Explosive volcanism on the ultraslow-spreading Gakkel ridge, Arctic Ocean

Roughly 60% of the Earth's outer surface is composed of oceanic crust formed by volcanic processes at mid-ocean ridges. Although only a small fraction of this vast volcanic terrain has been visually surveyed or sampled, the available evidence suggests that explosive eruptions are rare on mid-oc...

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Veröffentlicht in:Nature 2008-06, Vol.453 (7199), p.1236-1238
Hauptverfasser: Sohn, Robert A, Willis, Claire, Humphris, Susan, Shank, Timothy M, Singh, Hanumant, Edmonds, Henrietta N, Kunz, Clayton, Hedman, Ulf, Helmke, Elisabeth, Jakuba, Michael, Liljebladh, Bengt, Linder, Julia, Murphy, Christopher, Nakamura, Ko-ichi, Sato, Taichi, Schlindwein, Vera, Stranne, Christian, Tausenfreund, Maria, Upchurch, Lucia, Winsor, Peter, Jakobsson, Martin, Soule, Adam
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Sprache:eng
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Zusammenfassung:Roughly 60% of the Earth's outer surface is composed of oceanic crust formed by volcanic processes at mid-ocean ridges. Although only a small fraction of this vast volcanic terrain has been visually surveyed or sampled, the available evidence suggests that explosive eruptions are rare on mid-ocean ridges, particularly at depths below the critical point for seawater (3,000 m). A pyroclastic deposit has never been observed on the sea floor below 3,000 m, presumably because the volatile content of mid-ocean-ridge basalts is generally too low to produce the gas fractions required for fragmenting a magma at such high hydrostatic pressure. We employed new deep submergence technologies during an International Polar Year expedition to the Gakkel ridge in the Arctic Basin at 85° E, to acquire photographic and video images of 'zero-age' volcanic terrain on this remote, ice-covered ridge. Here we present images revealing that the axial valley at 4,000 m water depth is blanketed with unconsolidated pyroclastic deposits, including bubble wall fragments (limu o Pele), covering a large (>10 km2) area. At least 13.5 wt% CO2 is necessary to fragment magma at these depths, which is about tenfold the highest values previously measured in a mid-ocean-ridge basalt. These observations raise important questions about the accumulation and discharge of magmatic volatiles at ultraslow spreading rates on the Gakkel ridge and demonstrate that large-scale pyroclastic activity is possible along even the deepest portions of the global mid-ocean ridge volcanic system.
ISSN:0028-0836
1476-4687
1476-4679
DOI:10.1038/nature07075