Guide to Geography

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Karst Topography and Sinkholes

From Matt Rosenberg,

Your Guide to Geography.

Limestone, with its high calcium carbonate content, is easily dissolved in the acids produced by organic materials. About 10% of the earth's land (and 15% of the United States') surface consists of soluble limestone, which can be easily dissolved by the weak solution of carbonic acid found in underground water.

When limestone interacts with underground water, the water dissolves the limestone to form karst topography - an amalgamation of caves, underground channels, and a rough and bumpy ground surface. Karst topography is named for the Kras plateau region of eastern Italy and western Slovenia (Kras is Karst in German for "barren land").

The underground water of karst topography carves our impressive channels and caves that are susceptible to collapse from the surface. When enough limestone is eroded from underground, a sinkhole (also called a doline) may develop.

Sinkholes are depressions that form when a portion of the lithosphere below is eroded away.

Figure 1 Entrance to the Siburn Cavern system in Belize.
inkholes can range in size from a few feet or meters to over 100 meters (300 feet) deep. They've been known to "swallow" cars, homes, businesses, and other structures. Sinkholes are common in Florida where they're often caused by the loss of groundwater from pumping.

A sinkhole can even collapse through the roof of an underground cavern and form what's known as a collapse sinkhole, which can become a portal into a deep underground cavern.

While there are caverns located around the world, not all have been explored. Many still elude spelunkers as there is no opening to the cave from the earth's surface.

Inside karst caves, one might find a wide range of speleothems - structures created by the deposition of slowly dripping calcium carbonate solutions. Dripstones provide the point where slowly dripping water turns into stalactites (those structures which hang from the ceilings of caverns), over thousands of years which drip onto the ground, slowly forming stalagmites. When stalactites and stalagmites meet, they forum cohesive columns of rock. Tourists flock to caverns where beautiful displays of stalactites, stalagmites, columns, and other stunning images of karst topography can be seen.

Karst topography forms the world's longest cave system - the Mammoth Cave system of Kentucky is over 350 miles (560 km) long. Karst topography can also be found extensively in the Shan Plateau of China, Nullarbor Region of Australia, the Atlas Mountains of northern Africa, the Appalachian Mountains of the U.S., Belo Horizonte of Brazil, and the Carpathian Basin of Southern Europe.

See this topographic map of Mitchell, Indiana for an impressive example of karst topography (remember that contour lines with tick marks are depressions). On this map, each contour line represents 10 feet (3 meters).


Throughout the world karst landscapes vary from rolling hills dotted with sinkholes, as found in portions of the central United States, to jagged hills and pinnacle karst found in the tropics. The development of all karst landforms requires the presence of rock which is capable of being dissolved by surface water or ground water.

The term karst describes a distinctive topography that indicates dissolution (also called chemical solution) of underlying soluble rocks by surface water or ground water. Although commonly associated with carbonate rocks (limestone and dolomite) other highly soluble rocks such as evaporates (gypsum and rock salt) can be sculpted into karst terrain.

Understanding caves and karst is important because ten percent of the Earth's surface is occupied by karst landscape and as much as a quarter of the world's population depends upon water supplied from karst areas. Though most abundant in humid regions where carbonate rock is present, karst terrain occurs in temperate, tropical, alpine and polar environments. Karst features range in scale from microscopic (chemical precipitates) to entire drainage systems and ecosystems which cover hundreds of square miles, and broad karst plateaus.

Although karst processes sculpt beautiful landscapes, karst systems are very vulnerable to ground water pollution due to the relatively rapid rate of water flow and the lack of a natural filtration system. This puts local drinking water supplies at risk of being contaminated. In the mid 1980's, flooding of caves in the highly populated area of Bowling Green, Kentucky, caused industrial waste to leak into the vast system of underground fissures polluting the ground water in local wells. Due to urban expansion millions of dollars is spent annually in the United States to repair damage to roads, buildings and other structures which are built on unstable karst surfaces

Karst Topography

The degree of development of karst landforms varies greatly from region to region. Large drainage systems in karst areas are likely to have both fluvial (surface) and karst (underground) drainage components. As stated in the introduction, the term karst describes a distinctive topography that indicates dissolution of underlying rocks by surface water or ground water.

Water falls as rain or snow and soaks into the soil. The water becomes weakly acidic because it reacts chemically with carbon dioxide that occurs naturally in the atmosphere and the soil. This acid is named carbonic acid and is the same compound that makes carbonated beverages taste tangy. Rainwater seeps downward through the soil and through fractures in the rock responding to the force of gravity. The carbonic acid in the moving ground water dissolves the bedrock along the surfaces of joints, fractures and bedding planes, eventually forming cave passages and caverns.

