Image: Illustration, mantle plume
ESRF/Denis Andrault/Henri Samuel
An illustration showing how a mantle plume can be emitted from the core-mantle boundary of the Earth to reach the Earth's crust. Due to the movement of tectonic plates at the Earth's surface, the mantle plumes can create a series of aligned hot spot volcanoes. A mid-ocean ridge and a subducted plate are also shown in this schematic from a study in the July 19, 2012 issue of the journal Nature.
By Contributor
updated 7/18/2012 2:56:51 PM ET 2012-07-18T18:56:51

The world's most brilliant beam of X-rays now suggests that volcanic hotspots may indeed be caused by giant plumes of hot rock streaming upward from near the Earth's core, as volcano researchers have long suspected.

Volcanoes are usually located at the boundaries of Earth's tectonic plates, where those plates push and pull at each other. There, Earth's crust is relatively weak, and magma can easily break through.

Volcanic hotspots, though, are mostly located far away from plate boundaries, and explaining how magma makes its way through thicker portions of the crust poses a conundrum.

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A better understanding of hotspots and what drives them is able to not only shed light on their current effects on life, but also on the composition of the early Earth, said researcher Denis Andrault, a mineral physicist at Blaise Pascal University in Clermont, France. [ 50 Amazing Facts About Earth ]

Mantle plumes
One explanation for how these hotspots form suggests that narrow streams of hot rock with large, mushroomlike heads known as mantle plumes push up from deep within the Earth. The deepest are thought to rise from near the Earth's core and up through more than 1,800 miles of the Earth's mantle layer, pumping gigantic amounts of heat upward.

For instance, some geologists have argued that the Hawaiian island chain originated from a mysterious cluster of heat far beneath the Pacific Ocean. As the Pacific plate drifted over this mantle plume, volcanoes arose on the ocean floor that eventually grew to become islands rising above the ocean surface.

However, whether these mantle plumes exist remains hotly debated.

"We know less about the Earth's deep mantle than about the surface of Mars," Andrault told OurAmazingPlanet.

Lasers and X-rays
To see whether mantle plumes might actually be the cause of volcanic hotspots, scientists used lab experiments to recreate the extreme conditions at the core-mantle boundary to see what material from that region could rise through hundreds of miles of rock.

"It is impossible to drill a hole of even 20 kilometers [12 miles] into the Earth, so we have to recreate it in the laboratory," Andrault said.

The investigators started with tiny bits of rock up to 10 times thinner than a human hair. They compressed these specks of dust between the tips of two cone-shaped diamonds under extraordinary pressures of up to 120 gigapascals, more than 1,000 times the pressure found at the bottom of the Mariana Trench, the deepest point in the ocean. A laser beam then heated these samples to temperatures between 5,400 and 7,200 degrees Fahrenheit.

"Those extreme conditions of pressure and temperature is like traveling into the very deep Earth," Andrault said.

The researchers next used the most brilliant beams of X-rays in the world at the European Synchrotron Radiation Facility in Grenoble, France, focused to spots just a micron wide — a hundredth the diameter of a human hair — to scan these samples. The X-ray analysis revealed the iron content of the molten and solid parts of these specks.

"It is the iron content which is decisive for the density of molten rock at the core-mantle boundary," Andrault said. "Its accurate knowledge allowed us to determine that molten rock under these conditions is actually lighter than solid."

Their findings, detailed in the July 19 issue of the journal Nature, suggest that partially molten rock at the core-mantle boundary should be buoyant and thus rise toward Earth's surface, evidence supporting the idea of deep mantle plumes.

© 2012 OurAmazingPlanet. All rights reserved. More from OurAmazingPlanet.

Photos: Month in Space: January 2014

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  1. Southern stargazing

    Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them. (Y. Beletsky / ESO) Back to slideshow navigation
  2. A balloon's view

    Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich. (Kyle Moroney / AP) Back to slideshow navigation
  3. Spacemen at work

    Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment. (NASA) Back to slideshow navigation
  4. Special delivery

    The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps. (NASA) Back to slideshow navigation
  5. Accidental art

    A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288. (NASA / ESA) Back to slideshow navigation
  6. Supersonic test flight

    A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

    More about SpaceShipTwo on PhotoBlog (Virgin Galactic) Back to slideshow navigation
  7. Red lagoon

    The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes. (ESO/VPHAS team) Back to slideshow navigation
  8. Fire on the mountain

    This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people. (NASA via AP) Back to slideshow navigation
  9. Where stars are born

    An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues. (NASA / JPL-Caltech) Back to slideshow navigation
  10. Cygnus takes flight

    Orbital Sciences Corp.'s Antares rocket rises from NASA's Wallops Flight Facility on Wallops Island, Va, on Jan. 9. The rocket sent Orbital's Cygnus cargo capsule on its first official resupply mission to the International Space Station. (Chris Perry / NASA) Back to slideshow navigation
  11. A long, long time ago...

    This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang. (NASA / NASA via AFP - Getty Images) Back to slideshow navigation
  12. Frosty halo

    Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.

    Slideshow: The Year in Space (Brian Peterson / The Bismarck Tribune via AP) Back to slideshow navigation
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