by Caroline Mather
This is a question that researchers are trying to answer at Murujuga (the Dampier Archipelago), one of the world’s largest rock art provinces, located on the Pilbara coast.
The study is part of an ARC Linkage Project: Dating Murujuga’s Dreaming, being undertaken by researchers from The University of Western Australia (UWA), The University of Melbourne and The University of Wollongong in collaboration with Murujuga Aboriginal Corporation, Rio Tinto and Woodside.
The project, led by CRAR+M Director Professor Jo McDonald, is using a number of scientific analyses of landscapes to date and contextualise this extraordinary rock art province. Knowledge of how the climate and landscape of Murujuga has changed over time can help us understand how Aboriginal people lived, moved and created rock art in the landscape over the past ~50,000 years.
Recent fieldwork has focussed on collecting data to improve knowledge of the hydrological functioning and potential permanence of water holes that would have sustained people living in the landscape, particularly since the area became an Archipelago ~8,000 years ago. Many of the pools are surrounded by evidence of human activity, including extensive rock art and shell midden deposits.
Often considered as permanent, the recent succession of dry summers, with no significant cyclonic rainfall events, has left surface pools increasingly dry. Visits to a number of “permanent” pools in early May 2022 found small puddles or shallow pools well below the usual water levels and with notable vegetation loss in the vicinity.
This work builds on inland Pilbara studies by project researchers Shawan Dogramaci and Greg Skrzypek and will improve our knowledge on the hydrological functioning of ephemeral waterholes in semi-arid and arid environments.
With support from partner researchers at Rio Tinto, in-situ monitoring of water holes is being implemented to understand how the pools are recharged and sustained. AQUA Troll loggers were installed at pools on Enderby Island and Burrup Peninsula, to measure water level, electrical conductivity and temperature over coming years. These pools are surrounded by extensive rock art assemblages demonstrating these were important foci in the landscape through time.
While the team were in the field, an unseasonal northwest cloud band traversed the Pilbara bringing record-breaking rain to the region. A rapid increase in surface water in creeks and pools was noted; creeks flowed again and the water level in one pool increased by over 1.7 m.
Luckily the team had installed the loggers prior to this rain events and will have recorded the shift in water level (and hopefully remain secured after the creek flows). Caroline Mather and other members of the the team also collected surface water and rainfall samples to analyse the chemistry and stable isotope signatures and be able to relate surface water recharge to rainfall events. Further catchment-scale hydrological studies are underway by UWA PhD Candidate Diego da Silva Turollo. His modelling of the hydrological system to understand how waterholes may have changed under changing climatic regimes during the last 10,000 years, will be reported on soon!
Once the geochemical data are available, the project researchers can calculate the evaporative loss and estimate the persistence of Murujuga's waterholes. Project fieldwork continues in a few weeks, focussing on collecting geological samples and vegetation data for pollen analysis.
Images here taken by Caroline Mather, Jo McDonald and Victoria Wade.