Limestone is a sedimentary rock consisting primarily of calcium carbonate in the form of the mineral calcite. Rainwater dissolves the limestone by the following reaction: Calcite + Carbonic acid = Calcium ions dissolved in ground water + Bicarbonate ions dissolved in ground water.

Cracks and joints that interconnect in the soil and bedrock allow the water to reach a zone below the surface of the land where all the fractures and void spaces are completely filled (also known as saturated) with water. This water-rich zone is called the saturated zone and its upper surface is called the water table. The volume of void space (space filled with air or water) in soil or bedrock is termed porosity. The larger the proportion of voids in a given volume of soil or rock the greater the porosity. When these voids are interconnected, water or air (or other fluids) can migrate from void to void. Thus the soil or bedrock is said to be permeable because fluids (air and water) can easily move through them. Permeable bedrock makes a good aquifer, a rock layer that holds and conducts water. If the ground water that flows through the underlying permeable bedrock is acidic and the bedrock is soluble, a distinctive type of topography, karst topography, can be created.

The first part of our animation shows evolution of karst landforms created by downward movement of water accompanied by dissolution of rock and mass transport of sediments in stream channels. In tropical areas with thick massive limestones, a remarkable and distinctive landscape of jagged hills and narrow gorges completely dominates the landscape. Movement of solution along fractures and joints etches the bedrock and leaves limestone blocks as isolated spires or pinnacles. Pinnacles range from small features a few inches tall to intermediate forms a few feet tall to large pinnacles hundreds of feet tall. Besides the etching of pinnacles and residual hills, sheets of flowing water move down sloping surfaces creating a variety of etched surface features. Our computer animation shows the dominant landforms, such as pinnacles, cones, and towers, commonly found in the tropical karst environment of northern Puerto Rico.

Our paper model represents another type of karst landscape, that of a rolling limestone plain such as is found in south-central Kentucky, northern Florida, and the Highland Rim of central Tennessee where doline karst is the dominate feature. Doline karst is the most widely distributed type of karst landscape. The landscape is dotted with sinkholes (dolines) which can vary widely in number and size. For the Sinkhole Plain in central Kentucky, there are approximately 5.4 sinkholes per square kilometer over a 153 square kilometer area. For north Florida there are almost 8 sinkholes per square kilometer over a 427 square kilometer area (White, 1988, table 4.1, page 100).

Karst topography dominated by sinkholes or dolines usually has several distinct surface features. Our paper model shows features normally associated with karst topography. Sinkholes (also known as dolines) are surface depressions formed by either: 1) the dissolution of bedrock forming a bowl-shaped depression, or 2) the collapse of shallow caves that were formed by dissolution of the bedrock. These sinkholes or shallow basins may fill with water forming lakes or ponds. Springs are locations where ground water emerges at the surface of the earth. Disappearing streams are streams which terminate abruptly by flowing or seeping into the ground. Disappearing streams are evidence of disrupted surface drainage and thus indicate the presence of an underground drainage system. Cave entrances are natural openings in the earth large enough to allow a person to enter. Caves may reflect a complex underground drainage system.

A Brief list of the longest caves in the United States
name and Location of Cave Kilometers Mapped *

Mammoth Cave-Flint Ridge System - Kentucky 500
Jewel Cave - South Dakota 118
Wind Cave - South Dakota 73
Friars Hole System - West Virginia 68
Fisher Ridge Cave System - Kentucky 64

* Numbers are rounded to nearest kilometer

What do Caves Contain?

Moving water may transport earth materials into and through caves physically or chemically. Caves contain interesting features as a result of the physical and chemical processes that form them. Among these features are breakdown blocks of rock formed by collapse of cave ceilings. Also seen are sediments containing boulders, sand, silt, and clay deposited from water flowing in and through cave passages and conduits. Speleogens are irregular or distinctive shapes of carbonate rock etched from bedrock by dripping or running water. Speleogens can form where bedrock is not uniform in chemical composition. Consequently, the less soluble rock dissolves slower than adjacent more soluble rock through time. The less soluble rock tends to stand in relief and projects from walls and ceilings of caves.

Away from their entrances, caves usually provide a relatively constant temperature and humidity over a long period of time. Thus, caves provide an ideal environment for chemical deposition of minerals. As water laden with dissolved carbonate seeps into the air-filled cave passage, it may lose excess carbon dioxide to the cave atmosphere, or the water itself may evaporate, causing the dripwater to precipitate secondary carbonate or other minerals from solution, creating cave formations or speleothems including cone-shaped stalactites , stalagmites , flowstone or rimstone, or other interesting shapes. Caves in karst areas often have stalactites (icicle-like masses of chemical limestone) that hang from cave ceilings and stout stalagmites protruding from the cave floor. Stalactites and stalagmites can be a few inches to several feet long. Sometimes the drip water will flow down the walls and over the cave floor creating flowstone or rimstone deposits. Where drip water seeps from a joint and then drips over the edges of ledges, deposits of great complexity known as draperies are formed. The color of dripstones and flowstones comes from organic and/or iron oxide compounds brought in from the surface, giving the speleothems an orange brown color or from the presence of oxides and hydroxides of iron and manganese which give the speleothems a deep brown or black color.

