Collision between these occurred in the Paleozoic period and caused thickening of the Earth's crust, which then downwarped under its own weight to form a depression in the ground, the Fazzan Basin.
[1] The climate of this region has varied greatly in the past, with pluvial and dry periods alternating; the current arid phase averages less than 20 mm (0.8 in) of precipitation per year.
[2] During its geologic history, the Fazzan Basin has on at least four occasions during the Pleistocene been inundated with water to form a large lake.
[4] Although there is some disagreement about the exact timing and the size of Lake Megafazzan, both authorities agree that there has been no lacustrine activity between MIS 5 and the Holocene.
In the late Miocene and early Messinian, increased volcanic activity in northeastern Libya resulted in the damming back of the Wadi Nashu, which caused water to accumulate in the Fazzan Basin, forming the proto-Lake Megafazzan during humid periods.