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The Mysteries of an Active Volcano System: The Magma Plumbing System Gives Clues about how Oceanic Crust is formed
Until recently, researchers mostly believed that the oceanic crust is formed at mid-ocean ridges from a single magma body called the axial magma lens and located in the middle of the earth’s crust. Now, findings obtained from the East Pacific Rise, offshore Mexico, and the Juan de Fuca Ridge, offshore US and Canada, support the theory that magma stored in multiple layers within the earth’s crust is responsible for the formation of the oceanic crust. This research was recently published in Nature Geoscience.
This article is one in a series of papers on oceanic crustal formation that our team has published in the past decade in various journals, including five alone in Nature and Nature Geoscience.
The axial magma lens was for the first time imaged in 1978 across the East Pacific Rise. Magma is stored in this lens before it cools down to form rocks either abruptly by breaking to the seafloor in a volcanic eruption or gradually within the crust. Improved imaging instrumentation now allows researchers to see below this layer, and they are discovering that there are deeper lenses holding magma that can rise to the axial melt lens above to contribute to an ongoing volcanic eruption or, in absence of a volcanic eruption can gradually cool down forming the oceanic crust in situ.
Advancements in seismic equipment used to image the subsurface have meant an increase in the quality of data obtained, and a more accurate image of what’s occurring below ground.
Processes that lead to a volcanic eruption occur naturally. Pressure gradually (over years) builds within the magma lenses, while the stresses in the rocks above that keep a lid on magma diminish as the earth’s tectonic plates slowly move apart until the magma spouts to the surface. The resulting volcanic eruption last for months and releases much of the pressure that was built in the magma lenses and new cycle starts. Magma, considered lava after it erupts on the surface, cools to become the oceanic crust.
“Our new seismic images favor the emerging view that the formation of oceanic crust is much more complex than previously thought. There are processes occurring below ground that we are only beginning to see now with new equipment and advanced imaging methodology.” Mladen Nedimović, Associate Professor at Dalhousie University.
“We now see that during an eruption we may have magma moving from one level to another.” Suzanne Carbotte, coauthor and geophysicist at Columbia University’s Lamont-Doherty Earth Observatory.
“It is much less expensive to study a volcanic system that is below sea level simply because we can run a big ship towing thousands of instruments, whereas on land we would have to plant each instrument separately and that would take forever. The volcanic systems in the oceanic crust are easier to image because the crust is thinner (6 km thick), opposed to 40 km thick continental.” Mladen Nedimović, Associate Professor at Dalhousie University.
|Mladen Nedimović on a research vessel.
Photo Credit: Provided photo.
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