This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Lord Howe Island sits about 600 kilometers (370 miles) off the New South Wales coast, a crescent of rainforest and sea cliffs that draws visitors to its beaches and birdlife. Few people realize they are standing on the worn-down remains of a volcano.
Lord Howe is one island in a chain of seamounts off the east coast of Australia. It's the only island above sea level—the rest are submerged in the Tasman Sea, between southeastern Australia and New Zealand. Roughly 650 kilometers (400 miles) west runs a second chain, the Tasmantid seamounts, tracing almost the same path.
Two nearly identical chains of volcanoes, side by side, in the middle of a tectonic plate. Now, for the first time, our research, published in Gondwana Research, can answer how this happened. Most volcanoes occur where tectonic plates meet, but there are a few exceptions.
Hawaii is the most famous example. A plume of hot rock rose from deep inside Earth, burning through the middle of the Pacific plate. As the plate drifted overhead, the plume punched a new hole in it, then another, like a blowtorch under a moving sheet of metal.
This is exactly what the Tasmantid and Lord Howe chains look like. Both chains get steadily younger the farther south you go, tracking the northward drift of the Australian plate over the past 40 million years. Plumes this close don't usually stay separate.
In computer models, any two within about 1,000 kilometers (620 miles) of each other tend to drift together and merge. But these remained side by side for 40 million years. The lava from both chains is chemically nearly identical.
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