Ga’ara Depression is the largest natural depression in the Iraqi Western Desert. The oldest and youngest exposed rocks in the area are of Permian and Eocene ages. Although the beds are almost horizontal in the area; towards the east, but the exposed formations on the four rims are not the same, large differences occur in ages of the exposed formations. Ga’ara Depression covers an area of about 1383 Km2, it has a rectangular shape; elongated in E – W direction. The southern rim is the highest and steepest, whereas the eastern one is the lowest with gentle slopes. The maximum and minimum elevations on the surrounding rims are 613 m and 423 m (a.s.l.), respectively. The four rims suffer from different type of mass movements. The depression is known to be a structural high and a topographic low. The structural high is confirmed by the exposure of Permian rocks, beside the presence of dense tension and shear joints; especially in the western, northwestern and southwestern sides of the depression. Those areas are also characterized by the presence of dense karst forms. The geomorphology and geology of the depression indicates that it started in development since the Oligocene Period, the area suffered from non-deposition; therefore, the whole deposited sequence above was subjected to intense erosion leading to the development of the depression and continuous retreatment of the rims, which is still active. The estimated numerical age of the nowadays depression is about 540655 years.
Keywords: Ga’ara Depression, Alluvial Fans, Calcrete, Mass movements, Iraq.