What Lives Underground?
Some scientists are interested in cave ecology and how cave animals interact with cave microclimates. Animals found in caves include everything from surface dwelling animals like raccoons that occasionally use the cave, to animals that have adapted exclusively to life in the cave (troglobites) . Troglobites cannot survive outside caves. These may include such diverse animals as eyeless fish and crayfish, cave beetles, flatworms, and other unusual types of insects. Many of these animals have lost body pigmentation and are white or transparent in color. Although the cave environment appears to be stable, change can and does occur. The temperature of the cave varies due to air movement near the entrances and the temperature of water entering the cave. In reality, some caves have their own weather systems which create wind due to temperature and pressure differences between the entrance and interior passageways.

Many animals, such as bats, cave crickets, and pack rats, regularly visit, raise their young, or hibernate in caves. These animals are called trogloxenes . Caves may support large numbers of different types of bats. Bats may be among the most beneficial animals to people and the ecosystem as insect-eaters and plant pollinators. The little brown bat can eat 600 mosquitoes in an hour thus performing the work of a "natural insecticide," helping control crop pests and other insects. The Mammoth Cave-Flint Ridge System in Kentucky, which is the most extensive cave system in the world, has a biodiversity of 43 mammals, 15 reptiles, 19 amphibians and 3 fish. In 1981, the United Nations designated Mammoth Cave National Park as a World Heritage Site. An excellent summary of the Mammoth Cave area and other caves found in the U. S. National Park System can be found on the World Wide Web at:

In 1988 the United States passed the Federal Cave Resource Protection Act which preserves and protects all significant caves found on federal land for future generations of Americans.

What's in it for Me?

Knowing where karst features are located could help city and town planners, as well as individual landowners, to make decisions on where to build houses and other structures. This information could save cities thousand of dollars in repairs to buildings that are built on unstable karst terrain.

Karst springs supply drinking water to millions of people. Knowledge of karst terrain and the movement of water in underground drainage systems is important for maintaining good quality and safe drinking water. Pollution of ground water is a major problem in karst terrain.

Caves provide a venue for recreation. Although most of the caves located in National Parks are protected, there are over 200 commercial show caves nationwide which are open to the public. Recreational caving has become a popular hobby. The National Speleological Society has about 20,000 active affiliates nationwide.

Deposits preserved in caves can tell geologists about past climates. Fossils and artifacts found in caves help geologists and archaeologists unravel the prehistory of an area.

Caves support a unique community of bacteria, fungi and animals not seen on the surface of the Earth.


Breakdown - An underground rock fall. Blocks of rock become detached from the roof of the cave. The accumulation produces a series of rough angular rock fragments scattered on the cave floor.

Carbonate rocks - Sedimentary rocks composed mainly of calcium carbonate.

Carbonic acid - A mild acid formed when water and carbon dioxide chemically combine in the atmosphere and soil.

Cave - A natural opening in rock large enough to be entered by man and extending to points where daylight does not penetrate.

Cave system - A cave or caves having a complex network of interconnected chambers and passages that constitute an underground drainage system.

Disappearing streams - In karst areas, streams often disappear into the ground usually at a sinkhole.

Dissolution (also called chemical solution) - The process of chemical weathering of bedrock in which the combination of water and acid slowly removes mineral compounds from solid bedrock and carries them away in liquid solution.

Dolines (also known as sinkholes) - A closed surface depression draining underground in karst landscape. Dolines are usually "bowl-shaped" and can be a few to many hundreds of meters in diameter.

Flowstone - A general term referring to a deposit formed from thin films or trickles of water, the minerals are usually calcium carbonate and encrust floors or walls.

Fluvial - Pertaining to a river or rivers.

Ground water - Water below the level at which all voids in the rock are completely filled with water.

Karst - A distinctive topography that indicates dissolution of underlying soluble rocks by surface water or ground water.

Microclimate - The climate (temperature, humidity, air flow) of a local or confined area such as part of a cave.

Permeability - The property of rock or soil that permits water to pass by flowing through interconnected voids (spaces). Permeable bedrock makes a good aquifer, a rock layer that yields water to wells.

Porosity - The volume of void space (space filled with air or water) in soil or bedrock. When these voids are interconnected, water or air (or other fluids) can migrate from void to void. Thus interconnected pores make the soil or bedrock permeable.

