwater level ensures vertical circulation of surface water seeping into the ground.

As already mentioned, karst topography differs significantly in temperate and tropical latitudes. In temperate latitudes, karst processes depend on the depth of groundwater, which for karst is the basis of denudation. On this basis they distinguish small And deep karst. Small karst is characterized by a rapid pace of development, but less rugged terrain. Deep karst takes longer to develop, but at the same time deep depressions and numerous caves are formed on the surface.

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

TO superficial The forms of karst include karrs (shratta), funnels, basins (uvala), and fields.

Carry- a complex of narrow furrows 1-2 m deep, separated from each other by sharp ridges. Karrs are forms of microrelief that are formed due to the dissolution and mechanical destruction of rock cracks by surface water. The area covered with karami is called carr field. The carr fields eventually turn into undulating plains with chaotic accumulations of limestone blocks. They are lifeless, difficult to pass, and cannot even be used for grazing.

Funnels widespread in conditions of both bare and covered karst, both in the interfluves and along the bottoms of gullies. These are round, usually cone-shaped depressions different sizes(up to tens, less often hundreds of meters in diameter) and different depths (from a few meters to tens of meters). Small, flat-bottomed funnels are called saucers. Based on their origin, funnels are: surface leaching(in bare karst conditions), failed- as a result of the collapse of the roof over underground voids (in both bare and covered karst conditions) and pro-suction(in conditions of covered karst), when vertical channels at the bottom, the so-called blasphemy(from the word “hole”), insoluble rock is involved along with water. In the event of siltation of the ponor or an increase in the groundwater level, the sinkholes can turn into permanent or temporary lakes, which are characterized by seasonal fluctuations in water levels.

When connecting many funnels due to the destruction of jumpers between them, extensive closed depressions are formed - basins, or uvala. They usually have steep scalloped slopes, uneven bottoms, large sizes: length - kilometers, width - hundreds of meters, depth - a few tens of meters.

The largest karst forms are in Lya resemble a graben in miniature. These are extensive elongated closed depressions with an area of ​​more than 200-300 km, hundreds of meters deep, with steep slopes, with hills-remnants at the bottom, with streams and even villages. The largest fields are Lebanese with an area of ​​379 km 2 in Bosnia, Popovo - 180 km in Herzegovina. Apparently, they are formed when basins merge along tectonic fault lines, i.e., they are predetermined by tectonics.

Underground forms of karst - wells, shafts, 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 measure up to 20 m in width and depth.

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

Combinations of natural mines with horizontal and inclined caves are usually called karst chasms. The deepest karst chasm in the world is Jean-Bernard, 1535 m deep 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 ability of water in rock cracks. By expanding them, water creates a complex system of channels. Where water circulates in a horizontal direction, its dissolving effect is greatest - a main channel is formed. Water is drawn into it from neighboring crack channels, and an underground river gradually forms in the tunnel. When vaults collapse, grottoes are formed. With a decrease in the basis of denudation of surface and underground rivers the latter can pave a new channel for themselves, at a lower level. At the same time, the former galleries become dry, and the caves become multi-story.

Depending on the number and location of entrance holes, caves are divided into open and blind. Pass-through (through) the caves have openings at both ends (entrance and exit), are well ventilated, and the temperature in them is close to the temperature of the outside air. Blind caves have one entrance hole and according to temperature conditions they are divided into warm and cold depending on the location of the entrance hole relative to the cave cavity. IN warm In caves, the entrance is located in its lower part, so that the cold air that fills the cave in winter flows out of it in summer, giving way to warm air. In warm caves, archaeologists often find rock paintings, utensils, and even the remains of ancient people. Cold the caves have an entrance at the top. In winter, cold air enters them and, being heavy, remains there in the summer without having time to warm up, and the moisture that gets in in winter can turn into ice. Ice caves with temperatures below 0 °C are common only in areas with frosty winters. For example, in the Perm region there is the Kungur ice cave in gypsum, 4.6 km long.

Caves are characterized by sintered calcite formations: stalactites- icicles, tubes, fringes hanging from the ceiling, and stalagmites- pillars rising up from the bottom of the cave towards the hanging stalactites. Combining, they form stalagnates- sinter columns. All these picturesque forms turn the caves into fairy-tale palaces.

The largest karst cave system in the world is the Flint Ridge Mammoth, 341 km long in the western foothills of the Appalachians, in limestone, discovered in 1809. The caves are widespread in the Alps, Dinaric Mountains, Apennines, Crimea, the Caucasus, southern China, in the Appalachians, Tien Shan, Podolsk Upland and other places.

Caves are interesting natural objects with a special climate, hydrography, and organic world. International tourism is associated with the caves: there are more than 150 large caves but tourist complexes (Yugoslavia, Czech Republic, USA). Archaeological finds are not uncommon in warm caves. Underground gas storage facilities are installed in caves, mushrooms (champignons) are grown, and bronchial asthma is treated in salt caves. Science studies caves in various aspects - their morphology, hydrology, climate, origin, tourist and economic use speleology.

Karst landscapes of temperate latitudes have specific natural features. First of all, this is the dominance of concave closed relief forms on the surface and the presence of voids in rock strata reaching the size of large caves. The hydrogeological conditions are peculiar - poor development of surface waters: there are few rivers and lakes, the territories are almost waterless even in a humid climate. Small rivers can go into pores and then reappear downstream on the surface. So a system of intermittent river valleys is formed, the elements of which are blind valleys that do not have a mouth, and bag-shaped valleys with closed upper reaches. Groundwater in karst areas is characterized by strong fluctuations in water levels. In the river valleys there are powerful “Vaucluse” springs (named after the Vaucluse spring in Southern France) with a large but variable water flow, reaching 30-50 m 3 /s. The soil and vegetation cover is also unique. Humus-carbonate soils on limestone eluvium have a neutral or alkaline soil solution, a high percentage of humus, and are usually crushed stone. Among the plants there are many drought-resistant plants, calcephytes are typical.

In karst areas, hydraulic engineering construction is difficult due to possible leakage of water from reservoirs, construction of railways and highways due to inevitable failures, construction of civil and industrial facilities, especially nuclear power plants, due to possible deformation of buildings.

Karst relief takes on a special character in the humid climate of equatorial-tropical latitudes. Tropical karst is remnant karst in the form of domes, towers, truncated cones against the background of a leveled surface. Tropical karst is a more mature form of karst denudation, when the karst, usually limestone, strata have largely been destroyed as a result of intense leaching and only remnants remain. Constantly hot weather contributes to this humid climate, and therefore the karst process develops on the surface all year round. In addition, conditions favorable for karst exist there over several geological periods - millions of years. Due to the intensive development of organic life, there is an abundance of carbon dioxide and, accordingly, greater aggressiveness of surface and groundwater. And one more necessary condition is a thick layer of chemically pure massive fractured limestone. Otherwise, concave karst forms develop, as in temperate latitudes.