Erg Admer. Isolated sandstone rock amongst sand in the Erg Admer, Tassili National Park, Algeria. An erg is a vast flat area covered with wind-blown sand. Many are found within the Algerian Sahara. Ergs are located downwind of flat arid areas subject to extensive wind erosion. The formation of the erg is due to the huge fluctuations in climate regime over the past few thousand years. At the end of the Upper Pleistocene period, (10,000 years ago) this area was covered by surface water.