Sinkholes (also known as dolines) - A closed surface depression draining underground in karst landscape. Sinkholes are often "bowl-shaped" and can be a few to many hundreds of meters in diameter.

Speleology - The exploration and study of caves.

Speleothems - A deposit, usually calcium carbonate, formed in caves by chemical precipitation from drips or thin films of water. Common speleothem forms are: Stalactite: which hangs downwards from a roof or wall of a cave and Stalagmite: which projects vertically upwards from a cave floor.

Stalactite - See speleothems (above).

Stalagmite - See speleothems (above).

Spring - A spring or resurgence is the point where ground water reappears at the earth's surface and begins flowing downhill as a surface stream. The opposite of a sinking stream.

Troglobites ("cave dwellers") - These animals can only complete their life cycle in caves and typically exhibit adaptations to the totally dark cave environment, including low metabolism, unpigmented skin, long feelers or pedipalps, and loss of eyes in adult forms.

Trogloxene - An animal which spends only part of its life cycle in caves, such as a bat.

Water table - The surface between the zone of pure saturation and zone of pure aeration underground.


Karst is a German name for an unusual and distinct limestone terrain in Slovenia, called Kras. The karst region in Slovenia, located just north of the Adriatic Sea, is an area of barren, white, fretted rock. The main feature of a karst region is the absence of surface water flow. Rainfall and surface waters (streams, for example) disappear into a drainage system produced in karst areas. Another feature is the lack of topsoil or vegetation. In geology, the term karst topography is used to describe areas similar to that found in Kras. The most remarkable feature of karst regions is the formation of caves.


Figure 2 Source of the Loue by Ouhans (Franche-Comté)

arst landscapes develop where the bedrock is comprised of an extremely soluble calcium carbonate rock such as limestone, gypsum, or dolomite; limestone is the most soluble calcium carbonate rock. Consequently, most karst regions develop in areas where the bedrock is limestone. Karst regions occur mainly in the great sedimentary basins. The United States contains the most extensive karst region of the world. Other extensive karst regions can be found in southern France, southern China, Central America, Turkey, Ireland, and England.

Karst regions are formed when there is a chemical reaction between the groundwater and the bedrock. As rain, streams, and rivers flow over the earth's surface, the water mixes with the carbon dioxide that naturally exists in air. The water and carbon dioxide react to form a weak carbonic acid, which causes the soil to become acidic and corrode the calcium carbonate rock. The carbonate solution seeps into fissures, fractures, crevices, and other depressions in the rock. Sinkholes develop and the fissures and crevices widen and lengthen. As the openings get larger, the amount of water that can enter increases. The surface tension decreases, allowing the water to enter faster and more easily. Eventually, an underground drainage system develops. The bedrock is often hundreds of feet thick, extending from near the earth's surface to below the water table. Solution caves often develop in karst regions. Caves develop by an extensive enlargement and erosion of the underground drainage structure into a system of connecting passageways.

There are many variations of karst landscape, often described in terms of a particular landform. The predominant landforms are called fluviokarst, doline karst, cone and tower karst, and pavement karst. Some karst regions were etched during the Ice Age and may appear barren and very weathered (pavement karst). Other karst areas appear as dry valleys for part of the year and after seasonal floods, as a lake (one example of fluviokarst). In tropical areas, karst regions can be covered with forests or other thick vegetation. Sometimes, the underground drainage structure collapses, leaving odd formations such as natural bridges and sinkholes (doline karst). Tall, jagged limestone peaks are another variation (cone or tower karst).

Chemistry of karst landscapes

Karst landforms are generally the result of mildly acidic rainfall acting on soluble limestone or dolostone bedrock. The process of subsurface rock dissolution results in a topography with distinctive features, including sinkholes or dolines (closed basins), vertical shafts, disappearing streams, and springs. With a sufficiently low base level and sufficient time, complex underground drainage systems (such as karst aquifers) and extensive caves and cavern systems may form.

The carbonic acid that causes these features is formed as rain passes through the atmosphere picking up CO2, which dissolves in the water. Once the rain reaches the ground, it passes through the soil, gathering up more CO2 to form a weak carbonic acid solution: H2O + CO2 → H2CO3.

This mildly acidic water begins to dissolve any fractures and bedding planes in the limestone bedrock. Over time these fractures enlarge as the bedrock continues to dissolve. Openings in the rock increase in size, and an underground drainage system begins to develop, allowing more water to pass through and accelerating the formation of underground karst features.

Somewhat less common than this limestone karst is gypsum karst, where the solubility of the mineral gypsum provides many similar structures to the dissolution and redeposition of calcium carbonate.

