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A Volcano under an Ice-Sheet

    Naturevolume 139page278 (1937) | Download Citation



    AT an evening meeting of the Royal Geographical Society on February 8, Dr. Niels Nielsen gave an account of volcanic eruptions in 1934 and 1936 underneath the ice-cap of Vatnajokull in Iceland. Subglacial volcanic outbursts of this character have been known for many years from the catastrophic floodsknown in Icelandic as Jokullhlaupwhich result from the melting of the ice adjacent to the hot lavas and ashes, but until the investigations of Dr. Nielsen and his collaborators, no scientific accounts of these phenomena were available. It appears likely that there are at least two types of these volcanic outburstsone, as at Grimsvotn, probably of central type, with a relatively small output of ash material but enormously energetic, forming craters in the ice; and another at Hagongur, perhaps a fissure eruption, which produced a considerable amount of lava but so little energy that it was unable to penetrate through an ice-sheet only 100-200 metres thick. The volume of glacial melt-water liberated by the first of these volcanic outbursts was in the neighbourhood of ten thousand million cubic metres. The geological interest of these remarkable phenomena is great. Following upon the University of Glasgow geological expedition to Iceland in 1924, Dr. Martin Peacock postulated that the early-glacial ‘palagonite formation’, a great series of globular basalts and tuffs which covers very extensive areas in Iceland and builds up some of the Tiighest mountains in that island, was formed by the extrusion of lavas under the thick Pleistocene ice-sheet. Dr. Nielsen (Geografisk Tidsskrift, Dec. 1936) has shown that rocks wholly similar to the palagonite formation have been formed in these recent eruptions, with the result that Peacock's hypothesis is now brought within the realms of established fact.

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