Spring mounds of the Nefzaoua oases in Tunisia: Irreversible degradation of exceptional geomorphic structures

The oases in the arid the Nefzaoua region in central-western Tunisia are associated with spring mounds. Spring mounds result from an exceptional succession of geomorphological, hydrogeological and climatic conditions and processes that follow each other in a specific order. They look like small volcanoes that range from 200 m to more than 2000 m in diameter and 3–30 m in height, which centres were once occupied by a pond fed by an artesian spring. They are at the origin of each oasis's irrigation system, which radiates from the mound's foot. Due to intense irrigation of intensive date palm plantations (Phoenix dactylifera) in recent decades, all artesian springs dried out. We established a complete inventory and typology (i.e. location, dimension, and types of degradation) of all spring mounds in the Nefzaoua region. Overall, in an area of 3000 km2, 126 spring mounds of 7 types were identified, of which 112 (89%) were degraded. Due to the low salt content in spring mound sediments, they are excavated and used as a soil amendment to expand new palm plantations. Only 14 mounds (11%) are presently preserved. Their qualification as a geomorphosite could preserve them from complete destruction.