Large closed depressions with flat floors across which streams flow are called poljes. These features can be compact or irregular, and may be oriented along a tectonic axis. A sharp break exists between the floor and steep walls. The streamsinks in the poljes are called ponors; residual hills of limestone protruding from the floor are called hums. 출처 Jennings, J. N. Karst. The M.I.T. Press, Camb..
