Neotectonics related landslide of Ambal salt piercement within the Upper Gotvand dam reservoir, Iran

The Upper Gotvand dam is the highest rock-fill dam of Iran with a clay core and was constructed over the longest and biggest river of the country, Karun river, in Khuzestan Province. It is located in the Zagros Active Fold Belt with the unique exposure of salt piercement in its reservoir known as Ambal salt pillow or ridge. The occurrence of this salt piercement imposed some problems to the project including subsidence and land sliding of highly soluble layers within the dam reservoir. The piercement is composed of Gachsaran Formation of Oilgo-Miocene Age with dominant salt, gypsum and marly layers. Most of the formation exposures in the study area are fault related. The region is affected by neotectonic faulting in such a way that Ambal piercement is aligned with an N-S basement lineament. Based on a two year field observation and monitoring, a gradual and continuous sliding is occurring that is intensified by ground water circulation through evaporite karstic sinkholes and fracture systems. Subsidence and sliding of the Gachsaran evaporitic layers into the dam reservoir water increases the river salinity continuously and is considered as a critical geohazard for downstream areas.

Neotectonics, landslide, Ambal piercement, Upper Gotvand dam.