22-27 September 2019
Trade Fairs and Congress Center (FYCMA)
Europe/Madrid timezone

Rapid karst development in salt layers during and following flash floods along the shores of the Dead Sea

26 Sep 2019, 11:30
15m
Multiuse room 1 ()

Multiuse room 1

Oral Topic 7 - Karst Hydrogeology Parallel

Speaker

Dr Ittai Gavrieli (Geological Survey of Israel)

Description

The Dead Sea is a hypersaline terminal lake, located within a pull apart basin along the Dead Sea Transform. The lake’s surface water is the lowest on Earth. As such, it forms a regional drainage basin for both surface and underground water systems. At around 11,000 BP Lake Lisan, the precursor of the Dead Sea, underwent a dramatic water level decline accompanied by the precipitation of a 10-30 m halite layer. This layer was since covered by clastic sediments, and as long as it was in contact with the halite-saturated Dead Sea brine it remained intact. However, over the last few decades the Dead Sea experiences a dramatic water level decline, leading to its shrinkage and to the exposure of large mudflats, mostly along its western shores, where the bathymetry is moderate. Concurrently, the water level in the adjacent coastal aquifer drops, and the halite-saturated brine in the subsurface is being flushed towards the receding lake by less saline groundwater. As these halite-undersaturated waters encounter the salt layer, it initiates dissolution, creating underground cavities, which consequently collapse to form thousands of sinkholes along the retreating shore.
Over the past few years it became apparent that besides the sinkholes that puncture the surface, a highly developed karst-like system connected to the surface rapidly develops within the salt layer, mostly adjacent to the gullies that drain surface runoff to the Dead Sea. Flash floods are drained into sinkholes (swallow-holes) within these gullies and the water reappears in sinkholes within the mudflats hundreds to thousands of meters away, closer to the shoreline. The rapid inflow and emergence of the water in the sinkholes is accompanied by collapse of the surrounding sinkhole walls thereby enlarging them. As the water is swallowed, additional sinkholes develop in the gullies’ floor only to be filled by the sediments carried by the flood water or from the collapsing walls. Comparison of water travel time in the subsurface between two flood events reveal that it has been significantly shortened. During the weeks that follow each event additional sinkholes develop within the gullies as well as in the vicinity of the outflow sinkholes. These observations suggest that the subsurface salt karstic-like system undergoes rapid development during and following these flood events. In the course of the talk, we will present a film produced from several time lapse cameras (TLC) installed to capture such events.

Primary authors

Dr Ittai Gavrieli (Geological Survey of Israel) Dr Gidon Baer (Geological Survey of Israel) Iyad Swaed

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