Answer:
Water dissolved minerals in the rock, leaving residue and open spaces within the rock. (This is called "weathering".)
Water washes away the soil and residue from the voids in the rock.
Lowering of groundwater levels can cause a loss of support for the soft material in the rock spaces that can lead to collapse.
Changing groundwater gradients (due to removing or introducing water to the system) can cause loose material to flush out quicker from the voids and the surface to collapse in response.
Any change to the hydrologic system (putting more water in or taking it out) causes the system to become at least temporarily unstable and can lead to sinkholes.
Sinkholes can result from seasonal changes in the groundwater table, freeze and thaw of the ground, and extremes in precipitation (drought vs heavy rain).
