Collapse Doline

Sinkhole

Sinkholes are drainless depressions that mainly occur in karst areas. Collapse dolines or sinkholes occur when a cave ceiling collapses and this mechanical cause creates a drainless depression on the earth’s surface.

Cylindrical doline, the entrance to Dunmore Cave, Ireland. Image by **Mathias Duckeck**.

The big doline from some distance. Spilaia Didymou - Didyma Caves, Greece.

The term collapse doline is often equated with certain spectacular and common subtypes. Many people assume that a collapse produces a shaft with vertical walls that is somehow connected to the cave at the bottom. If the connection is dry, they are called a daylight shaft. If the cave is filled with water, the special form of the cenote results. And yet this is only half the truth. In fact, every hollow shape whose formation is caused by the collapse of caves is a collapse doline. In many karst areas, these are simply depressions without a drain, which do not even have to have particularly steep walls. And this fact also explains why the term doline summarises two such different things as solution dolines and collapse dolines. Quite simply because very often they cannot be easily distinguished in nature. Doline is a morphological term, which is based solely on the visible form, the morphology. A collapse doline, on the other hand, is a genetic term based on the underlying geological situation and the processes based on it. A doline is a collapse doline if it was created by a collapse.

When a cave grows, there may be a point where the roof of a cavern is not stable enough. This leads to (often several) collapses of the roof, which usually result in a dome-like roof of the cavity that can withstand the pressure much better. A vault, a round arch, is a statically very stable form because it deflects the forces from above very well to the side. When the effects of the collapse, the subsidence of the rock, reaches the surface, especially if the cave is close to the surface, a sinkhole occurs. This collapse is often a natural entrance to the cave. In this case, there is a pile of debris from the collapse directly below the opening. If a river flows through the cave, it can carry the debris away. However, it is also possible that the debris from the collapse completely fills the cave in the area of the sinkhole and therefore no access to the cave is possible.