- Paleocollapse
Paleocollapse is a rock structure resembling the
karst landform, but is formed essentially by the dissolution of underlyingsedimentary rock . It has also been called paleo-karst collapse. [ [http://www.dot.state.fl.us/statematerialsoffice/geotechnical/conference/materials/yuhr-benson-kaufmann-casto-jennings.pdf A CASE HISTORY OF A LARGE KARST INVESTIGATION: Lynn Yuhr, Richard C. Benson, Ronald D. Kaufmann, Daniel Casto and ^John Jennings] ] , [ [http://www.igsb.uiowa.edu/Browse/palokrst/palokrst.htm Paleokarst in Iowa by Robert M. McKay] ] . This has the effect of collapsing the formerly intact rock above, forming extensive fractures, debris pipes, and opencaverns . Normally, the process was started and completed in the geologic past.The mechanism of its formation is relatively simple. As in the illustration, a deeper layer of
salt (or otherevaporite ) is dissolved, through some process. The support for the upper rock vanishes, and starts the collapse process. This is much like the subsidence associated with oldcoal mines . Eventually, the caving process reaches the surface, and can be associated with debris pipes, rock fractures, and open caverns. At some later date, undisturbedsediments , orglacial till may fill the collapse zone.Paleocollapse geology can be remarkably stable (unlike karst), but poses some serious challenges to
engineering orenvironmental geology . Primarily, the collapse zone is extremely permeable. This can provide a conduit for groundwater, or contaminant transport [ [http://www.pela-tenn.com/PELA%20publications/papers%20in%20PDF%20format/paleocollapse%20in%20karst.pdf Paleocollapse structure as a passageway for groundwater flow and contaminant transport: W.F. Zhou] ] . As well, these zones may only be marginally stable, in that they can be reactivated by human activity, or events such asearthquakes . In China, underground mines have become suddenly flooded, due to paleocollapse features.In order to fully characterize the hazard, investigations may be undertaken, using dye tracers, or
exploration geophysics . Of particular importance is understanding the true stability of the region. The paleocollapse process may continue at some future date, due to deep groundwater flow changes. Or perhaps, the reason that a certain evaporite zone has dissolved, is because of underlying faults in the bedrock.References
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