18.5: Sand Deposits

Sand Deposits

While deserts are defined by dryness, not sand, the popular conception of a typical desert is a sand-sea called an erg Links to an external site.: a broad area of desert covered by a sheet of fine-grained sand often blown by aeolian (wind) forces into dunes. The best-known erg is the Empty Quarter (Rub’ al Khali) of Saudi Arabia, but other ergs exist including in parts of Death Valley National Park.

Sand builds up the crest of the dune and pours over the top until the leeward (downwind or slip) face of the dune reaches the angle of repose Links to an external site., the maximum angle which will support the sand pile. Dunes are unstable features and move as the sand erodes from the stoss side and continues to drop down the leeward side covering previous stoss and slip-face layers and creating cross-beds Links to an external site.. Fossil ergs are represented by the Navajo Sandstone and Zion National Park of Utah Links to an external site. (Figure 18.12).