Volcanoes that just kept on giving

A volcanic province in the Indian Ocean was the most continuously active in the world, erupting for 30 million years, according to Australian and Swedish geologists.

It was fuelled by a constantly moving “conveyor belt” of magma created by shifts in the seabed, which continuously made space available for the molten rock to flow, beginning around 120 million years ago, they write in a paper in the journal Geology.

“The Kerguelen Plateau is gigantic, almost the size of Western Australia,” says research lead Qiang Jiang, from Australia’s Curtin University. “Now imagine this area of land covered by lava, several kilometres thick, erupting at a rate of about 0.2 millimetres every year.”

As always, comparisons to Olympic swimming pools are appropriate: in this case, we’re talking 184,000 a year, the researchers say, or around 5.5 trillion over the 30 million years of continuous activity.

The eruption rates then dropped drastically some 90 million years ago, for reasons that are not yet fully understood.

“From then on, there was a slow but steady outpouring of lava that continued right to this day,” says Jiang, “including the 2016 eruptions associated with the Big Ben volcano on Heard Island, Australia’s only active volcano.”

The researchers – from Curtin, the University of Tasmania and Sweden’s Uppsala University – used an argon-argon dating technique to date the lava flows, analysing a range of black basaltic rocks taken from the sea floor.

Finding such a long continuous eruption activity is important, they say, because it helps geologists understand what factors can control the start and end of volcanic activity. And, suggests Curtin’s Hugo Olierook, it required very peculiar geological conditions.

“After the partial breakup of the supercontinent Gondwana into the pieces now known as Australia, India and Antarctica, the Kerguelen Plateau began forming on top of a mushroom-shaped mantle upwelling, called a mantle plume, as well as along deep sea, mid-oceanic mantle ridges,” he says.

“The volcanism lasted for so long because magmas caused by the mantle plume were continuously flowing out through the mid-oceanic ridges, which successively acted as a channel…”

Other volcanoes would stop erupting, Olierook adds, because when temperatures cooled the channels became clogged by “frozen” magmas. “For the Kerguelen Plateau, the mantle plume acts as a Bunsen burner that kept allowing the mantle to melt, resulting in an extraordinarily long period of eruption activity.”

The Royal Institution of Australia has an Education resource based on this article. You can access it here.