Caves and Karst

A Brief Introduction to the Cave and Karst Processes, by Dean Smart

To understand how caves and karst are born, live and die, it is necessary to know what they are first. The International Union of Speleology (the study of caves) defines a cave as:

“Any natural underground space, without natural light large enough for a human being to enter”.

This definition is deliberately broad and includes any completely dark, suitably sized cavity, in any rock, formed in any way, at any time, anywhere in the universe.

Karst is most commonly defined as:

“A group of landforms including towers, pinnacles, dolines or ‘sinkholes’, karren (small-scale sculpturing on the surface of the rock), sinking and rising streams, underground drainage and caves. The bedrock is dissolved away by the action of water (like sugar in a cup of tea) and not eroded away as in most rocks”.

Limestone is the most common karst rock, although marble, gypsum and rock salt also make karst. Even quartzite can develop karst given enough time. The landforms of karst are also seen in rocks such as sandstone where normal erosion has created them. This is called ‘pseudo-karst’.

Karst is a complicated natural process where caves are just a small part (about 1%). Creating karst involves the air, the water, the rock, the vegetation, the soil, the ‘energy’ available and time. When any one of these ingredients is upset, the whole system may be damaged, including the caves. Great care is needed when exploring or enjoying a karst area as your impact may have greater consequences than you think and may even be felt many kilometers from where the damage happened.

Although caves are a tiny part of the overall karst system, they are certainly the most famous. Everybody has either been into a cave already or will go into a cave in the future. How did the cave get there? How old is it? Does a stalactite go down or up? What lives in caves? I’ve been asked these questions many times and here are the answers!

As rainwater falls through the air it dissolves carbon dioxide gas. When it soaks into the soil, it dissolves even more. The water and carbon dioxide create an acid – carbonic acid. Limestone can dissolve easily into this acid and karst is created.

Small cracks in the limestone let the acidic water disappear underground. Once here, the water starts to dissolve the sides of the crack away, slowly widening it over many thousands of years. Eventually, a cavity large enough for people to enter forms and a cave is created. The cave may go all the way from where the water sinks on top of the mountain to where it rises in the bottom of a valley. Many streams may link up underground to make a cave system. Dry, ‘fossil’ caves are usually found high up in the mountains.

These caves used to carry streams, but have been overtaken by newer, lower passages and may be very old. The oldest cave in Thailand is at least 9.4 million years old.

Speleothems is the scientific name for stalactites, stalagmites and all other mineral growths in caves. They form where water enters a cave and loses some of the minerals it has dissolved. Stalactites (down), stalagmites (up), columns (join roof and floor), helictites (curly horizontal), straws (tube stalactites), curtains (sloping, hanging sheets), oolites (round balls) and flowstone (irregular floor or wall covering) are all very common and add to the natural beauty of caves. Speleothems form very slowly and are easily damaged. So, be careful! Stream sediments are often left behind in caves by flowing water. These can give us information about the outside climate at the time when they were deposited. Data for past weather patterns is essential for knowing how much the greenhouse effect is affecting our ecosystem.

Cave Life

Caves are not so devoid of living creatures as you may think. Bats and birds are obvious cave dwellers. So too are fish, insects, spiders, centipedes, millipedes, crabs, shrimp, and many other tiny creatures including bacteria and fungi. Living in the eternal darkness of a cave makes eyes and color useless and some animals lose them. Cave-adapted creatures, ‘troglodytes’, look white, or pink, and have no eyes. Instead, they develop extra-sensitive touch organs for feeling their way around. There are more than 50 troglodytes living in caves in Thailand and nowhere else on the Earth. Green plants provide food for surface animals, but do not grow in caves. All food for the troglodytes comes from outside. This may be brought in by streams, airflow or in the form of excrements from animals that travel outside, e.g. bats. Some larger animals like bears, porcupines, snakes and rats use caves occasionally for shelter.

People and Caves

People have used caves for thousands of years as places of shelter, ritual and fun. Prehistoric people have left pottery, stone tools, iron and bronze artifacts in caves. Some people buried their dead in caves or painted scenes of their life or rituals. Here the remains have stayed, preserved by the stable environment of the cave and are now probably the best places for archaeologists to try to unlock our past.

Modern day people still use caves in many ways. There are hundreds of Buddhist temple caves all over SE Asia. Some local people collect guano for fertilizer or birds’ nests for soup and gain an income. Many caves are open for tourists to visit. Caves have also been safe places for hiding valuable objects, kings or dissidents.

Caves are interesting for many reasons. Very often we do not know how interesting because the information we have is very limited. Caves need to be preserved now before the data contained in them is lost. Good management and visitor behavior helps enormously.

The following rules are practiced by cave visitors the world over:

1. Take Nothing But Pictures. This means remove nothing from the cave that is found there naturally, i.e. speleothems, animals, etc. Be careful when using flashes to photograph bats, they hate it! You can remove litter and rub out graffiti left by other, idiot visitors.

2. Leave Nothing But Footprints (Air Bubbles in the case of divers). Do not leave litter, food scraps, spent batteries, graffiti or other non-cave items underground. Take care not to leave footprints over sensitive parts of the cave, e.g. floor speleothems, sediments. If possible, walk and dive single file.

3. Kill Nothing But Time. Don’t disturb cave-adapted animals or touch speleothems. Try to leave the cave environment in the same state as you found it. Do not forget such things as temperature and humidity and try not to use ‘hot’ torches or stay in one place for too long.

With these simple rules you can help preserve the natural and cultural heritage of SE Asia. It is not difficult, please help solve the problem, don’t become part of it!!