Explosive volcanism on the ultraslow-spreading Gakkel ridge, Arctic Ocean
Abstract
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 (3,000m). A pyroclastic deposit has never been observed on the sea floor below 3,000m, 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 4,000m water depth is blanketed with unconsolidated pyroclastic deposits, including bubble wall fragments (limuoPele), covering a large (>10km2) area. At least 13.5wt% 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.
- Publication:
-
Nature
- Pub Date:
- June 2008
- DOI:
- 10.1038/nature07075
- Bibcode:
- 2008Natur.453.1236S