Ethiopia’s giant underground blob of magma puzzles scientists
Ethiopia’s giant underground blob of magma puzzles scientists
Sep. 17, 2013 at 10:01 PM ET
The Afar Rift in Ethiopia is marked by enormous gashes that signal the breakup of the African continent and the beginnings of a new ocean basin, scientists think.
The fractures appear eerily similar to seafloor spreading centers, the volcanic ridges that mark the boundaries between two pieces of oceanic crust. Along the ridges, lava bubbles up and new crust is created, slowly widening the ocean basin.
But a look deep beneath the Afar Rift reveals that the birth announcements may be premature. “It’s not as close to fully formed seafloor spreading as we thought,” said Kathy Whaler, a geophysicist at the University of Edinburgh in Scotland.
Whaler and her colleagues have spotted 120 cubic miles (500 cubic kilometers) of magma sitting in the mantle under the Afar Rift. Hot liquids such as magma like to rise, so the discovery is a conundrum.
“We didn’t expect this, because magma wants to pop up like a cork in water; it’s too buoyant compared to the surrounding medium in the mantle,” Whaler told LiveScience’s OurAmazingPlanet.
Models predict that at spreading ridges, magma should sit just under the rifts, in the crust. That’s what geoscientists see in the oceans, at places such as the Mid-Atlantic Ridge and the Juan de Fuca Ridge. But not only is the giant pool at Afar extremely deep, but it is also mostly below the sleeping Badi volcano, many miles west of the scene of a 2005 series of underground magma intrusions, Whaler said.
“You just wouldn’t expect to have a blob of magma still underneath this other area,” Whaler said. “It’s one of the things we’re still having a lot of discussions about.”
The findings, published Sept. 5 in the journal Nature Geoscience, add a new twist to the Afar Rift puzzle. Thanks to intense international attention — from scientists intrigued by the 2005 intrusions — the region is one of the best-studied spreading centers in the world. But a lively debate continues over whether the Afar Rift is a unique case or a textbook example of a fracturing continent.
The Afar region sits at the junction of three tectonic plates, all of which are spreading apart. Here, Earth’s brittle crust fractures as the plates tear away from one another, but the mantle underneath adjusts by stretching like warm plastic. The mantle rocks rising beneath the thinning crust melt from lowered pressure, creating magma. [Infographic: Tallest Mountain to Deepest Ocean Trench]
In 2005, a series of earthquakes in Dabbahu, Ethiopia, announced the arrival of new magma squeezing into the crust. Vertical fingers of molten rock shot into underground fractures, 14 in all. The longest intrusion was about 26 feet (8 meters) wide and spread through 37 miles (60 kilometers) of crust in just 10 days.
Whaler and her colleagues searched for the source of these vertical injections, called dikes, with instruments that measure changes in magnetic and electric fields in the Earth. Both are sensitive to underground liquids, which have a higher electrical conductivity than rock (meaning electrons have an easier time moving through them).
The team discovered the feeder for the magma intrusions: a shallow, small chamber directly under the dikes, about 4 miles (7 kilometers) wide and 3 to 6 miles (5 to 10 kilometers) below the surface.
But in the mantle, the layer beneath Earth’s crust, a huge 18-mile-wide (30-kilometer-wide) region of very high conductivity reaches down to a depth of 20 miles (35 kilometers), well below the 12-mile-thick (20-kilometer-thick) crust. This giant magma zone isn’t one big pool, but a series of interconnected pockets, scientists think.
The findings were bolstered by research in geochemistry, rock composition and seismology from other teams, Whaler said. “The results from standard electrical conductivity get a huge range, so the additional information gives additional bounds. I suspect nobody would have believed us without some supporting evidence from other techniques.”
For example, a study published in the journal Nature on July 4 shows the mantle under the Afar region is about 180 degrees Fahrenheit (100 degrees Celsius) hotter than it should be. And although the crust is thinner than in other spots around the planet, it is actually thicker than models predict. [What is Earth Made Of?]
Taken together, the recent discoveries suggest researchers still don’t understand how the final stages of breakup occur in continental crust, Whaler said.
