Kuma-Manych Depression

Geological depression separating the Russian plain from the North Caucasian foreland; it is sometimes regarded as the southern boundary between Europe and Asia. It is tectonic (resulting from distortion of the earth's crust due to forces within it). The Kuma-Manych is 20-30 km/12-19 mi wide (narrowing to as little as 1-2 km in the centre), and contains salt lakes, reservoirs, and parts of the West and East Manych and Kuma rivers. In Pleistocene times, the Caspian Sea used to overflow via the depression into the Sea of Azov.