Mark Wilson March 17th, 2012
MITZPE RAMON, ISRAEL–Since the water level in the Dead Sea is dropping an astounding one meter per year, the drainage base level is dropping along with it. This means that gullies and canyons feeding into the Dead Sea are eroding deeply into their channels. Where the soft Dead Sea sediments are exposed, this erosion is stupendous. Would you believe that the canyon above was cut in less than three years? Today we explored these new canyons near the site of the pumping station (see previous post). Here we are looking primarily at the sediments themselves. Later we will examine the patterns of erosion and subsidence.
These are ripples of sand, silt and clay in a cross-section of Dead Sea sediments a few hundred years old. They started, at least, as wave ripples on the floor of the Dead Sea. Some have been modified by later storm currents. There is also an element of loading and compaction here. I suspect another factor in their morphology is the dissolution of any salt that was deposited with them.
This is one of the simpler seismites. These are beds of sediment that have been disturbed by the shaking of an earthquake. Since these sediments were originally deposited horizontally, they do not show gravitational rolling features. Instead they show upward movement and considerable plasticity. Recently Israeli geologists have carbon-dated these newly-revealed seismites and correlated many to known historical earthquakes. They show that in this region there is a periodicity of about 80 years for major ‘quakes. (The next one is now several years overdue — just saying.)
It is only near the top of the sequence, in the most recent beds, that we see salt deposits. The older salts were dissolved away by fresh groundwater coming from the alluvial fans. This is always a lesson in sedimentary geology — think of what you don’t see. The previous salt beds were erased from the record as the other sediments collapsed down into their places.
The rapid decline of the Dead Sea is an environmental disaster with many ramifications. Nevertheless, the resulting massive erosion of the Dead Sea sediments has given us much information about the past, and data with which we can predict the future.