Geophysical damage of rock art sites can be occasioned by large-scale human modifications of the lithosphere. Examples are the extraction of minerals, such as coal, by the ‘long-wall’ mining method, or the extraction of oil, gas or water. These methods lead to subsidence of upper strata, and consequently affect features such as rockshelters in these surface facies. In Australia, such subsidence is attributable to underground coal mining in the Woronora Plateau where it has caused damage to shelters containing rock art (Sefton 1995). Monitoring provides the opportunity for appropriate conservation measures.

Dust can be a significant factor in the deterioration of sheltered rock art, particularly through trampling of the floor sediment and archaeological excavations (Morwood 1994). Moreover, Watchman (1998) has shown that dust raised from vehicular traffic on a nearby unsealed road can be highly effective in establishing a dust cover over rock art. His painstaking work at Split Rock, north Queensland, has also shown that such dust particles can comprise carbon-rich compounds probably created in diesel exhausts which become attached to the dust while still hot. Transported as aerosols in the wind, this material not only settles on rock art, it can significantly distort the carbon system of the surface deposit (the hydrocarbons are 14C-free). Watchman rightly emphasises the importance of detailed observations of all aspects of a site before it is developed for tourism. Airborne dust occurs naturally, but many human activities exacerbate the problem significantly (construction, land degradation, deforestation etc.). While it is washed off by rain at open sites, it accumulates in sheltered locations and often becomes incorporated in surface mineral deposits.

Humanly caused phenomena impact in many other ways on rock art and its support. The perhaps most commonly cited is the anthropogenic acidification of rain, caused essentially by the industrialisation of recent centuries (actually, anthropogenic contamination of the atmosphere began long before the industrial revolution; for instance in response to the massive increase in inefficient silver smelting at Roman times, the lead content of aerosols rose rapidly). A lowering of pH leads to the mobilisation especially of iron ions and thus the destruction of rock varnishes on which many petroglyphs depend for their survival. This is the main reason for the gradual destruction of the petroglyphs of the Dampier Archipelago (see Save the Dampier Rock Art site). However, other cations are also affected, which leads to increased weathering rates. Rock types particularly affected are limestone, dolomite and carbonate-cemented sandstones.

Rock art has also been destroyed by numerous development projects, including the construction of railways, roads, dwellings and particularly dams. In Portugal alone, hundreds of rock art sites have been inundated by hydro-electric schemes, until 1994 with the complicity of the state’s archaeological protection authority. Throughout the world, rock art has been shot at, painted over, hacked out and sawn off. Australia might pride itself in having an enlightened attitude — and some of the world’s least damaged rock art. But great numbers of petroglyphs at Port Hedland and Dampier sites were needlessly sacrificed to ‘economic progress’, and no doubt elsewhere in the country too. Rock art has been dynamited in Rio Tinto Gorge, Western Australia, by a man who found Aboriginal art annoying. In other parts of the world the same kind of action has at least a ‘rational’ intent: for instance, in Bolivia (Toro Muerto) and Macedonia, rock art is being destroyed in this way by treasure hunters who believe it indicates the presence of hidden riches. This depressing litany of humanly caused destruction to rock art could be continued ad infinitum. If there should be any doubt about what the principal threat to rock art is, it would be well to recall that some of the best-preserved rock art can be found within the exclusion zones of American radioactive waste dumps.
REFERENCES –Bibliography of Rock Art Conservation