Nowdays the name "Sossusvlei" applies to the whole area of Namib desert which has the famously high and spectacular sand dunes although itself is "only" a part of the system, a huge clay pan almost entirely surrounded by giant sand dunes. "Vlei" is the Afrikaans word for shallow depression filled with water, which only occurs every 10-15 years. Indeed only a heavy rainfall, which is a rare event in this area, does the vlei fill with water. Origins of Namib desert dunes are distant in space and time. They have developed over a period of many millions of years. Scientist think that the vast quantities of sand were driven towards the Atlantic Ocean from the distant plateau of Lesotho by the Orange River. This material was subsequently moved northwards by Benguela current to be dumped back onto the land by surf and spread on a surface of about 50.000 kmq. Dunes walk northwards aroud twenty meters every year.
Dead Vlei, like Sossusvlei, was formed by nearby Tsauchab River floodings. The water was present long enough for Camelthorn trees (Acacia Erioloba) to take root. But when a sand barrier diverted the original drainage route the vlei "dead". The specter Trunks have been there for an estimated 700-1000 yers, not rotting away due to lack of tree-eatings insects and extreme aridity of desert. The intense scorching sun blackened them like a fire