The Great Rift Valley is a vast geographical and geological feature, approximately 6,000 kilometres (3,700 mi) in length, which runs from northern Syria in Southwest Asia to central Mozambique in East Africa. Caused by the geological process of rifting, it is a complex feature where several plates of the earth's crust join. The rift valley varies in width from thirty to one hundred kilometers, and in depth from a few hundred to several thousand meters. It was named by the explorer John Walter Gregory.