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Subglacial and Intraglacial Volcanic Formations in Iceland Volcanol

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Subglacial and Intraglacial Volcanic Formations in Iceland Volcanol B. S. Harðarson, J. G. Fitton and Á. Hjartarson Reviewed research article Richards, M. A., R. A. Duncan and V. E. Courtillot 1989. Flood Storey, M., R. A. Duncan and C. Tegner 2007. Timing and dura- basalts and hot-spot tracks:/ plume heads and tails. Science tion of volcanism in the North Atlantic Igneous Province: Im- 246, 103–107. plications for geodynamics and links to the Iceland hotspot. Rossi, M. J. and A. Gudmundsson 1996. The morphology and for- Chemical Geol. 241, 264–281. mation of ow-lobe tumuli on Icelandic shield volcanoes. J. Sun, S.-S. and B. Jahn 1975. Lead and strontium isotopes in post- Subglacial and intraglacial volcanic formations in Iceland Volcanol. Geotherm. Res. 72, 291–308. glacial basalts from Iceland. Nature 255, 527–530. Sæmundsson, K. 1967. An outline of the structure of SW-Iceland. Vink, G. E. 1984. A hotspot model for Iceland and the Vøring 1 2 In: S. Björnsson ed. Iceland and Mid-Ocean Ridges, Soc. Sci. Plateau. J. Geophys. Res. 89, 9,949–9,959. Sveinn P. Jakobsson and Magnús T. Gudmundsson Islandica, Rit 38, Reykjavík, Iceland. Vogt, P. R. 1971. Asthenosphere motion recorded by the ocean 1 Sæmundsson, K. 1974. Evolution of the Axial Rifting Zone in oor south of Iceland, Earth Planet. Sci. Lett. 13, 153–160. Icelandic Institute of Natural History, Hlemmur 3, 105 Reykjavík, Iceland 2 Northern Iceland and the Tjörnes Fracture Zone. Geol. Soc. Vogt, P. R. 1983. The Iceland mantle plume: status of the hypoth- Institute of Earth Sciences, University of Iceland, Sturlugata 7, IS-101 Reykjavík, Iceland Am. Bull. 84, 495–504. esis after a decade of new work. In: Bott M. H. P., S. Saxov, [email protected] Sæmundsson, K. 1980. Outline of the geology of Iceland. Jökull M. Talwani and J. Thiede eds. Structure and Development of 29, 7–28. the Greenland-Scotland Ridge, New Methods and Concepts, Sæmundsson, K. 1986. Subaerial volcanism in the western North Plenum, New York. Atlantic. In: Vogt P. R. and B. E. Tucholke eds. The Geol- Walker, G. P. L. 1960. Zeolite zones and dike distribution in rela- ogy of North America, vol. M., The Western North Atlantic tion to the structure of basalts of eastern Iceland. J. Geol. 68, Abstract — Landforms created in eruptions within glaciers are conspicuous features of the volcanic zones Region, 69–86, Geol. Soc. Am., Boulder, Colorado. 515–528. in Iceland and eruptions occur frequently under present-day glaciers. The subglacially and intraglacially Sæmundsson K. and H. Noll 1974. K/Ar ages of rocks from Walker, G. P. L. 1963. The Breiddalur central volcano, eastern created landforms include volcanic structures like tuyas, tindars, móberg sheets, and a variety of proximal Húsafell, western Iceland,and the development of the Iceland. Quart. J. Geol. Soc. Lond. 119, 29–63. sedimentary beds. These landforms constitute a prominent part of the Móberg Formation, a term used for rocks Húsafell central volcano. Jökull 24, 40–58. Walker G. P. L. 1965. Some aspects of Quaternary volcanism in Sæmundsson, K., L. Kristjansson, I. McDougall and N. D. Iceland. Trans. Leicester. Phil. Soc. 59, 25–40. generated during the Brunhes geomagnetic epoch to the end of the Pleistocene (0.78–0.01Ma). Subglacial and 2 Watkins 1980. K-Ar dating, geological and paleomagnetic Walker G. P. L. 1966. Acid volcanic rocks in Iceland. Bull. Volc. intraglacial rocks of the Móberg Formation cover about 11,200 km of the presently ice free areas. These rocks study of a 5 km lava succession in northern Iceland. J. Geo- 29, 375–406. are predominantly basaltic and the main units of the volcanoes are pillow lava, hyaloclastite tuffs, flow-foot phys. Res. 85, 3628–3646. Walker G. P. L. 1971. Compound and simple lava ows and ood breccias, cap lavas and minor intrusions. Recent eruptions within glaciers have generated tindars and mounds, Sandwell, D. T. and W. H. F. Smith 1997. Marine gravity anomaly basalts. Bull. Volc. 35, 579–590. from Geosat and ERS-1 satellite altimetry. J. Geophys. Res. Walker, G. P. L. 1975. Excess spreading axes and spreading rate lead to the formation of widespread basaltic tephra layers, and caused major jökulhlaups. No intraglacial tuya- 102, 10,039–10,054. in Iceland. Nature 255, 468–470. forming eruptions have been observed. Much of the basaltic glass formed in subglacial eruptions during the Schilling, J.-G. 1973. Iceland mantle plume: Geochemical study Watkins, N. D. and G. P. L. Walker 1977. Magnetostratigraphy of Pleistocene has been altered to palagonite, forming consolidated edifices resistant to glacier erosion. Data from Eastern Iceland. Am. J. Sci. 277, 513–584. of the Reykjanes Ridge. Nature 242, 565–571. recent submarine and subglacial eruptions (Surtsey 1963–1967, Gjálp 1996) indicate that palagonitization and Schilling, J.