Current Assessment of the Impact of Pollution on Murujuga Rock Art
John L Black in collaboration with Stéphane Hoerlé and Ron Watkins
Summary of a presentation in Karratha at the Murujuga World Heritage Summit – 6 August 2018
The petroglyphs of Murujuga are unique in the world. The Dampier Archipelago is the only known place where at least 45,000 thousand of years of human culture and spiritual beliefs through a changing environment are captured in rock engravings. Murujuga is also the location for a major petrochemical industrial complex which is served by one of the largest bulk handling ports in the world. Emissions from industry have increased acidity of rock surfaces at some rock art sites by more than 1000-fold from near neutral pH of 6.8 ± 0.2 pre-industry to as low as 3.8 ± 0.15 in 2017. Maintaining integrity of the outer rock patina is essential for survival of the petroglyphs. The patina is formed at an extremely slow rate of around 10 microns per 1000 years through biological and chemical processes under neutral to weakly alkaline conditions of desert environments. Acid dissolves the manganese and iron oxides in the patina. Theoretically, petroglyphs at some locations on Murujuga are now being degraded by acids emitted from industry and shipping. However, there has not been credible research to determine whether this is occurring. Research is needed urgently to show whether the combined emissions from industry, shipping and the environment are dissolving the patina, the concentrations needed for dissolution and the rate it is occurring. The research must also examine the impact of nitrogenous emissions on the growth of microorganisms and fungi and the role of their organic acids in degrading the petroglyphs. A full understanding of the chemical reactions involved in degradation of the patina and its attachment to the underlying weathering rind is required to develop simulation models for predicting the likely impacts of future industrial emissions and to identify potential methods to arrest patina degradation. In the meantime, the Western Australian Government should invoke the Precautionary Principle from the Environmental Protection Act 1986 by restricting further industrial development on Murujuga and by setting regulations that limit industrial emissions to near zero.