Wellington Caves as natural laboratories for groundwater and climate research

Posted 10 June 2010

Stalagmites and stalactites

UNSW has commenced a major new research initiative investigating how to obtain more accurate records of past climatic and environmental change from the mineral deposits that form in caves.

The new project at Wellington Caves, NSW, takes advantage of the nearby National Centre for Groundwater Research and Training (NCGRT) teaching and research facility, and groundwater and surface climate monitoring facilities supported by funds from the Federal Government Groundwater Environmental Infrastructure Fund (EIF).

Stalagmites and stalactites found within limestone caves can be viewed as 'time capsules' that preserve records of the past. Formed from the mineral calcium carbonate, they can contain evidence of surface and cave climate as well as the overlying soil and vegetation and can be precisely dated using the decay of naturally occurring isotopes of uranium. Stalagmites, stalactites and other carbonate mineral formations found in caves are collectively known as speleothems (meaning 'cave deposits').

Speleothems grow over time from groundwater percolating into the parts of caves that are above the water table (in the unsaturated zone of an aquifer).

Because the growth of speleothems is directly linked to the groundwater supply, and this supply is influenced by climate and environmental changes that affect the rate of groundwater flow over time and the nature of the groundwater flow path into the cave, speleothems can provide a record of changes in climatic and environment conditions during the time periods when they formed.

Additionally, fluctuations in the water table over time may flood the caves and stop speleothems growing. It is possible to determine when these changes in water table occurred in the past by dating the timing of speleothem growth before and after these events.

The effects of groundwater flow paths into caves are poorly understood at present and are the focus of the current research that uses caves as 'natural laboratories' to investigate the properties of groundwater percolating into them.

At the Wellington Caves, UNSW researchers have for the first time installed a large number of state-of-the-art loggers that automatically measure the water flow rates from stalagmite-forming drip waters. This will allow them to quantify the variability of the flow and relate it to properties of the aquifer such as sedimentary structure and fracturing of the surrounding rock, as well as local and regional groundwater levels measured in flooded cave passages and boreholes.

This in turn will allow researchers to better understand the how to use the information obtained from stalagmites to interpret past changes in climate and vegetation, and to evaluate how well speleothems record groundwater variability.

The research team includes CWI staff Professor Andy Baker, Professor Ian Acworth, Dr Martin Andersen and Dr Matt McCabe; as well as research students and visiting researchers. Catherine Cockburn (MSc Hydrogeology) is investigating the sources of rainfall reaching the Wellington Region and PhD student Cecilia Azcurra is refining a limestone unsaturated zone isotope hydrology model in collaboration with visiting researcher Dr Chris Bradley (University of Birmingham, UK).

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