Vandals, and thieves.
Unknowledgeable people touching and making rubbings as finger oils and friction
erode coatings protecting images.
Walking near rockart allows dust to settle on the images which can't be cleaned
Wind/Sun/Wave action erosion
Exfoliation=heat and cold flakes pieces off from main boulder with art on the
Ground water deposits minerals on the art
Algae growing right over the images
Making locations public allowing access for vandals
Plant growth touching surface and aiding algae growth
Basalt crystals falling off panels leaving partial images
Moving boulders/panels to museums like at Kennewick/Prosser/etc
Fencing in sites like at Kila, Montana
Spraying algae inhibitors, (this is just an idea as I don't know of this being
Pruning vegetation so there is no source for fire
Putting images on Internet so people can learn without impacting and view
without visiting location.
Having a person on site like at Vantage to observe visitors.
Tours only like at Horsethief Lake
Keeping locations of rock art secretive
Creating shade to inhibit sun erosion
If anyone knows of other sources or methods for the list above please submit
through email here and I will
immediately post them.