along the river with the bare rock walls of the towers is dramatically echoed in sev-
eral other places such as Malaysia and Thailand.
Caverns are underground expressions of karst. These are large openings and
tunnels formed along bedding planes and can extend many kilometers. Careful
mapping points to the interconnectedness of some caverns in a grid network
because of prominent jointing in the rock. Caverns are formed, at first, by solution
and then sometimes enlarged by the presence of a stream. In some caverns, water
dripping from small openings in the walls and ceilings undergoes dissolution of its
minerals because the carbon dioxide comes out of solution as the water enters the
cavern. The dripping water leaves behind mineral deposits, most usually of cal-
cium, that decorate the cave ceilings, walls, and floors with fanciful, delicate
forms known as speleothems; these include stalactites hanging from ceilings and
stalagmites growing from the floors.
Human interaction with karst has been long and tenuous. Because of the under-
ground drainage, running water at the surface and soil moisture are limited even in
precipitation-rich areas. Agricultural activities avoid the sinkholes but the land-
scape can be used. An interesting example can be found in western Ireland. The
Burren (Boireann), a karst plateau of 250 sq km, is used for grazing in the winter
season. The relative lack of winter grasses in the surrounding valleys forced
Karst 195These eroded pillars of limestone, located near Guilin, China, are a classic example of karst
topography. (Steve Allen/Dreamstime.com)