The sleeping volcanoes of Mount Gambier and Millicent are in the region’s south are the western extremity of a volcanic plain extending eastward to Melbourne. Their activity is linked to the disturbance in the earth’s crust when Tasmania separated from Antarctica

The group near Mount Burr, outside of Millicent, were active from 1 million to 20,000 years ago, while those nearest to Mount Gambier last erupted about 4,000 years ago: the most recent eruptions on the Australian continent.