doline

A doline is a closed surface depression formed in karst landscapes, commonly referred to as a sinkhole. It occurs in soluble rocks such as limestone, dolostone, or gypsum and is a hallmark of karst terrain, found in many parts of the world where these rocks are exposed at the surface.

Most dolines develop as water infiltrates soluble rock, enlarging joints and dissolution channels. Over time, rock above a void can lose support, creating a bowl-shaped depression at the surface. In some cases, substantial underground cavities collapse, producing a collapse doline or sinkhole with a more abrupt and often broader basin. The resulting features can be dry or filled with water, depending on local drainage and rainfall.

Morphology varies widely. Dolines are typically circular or oval, but can be irregular in outline. Diameters range from a few meters to tens of meters, and depths can also vary from shallow depressions to deep depressions several tens of meters deep. The bottoms may be flat, sloped, or layered with sediments, and many collect rainwater to form temporary or permanent ponds.

Hydrology and ecology are closely tied to dolines. They act as surface recharge points feeding underground drainage systems and caves, and they influence local groundwater flow. Dolines can support unique microhabitats and vegetation around their rims, and they often contribute to biodiversity in karst regions.

Classification commonly distinguishes dissolution dolines, formed mainly by rock dissolution without collapse, from collapse dolines, created by sudden roof failure of an underlying cave or void. Dolines are important indicators of karstification and can pose geotechnical hazards for construction in susceptible areas.