Scientists Discover 'Fingers' of Heat Deep Beneath Earth's Surface

Deep beneath Earth's surface, geological processes are constantly shifting and changing our world. Now, scientists have used seismic waves to detect previously unknown "fingers" of heat, some thousands of miles long, in Earth's upper mantle. The findings could allow researchers to better understand how volcanic islands like Hawaii and Tahiti form.

Some volcanoes arise at collision zones between tectonic plates. Others, though, are created in the middle of plates and are called hotspot volcanoes. These latter volcanoes are made by upwellings of hot, buoyant rock that rise as plumes from deep within Earth's mantle.  Yet this theory doesn't fully explain how some hotspot volcano chains are formed. It's very likely that more complex interactions are taking place between the hot plumes and the upper mantle. That's why researchers decided to investigate a bit further.

The scientists used seismic tomography in order to examine what lay below the Earth's crust. Seismic waves are waves of energy that can be produced by earthquakes, explosions and volcanic eruptions. These waves can travel below the Earth's surface, their shape changing depending on what material they travel through. A global network of seismographs can then detect these waves. This, in turn, allows scientists to examine the structures beneath the Earth.

In order to gather a complete picture of the world below, the researchers compared waveforms from hundreds of earthquakes recorded at locations around the world. Working much in the way that CT scans work, they were able to see the structures beneath the surface.

"The Earth's crust varies a lot, and being able to represent that variation is difficult, much less the structure deeper below," said Vedran Lekic, one of the researchers, in a news release.

In the end, the researchers discovered finger-like channels of low-speed seismic waves flowing about 120 to 220 miles below the sea floor and stretching out in bands about 700 miles wide and 1,400 miles apart. The scientists also discovered that at this depth, seismic waves typically travelled about 2.5 to 3 miles per second, but the average seismic velocity in the channels was about four percent slower. This meant that the channels were hotter than the surrounding material.

"This global pattern of finger-like structures that we're seeing, which has not been documented before, appears to reflect interactions between the upwelling plumes and the motion of the overlying plates," said Lekic in a news release. "The deflection of the plumes into these finger-like channels represents an intermediate scale of convection in the mantle, between the large-scale circulation that drives plate motions and the smaller scale plumes, which we are now starting to image."

The findings reveal a little bit more about what occurs beneath Earth's surface. The exact nature of these interactions need further study, though. Yet for now, scientists have a clearer picture of the "plumbing" of Earth.

The findings are published in the journal Science.