Complex sentence: Also an oasis, about 100 km. east of Touggourt and north of the erg, the thirst of El Oued is quenched by a subterranean river.
Split into simpler sentences: Also an oasis, it's located about 100 km. east of Touggourt and by the northern frontier of the erg. The thirst of El Oued is quenched by a subterranean river.