The Sahara is the world's second-largest desert, but its largest hot desert. The Atlas Mountains bound the western Sahara on the north, and the Sahel — a savannah-like strip — bounds it on the south. It is dominated by rocky regions (hamada), sand seas (ergs), and salt flats (shatt), and dry river valleys (wadi) that are subject to flash floods. The Berber and Tuareg peoples are native to the Sahara.