The Nullarbor Plain, which borders much of the length of the Bight's coastline, is a former seabed, uplifted during the Miocene. Consisting of limestone, it is very flat, and has an arid or semi-arid climate with very little rainfall, and high summer temperatures and high evaporation rates. It has no surface drainage, but has a karst drainage system through cave formation in the underlying limestone. North of the Nullarbor lies the Great Victoria Desert, which has an internal drainage system terminating in numerous small salt lakes.