North and northeast of Lake Chad, the basin extends for more than 800 kilometers, passing through regions characterized by great rolling dunes separated by very deep depressions. Although vegetation holds the dunes in place in the Kanem region, farther north they are bare and have a fluid, rippling character. From its low point in the Djourab, the basin then rises to the plateaus and peaks of the Tibesti Mountains in the north. The summit of this formation—as well as the highest point in the Sahara Desert—is Emi Koussi, a dormant volcano that reaches 3,414 meters above sea level.