sink hole

The physical weathering and erosion of a limestone landscape. The freezing and thawing of rain and its mild acidic properties cause cracks and joints to enlarge, forming limestone pavements, potholes, caves, and caverns.

A limestone sink hole in Oman. Sink holes can be many metres deep, and often lead to underground caves. They are usually formed when water dissolves the edges of a join or crack, gradually enlarging it.

Funnel-shaped hollow in an area of limestone. A sink hole is usually formed by the enlargement of a joint, or crack, by carbonation (the dissolving effect of water). It should not be confused with a swallow hole, or swallet, which is the opening through which a stream disappears underground when it passes onto limestone.