The Sahara is diagonally split into a western and an eastern half by a series of highlands. In the West one seldom needs to travel more than 100 kilometres between areas with water and vegetation, and the whole area is well criss-crossed by desert tracks. The eastern half is triangular in shape, bordered on the west by the highlands, the Mediterranean on the north, and the river Nile to the east, it roughly resembles India both in shape and size. This whole vast area, the Libyan Desert, is totally unfit for human habitation. Its central part is a place of extreme aridity, there are periods of 20-30 years with no rainfall. This region was selected by NASA as the earthly region most similar to conditions on Mars during the Viking lander projects.

There is no permanent human habitation, no roads or tracks, just the great open void. This explains why relatively few people do venture into the deeper reaches, as opposed to the western part of the Sahara, where pistes and a denser pattern of oases make travelling easier.

Since the second world war the north-eastern part of the Libyan desert, lying in Egypt, is usually referred to as the Western Desert (that is, lying to the west of the Nile). The whole area is composed of a flat plain gently sloping towards the Mediterranean Sea. The tilted rock strata are eroded as the land rises southwards, resulting in a series of scarps that run parallel to the sea, and form cliffs sometimes several hundred metres high. At some points at the base of the scarps the wind has excavated depressions which reach into an aquifer layer lying under the whole of the Libyan desert, forming oases.

There is a large depression, the Qattara depression, just to the south of the northernmost scarp, with Siwa oasis at its western extremity. A belt of inhabited oases, Baharya, Farafra, Dakhla & Kharga are located west of the Nile. There are a few other scattered uninhabited small oases, usually linked to the major depressions, where water can be found by digging to a few feet in depth. In the west, a series of oases run south - south west from Siwa. These, Jaghbub, Jalo, and the Kufra group lie in Libyan territory.

Aside the scarps, the general flatness is only interrupted by a series of plateaus and massifs near the centre of the Libyan Desert, around the convergence of the Egyptian-Sudanese-Libyan Borders. The Gilf Kebir plateau rises about 300 metres above the general plain, and lies entirely in Egypt. It roughly equals Switzerland in size, and is similar in structure to the other sandstone plateaus of the central Sahara. Slightly further south are the massifs of Arkenu, Uweinat and Kissu. These granite mountains are very ancient, having formed much before the sandstones surrounding them. Arkenu and Western Uweinat are ring complexes very similar to those in the Air mountains. Eastern Uweinat (the highest point
in the Libyan desert) is a raised sandstone plateau adjacent to the granite part further west.

The huge volume of sand excavated by the wind from the Quattara and other lesser depressions have been organised into a huge area of parallel sand dunes, hundreds of kilometres in length, and occasionally reaching heights of a hundred metres. This Great Sand Sea occupies most of the north-eastern part of the Libyan Desert south of Siwa and to the west of Baharya and Farafra, giving way to gravel plains, mudpans and the perfectly flat and featureless Selima Sand Sheet plains further south roughly along latitude 23 North.

In a small localised area north of the Gilf Kebir plateau one may find chunks of Lybian Desert Glass on the surface between dunes.

• Link to an article by Gerhard Müehle on Libyan Desert Glass

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