Karst formations

Erosion along limestone shores, common in the tropics, produces typical karst topography, including a sharp makatea surface above the normal reach of the sea and undercuts that are mostly the result of biological activity or bioerosion at or a little above mean sea level. Some of the most dramatic of these formations can be seen in Thailand's Phangnga Bay and Halong Bay in Vietnam.

Figure 3 The Witch's Finger, a stalagmite in the Carlsbad Caverns. NPS photo by Peter Jones,
alcium carbonate removed by water may deposit elsewhere. In caves, stalactites and stalagmites are formed by deposition of calcium carbonate and other dissolved minerals as the water drips from above. An example is the Gruta Rei do Mato in the Lagoa Santa Karst formation around Sete Lagoas, Brazil with a stalactite of 20 meters height.

Other formations consist of shields (where the flow is from a fissure rather than from a point), and flowstone, which occurs when the flow of calcite-rich water is somewhat impeded and calcite is deposited in the flow. Helictites are curlicue-shaped formations associated with the roofs and walls of caves. Larger flow-type formations are rimstone pools and gours, which are bathtub-shaped and may contain large calcite or aragonite crystals as a result of slow evaporation. Rivers which emerge from limestone caves may also produce tufa terraces, consisting of layers of calcite deposited over extended periods of time as the water leaves the CO2-rich cave environment.

Water drainage and problems

Farming in karst areas must take into account the excessive drainage. The soils may be fertile enough, and rainfall may be adequate, but rainwater quickly moves through the crevices into the ground, sometimes leaving the surface soil parched between rains.


Figure 4 Karst lake (Doberdo' del Lago, Italy), from underground water springing into a depression. Karst lakes have no affluent or effluent

ater supplies from wells in karst topography are inherently hazardous, as the well water may simply run from a sinkhole in a cattle pasture through a cave and to the well, bypassing the normal filtering that occurs in a porous aquifer. Karst formations are cavernous and therefore have high rates of permeability. This results in very little time for contaminants to be filtered out naturally through the pores of strata.

Groundwater in karst areas is just as easily polluted as surface streams. All too often, sinkholes have been used as farmstead or even community trash dumps. In karst areas where septic tanks are the main sewage disposal system, overloaded or malfunctioning systems dump raw sewage directly into underground channels.

The karst topography itself also poses some difficuties for human inhabitants. Sinkholes can develop gradually as surface openings enlarge, but quite often progressive erosion is unseen and the roof of an underground cavern suddenly collapses. Such events have swallowed homes, cattle, cars, and farm machinery.

The Driftless Area National Wildlife Refuge in Iowa protects ice age snails surviving in air chilled by flowing over buried karst ice formations.

Partial list of karst areas


  • The Stone Forest (Yunnan Province, China)

  • Area around Guilin and Yangshuo in Guangxi Zhuang Autonomous Region, China

  • Ofra region, Israel.

  • Vang Vieng, Laos

  • Gunung Mulu National Park Malaysia

  • Krabi region, Thailand

  • Phangnga Bay Area, Southern Thailand

  • Halong Bay, Vietnam


  • Jenolan Caves, New South Wales, Australia

  • Waitomo, Oparara regions of New Zealand

  • The Nakanai Mountains, East New Britain, Papua New Guinea


  • Herzegovina region of Bosnia-Herzegovina

  • The regions of Dalmatia, Lika, Gorski kotar, Kvarner and the islands in Croatia

  • Moravian Karst

  • The White Peak of the Peak District, UK, around Matlock, Castleton, and Thor's Cave

  • Yorkshire Dales (including the spectacular Malham Cove), England

  • The Burren (Co.Clare, Ireland)

  • The Apuseni Mountains, Romania

  • Assynt, SE Skye and near Kentallen in Scotland

  • Slovak Paradise and Slovak Krast [1], Slovak republic

  • The region of Inner Carniola in Slovenia

  • Kras, a plateau in southwestern Slovenia and northeastern Italy


  • Anjajavy Forest, western Madagascar

  • Madagascar dry deciduous forests

North America

  • The Nahanni region in the Northwest Territories, Canada

  • The Viñales Valley in Cuba

  • The Cenotes of the Yucatan Peninsula, Mexico

  • Huntsville, Alabama, and the North Alabama Region, U.S.A.

  • Coulee Region in the American Midwest, U.S.A.

  • The Florida peninsula, U.S.A.

  • Mammoth Cave area and Bluegrass region of Kentucky, U.S.A.

  • Southeastern Minnesota, U.S.A.

  • The Ozark Plateau of Missouri and Arkansas, U.S.A.

  • The Karst forest in Puerto Rico, U.S.A.

  • The Cumberland Plateau in Middle Tennessee, U.S.A.

  • The Hill Country of Texas, U.S.A.

