Victorian lava caves: investigation and risk management

Small to medium sized subcrustal lava caves occur in Western Victoria in the Neogene to Quaternary Newer Volcanics Basalt. Subsurface voids created by these lava caves and the potential collapse can present a significant risk to developments in areas underlain by the Newer Volcanics. The size, depth and spatial distribution of lava caves can be difficult to determine and investigations in such areas are not routinely designed to detect lava caves. This paper briefly describes lava cave formation in Victoria and resources that inform locations and features of known lava caves. Two case studies are discussed, an investigation of a known lava cave for a proposed development and an unexpected void or blister cave encountered during construction. The paper then discusses strategies to mitigate the risk of encountering unanticipated subsurface voids or lava caves within the Newer Volcanics Basalt.