Volcanic eruptions can destroy essential infrastructure, ground air traffic for days, wipe out entire cities, disrupt the climate for years, and even wipe out life on Earth, so it’s important to know what causes them to blow.
New research has revealed that specific features deep within Earth can be linked directly to such cataclysmic eruptions.
Thousands of kilometers below Earth’s surface, there is a solid layer of hot rock called the lower mantle. Textbook diagrams would have you believe this is a smooth layer, but the lower mantle actually contains a mountainous topography, with two continent-sized structures, possibly made of different materials than their surrounds.
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These hidden structures feature craggy ranges that shift and buckle much like the tectonic plates far above them.
Volcanologist Annalise Cucchiaro from the University of Wollongong in Australia and her colleagues have found these big lower-mantle basal structures – termed ‘BLOBS’ by the research team – have a direct influence on volcanic activity at Earth’s surface.
When scorching columns of rock, known as deep mantle plumes, first rise from depths of nearly 3,000 kilometers (almost 2,000 miles), we get the kinds of Earth-shattering volcanoes that wiped out most of life on Earth, and had a hand in the extinction of the dinosaurs.
The BLOBS seemed a likely source of these subterranean plumes, and Cucchiaro’s team has now confirmed this connection using three different datasets that provide extensive detail on large volcanic eruptions that happened around 300 million years ago.
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“This work highlights the importance of mantle plumes in acting as ‘magma highways’ to the surface, creating these giant eruptions,” Cucchiaro says.
“It also shows that these plumes move along with their source, the BLOBS.”
There are two BLOBS within the lower mantle. One is below the African hemisphere, and the other, under the Pacific.
We still don’t know if the BLOBS are ever fixed in place, or if they’re always moving around via convection, but the new research suggests it’s a dynamic system with direct repercussions for us surface dwellers.
By simulating the movements of BLOBS 1 billion years ago, the team showed that they produced mantle plumes that were sometimes slightly tilted as they rose. This meant eruptions occurred either directly above the BLOBS, or close to it – and these locations matched that of known eruptions.
“We used statistics to show that the locations of past giant volcanic eruptions are significantly related to the mantle plumes predicted by our models,” Cucchiaro and her colleague, geoscientist Nicholas Flament, explained in The Conversation.
“This is encouraging, as it suggests that the simulations predict mantle plumes in places and at times generally consistent with the geologic record.”
As much as they destroy, large eruptions also have the power to create, and knowing where they may occur – either historically or in the future – could also help us to find magmatic treasures like kimberlite and diamonds, and minerals that could be used in harnessing renewable energy.
“This research cracks open one of the questions that has long plagued scientists – are the BLOBS stationary or mobile and how do they relate to giant volcanic explosions – so it is a thrill to finally [be able] to unravel these mysteries,” says Flament.
This research was published in Communications Earth & Environment.