Another Glossary


abîme. (French.) 1. An abyss. 2. A wide, deep shaft, in limestone, the walls of which are vertical or overhanging[10].

accelerated corrosion. A localized concentration of solution intensity, produced by factors favoring greater aggressivity of the water in certain parts of the karstland creating differential solution rates and thereby a marked unevenness in the overall erosion of the karstland[19]. See also corrosion; alluvial corrosion.
accretion. Land addition by sediment deposition of a stream[16].
accumulation. Building of new land by addition of sedimentary deposits[16].
acid mine drainage. Acid waters originating from surface or underground mine workings[16].
active cave. 1. Cave containing a running stream. 2. Cave in which speleothems are growing. (Less common and less desirable usage.) Compare live cave[10].
active glacier. Glacier in the stage of actively enlarging and moving as a result of accumulation of precipitation that exceeds the rate of ablation.
active water. Water with corrosive properties[16].
aggradation. Land addition through sediment deposition[16].
aggrading river. River that is actively elevating its bed by deposition of sediments[16].
aggressive water. 1. Water having the ability to dissolve rocks. In the context of limestone and dolomite, this term refers especially to water containing dissolved carbon dioxide to form carbonic acid or, rarely, other acids. 2. Quality of waters that attack metals and concrete chemically by dissolution[10].
aisle. An elongated high narrow traversable passage in a cave[10]. See also crawl,
algal limestone. Type of limestone formed by calcium secreting algae[16].
allogene stream. A surface-water course flowing over a karst terrane, but fed by a spring (or springs) issuing from a nonkarst terrane[20].
allogenic drainage. Underground karst drainage that is derived entirely from surface run-off that originates on adjacent non-karstic, generally impermeable, rocks. Also allochthonous drainage. See also autogenic drainage[9].
allogenic valley. A karst valley incised by a watercourse originating on impervious rock with a volume sufficient for it to traverse a limestone area on the surface. The valley is incised from the limestone contact and with the passage of time the river is increasingly likely to pass underground as the waters enlarge joints. Occasionally such a valley may represent the large-scale collapse of the cavern system along a subterranean stream or the enlarging of a series of karst windows[19].
alluvial. Pertaining to or composed of alluvium or deposited by a stream or running water[6]. Also applies to material lining the floor of a cave and deposits at the mouth of a spring.
alluvial apron. A fan-like plain from the deposition of glacial outwash[16].
alluvial corrosion. Greater intensity of solution, caused by the passage of water through unconsolidated deposits rich in carbon dioxide, thus increasing aggressivity[19]. See also corrosion, accelerated corrosion.
alluvial fan. A fan-like deposit of detrital material from steep mountain slopes[16].
alluvial plain. A plain formed by the deposition of water borne sediments[16].
alluvial veneer. A very thin cover of water borne sediments[16].
alluvium. A general term for clay, silt, sand, gravel, or similar unconsolidated material deposited during comparatively recent geologic time by a stream or other body of running water as a sorted or semisorted sediment in the bed of the stream or on its floodplain or delta or as a cone or fan at the base of a mountain slope[6].
alpine karst. 1. Karst formed at high latitude, or in polar regions regardless of altitude. 2. Almost synonymous with glaciokarst but restricted to areas of high altitude and relief[9]. Synonyms: glaciokarst; nival karst.
alveolization. (From the Latin word ‘alveolatus,’ meaning hollowed out.) Pitting of a rock surface produced by wind loaded with sand, by water charged with carbonic acid, or by plant roots[10].
anastomotic cave pattern. A type of maze cave consisting of tubular passages or holes in a cave or in a solution-sculptured rock. A complex of many irregular and repeatedly connected passages. Synonym: labyrinth.
annual frost zone. The top layer of ground subject to annual freezing and thawing[16].
antecedent stream. A stream having established its course before occurrence f orogenic events that would later alter the general drainage pattern[16].
apron. A smooth bulging mass of flowstone covering sloping projections from walls of caves or limestone cliffs[10].
aquiclude. A formation which, although porous and capable of storing water, does not transmit it at rates sufficient to furnish an appreciable supply for a well or spring. See also confining unit[22].
aquifer. 1. A formation, group of formations, or part of a formation that contains sufficient saturated permeable material to yield significant quantities of water to wells and springs[6]. 2. A ground-water reservoir. 3. Pervious rock that is completely saturated and will yield water to a well or spring. Historically the term has been applied to beds favoring early cave development, probably synonymous with some inception horizons[18].
aquifer, artesian. A confined aquifer where the potentiometric surface rises above the top of the aquifer bed[16].
aquifer, coastal. An aquifer in a coastal region open to salt-water intrusions[16].
aquifer, flowing artesian. An artesian aquifer in which the water, under hydrostatic pressure rises above the land surface.
aquifer, karst. An aquifer in which the flow of water is or can be appreciable through one or more of the following: joints, faults, bedding-plane partings, and cavities — any or all of which have been enlarged by dissolution[18].
