Lord Howe Island sits about 600 kilometres off the New South Wales coast, a crescent of rainforest and sea cliffs that draws visitors for its spectacular beaches and its unique birdlife. Few realise they are standing on the weathered remains of a volcano.

And that volcano has family.

Lord Howe is part of a chain of islands, called “seamounts”. It is the only island above sea level – the rest are submerged in the Tasman Sea. Roughly 650 kilometres west runs a second chain, the Tasmantid seamounts, tracing almost the same path.

Two nearly identical chains side by side in the middle of a tectonic plate is unusual. For the first time, in a new paper published in the journal Gondwana Research, we can answer how this happened.

A blowtorch under a moving tectonic plate

Most volcanoes occur where tectonic plates meet. There are a few exceptions, Hawaii being the most famous: a plume of hot rock rises from deep inside the Earth and melts its way through the middle of the Pacific plate.

As the tectonic plate drifts overhead, the plume burns a new hole in it, then another, like a blowtorch under a moving sheet of metal, until a chain of seamounts is formed.

That is exactly what the Tasmantid........

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