HR: 1340h
AN: G43B-1194    [Abstracts]
TI: Continuing subsidence and deformation of the Surtsey volcano, 1991 - 2002, Iceland
AU: * Sturkell, E
EM: sturkell@hi.is
AF: Nordic Volcanological Center, University of Iceland, Sturlugata 7, Reykjavik, 101, Iceland
AU: Einarsson, P
EM: palli@raunvis.hi.is
AF: Institute of Earth Sciences, University of Iceland, Sturlugata 7, Reykjavik, 101, Iceland
AU: Geirsson, H
EM: dori@vedur.is
AF: Icelandic Meteorological Office, Bustadavegur 9, Reykjavik, 150, Iceland
AU: Moore, J G
EM: jmoore@usgs.gov
AF: US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, United States
AU: Jakobsson, S P
EM: sjak@ni.is
AF: Icelandic Museum of Natural History, Hlemmi 3, Reykjavik, 125, Iceland
AU: Sigmundsson, F
EM: fs@hi.is
AF: Nordic Volcanological Center, University of Iceland, Sturlugata 7, Reykjavik, 101, Iceland
AB: The Surtsey island was formed off the south coast of Iceland in a series of eruptions in 1963-1967. A submarine eruption was first detected on November 14, 1963, and the new island of Surtsey was built from the seafloor at 130 m depth. Two tephra cones formed above the sea level and when the magma conduit became isolated from the seawater the activity changed into lava effusion. A lava shield was produced as the lava flowed into the sea making a lava-fed delta. When the eruptions ceased the volume of Surtsey was about 0.8 km3 and with a surface of 2.65 km2. With crustal deformation observations on Surtsey, it is possible to follow the development of a pristine island. The vertical signal gives most information on the processes that are currently active. A levelling dataset, extending back to 1967, and the later GPS data give good opportunity to unravel the different processes. The GPS data improve the possibility to tie the vertical displacements to a reference frame outside the island and thus reduce the uncertainties in the absolute height determinations. Surtsey subsided rapidly during the first 10- 15 years and later on the rates decayed. The decaying rate was confirmed by GPS during 1992 to 2002. In the period 1992 - 2000 the rate was approximately 1 cm/yr, and for the 2000 - 2002 period approximately 0.5 cm/yr. The vertical displacement is not distributed uniformly over the island. The deformation processes currently active on Surtsey are: compaction of the volcanogenic material, slumping of the flanks of the island, the lithostatic load of the erupted material and compaction of the seabed sediments. Palagonitization of the tephra causes consolidation by growth of secondary minerals and thereby reduces the compaction. The amount of subsidence caused by the flexure of the lithosphere in this case is most dependent of the thickness of the elastic plate as it is the least constrained parameter. We estimate the most likely thickness to be 7-10 km. This gives a range of the total subsidence -0.53 m to -0.31 m from the load of 0.8 km3 erupted material. The compaction of the tephra and hyaloclastite is not uniform as the core of the island is palagonitized and consolidated while the flanks are still unconsolidated. The largest amount of subsidence is observed (15 cm in 11 years) along the side of the tuff cones where the lava overlays the delta. This vertical signal is non-uniformly distributed and is caused by submarine slope failure of the side of the island. The coastal erosion reduces the area of the island by one hectar per year, in the part of the island which consists of a lava-fed delta overlaid by sub-aerial lava flows. The palagonitized tuff cone is more resistant to the sea erosion as it virtually lacks open cracks. In the future only the palagonitized tuff cone will remain.
DE: 1200 GEODESY AND GRAVITY
DE: 1295 Integrations of techniques
DE: 9335 Europe
SC: Geodesy [G]
MN: 2007 Fall Meeting