Australia has lots of ancient volcanoes. But how did they form?

If you are heading on a road trip this summer, you might drive past several ancient sentinels of Australia’s volcanic past.

Many of them, like the Glass House Mountains, are hard to miss.

These ancient volcanic plugs are all that is left of eruptions that occurred around 25 million years ago.

They are among hundreds of ancient volcano remnants that extend 3,500 kilometres from Tasmania to northern Queensland.

While the Glass House Mountains stand out in the landscape, other remnants are just weathered nubs hidden in the bush or a series of caves hollowed out by lava.

But just why there have been so many eruptions over the past 100 million years in eastern Australia — some of them as recent as a few thousand years ago — is a mystery.