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Sökning: L773:0028 0836 OR L773:1476 4687 > (2000-2009) > Samhällsvetenskap

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1.
  • Gustafsson, Bengt (författare)
  • Sanctions against scientists threaten progress
  • 2009
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 461:7265, s. 723-723
  • Tidskriftsartikel (refereegranskat)
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2.
  • Nyberg, Johan, et al. (författare)
  • Is recent major hurricane activity normal? Reply
  • 2008
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 451:7181, s. E6-E6
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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  • Sohn, Robert A., et al. (författare)
  • Explosive volcanism on the ultraslow-spreading Gakkel ridge, Arctic Ocean
  • 2008
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 453:7199, s. 1236-1238
  • Tidskriftsartikel (refereegranskat)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 (3,000 m)1. 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)2, covering a large (>10 km2) area. At least 13.5 wt% CO2 is necessary to fragment magma at these depths3, which is about tenfold the highest values previously measured in a mid-ocean-ridge basalt4. These observations raise important questions about the accumulation and discharge of magmatic volatiles at ultraslow spreading rates on the Gakkel ridge5 and demonstrate that large-scale pyroclastic activity is possible along even the deepest portions of the global mid-ocean ridge volcanic system.
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  • Resultat 1-6 av 6

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