MOUNT GAMBIER: VOLCANOES, CAVES AND FAULTLINES
Thursday February 3rd 2022
Mawson Lecture Theatre
North Terrace Campus
University of Adelaide
Department for Environment and Water
The talk will provide details and integrate a summary of the knowledge gained over the last 50 years about the drivers of geological features in the Gambier Karst Province, also known publicly as the Limestone Coast Region (after the geology) or the Green Triangle (based on its abundant groundwater resources). Three major faultlines are traceable across the land surface of the South East: the Kanawinka Fault, the Tarwaup Fault and the Nelson Fault. Best known is the Kanawinka Fault which connects the caves and other features at Naracoorte. This talk will focus on the Tartwaup and Nelson Faults, and their relevance to the cave systems and volcanic activity in the Mount Gambier region.
On the geology maps of the 1960’s and 70’s, the Tartwaup and Nelson Faults are indicated as of relatively short length, as interpreted by Reg Sprigg of the Department of Mines. At the time he was coordinating the regional geological assessment as part of the Oil and Gas search of the Western Otway Basin.
But Reg didn’t know the caves and hadn’t dived in the sinkholes. I’m sure he would have, if he could have! Much has been discovered about each of these faults in the 50 years since, as has happened for the Kanawinka Fault at Naracoorte, with the primary contribution from the discovery, mapping and geological assessment of the renowned caves and sinkholes of the region. Such exploration and diving only began systematically in the 1960’s.
For instance, the Tartwaup Fault (sometimes known as the Tartwaup Hinge Zone) has been detected by soundings and diving as a 2m step right across the bottom of the famous Blue Lake, confirming that the eruptions occurred upwards through the fault zone itself, probably initiated by fault movement. Many caves and sinkholes, of different character to the Naracoorte Caves, have developed along the Tartwaup and Nelson Faults which have proven since Reg Sprigg’s time to be the loci of cavern formation, as the Kanawinka Fault is at Naracoorte. Similarly (and not coincidentally!), the Tartwaup and Nelson Faults are the locus of the volcanic activity.
The talk will take the audience along the parts of both faults observing various geological features covering volcanoes, caves, sinkholes, dolomite outcrops and springs. These great fractures have also become conduits focusing the regional fresh groundwater flow, so naturally hydrogeology will also feature in this talk which will also cover aspects of our planned visit.
Ian Lewis, hydrogeologist and Caveman, is a geoscientist with the Groundwater Team, Groundwater Assessment and Reporting, Water Science and Monitoring Branch, Water and River Murray Division, of the Department for Environment and Water.