aquifer, leaky. An aquifer overlain or underlain by semipermeable strata from or into which water will flow[16]
aquifer system. A body of permeable and poorly permeable material that functions regionally as a water-yielding unit; it comprises two or more permeable beds separated at least locally by confining beds that impede ground-water movement but do not greatly affect the regional hydraulic continuity of the system; includes both saturated and unsaturated parts of permeable material[22].
arête and pinnacle karst. A landscape of naked reticulated raw-topped ridges having almost vertical slopes and a relief of as much as 120 meters. The ridges rise above forest- covered corridors and depressions. Found in New Guinea at elevations of 2,000 meters and more[10]. Both pinnacle karst and arête karst are varieties of limestone landscape formed under equatorial rain forest cover. They are characterized by vertical sided blades of bare rock fretted by dissolution[9].
argillaceous. The property of rocks containing clay in non-negligible proportions[16].
artesian flow. Flow through a confined aquifer where the elevation of the overlying aquiclude is locally depressed so that the entire aquifer is saturated and the flow is under hydrostatic pressure. Some maze cave development in cavernous limestones may be due to artesian flow, which is commonly related to synclinal fold structures[9].
artesian spring. See spring, artesian.
artesian well. A well deriving its water from a confined aquifer in which the water level stands above the ground surface[6]. Synonym: flowing artesian well.
arthropods. Animals with jointed legs and bard external skeletons (exoskeletons). The group includes insects, crustaceans, spiders, millipedes, and several other types of animals commonly found in caves[23].
artificial discharge. The discharge of ground water by pumping wells[16].
artificial recharge. Recharge at a rate greater than natural, resulting from deliberate or incidental human activities[6].
ascender. A mechanical device used by cavers who are either ascending or are descending through a vertical opening in a cave (e.g. vadose shaft) that uses a cam to grip a rope while downward pressure is being applied to the device[13]. See also mechanical ascender; prusiking; prusik knot.
association. A relatively stable community of different species living in a characteristic habitat[25].
autogenic, authigenic. Formed or generated in place[1]. See also allogenic; recharge, autogenic; recharge, allogenic.
autogenic drainage. Underground karst drainage that is derived entirely by absorption of meteoric water into the karst rock surface[9]. Synonym: autochthonous drainage. See also allogenic drainage.
available water. The water available to plants in the soil zone as defined by the interval between field capacity and wilting point[16].
aven. 1. A hole in the roof of a cave passage that may be either a rather large blind roof pocket or a tributary inlet shaft into the cave system. A feature described as an aven when seen from below may equally be described as shaft when seen from above, and the naming of such a feature commonly depends purely upon the direction of exploration. Many avens close upwards to impenetrable fissures but may still be important hydrological routes; few caves are without them. In parts of France, aven is equivalent to the British term, pothole[9]. 2. (French.) A vertical or highly inclined shaft in limestone, extending upward from a cave passage, generally to the surface; smaller than an abîme. Commonly related to enlarged vertical joints. Compare cenote; natural well; pothole. 3. (British.) A vertical extension from a shaft in a passage or chamber roof that tapers upward rather like a very elongate cone[10]. Compare dome pit.
backflooding. 1. Temporarily rising water level in a cave caused by downstream passage being too small to pass an abnormally high discharge. The excavation and reexcavation of some caves is ascribed to the enlargement of a passage at or near the water table by gravity flow alternating with periods of calcite precipitation[10]. 2. Flooding due to backup of excess flow behind a constriction in a major conduit. Water that is ponded in tributary passages and proto-caves upstream of the constriction may contribute to the enlargement of maze caves[9].
backwater. The accumulated water above the normal level of a water course due to impoundment at a point downstream[16].
bacon. Thin, elongated, translucent flowstone having parallel colored bands on or projecting from roofs and walls of some caves[10]. See also blanket; curtain; drapery.
balcony. Any projection on the wall of a cave large enough to support one or more persons[10].
bank. Ascending slope bordering a river[16].
bank erosion. Erosion of a river bank[16].
bank storage. 1. Subsurface conduit water that has been driven back up into older, higher karst levels and into the surrounding rock matrix during a high flow period. 2. River water that has infiltrated river banks during a high flow period and being retained in temporary storage[16].
bare karst. A type of karst landscape lacking soil cover and where dissolution of carbonate rocks to form karst landforms occurs primarily on the exposed bedrock surface[9]. See naked karst
barrier. A geological formation or part of a formation having become impervious to ground-water flow due to a facies change[16].
barrier, freshwater. Barrier of freshwater

injected into an aquifer to stop the inflow

of seawater into a coastal aquifer[16].

