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MPV-05 Volcanic eruptions: Chamber-, conduit-, and depositional processes and their implication for monitoring and hazard assessment
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Current crustal deformation at volcanoes in Iceland
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Erik Sturkell, Nordic Volcanological Center, University of Iceland (Iceland)
Pall Einarsson, Institute of Earth Sciences, University of Iceland (Iceland)
Freysteinn Sigmundsson, Nordic Volcanological Center, University of Iceland (Iceland)
Benedikt G. Ofeigsson, Institute of Earth Sciences, University of Iceland (Iceland)
Halldor Geirsson, Physics Department, Icelandic Meteorological Office (Iceland)
Rikke Pedersen, Nordic Volcanological Center, University of Iceland (Iceland)
Thora Arnadottir, Nordic Volcanological Center, University of Iceland (Iceland)
Halldor Olafsson, Nordic Volcanological Center, University of Iceland (Iceland)
Elske de Zeeuw-van Dalfsen, Institut de physique du Globe. Equipe de Dynamique des Fluides Geologiques (France)
Alan T. Linde, Department of Terrestrial Magnetism, Carnegie Institution of Washington (United States)
Selwyn I. Sacks, Department of Terrestrial Magnetism, Carnegie Institution of Washington (United States)
Pete C. LaFemina, Department of Geosciences,Pennsylvania State University University Park (United States)
Carolina Pagli, School of Earth and Environment, University of Leeds (United Kingdom)
Thierry Villemin, Laboratoire Environnements Dynamiques et Territoires de Monagne, Université de Savoie (France)
Hazel Rymer, Volcano Dynamics Group, Department of Earth Sciences, The Open University (United Kingdom)
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The high rate of magmatism in Iceland is caused by the interaction between the Iceland hotspot and the divergent mid-Atlantic plate boundary. Iceland hosts about 35 volcanoes or volcanic systems that are active. In the last hundred years unrest has occurred at 11 different volcanoes, with one to several eruptions or intrusions. An eruption takes place every two to three years on average in Iceland. Here we review the achievements of volcano geodesy in Iceland using a variety of geodetic techniques, including leveling, electronic distance measurements, campaign and continuous Global Positioning System (GPS) geodesy, and interferometric analysis of synthetic aperture radar images (InSAR). The geodetic techniques are complemented with seismic and micro-gravity methods. Seismic monitoring is an important tool to follow magma movements. Results from these measurements provide a comprehensive view of the behavior of Icelandic volcanoes. Between inflation, intrusion, and eruption episodes, volcanoes are likely to deflate or show no sign of activity. Subsidence rates are often in the range of a few millimeters to a few centimeters a year, decreasing progressively with time since the last eruption or intrusion at the volcano. Subsidence in volcanoes is commonly aseismic and can only be detected by geodetic means. Cooling and consequent contraction of magma will cause subsidence above the magma chamber. This process may also be accompanied by drainage of the magma chamber. Volcano subsidence or lack of deformation is often interrupted by episodic magma flow to shallow levels. Such magma recharge has been observed geodetically at Hengill, Hekla, Eyjafjallajökull, Katla, Grimsvö ötn, and Krafla volcanoes, with inflow inferred to last from a few months up to two decades. In recent years, the Grimsvötn and Katla volcanoes have exhibited continuous inflation of a few centimeters per year, which at Grimsvötn culminated in an eruption on 1 November 2004. Inflation at Katla began in 1999, but slowed down in 2004. Currently the deformation rate is low at Katla. The deformation within the Torfajökull volcano is dominated by low rate subsidence in its central part. Most volcanoes give several long-term precursors such as increase in the seismic activity; land rise and a net microgravity increase as magma accumulates under the volcano. Hekla is an exception as it shows few long-term precursors prior to eruptions; optical tilt, GPS and InSAR give indications of magma accumulation under the volcano. The short-time precursors, spanning less than 80 minutes before the eruption, are seismic unrest and strain changes. Hekla deflated during the eruptions of 1991 and 2000 but has now re-inflated to its pre-eruption level. A time series of ground tilt at a station 11 km west of Hekla summit indicates magma pressure at the same scale as prior to the two most recent eruptions, suggesting short time until the next eruption.
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