1. The Global Volcano Model (GVM; http://globalvolcanomodel.org/) was launched in 2011 and has grown to include 31 partner institutes collaborating from across the globe representing scientists from disciplines including volcanology, engineering and social science as well as private sector institutions. GVM is an international collaborative platform to integrate information on volcanoes from the perspective of forecasting, hazard assessment and risk mapping. The network aims to provide open access systematic evidence, data and analysis of volcanic hazards and risk on global and regional scales, and to support Volcano Observatories at a local scale. 2. The International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI; http://www.iavcei.org/) is an association of the International Union of Geodesy and Geophysics (IUGG). IAVCEI is the international association for volcanology with about 2000 members. The Association represents the primary international focus for: (1) research in volcanology, (2) efforts to mitigate volcanic disasters, and (3) research into closely related disciplines. There are 22 topic focussed Commissions of IAVCEI covering all aspects of volcanology, including hazards and risk. Contributors to report Prepared by: Brown, S.K.1, Loughlin, S.C.2, Sparks, R.S.J.1, and Vye-Brown, C.2 Reviewed by: Barclay, J.3, Calder, E.4, Cottrell, E.5, Jolly, G.6, Komorowski, J-C.7, Mandeville, C.8, Newhall, C.9, Palma, J.10, Potter, S.6, and Valentine, G.11 Content and Case Study Andreastuti, S.12, Aspinall, W.1,13, Auker, M.R.1, Baptie, B.2, Barclay, contributors: J.3, Baxter, P.14, Biggs, J.1, Calder, E.S.4, Costa, A.15, Cottrell, E.5, Crosweller, S.1, Daud, S.17, Delgado-Granados, H.16, Deligne, N.I.6, Ewert, J.8, Felton, C.17, Gottsman, J.1, Hincks, T.1, Horwell, C.18, Ilyinskaya, E.2, Jenkins, S.F.1, Jolly, G.6, Kamanyire, R.19, Karume, K.20, Kilburn, C.21, Komorowski, J-C.7, Leonard, G.6, Lindsay, J.M.6, Lombana-Criollo, C.22, Macedonio, G.15, Mandeville, C.8, Marti, J.23, Marzocchi, W.15, Mee, K.2, Mothes, P.24, Newhall, C.9, Oddsson, B.25; Ogburn, S.E.11, Ortiz Guerrero, N.16,22, Pallister, J.26, Palma, J.10, Poland, M.27, Potter, S.6, Pritchard, M.28, Ramon, P.24, Sandri L.15, Sayudi, D.12; Selva, J.15, Solidum, R.U.29, Stewart, C.30, Stone, J.3, Subandriyo, J.12, Sumarti, S.12, Surono,12 , Tonini, R.15, Valentine, G.11, Wadge, G.31, Wagner, K.11, Webley, P.32, Wilson, T.M.33 Institutions: 1University of Bristol, UK; 2British Geological Survey, UK; 3University of East Anglia, UK; 4University of Edinburgh, UK; 5Smithsonian Institution, USA; 6GNS Science, New Zealand; 7Institut de Physique du Globe de Paris, France; 8U.S. Geological Survey, USA; 9Earth Observatory of Singapore, Singapore; 10University of Concepcion, Chile; 11University at Buffalo, USA; 12Geological Agency of Indonesia, Indonesia; 13Aspinall & Associates, UK; 14University of Cambridge, UK; 15Istituto Nazionale di Geofisica e Vulcanologia, Italy; 16Universidad Nacional Autónoma de México, México; 17Civil Contingencies Secretariat, Cabinet Office, UK; 18Durham University, UK; 19Public Health England, UK; 20Observatoire Volcanologique de Goma, DRC; 21University College London, UK; 22 Universidad Mariana, Colombia; 23Consejo Superior de Investigaciones Científicas, Spain; 24Instituo Geofísico EPN, Ecuador; 25Department of Civil Protection and Emergency Management, Iceland; 26Volcano Disaster Assistance Program, US Geological Survey, USA; 27Hawaiian Volcano Observatory, U.S. Geological Survey, USA; 28Cornell University, USA; 29Philippine Institute of Volcanology and Seismology, Philippines; 30Massey University, New Zealand; 31University of Reading, UK; 32Alaska Volcano Observatory, USA; 33University of Canterbury, New Zealand. Acknowledgments We are indebted to colleagues around the world in the volcanological community who have generated the contemporary understanding of volcanoes on which this study draws. Support for this work was provided by the European Research Council and the Natural Environment Research Council of the UK (NERC) through their International Opportunities Fund. This is Section II of IV of the GVM/IAVCEI contribution to the UN ISDR GAR-15. Suggested citation: Brown, S.K., Loughlin, S.C., Sparks, R.S.J., Vye-Brown, C. et al. (2014) Global volcanic hazards and risk: Technical background paper for the Global Assessment Report on Disaster Risk Reduction 2015. Global Volcano Model and IAVCEI. Cover image: The incandescent lava dome at the summit of Soufriere Hills Volcano, Montserrat. Photograph by Paul Cole. Contents 1 Introduction .................................................................................................................................... 1 2 Background on volcanoes and volcanic eruptions .......................................................................... 3 2.1 Causes of volcanism ................................................................................................................ 3 2.2 Magma .................................................................................................................................... 5 2.3 Magma chambers ................................................................................................................... 5 2.4 Types of volcanoes .................................................................................................................. 7 2.5 Styles of eruption .................................................................................................................... 9 2.6 Size and intensity of eruptions .............................................................................................. 12 3 Volcanoes and volcanic eruptions ................................................................................................ 13 3.1 Volcano inventory ................................................................................................................. 13 3.2 Rates of eruption .................................................................................................................. 14 3.3 Examples of volcanic activity ................................................................................................ 15 4 Volcanic hazards and their impact ................................................................................................ 20 4.1 Ballistics ................................................................................................................................. 21 4.2 Volcanic ash and tephra ........................................................................................................ 22 4.3 Pyroclastic flows and surges ................................................................................................. 23 4.4 Lahars and floods .................................................................................................................. 24 4.5 Debris avalanches, landslides and tsunamis ......................................................................... 24 4.6 Volcanic gases ....................................................................................................................... 25 4.7 Lava ....................................................................................................................................... 25 4.8 Volcanic earthquakes ............................................................................................................ 26 4.9 Lightning ................................................................................................................................ 26 4.10 Environmental and secondary effects on communities ....................................................... 26 4.11 Fatalities ................................................................................................................................ 26 5 Monitoring and forecasting volcanic eruptions ............................................................................ 29 5.1 Monitoring ............................................................................................................................ 31 5.2 Volcanic unrest ...................................................................................................................... 37 5.3 Forecasting and early warning .............................................................................................. 38 5.4 Volcano Observatories .......................................................................................................... 39 5.5 Volcano Observatories and aviation safety .......................................................................... 40 5.6 Global monitoring capacity ................................................................................................... 42 5.7 Low-cost systems for monitoring volcanoes in repose ......................................................... 43 6 Assessing volcanic hazards and risk .............................................................................................. 43 6.1 Hazard maps ......................................................................................................................... 44 6.2 Probabilistic hazard and risk assessment.............................................................................. 46 6.3 Event trees ............................................................................................................................ 47 6.4 Exposure and vulnerability...................................................................................................