Deep-sea Volcanoes Proven to Explode
|Bands of glowing magma from submarine volcano. McGill geology researchers’ discovery of high concentrations of CO2 at mid-ocean ridges?confirms explosive nature of certain volcanic eruptions. Courtesy of NOAA/National Science Foundation|
Between 75 and 80 percent of all volcanic activity on Earth takes place at deep-sea, mid-ocean ridges. Most of these volcanoes produce effusive lava flows rather than explosive eruptions, both because the levels of magmatic gas (which fuel the explosions and are made up of a variety of components, including, most importantly CO2) tend to be low, and because the volcanoes are under a lot of pressure from the surrounding water.
Over about the last 10 years, however, geologists have speculated that explosive eruptions also can occur in deep-sea volcanoes, based on the presence of volcanic ash in certain sites. But, no one has been able to prove it until now.
By using an ion microprobe, Christoph Helo, a Ph.D. student in McGill University’s Department of Earth and Planetary Sciences, has discovered very 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.
These entrapped droplets represent the state of the magma prior to eruption. As a result, Helo and fellow researchers from McGill, the Monterey Bay Aquarium Research Institute, and the Woods Hole Oceanographic Institution, have been able to prove that explosive eruptions can indeed occur in deep-sea volcanoes. Their 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 that have yet to be explored.
This research was funded by R.H.Tomlinson, GEOTOP, and J.W. McConnell Memorial Fellowships
David and Lucille Packard Foundation; Natural Sciences and Research Council of Canada (NSERC).
For an abstract of the article, visit: http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1104.html