3D map of Earth’s core shows how volcanoes are formed

7 Sep 2015

Seismologists have created the first 3D visualisation of the Earth’s interior, showing the role that plumes of hot rock spewing out of the planet’s core have in the formation of volcanic islands.

Researchers at UC Berkeley managed to generate the map with the help of a US department of energy supercomputer, showing how the hot molten rock doesn’t rise up in a straight line.

Also, the base of the island may not be directly beneath it.

Rather, the plumes – which are 400-degrees hotter than surrounding rock, and are far wider below the surface than geophysicists had presumed – rise haphazardly and then widen as they get to the surface.

The latter aspect is what shapes volcanic islands, like Hawaii, with the lower rock often not directly connected to what we consider islands, thanks to a meandering rise.

The research actually shows two huge, 5,000km-across “blobs” of hot rock, directly opposite each other under Africa and the Pacific Ocean, which have stayed in position for 250 million years.

It paints a new image of how the onion-like make up of the planet actually works.

At the Earth’s core lies solid iron, with an outer core of liquid, molten iron and nickel.

Wrapped around that is hot, solid rock almost 3,000km thick, with our oceans and continents on top of that.

The way the hot rock rises, though, means it is probably entirely different to the cooler rock it envelops.

The 1,800-mile thick mantle under the Pacific Ocean contains rising plumes of hot rock that fan out at the surface to stationary hotspots, where they generate island chains as Earth’s crust moves due to plate tectonics. Scott French image.

The 1,800-mile thick mantle under the Pacific Ocean, rising erratically, via Scott French

“These columns are clearly separated in the lower mantle and they go all the way up to about 1,000 km below the surface, but then they start to thin out in the upper part of the mantle, and they meander and deflect,” said senior author Barbara Romanowicz.

“So while the tops of the plumes are associated with hotspot volcanoes, they are not always vertically under them.”

This research, published in Nature, means that those childhood schoolbooks that showed volvanoes, with a red line of lava going straight down the middle, directly into the Earth’s core, are wrong.


Most volcanic hotspots are linked to plumes of hot rock (red) rising from two spots on the boundary between the metal core and rocky mantle 1,800 miles below Earth’s surface

However, the techniques used to generate the map – studying the seismic waves from 273 earthquakes over the last 20 years – is not perfect. For example, Yellowstone’s volcano was not accurately portrayed.

The plumes that feed them may be too thin to be detected given the computational limits of the global modelling technique, said co-author Scott French.

The duo hope that a swathe of higher-resolution imagery from supercomputers can be achieved, allowing them to zoom in on particular areas.

“Tomography is the most powerful method to get this information, but in the future it will be combined with very sensitive gravity measurements from satellites and maybe electromagnetic sounding, where people do conductivity measurements of the interior,” said Romanowicz.

Main image via Shutterstock

Gordon Hunt was a journalist with Silicon Republic