Arctic Gakkel Ridge Eruption Reveals Magma From Earth's Mantle
Boulder, Colo.It's exciting to be the first scientist to observe a volcanic eruption on an ultraslow-spreading mid-ocean ridge, an event in and of itself that rarely occurs. Even better is discovering that the USS Hawkbill, a submarine equipped with scientific mapping tools, just happened to have passed by at the same time and recorded the event while the scientists on board were completely unaware of the eruption.
Intense seismic activity began in Gakkel Ridge in January of 1999 and continued for seven months. Gakkel Ridge, the slowest spreading ridge in the world, is located in the Arctic Basin. Initial reports, such as the one published in the February 15, 2001 issue of NATURE magazine, have sparked much interest in the area culminating in the recent excursion of the U.S. Coast Guard icebreaker Healy.
Maya Tolstoy, an Associate Research Scientist at the Lamont-Doherty Earth Observatory at Columbia University, was the first scientist to discover these volcanic eruptions and she was a co-author of the NATURE article.
More recently, she discovered that the magma body, which was the source of the eruption, might have come from the mantle of the Earth and not the crust. She reports these new findings in the December issue of GEOLOGY.
"While there have been various pieces of geological and geophysical evidence that magma bodies might exist in the mantle, this is the first time that we have had evidence that they could be the direct source of a seafloor eruption," she said.
Before this discovery, scientists generally thought that eruptions were caused by mid-crustal magma bodies. Now they can better understand how the crust is formed and how volcanic eruptions occur at ultraslow-spreading rate, mid-ocean ridges.
"This means that a crustal magma body might not be necessary for a ridge to have an eruption," Tolstoy said. "It will also have an effect on the geochemistry of the crust that is formed, since the travel path/transit time of the magma will be affected. In locations where this is occurring, it gives geochemists the opportunity to sample rocks that have come directly from the mantle."
Tolstoy happened to discover the Gakkel eruptions in the summer of 1999 when she was looking at Arctic seismic data for a hydroacoustic monitoring project.
"As I looked through the historic data, I saw the early 1999 swarms and thought that if ever we were to see volcanism on an ultraslow-spreading ridge, this is what it would look like. The volcanism we see in the Pacific is much shorter lived with lower magnitude events, but with the cold brittle crust at an ultraslow-spreading ridge, you might expect it to take a lot more work (and hence larger eruption) to break through it.
"Having convinced myself that it was probably an eruption, I started looking around for other data that might confirm this. The USS Hawkbill just happened to be in the area, and in fact they didn't even know the swarm had occurred until many months after they had returned. It was just luck that they had gone over the right area at the right time."
The Lamont-Doherty Earth Observatory is a leading research center examining the planet from its core to its atmosphere, across every continent and every ocean. From global climate change to earthquakes, volcanoes, shrinking resources, environmental hazards, and beyond, LDEO scientists continue to provide the basic knowledge of earth systems that must inform the difficult choices needed to maintain the health and habitability of our planet.
By Kara LeBeau, GSA Staff Writer
Associate Research Scientist
Lamont-Doherty Earth Observatory
Palisades, NY 10964-8000.
Phone: (Temporarily at UCLA) 310-825-9296; otherwise, call 845-365-8791
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Geological Society of America: www.geosociety.org
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