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March 29th, 2017
7:00-8:30 PM

Kirkwood Station Brewing Co., Kirkwood, MO

What Goes Down Must Come Up:
The Mariana Trench and the Earth's Deep Water Cycle

Robert S. Brookings Distinguished Professor of Earth and Planetary Sciences

Moderated by: Cynthia Wichelman, M.D.

Have you ever wondered where the lava and gasses that erupt from volcanoes come from? Most of the known volcanoes worldwide occur along subduction zones, where one of Earth's huge tectonic plates dives deep into the planet's interior. For these volcanoes, the composition of the erupted material shows that much of it was previously carried down from the ocean floor into the Earth's interior at deep ocean trenches. Water is a key part of this process, since water lowers the melting point of the Earth's mantle rocks, allowing them to melt and form magma. To study the relationship between subduction and melting, my research group deployed ocean bottom seismographs (OBSs) to depths of up to 4 miles beneath the surface at the Mariana and Tonga Trenches. The seismographs remained on the ocean bottom for up to one year recording seismic waves from earthquakes. We used these seismic signals to image the Earth's structure and to trace the pathways of the down-going water and rocks, as well as of the rising magma generated beneath the volcanoes. Our results show that a large amount of ocean water is incorporated into the subducting plate at the deep ocean trenches, where it moves down cracks and faults created as the plate bends and reacts with rocks to form the hydrous mineral serpentinite. The water is then carried down to depths of about 60 miles where it is released from the plate and causes the hot mantle to melt, forming magma that moves to the surface and erupts from the volcanoes at nearby islands. An important unresolved question is whether the amount of water coming out of the deep earth is equal to the amount going in, or if there is a net flux of water into or out of the Earth's interior over geologic time.

Science On Tap highlighted on St. Louis Public Radio and Voice of America!

Science On Tap is a place where, for the price of a beverage, anyone can come to explore the latest ideas in science and technology. Meetings take place outside a traditional academic context, at the Kirkwood Station Restaurant & Brewing Co.

Meetings are held on the last Wednesday of the month during the academic year, usually from 7:00 - 8:30 PM. The standard format is as follows: about 45 minutes of presentation, followed by discussion until 8:30 PM.

Kirkwood Station Restaurant & Brewing Co.
105 E. Jefferson Ave.
Kirkwood, MO 63122

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For more information: e-mail scienceontap@wustl.edu
or call (314) 935-9495

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