"The Virtual Cave: Karst"

Karst is a term used to describe the distinctive surface landscapes of cave country, shaped by dissolution of soluble bedrocks such as limestone, dolomite, or gypsum. The surface character of karst results from both surface dissolution of exposed bedrock and dissolution beneath the surface as caves are formed. Voids forming beneath the surface result in slumping or collapse. Streams sink underground and may not reappear until miles away as springs or birthplaces of rivers. Karst landscapes encompass some 10-15% of the earth's land mass and millions of people live in or among karst. This page will attempt to convey both the diversity and beauty of the world's karst.

The Quintessential Karst

We begin with an image that absolutely screams "karst" because it is part of the actual landscape which gave rise to the name. Here, the river Reka flows through a large arch dividing two adjacent sinkholes. The river rises or resurges from a cave in the distant sink, its entrance just visible in the distance about the 4:00 direction from the church on the ridge. The river sinks again beyond. This scene is in the Škocjan Caves Regional Park in Slovenia. The region it is found has similar landforms throughout and is called Kras locally but karst in German. Now the term is used to refer to similar yet quite varied and beautiful landforms. At the top of the page is a karst ridge in central Laos near Vang Vieng. It also houses many caves.

Photo by Dennis Tang, Wikipedia Creative Commons

Distribution of Karst: USA

Carbonate rocks are found in almost every state, with the exception of Delaware and Rhode Island. Not surprisingly the states with the largest amount of karst contain the most caves, with Tennessee the clear winner with over 8000 caves followed by Missouri with 4000+. In the map on the right one sees lava flows marked as "pseudokarst," because these landforms may contain features associated with karst such as caves (lava tubes), collapses and pits. However, there are not due to solutional processes and hence the "pseudo" part of the name. In Florida the karst is young and caves are actively forming below the water table; the longest cave systems there are still completely submerged and being explored by cave divers. The U.S. National Park Service has created a nice poster map showing all the park units with caves and karst.

Distribution of Karst: Worldwide

Carbonate rocks are found throughout the world but by no means evenly distributed. South America and Australia have relatively little karst for their size. By far the hightest proportion of karst is found in China, which contains something like 40% of the world's karst. Europe is also heavily karsted as is the island of Cuba. Canada, though shown as having large amounts of karst, does not have a correspondingly large number of caves. Because glaciers covered much of this area, many cave openings likely became filled with glacial sediments and shallow caves crushed under their weight.

Sinking Streams

In mature karst, surface streams tend to sink and travel underground, sometimes in flooded conduits, sometimes in enterable caves. A big cave system may have dozens of sinking streams (also known as insurgences) merging underground to form a larger stream or river. Speleologists sometimes conduct dye tracing studies to determine whether a given sink point contributes to the water in a particular cave system. Sinking streams may travel tens of kilometers before resurging again on the surface.

Resurgence from a large cave entrance.

Springs and Regurgences

All that water that sinks has to come out again somewhere. When it does we may call it simply a spring, which may form little more than a small pond. But a resurgence may also be a larger volume of water, even the birthplace of a river. Below is Vasey's Paradise, a major spring in the Grand Canyon emerging from the Redwall Limestone.

A karst spring in Spain shows the deep blue color afforded by dissolved limestones.

Sinkholes and dolines

As caves are dissolved away beneath the surface, the underlying void allows soils to drain away through subsurface collapse. Sinkholes are perhaps the most common surface expression of underlyng caves.

Pits and Shafts

A feature related to sinkholes is that of shafts and pits, otherwise known as "vertical" caves. In many cases these are basically sinkholes where collapse has led to steep sides. Often these may require rope to enter safely. The walls may be shear on all sides or have a debris slope as on the bottom left. Middle left, in a view from the bottom of a shaft, we can see the vertical grooves associated with erosion from surface water entering the pit. But the original enlargement probably occured below the water table. Top right, a pit in a heavily mantled (i.e. soil covered) karst. On the right are two examples of the extremes of the genre: A broad pit in Mexico, top, and a huge Tianxeng in China with a cave on the opposite wall.

Often cave entrances in karst occur in the many fissures that form from solution. But there may be hundreds in a small area and most won't open into caves.

This image taken in conjunction with the Passmore Lab film project "Inner Earth"

Zoom in to see how huge this pit is - there is a climber on the far side, 650 feet from the camera. The pit is 633 feet deep.

This massive pit is 613 meters deep, and 600 x 420 meters across. It is exceeded in size by only one other Tiankeng, also in China.

Karst Landforms-unmantled landscapes

When soil has been washed away or drained through the karst, leaving bare rock, we refer to it as an unmantled karst. On the left, karst on the south island of New Zealand. On the right, alpine karst in Montana (top) and in Spain (lower right). Below, karst exposed by hydraulic mining in the Mother Lode country of California. The rounded tops are typical of dissolution that has occured mostly beneath soil cover.

Photo by Chensiyuan, Wikipedia Creative Commons

Karst Landforms: Cone Karst

A mature karst form common to Southeast Asia is tower or cone karst. Rounded karst hills are typically classed as Fengcong when they cluser together and Fenglin when they occur as isolated cones surrounded by flat plains.

Perhaps the most famous and best developed of this form of karst is found in Guangxi Province, China. These images were taken from above or on the Li River, which cuts through the karst. In its flood plain are found more of the Fenglin, and further away are the larger mulit-peaked clusters of Fengcong karst.

Karst Landforms:
Flooded Cone Karst

In some coastal regions cone karst has been flooded by rising sea levels since the last ice age. Notable areas include Vietnam's Ha Long Bay (left two images) and Phang Nga Bay in Thailand (right two images). Like regular cone karst, the individual islets may contain remnants of phreatic caves which were dissected as the bedrock around them was eroded away leaving the isolated cones. In addition there are "foot caves" which have formed at the intertidal zone through a combination of dissolution and littoral enlargement.

Some of these islands contain inner lagoons which are basically flooded dolines.

Karst Landforms:
Pinnacle Karst

Perhaps the most extreme of karst forms is pinnacle karst, an erosional form which results in razor-sharp, vertical blades. An immature form is seen in Laos, left, while one of the most impressive displays known is this group of pinnacles in Guung Mulu National Park, Malaysia.

Photo by Paul White, Wikipedia Creative Commons

Surface karst features

Surface karst features, often referred to as karren, include fissures, knife-edge blades, small channels, solution tubes, and other features. Some have catalogued these features with names like rillenkarren, spitzkarren, and so forth. These images, from karst areas in France, New Zealand, and the USA, show the variety and beauty of surface karst.