Follow the Water Stop 10 of 13 (Site 10c)

Follow the Water Stop 10 of 13 (Site 10c)

Rock Varnish: This boulder is sitting on a relatively stable alluvial-fan surface that has not seen  activity in probably a hundred thousand years.  The deep and dark sheen on the rock is called rock varnish (sometimes also called desert varnish).  Rocks with rough textures, like this basalt boulder, trap dust particles from the passing wind.  In the dust particles are small amounts of manganese.  Microorganisms oxidize the manganese, and this process in turn cements clay minerals in the dust to the rock.  Overtime, layers of manganese build up and generate the eye catching dark coating on the rocks that are stable for long periods of time.  To learn more about rock varnish and how it forms, you are welcome to read this paper.

Tanzhuo Liu, Ph.D. of Arizona State University in Geography, and now a scientist at Columbia University, has developed a method to estimate the ages of land surfaces using the layering pattern of black, orange and yellow layers that are deposited in varnish.  These are microscope pictures of cross-sections of varnish from shorelines of different lakes and features in the region, including the stops of Searles Lake, Panamint Lake, and even Dry Falls.  The black layers (WH for Wet Holocene) indicate wetter periods when more manganese was deposited. If you want to learn more about this amazing way to figure out the past, just visit the VML website.