-G., P. S. Meyer and R. H. Kingsley 1982. Evolution Watkins, N. D., I. McDougall and L. Kristjansson 1977. Upper of the Iceland hotspot. Nature 296, 313–320. Miocene and Pliocene geomagnetic secular variation in the consolidationtakes place during the first years after eruption driven by mild hydrothermal activity in the interior Schilling, J.-G., P. S. Meyer and R. H. Kingsley 1983. Rare el- Borgarfjördur area of western Iceland. Geophys. J. R. Astr. parts of the edifices. On the outer slopes of the volcanoes the alteration of the hyaloclastites is dominantly ement geochemistry of Iceland basalts: spatial and tempo- Soc. 49, 609–632. diagenetic. The height of tuyas and tindar in Iceland indicates that they were formed within a glacier that ral variations. In: Bott M. H. P., S. Saxov, M. Talwani and Welke, H., S. Moorbath, G. L. Cumming and H. Sigurdsson 1968. J. Thiede eds. Structure and development of the Greenland- Lead isotope studies on igneous rocks from Iceland. Earth was considerably less than 1 km thick and probably smaller than the Weichselian ice sheet at its maximum. A Scotland Ridge. New Methods and Concepts, Plenum, New Planet. Sci. Lett. 4, 221–231. possible explanation for this might be that tuya-forming eruptions in Iceland were linked to increased magma York. White N. and B. Lovell 1997. Measuring the pulse of a plume generation caused by declining pressure in the mantle under a decreasing ice sheet. Shen, Y., S. C. Solomon, I. Th. Bjarnason and C. J. Wolfe 1998. with sedimentary record. Nature 387, 888–891. Seismic evidence for a lower-mantle origin of the Iceland White R. S., J. W. Brown and J. R. Smallwood 1995. The temper- plume. Nature 395, 62–65. ature of the Iceland plume and origin of outward-propagating INTRODUCTION submarine and subaqueous eruptions (e.g. Moore and V-shaped ridges. J. Geol. Soc. London 152, 1039–1045. Sigmundsson, F. 2006. Iceland Geodynamics. Crustal Deforma- Calk, 1991; Smellie, 2000, 2006; Gudmundsson et tions and Divergent Plate tectonics. Praxis Publishing, Chis- Wolfe, C. J., I. Th. Bjarnason, J. C. VanDecar and S. Solomon Interaction of water and magma has a major effect on 1997. Seismic structure of the Iceland mantle plume. Nature al., 2004). ester, UK. the style of volcanic activity and the morphology of Sigurdsson, H. 1970. The petrology of the Setberg volcanic region 385, 245–247. and of the intermediate and acid rocks of Iceland. Unpubl. Wood D. A. 1978. Major and trace element variations in the Ter- volcanic landforms. At high water pressures effusive Volcanic activity within glaciers has been and still Ph.D. thesis, Univ. Durham, Durham, England. tiary lavas of eastern Iceland and their signicance with re- activity dominates leading to pillow lava formation, is very common in Iceland (e.g. Kjartansson 1960; Sigvaldason, G. E. and S. Steinthorsson 1974. Chemistry of spect to the Iceland geochemical anomaly. J. Petrol. 19, 394– while at lower pressures magma fragmentation and Saemundsson, 1980; Gudmundsson, 2005). The 436. tholeiitic basalts from Iceland and their relation to the Kverk- explosive activity are most common (e.g. Wohletz, terms subglacial and intraglacial are often used to fjöll hot spot. In: Kristjansson L. ed. Geodynamics of Iceland Wood D. A. 1979. Dynamic partial melting: its application to the and the North Atlantic Area. D. Reidel Publ. Company, Hol- petrogenesis of basalts erupted in Iceland, the Faroe Islands, 1986; Stroncik and Schmincke, 2002; White et al., classify the volcanic eruptions and the resulting land- land, 154–164. the Isle of Skye (Scotland) and the Troodos Massif (Cyprus). 2000; Chapman et al., 2000). Eruptions under ice forms. Strictly speaking, the term subglacial only Símonarson, L. A. and J. Eiríksson 2008. Tjörnes - Pliocene and Geochim. Cosmochim. Acta 43, 1031–1046. share the same characteristics in terms of style of vol- applies to processes occurring under ice cover with- Pleistocene sediments and faunas. Jökull 58, this issue. Wood D. A., J. L. Joron, M. Treuil, M. Norry and J. Tarney canic activity while ice confinement and changes in out direct contact with the atmosphere. The term Steinthorsson, S., N. Oskarsson and G. E. Sigvaldason 1985. Ori- 1979. Elemental and Sr isotope variations in basic lavas from gin of alkali basalts in Iceland: a plate tectonic model. J. Geo- water level due to drainage of meltwater are among intraglacial is more general since it also applies to Iceland and the surrounding ocean oor. Contrib. Mineral. phys. Res. 90, 10,027–10,042. features that distinguish subglacial volcanism from eruptions and volcanoes that have broken through the Petrol. 70, 319–339. 178 JÖKULL No. 58, 2008 JÖKULL No. 58, 2008 179 S. P. Jakobsson and M. T. Gudmundsson Subglacial and intraglacial volcanic formations in Iceland glacier. About 20% of the active volcanic zones is clastites (Table 1) and cap lavas, have sometimes been 24°W 22°W 20°W 18°W 16°W 14°W at present ice covered, including many of the most called the Móberg Formation sensu stricto (Kjart- active central volcanoes such as Grímsvötn and Katla ansson 1960).
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