TRATEBAS, ALICE M. Bureau of Land Management, P.O. Box 883, Newcastle, WY 82701. - Biodeterioration of Rock Art and Issues in Site Preservation.
Lichens, algae, and mosses growing on rock surfaces that have
prehistoric or historic rock art are a major problem for preserving
these fragile remains of the past. Most rock art is surficial or
shallowly pecked or incised into the rock surface. Breakdown of the
rock by microflora can easily erase these images. The problem is
worldwide. Archaeologists have several major issues for site
preservation where biodeterioration is a factor. One issue is whether
the rock surface is now so deteriorated that the lichen structures are
holding it in place. Killing the lichens would release the undermined
rock and leave the remaining rock art unprotected. If we kill the
lichens, what method should we use? The recent development of dating
techniques that analyze rock coatings, such as rock varnish, oxalate,
and silica, means that we cannot contaminate the surface with
chemicals that would prevent future dating. An associated issue is
keeping any chemicals from getting into the environment, such as not
contaminating archaeological deposits below the rock art. We cannot
just spray on chemicals, but would need to carefully dab them on, time
consuming work. A crucial issue is how fast the lichens are growing
and whether they will deteriorate more of the panel. A slow growing
lichen leaves plenty of time to investigate, conduct experiments, and
make decisions. If removed, how fast will the lichen regrow? If
removal leaves a fragile, exposed surface, should we use a rock
consolidant to preserve the site? All known consolidants alter the
rock porosity, which could negatively impact the rock art. Instead of
major interventions, can we alter the microenvironment to discourage
lichen growth? This ideal solution may be difficult in many settings.
A final issue is the ethics of altering the natural environment. Whose
sites are these and what is their view?
Key words: archaeology, biodeterioration, lichen, rock art