Karst window

Unroofed portion of a cavern which reveals part of a subterranean river

A karst window, also known as a karst fenster, is a geomorphic feature found in karst landscapes where an underground river is visible from the surface within a sinkhole. In this feature, a spring emerges, then the discharge abruptly disappears into a sinkhole. The word fenster is German for 'window', as these features are windows into the karst landscape.

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