Sinkholes are cavities in the ground that form when water erodes an underlying rock layer.
Two types of sinkholes exist. One forms when the roof of a cave collapses and exposes the underground cavern. The second type forms when water dissolves the rock underneath soil and creates an underground chasm. Without rock to support it, the soil layer collapses and creates a hole on the surface.
Sinkholes have both natural and human causes. Land made of a soft underground rock layer, such as rock salt around the Dead Sea or limestone in Mexico’s Yucatan Peninsula, are often riddled with sinkholes, since the rock layer is easily dissolved.
Manmade sinkholes are created when city development compromises the structural integrity of underlying rock. Roads, buildings, and other types of construction may cause water to collect in certain areas and wash away the supporting rock layer (especially at low sea levels and after a heavy rainfall).