Surface Operations in Dune Fields Surface operations in the hyperarid regions of the world, particularly in the Sahara, presents a distinctive set of problems. The landscape is totally alien looking. At certain times of the year, extreme temperatures, low humidity, and episodic regional dust storms (Khamsins) make any type of sustained effort away for a base camp very hazardous. There is a six-month period (October-March) however, when operations are more feasible if certain cautions are exercised. Bivouac, Stopping, and Assembly Sites: Sand plains Gravel plains Dunes – lee of isolated large barchan dunes Speed Restriction for Surface Vehicles – Roughness: Alluvial fans – coarse, highly arched Playas – dry, high clay content, desiccation cracks Playas – dry, silty/salty, salt ridges and polygons Ripples – truncated Ripples – granule Sand plains – areas where bedrock grazes the surface