Ron Schott posted this interpretation (copyrighted) of the slump on flickr, which shows that it is part of a much larger ancient slump/slide complex.Phil Pearthree here at AZGS suggests that this is a particular type of landslide that involves rotation of a block of more cohesive material like sandstone over finer-grained deposits and is pretty common along the cliffs of the Colorado Plateau in this general area. They were called Toreva blocks by Reiche (1937), named after a community on the Hopi Reservation. Based on the better photos we have just received, Charles Ferguson, another AZGS geologists says this looks more like a failure in the fine-grained deposits below the cliff.
It looks to me like the interpretation of this being an old Toreva-style landslide that has had a small reactivation along the roadway is right on. I think this aerial view with the interpretation lines drawn in says it all. I only wonder why the hummocky look along the cliff-edge at the Kayenta level. It looks like there are patches of white (carbonate cemented?) sandstone that helps protect the hummocks along the cliff edge. You can see that white material strewn along the old slide surface. Dean DuBois
ReplyDelete