Uncovering the Volcanic Secrets of Lord Howe Island

New research has shed light on the volcanic origins of Lord Howe Island, a World Heritage-listed island located 600 kilometres off the Australian mainland.

The island, known for its towering basalt peaks and coral reefs, is the eroded remnant of an extinct shield volcano formed from 7-million-year-old lava flows.

A Chain of Volcanoes

Lord Howe Island is at the southernmost end of a chain of mostly submerged, extinct volcanoes, known as seamounts, stretching 1,500km along Australia's east coast.

This chain, called the Lord Howe seamount chain, runs parallel to another line of undersea volcanoes, the Tasmantid chain, which has been in place for millions of years.

The long-standing coexistence of these two chains has intrigued scientists, with a recent research paper suggesting they formed from the same deep Earth hotspot.

The Research

The paper's lead author, Ben Mather, from the University of Melbourne's School of Geography, Earth and Atmospheric Sciences, explained that the hotspot acted like a blowtorch under the drifting Australian tectonic plate.

"With Lord Howe Island, enough material had erupted on the sea floor so that Lord Howe Island could actually penetrate the surface of the water and become a subaerial island that people can live on,"

said Dr Mather.

The research challenges previous ideas of mantle plumes, suggesting they can split into two branches.

"It's very unusual that the two volcanic chains should be so close together, and that they should sustained over such a long geological time period, over millennia, in the middle of a tectonic plate,"

Dr Mather said.

How Volcanic Chains Are Formed

Dr Mather explained that when the hotspot melts and punches through a weaker section of the plate, erupting lava accumulates and builds a seamount.

The plate, drifting slowly to the north, carries each new seamount away from the hotspot, forming a chain of undersea mountains over millennia.

A Twin Tasman Volcanic Chain

Dr Mather's team developed a 3D numerical modelling tool, which showed how the volcanic plume had split into two long-lived branches to move around an obstacle deep beneath the Tasman Sea.

"Reconstructing the past positions of these sunken slabs beneath the Tasman Sea reveals exactly the geometry our model predicts: a strip of slab material with gaps on either side, where each plume branch can rise to the surface,"

Dr Mather said.

Karin Orth, an earth scientist at the University of Tasmania, said the new modelling was a "very elegant" way of explaining the formation of two closely spaced parallel volcanic tracks.

"It's a bit forensic; it's a bit like a detective story,"

Dr Orth said.

Why Does This Matter?

The research offers potential insights into where future undersea volcanoes might emerge along the Tasmantid and Lord Howe chains millions of years in the future.

Dr Mather said their plume branching model might also explain other closely spaced plume tracks worldwide.