“Most people have said we can look at the Afar Rift and it’s a good on-land analogue of midocean ridges,” she said. “But what this result says is, there is still quite a distinct difference between the crust and upper mantle beneath a fully formed spreading ridge and the Afar Rift.”
For Roger Buck, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory who was not involved in the study, the discovery raises questions about what controls the timing of magmatic activity such as dike intrusions.
“A commonly held view is that long, quiet periods occur because there is no magma available in the crust to trigger dike opening and volcanism at spreading centers,” Buck wrote in an accompanying editorial published in Nature Geoscience. “However, the results … bring into question this standard view. Instead, there may always be large quantities of magma available in the mantle and shallow crust at many spreading centers.”
- Have There Always Been Continents?
- Amazing Images: Volcanoes from Space
- 7 Ways the Earth Changes in the Blink of an Eye
Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Once an $18,000 Home on a Decaying Street, Now a $5 Million Gem (The New York Times)
A Final Image of Earth (The New York Times)
Naughty Wives, Circa 1925 (The New York Times)
Major Plane Crashes Are Always Technology Failures, Not Human Error (The TIBCO Blog)
100 Year Starship symposium again lands in Houston this week
21 minutes ago
Move over, Scotty: Some real-life engineers and scientists are flocking to Houston this week to debate the future of interstellar space travel.
Members of the public, industry professionals and academics have descended upon the Texas city for the third annual 100 Year Starship symposium, which will discuss what the world needs to do in the next 100 years to take starship technology out of the realm of science fiction and into reality.
The conference started Thursday and runs through Sunday. It’s hosted by the 100 Year Starship initiative, which was started with seed money from the U.S. military’s Defense Advanced Research Projects Agency and seeks to develop a vehicle over the next century that could reach a far-off star within a reasonable amount of time. [Images: Amazing Visions of Interstellar Starship Travel]
The symposium “seeks to highlight the small incremental steps as well as radical leaps required to make significant progress to interstellar space, and how those steps will yield important benefits to life on Earth,” 100-Year Starship officials wrote in a release.
The 2013 100 Year Starship symposium will feature presentations by the SETI (Search for Extraterrestrial Intelligence) Institute’s Jill Tarter, former NASA astronaut and the first African-American woman in space, Mae Jemison, astrophysicist Hakeem Oluseyi and an international group of 75 other speakers. About 160 people are expected to attend the conference.
The symposium’s reach is wide. Speakers will present papers on topics such as future propulsion systems, the ethics and cultural implications of interstellar space travel and the economics of sending human technology to distant stars.
The conference also features an Earth-based focus. Some presenters will speak about “how these interstellar-driven innovations translate to help improve and enhance life here on Earth today and in the years to come,” symposium officials said in a statement.
Any interested member of the public can take part in the conference. Tickets to nighttime events — including a “Sci-Fi Night” that features a screening of the film “Europa Report” on Friday — are available for purchase. Space enthusiasts also can still register to attend daytime sessions.
Another notable event hosted by the 100 Year Starship symposium will attempt to bridge the gap between art and interstellar science.
“Saturday evening’s ‘Accelerating Creativity’ dinner features Bella Gaia, an amazing multimedia performance created and performed by Kenji Williams and company that interprets scientific data, actual space images and music to help us understand humanity’s connection and impact on Earth and with space,” officials wrote.
Visit Space.com this week for complete coverage of the conference. While the conference will not be webcast, 100 Year Starship officials will release video footage of the plenary sessions starting the last week in October.
Follow Miriam Kramer @mirikramer and Google+. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.
- Superfast Spacecraft Propulsion Concepts (Images)
- Star Trek’s Warp Drive: Are We There Yet? | Video
- How Interstellar Space Travel Works (Infographic)
Copyright 2013 Space.com, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Amazing Bird Photos You’ll Swear Are Fake (TreeHugger)
The F-35B Sticks a $1.5T Vertical Night Landing (Business Week)
Super-Earth Found With Water-Rich Atmosphere (redOrbit)
Antarctica; a world of living ice (Home | AAAS MemberCentral)
The ‘Year Without a Summer’ (Home | AAAS MemberCentral)
Is World’s Best Restaurant Worth the 12-Month Wait? (Business Week)