barrier, hydrologic. Lithologic formation preventing horizontal movement of ground water[16].
barrier, permeability. A geologic or petrographic feature in a bed obstructing free flow[16].
barrier spring. See spring, barrier.
base level. Lowest level of erosion by a stream[16].
base level of erosion. The lowest theoretical level of surface to be achieved by erosion[16].
base level, karst. See karst base level.
base of karstification. Level below which karstification has not occurred. See also karst base level.
basin. Hydrogeographic unit receiving precipitation and discharging runoff in one point[16].
basin characteristics. The physiographic, geologic, and ecologic characteristics of a basin[16].
basin, closed. Drainage basin with no surface flow outlet[16].
basin, drainage. The area contributing to runoff which sustains streamflow[16]. See also drainage basin.
basin, ground-water. The area throughout which ground water drains towards the same point. It can be larger than the associated drainage basin if permeable layers extend outside of the topographical divide[16]. In karst terranes, the groundwater basin often does not resemble the drainage basin.
basin, infiltration. Basin in which water is spread for recharge[16].
basin, intermontane. A basin lying between two mountain ranges[16].
basin mouth. The point at which runoff leaves a basin[16].
basin perimeter. The circumference of a basin following the divide[16].
basin relief, maximum. The elevation difference between basin mouth and the highest point within a basin perimeter[16].
basin, settling. A basin used for the settling out of solids from suspension[16].
beachrock. 1. Rock composed of sand grains and/or sand-sized shell fragments cemented by calcium carbonate, commonly formed very rapidly on some beaches in tropical and sub-tropical areas. Beachrock generally occurs as thin beds between bedding planes that dip seawards

at angles similar to those of the beach slope[9]. 2. A friable to indurated rock consisting of sand grains of various minerals cemented by calcium carbonate; occurs in thin beds dipping seaward at less than 15N. Also known as beach sandstone[10].

bed. 1. A layer in sedimentary rocks; a stratum[10]. 2. A sedimentary deposit of relatively small thickness and great areal extent, separated by bedding planes from over- and underlying deposits[16].
bed, mortar. Secondary calcium carbonate cementations in the lower part of a soil profile[16]. Synonym: hardpan.
bed, river. The channel of a river covered by water[16].
bed roughness. The roughness of a channel or river bed[16].
bed, stream. The bottom of a stream covered by water[16].
bedding. Applies to rocks resulting from consolidation of sediments and exhibiting surfaces of separation (bedding planes) between layers of the same or different materials (e.g., shale, sandstone, limestone, etc.).
bedding-plane cave. 1. Bedding planes are widespread and very significant features within most carbonate rocks, and cave passages are commonly guided by them. Their structure, their distribution and the chemical contrasts that some bedding planes provide may be the major influence during the earliest phases of development of a cave system. The term bedding-plane cave is strictly applied to a passage that has not enlarged by growth into a major tube or canyon, but has remained almost entirely on the bedding plane. A famous example is Hensler’s Passage, in Gaping Gill, Yorkshire, which is over 400 m long, nearly over 5 m wide and nowhere higher than 1 m[9]. 2. A passage formed along a bedding plane, especially when there is a difference in susceptibility to corrosion in the two beds[10]. 3. A cave whose location is controlled by the bedding of the enclosing formation or formations[20]. Synonyms:
bedload. The part of the total stream load that is moved on or immediately above the stream bed, such as the larger or heavier particles (boulders, pebbles, gravel) transported by traction or saltation along the bottom; the part of the load that is not continuously in suspension or solution[6].
bedrock. Solid rock underlying unconsolidated material[16].
bench mark. A relatively permanent mark, natural or artificial, furnishing a survey point at a known elevation in relation to an adopted datum[16]. Bench marks, or marked points, connected by precise leveling, constitute the control of landsurface settlement in subsidence studies[21].
B-horizon. Illuvial horizon in which soluble material from the overlying Ahorizon has been deposited[16].
bifurcation. The forklike separation of a water course into two arms[16].
biomass. The total weight of living matter, whether in an entire community, at a particular trophic level, or of a particular kind of organism in the community. Thus we may refer to the biomass of a pond community, of herbivores in the pond, or of copepods in the pond[23].
biomicrite. A microscopic-textured limestone composed of skeletal grains in a matrix of micrite; micrite is a finely crystalline carbonate sediment with the upper crystalline diameter being 4 microns[20].
biospeleology. 1. The study of subterranean living organisms, particularly in karst caves and other openings in rock formations[9, 21]. 2. The scientific study of cave animal life, or the biology of caves, karst, and groundwater. A biologist who specializes in this study is called a biospeleologist[23].

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