Dependiendo del tipo de terreno, creo que podrían usarse “basins” o “potholes”.

torca
Depresión circular con bordes escarpados en un terreno.

torcal
Terreno donde hay torcas.
http://buscon.rae.es/draeI/SrvltConsulta?TIPO_BUS=3&LEMA=tor...


DEPRESSION
in geology is a landform sunken or depressed below the surrounding area. Depressions may be formed by various mechanisms, and may be referred to by a variety of technical terms.

* A basin may be any large sediment filled depression. In tectonics, it may refer specifically to a circular, syncline-like depression: a geologic basin; while in sedimentology, it may refer to an area thickly filled with sediment: sedimentary basin.

* A depression may be a pothole - either a simple roadway depression or a fluvial erosional depression in a river streambed, or area affected by coastal water currents.

* A depression may be a sinkhole, an area of subsidence caused by the collapse of an underlying structure. Examples include sinkholes above caves in karst topography, or calderas or maars in volcanic areas.

* A blowout is a depression created by wind erosion typically in either a desert sand or dry soil (such as a post-glacial loess environment).

http://en.wikipedia.org/wiki/Land_depression





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Note added at 59 minutos (2008-03-27 21:11:54 GMT)
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Si se trata del Torcal de Antequera, al que alude Lisa, que es territorio de karst, entonces la traducción para los sumideros de piedra caliza es “sinkholes”.

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Note added at 4 días (2008-04-01 17:22:37 GMT)
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Eileen: si el terreno es Karst el sumidero es un “sinkhole”.