Waw an Namus (Caldera of Mosquitoes) is a volcanic field, cone and caldera in the southern Fezzan region of southern Libya. It is in the near-geographic center of the Sahara Desert.
The inside of the caldera houses an oasis of rich foliage and three small salt lakes of variable color which are the reason for the volcano's name. A volcanic field of dark basaltic tephra flow extends 10–20 kilometres (6.2–12 mi) around the caldera. The dark field's vast size allows it to be easily seen from space.
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Waw an Namus[/caption]The Libyan Desert, which covers much of Libya, is one of the most arid places on earth. In places, decades may pass without rain, and even in the highlands rainfall seldom happens, once every 5–10 years. At Uweinat, as of 2006 the last recorded rainfall was in September 1998. There is a large depression, the Qattara Depression, just to the south of the northernmost scarp, with Siwa Oasis at its western extremity. The depression continues in a shallower form west, to the oases of Jaghbub and Jalu.
Likewise, the temperature in the Libyan desert can be extreme; on 13 September 1922 the town of 'Aziziya, which is located southwest of Tripoli, recorded an air temperature of 57.8 °C (136.0 °F), considered to be a world record. In September 2012, however, the world record figure of 57.8°C was overturned by the World Meteorological Organization.
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There are a few 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 there is a widely dispersed group of oases in unconnected shallow depressions, the Kufra group, consisting of Tazerbo, Rebianae and Kufra. Aside from 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.
Slightly further to the south are the massifs of Arkenu, Uweinat and Kissu. These granite mountains are ancient, having formed long before the sandstones surrounding them. Arkenu and Western Uweinat are ring complexes very similar to those in the Aïr Mountains. Eastern Uweinat (the highest point in the Libyan Desert) is a raised sandstone plateau adjacent to the granite part further west. The plain to the north of Uweinat is dotted with eroded volcanic features. With the discovery of oil in the 1950s also came the discovery of a massive aquifer underneath much of the country. The water in this aquifer pre-dates the last ice ages and the Sahara desert itself. This area also contains the Arkenu structures, which have been hypothesized to be double impact craters.