geology

Deep-sea volcanoes air volatile side

MCGILL (CAN) — Deep-sea volcanoes do more than gush magma flow—in some cases high concentrations of CO2 cause massive underwater explosions.

Between 75 and 80 percent of all volcanic activity on Earth takes place at deep-sea, mid-ocean ridges. Most produce effusive lava flows rather than explosive eruptions, both because the levels of magmatic gas tends to be low, and because the volcanoes are under a lot of pressure from the surrounding water.

Geologists have speculated for the last 10 years that, based on the presence of volcanic ash in certain sites, explosive eruptions can also occur. But no one has been able to prove it until now.

Using an ion microprobe, Christoph Helo, a PhD student of earth and planetary science at McGill University discovered extremely high concentrations of CO2 in droplets of magma trapped within crystals recovered from volcanic ash deposits on Axial Volcano on the Juan de Fuca Ridge, off the coast of Oregon.

The research is reported in the journal Nature Geoscience.

The entrapped droplets represent the state of the magma prior to eruption, proof  that explosive eruptions can indeed occur in deep-sea volcanoes. The work also shows that the release of CO2 from the deeper mantle to the Earth’s atmosphere, at least in certain parts of mid-ocean ridges, is much higher than had previously been imagined.

Given that mid-ocean ridges constitute the largest volcanic system on Earth, this discovery has important implications for the global carbon cycle which have yet to be explored.

Researchers from Monterey Bay Aquarium Research Institute and the Woods Hole Oceanographic Institution contributed to the study.

More news from McGill University: www.mcgill.ca/newsroom/

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