Issaouane Erg confined to basins. Sand in the Issaouane Erg, below the level of the sand dunes, has accumulated to a depth of 20 to 30 meters. It has barchan dunes as well as star dunes of 300 to 430 meters high. The presence of both barchan dunes (which form due to unidirectional winds) and star dunes (which form when winds from various directions deposit sand) "suggests that wind regimes have changed over time". NASA's "Earth Observatory" notes all three types of erg dunes are present in the photos of the Issaouane Erg taken from the International Space Station: stationary mega dunes,
Grand Erg Oriental "Grand Erg Oriental". In addition to oil in Wargla and Hassi Messaoud (see above), other Algerian hydrocarbon sites include In Salah, a city (pop: 44,000) to the erg's southwest, yielding natural gas, and also El Adeb Larache, Edjelé, Tingentourine, and Zarzaïtine (south of the erg, close to Libya). One of Algeria's largest field of natural gas is near Ghardaïa, west of Touggourt. Gas pipelines have been constructed north to the Mediterranean port of Bourgie, and later northeast through Tunisia. Along the north rim of the "Grand Erg Oriental", both the physical ecology and the human culture surviving there since ancient