There are several other ergs such as Erg Chigaga near M'hamid. The Great Sandy Desert contains large ergs, often consisting of longitudinal dunes. Algeria also has ergs, or sand dunes, between mountains. Individual dunes in ergs typically have widths, lengths, or both dimensions greater than . Hamadas exist in contrast to "ergs", which are large areas of shifting sand dunes. When these are extensive, they are known as sand seas or ergs. It gives the energy formula 2 given from earthquakes from seismic waves in ergs. This is far shallower than ergs in prehistoric times were. There are multiple disadvantages to employees in ERGs. On December 5, 2010, The Ergs! On December 31, 2011, The Ergs! The Bouncing Souls who wanted the Ergs! There are numerous types of ERGs existing at different companies. Another benefit of ERGs is the professional development that they foster. By nature, ergs are very active.