Sinkholes are caused by erosion. They may appear suddenly and have devastating consequences. Sinkholes are cavities in the ground that form when water erodes an underlying rock layer. Sinkholes have both natural and human causes. Sinkholes are formed when the land surface above collapses or sinks into the cavities or when surface material is carried downward into the voids. Drought, along with resulting high groundwater withdrawals, can make conditions favorable for sinkholes to form.