What is the name of the vast Sahara sand sea spanning parts of Egypt and Libya?

The vast Sahara sand sea spanning parts of Egypt and Libya is called the Great Sand Sea.

The Great Sand Sea is a large erg, or region dominated by wind-blown sand, in the western Egyptian Desert and eastern Libya. It contains extensive dunes and sandy plains, forming one of the major dune landscapes of the Sahara. The area lies west of Egypt’s Nile Valley and includes the famous Siwa Oasis at its northern margin.

Although the names are related, the Great Sand Sea is not synonymous with the entire Libyan Desert. The Libyan Desert is a much broader geographic region that includes rocky and gravel landscapes as well as sand seas.

Wind direction, available sediment, and the shape of underlying terrain influence the Great Sand Sea’s dune patterns. Its remote location has also made it important in desert exploration and geographical study.