Station: [44] What is Karst?

Exactly – so what does "karst" mean?

The term "karst" comes from a region of the same name in Slovenia. More than 120 years ago, that was where the typical phenomena of a karst landscape were first scientifically studied and put into context. Its features include caves, swallets, karst springs, collapse dolines and poljes. More about caves later, but a swallet is an opening through which a stream disappears underground; a collapse doline occurs when the roof of a cave or cavity collapses, and a polje is an elongated basin with a flat floor and steep walls. Anyway, the term "karstification" doesn‘t refer to a landscape becoming desolate, though it’s often wrongly used in that way. Instead, it describes the process by which the runoff of precipitation increasingly moves under ground. This occurs in all climates, from the Arctic to the tropics and from deserts and mountains to swamplands.

One of the conditions required for karstification is invariably water-soluble bedrock. That usually means limestone, but could also be dolomite, gypsum or rock salt.

You’re probably familiar with having to descale your kettle or coffee machine. And may have wondered how the lime scale came to be in the water. It's quite simple: 

Water from precipitation penetrates the rock through fissures or other faults, dissolves the limestone and carries it along in solution – leaving a cavity in the rock that may grow into a cave over time. 

Instead of remaining on the surface, the water entering from above creates an outflow. It rapidly trickles down and runs to a water outlet at the lowest possible point: the result is a karst spring.

If you live locally, you now know where the rivers Wiesent, Trubach and not least Pegnitz come from... and also why there’s lime in your tap water!