The four extinct volcanoes in the cluster are calderas, which form after a volcano erupts and the land around them collapses, forming a crater. The largest is 1.5 km across the rim and it rises 700 metres from the sea floor. Read more
Volcano cluster thought to be 50 million years old accidentally discovered off coast of Sydney
Four extinct volcanoes likely to be 50 million years old have been accidently discovered about 250 kilometres off Sydney's coast. Australian research vessel Investigator found the volcanoes nearly five kilometres under the ocean surface while searching for nursery grounds for larval lobsters and fish. Read more