|
Dolines (sinks or sinkholes) are the closed depressions which are usually circular or oval in plan and vary in diameter and depth. Several types of dolines can form: solution, collapse, subsidence, and stream alluvial.
Solution dolines usually form where structural control such as intersecting joints leads to infiltration of surface water. As more water flows through the defect, the depression enlarges and leads to even more inflow. Solution dolines usually form in a conical shapes, although the structural control may alter the geometries. If sediment accumulates, the floor of a larger dolines can be swampy or contain small lakes or ponds.
Collapse dolines usually result from the collapse of a cave produced by underground solution. These dolines exhibit collapse features such as steep walls and an angular shape in plan. The depth-width ratio often is greater than for the solution dolines. If no further collapse occurs, these dolines eventually weather and appear more like a solution doline.
Subsidence dolines form when sinks form in karst rocks underlying a superficial deposit or thick residual soil. These dolines can also form through continuous piping of materials through widening joints or solution pipes. Alluvial streamsink dolines form in the alluvial material at the point where a stream sinks.
Cockpits, also a simple closed depression, are convex inward and occur among residual hills. The gullies between hills carry the runoff after heavy rains. These features usually develop in tropical regions.
|
