Dead Sea sediments and some impressive seismites

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.)

Another seismite showing well the upward injection of soft clays into overlying silts.

This is my favorite seismite. I can’t explain what happened here, but a whole lotta shaking was going on.

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.

11 Responses to “Dead Sea sediments and some impressive seismites”

  1. Peter Pozefskyon 18 Mar 2012 at 9:00 am

    Strange how disaster, in this case environmental, can be good for scholars. It creates opportunities to see things you would never otherwise see. I felt the same way observing the fall of the USSR. As Soviet society fell apart, you could see things that weren’t previously visible and aren’t necessarily visible in more stable communities. Does this create an ethical dilemma for scholars?

  2. Meagenon 18 Mar 2012 at 9:45 am

    Wow! Impressive (and beautiful) sedimentary structures.

  3. Brian Romanson 18 Mar 2012 at 10:00 am

    Fabulous photos! I’d love to see in person someday.

    I’m going to put my nit-picky professor hat on just for a moment. The term ‘seismite’ is very interpretive. This type of soft-sediment deformation can occur in a variety of depositional environments in the absence of an external trigger such an earthquake. All that’s needed is rapid deposition and a density contrast.

    I realize that, in this case, there is good chronology and paleoseismic records to correlate to, so the interpretation is likely strong (and very cool!). But, one could end up making some erroneous leaps of inference if they went somewhere else, documented soft-sediment deformation, and automatically conclude it must’ve been triggered by a seismic event.

  4. Mark Wilsonon 18 Mar 2012 at 11:36 am

    Thanks, Brian, and very good point. We do seem to be lucky in this case that there are such long historical records that correlations could be made between known earthquakes and the dated deformations. Without them it becomes much more problematic.

  5. William Burrison 19 Mar 2012 at 2:08 pm

    These are some pretty spectacular photos.

  6. Dianaon 20 Mar 2012 at 6:18 am

    It is hard to believe that those canyons are so young! I have to make time to go take a look.
    I am so enjoying this blog! Wish I could take you on one of our hikes so you could explain the geology to us. Some of the formations we see are hard to understand to say the least.
    Maybe on your next trip.

  7. [...] Yet more evidence that we should organise a field trip to the Dead Sea post-haste: fabulous sedimentary structures. Impressive incision rate too! Dead Sea sediments and some impressive seismites (woostergeologists.scotblogs.wooster.edu/) [...]

  8. [...] is an insight into the tectonic history of the region. Melissa Torma and I saw such a record of seismites in Dead Sea sediments last [...]

  9. [...] is an insight into the tectonic history of the region. Melissa Torma and I saw such a record of seismites in Dead Sea sediments last [...]

  10. [...] dropping about a meter a year, which is extraordinary. This reduction in base level also produces incredible erosional gullies as water from flashfloods cuts through the newly-exposed unconsolidated lake sediments with [...]

  11. Shmulikon 05 Oct 2014 at 6:47 am

    Nice photos! I just discovered this post and to my surprise there’s no mention of numerous geological studies that were published about this site. For example:
    Bookman, R., Enzel, Y., Agnon, A., and Stein, M., 2004, Late Holocene lake levels of the Dead Sea: Bull. Geol. Soc. Am., v. 116, p. 555-571.

    Filin, S., Avni, Y., Baruch, A., Morik, S., Arav, R., and Marco, S., 2014, Characterization of land degradation along the receding Dead Sea coastal zone using airborne laser scanning: Geomorphology, v. 206, no. 0, p. 403-420.

    Ken-Tor, R., Agnon, A., Enzel, Y., Marco, S., Negendank, J. F. W., and Stein, M., 2001, High-resolution geological record of historic earthquakes in the Dead Sea basin: J. Geophys. Res., v. 106, no. B2, p. 2221-2234.

    Ken-Tor, R., Stein, M., Enzel, Y., Agnon, A., Marco, S., and Negendank, J. F. W., 2001, Precision of calibrated radiocarbon ages of historic earthquakes in the Dead Sea Basin: Radiocarbon, v. 43, no. 3, p. 1371-1382.

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