Case Hardening Vignettes from the Western USA: Convergence of Form as a Result of Divergent Hardening Processes

The rock weathering literature contains the hypothesis that case hardening exemplifies equifinality, where the same end state can be reached by many potential processes in an open system. We present analytical data from six different sites in the western USA to assess the hypothesis of equifinality....

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Bibliographic Details
Published in:Yearbook - Association of Pacific Coast Geographers 2012-01, Vol.74 (1), p.53-75
Main Authors: Dorn, Ronald I., Dorn, Jacob, Harrison, Emma, Gutbrod, Eyssa, Gibson, Stephen, Larson, Philip, Cerveny, Niccole, Lopat, Nicholas, Groom, Kaelin M., Allen, Casey D.
Format: Article
Language:English
Subjects:
Case hardening
Desert varnish
Erosion
Geology
Glazes
Heavy metals
Lichens
National forests
National parks
Observations
Rocks
Sandstones
Weathering
Weathering processes
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Summary:The rock weathering literature contains the hypothesis that case hardening exemplifies equifinality, where the same end state can be reached by many potential processes in an open system. We present analytical data from six different sites in the western USA to assess the hypothesis of equifinality. Case hardening can be produced on: (1) sandstone in Petrified Forest National Park, Arizona, from the addition of silica glaze, rock varnish and heavy-metal skins; (2) sandstone in Whoopup Canyon, Wyoming, from silica glaze that formed originally inside subsurface joints combined with externally applied iron film, silica glaze, and rock varnish; (3) welded tuff in Death Valley, California, from the accumulation of rock varnish and heavy metal skins of Mn and Fe; (4) sandstone in Sedona, Arizona, from the protective effects of rock varnish accretion and heavy metal skins of Mn and Fe; (5) basalt on the Big Island, Hawai'i, from the accumulation of silica glaze inside vesicles; and (6) sandstone at Point Reyes, California, from a lithobiont mat of fungi and lichen. Each developed the general form of a case-hardened shell, protecting the surface from erosion. In accordance with the hypothesis of equifinality, the processes that led to similar appearance differ.
ISSN:0066-9628
1551-3211
1551-3211
DOI:10.1353/pcg.2012.0003