Despite looking like they’ve been created by haphazardly tossing rocks into a pile, these lava tumuli, or “lava blisters” are a naturally occurring—though rare—geological phenomena.
The naturally occurring volcanic formations are each about the size of a small house, formed when lava welled up beneath the surface, eventually causing the crust of the lava tubes above to buckle and bulge. Globs of molten lava oozed out of the newly made cracks, giving the formations their unique structures.
A trip down Old Crusher Road near Byaduk (just south of Hamilton, Victoria) brings you to Harman Valley, the remnants of a lava flow from nearby Mount Napier. The molten rock once flowed from here to the sea at nearby Port Fairy. The valley contains many stone fences that farmers erected from the rocks scattered across their paddocks. There are a number of tumuli just off the road.