Anthropogenic activities

Humans cutting impacting rock art panels may do considerably more damage than just cutting identified in incremental loss of stone.  Sometimes, humans break off chunks of rock from the panel.

Sandstone, central Utah	Sandstone, central Utah
Sandstone, central Wyoming	Granodiorite, central Arizona

Calcrete/Fissuresol wedging (or dust in fissuresol, or both)
 
 

Diorite, central Arizona	Diorite, central Arizona	Granodiorite, southern Nevada
Sandstone, central Wyoming	Granodiorite, southern Nevada	Sandstone, central Utah
Sandstone, central Wyoming	Sandstone, southeast Colorado	Basalt, Coso Range, California
Basalt, Mojave Desert, California	Sandstone, central Wyoming	Basalt, southeast Colorado
Sandstone, northern Arizona	Silicified Dolomite, South Australia	Basalt, southeast Colorado
Andesite, western Nevada	Basalt, southeast Colorado	Basalt, Mojave Desert, California
Granodiorite, southern Nevada	Basalt, Coso Range, California

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Fire
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Basalt, southeast Colorado	Sandstone, Black Hills, Wyoming	Sandstone, Black Hills, Wyoming
Sandstone, Black Hills, Wyoming	Sandstone, Black Hills, Wyoming	Sandstone, Black Hills, Wyoming

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Undercutting

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Sandstone, Black Hills, Wyoming	Sandstone, central Utah	Sandstone, central Wyoming
Basalt, Coso Range, California	Sandstone, central Wyoming	Sandstone, southeast Colorado
Sandstone, central Wyoming	Granodiorite, central Arizona	Sandstone, central Utah
Sandstone, Black Hills, Wyoming	Sandstone, Pryor Mountains, Montana

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Other natural causes (wedgework of roots, earthquakes, intersection of fractures, unidentified...)

Dorn, R.I. and Cerveny, N.V. (2005) Atlas of Petroglyph Weathering Forms used in the Rock Art Stability Index (RASI). http://alliance.la.asu.edu/rockart/stabilityindex/RASIAtlas.html (originally posted April 1, 2005; last modified March 10, 2007).