Mark Wilson March 17th, 2012
MITZPE RAMON, ISRAEL–In the image above, Yoav Avni is standing at the edge of an erosional gully that is less than a year old. In fact, it may have formed in less than three months. This little canyon is cutting through Dead Sea sediments (see previous post) that are exposed by the rapid fall of water level (about one meter per year). When the base level drops, erosion increases. It is especially rapid through these soft, unconsolidated clays and muds. Yoav is studying this phenomenon and he got so excited by the scale of this structure and others that we were afraid he was going to fall in with an edge collapse. (Note the cracks at the top of the opposite bank.)
A very serious problem related to the drop in the water level of the Dead Sea is the development of large sinkholes in the coastal plain. These holes develop with little warning (if any) and have caused significant damage to structures, roads and agricultural lands. They form when the salty groundwater is replaced by fresh water as the Dead Sea recedes. This fresh water begins to dissolve subsurface salt deposits, producing caverns that eventually collapse. There are over 3000 of these sinkholes now on the western side of the Dead Sea. It is increasingly difficult to plan roads and other developments when you wonder if the ground beneath is going to suddenly give out.
This is a chain of sinkholes that continues to grow. Note the circular tension cracks in the foreground. One of the issues now is whether these holes capture significant surface flows during floods, channeling still more water underground to dissolve more salt. There has been a nearly exponential increase in sinkholes, so it is likely some mechanism like this is also at work.
Noa Avni stands near an incipient sinkhole. They sometimes appear as these small, round holes. Looking inside, we could see that there is a significant room-sized cavern underneath. Soon the roof will collapse and a new mature sinkhole will appear.
Israeli geologists are under considerable pressure to predict the appearance of sinkholes and the large gullies so that engineers can either attempt to “fix” them or find other places to build infrastructure. The geological issues are very complex, though, and a significant amount of randomness exists in the systems. I’m glad I have the kind of geologist’s job that doesn’t involve such practical testing and high expectations.