BIBLIOGRAPHIC REFERENCE Potter, S. H.; Scott, B. J.; Jolly, G. E. 2012. Caldera Unrest Management Sourcebook, GNS Science Report 2012/12. 73 p. S. H. Potter, GNS Science, Private Bag 2000, Taupo B. J. Scott, GNS Science, Private Bag 2000, Taupo G. E. Jolly, GNS Science, Private Bag 2000, Taupo © Institute of Geological and Nuclear Sciences Limited, 2012 ISSN 1177-2425 ISBN 978-0-478-19892-8 i CONTENTS KEYWORDS ....................................................................................................................... IV EXECUTIVE SUMMARY ...................................................................................................... V Likely consequences of caldera unrest ..................................................................... vi Physical hazards ........................................................................................... vi Social effects ........................................................................................... vi New Zealand caldera unrest episodes ...................................................................... vi 1. INTRODUCTION ....................................................................................................... 1 1.1 What is a caldera?.......................................................................................... 3 1.2 What is caldera unrest? .................................................................................. 4 1.3 Physical hazards during caldera unrest .......................................................... 4 1.3.1 Ground shaking .................................................................................. 5 1.3.2 Ground deformation ............................................................................ 5 1.3.3 Gas poisoning ..................................................................................... 6 1.3.4 Hydrothermal system changes ............................................................ 7 2.0 CALDERA UNREST MANAGEMENT ....................................................................... 8 2.1 Volcanic Alert Levels, Aviation Colour Code and Volcanic Alert Bulletins ..... 10 2.2 Social consequences of caldera unrest ........................................................ 12 2.2.1 Psychosocial ..................................................................................... 12 2.2.2 Economic .......................................................................................... 13 2.3 Mitigation measures for caldera unrest ......................................................... 14 2.3.1 Planning .......................................................................................... 14 2.3.2 Education and communication .......................................................... 14 2.3.3 Economic .......................................................................................... 15 2.3.4 Future research ................................................................................ 16 2.3.5 General preparation .......................................................................... 16 3.0 NEW ZEALAND’S CALDERAS – ERUPTIONS AND HISTORICAL UNREST ....... 16 3.1 Raoul Island ................................................................................................. 17 3.1.1 Eruptions .......................................................................................... 18 3.1.2 Historical unrest ................................................................................ 19 3.1.3 Potential future activity ...................................................................... 20 3.2 Macauley Caldera ........................................................................................ 20 3.3 Mayor Island / Tuhua .................................................................................... 21 3.3.1 Eruptions .......................................................................................... 22 3.3.2 Historical unrest ................................................................................ 22 3.3.3 Potential future activity ...................................................................... 22 3.4 Okataina Volcanic Centre ............................................................................. 23 3.4.1 Eruptions .......................................................................................... 24 3.4.2 Historical unrest ................................................................................ 26 3.4.3 Potential future activity ...................................................................... 27 3.5 Rotorua ........................................................................................................ 27 3.6 Kapenga ....................................................................................................... 28 3.7 Ohakuri Caldera and Maroa Volcanic Centre ............................................... 29 3.8 Reporoa ....................................................................................................... 30 3.9 Mangakino ................................................................................................... 30 3.10 Whakamaru .................................................................................................. 30 3.11 Taupo ........................................................................................................... 31 3.11.1 Eruptions .......................................................................................... 31 GNS Science Report 2012/12 ii 3.11.2 Historical unrest ................................................................................ 32 3.11.3 Potential future activity ...................................................................... 33 4.0 INTERNATIONAL CALDERAS – ERUPTIONS AND HISTORICAL UNREST ........ 34 4.1 Introduction .................................................................................................. 34 4.2 Campi Flegrei (Italy) ..................................................................................... 34 4.2.1 Eruptions .......................................................................................... 35 4.2.2 Caldera unrest .................................................................................. 38 4.3 Long Valley (USA) ........................................................................................ 40 4.3.1 Eruptions .......................................................................................... 40 4.3.2 Caldera unrest .................................................................................. 41 4.4 Rabaul (Papua New Guinea) ........................................................................ 42 4.4.1 Pre-historic eruptions ........................................................................ 43 4.4.2 Historical caldera unrest and eruptions ............................................. 43 4.5 Chaitén (Chile) ............................................................................................. 46 4.5.1 Eruptions .......................................................................................... 46 4.5.2 Caldera unrest .................................................................................. 47 4.6 Yellowstone (U.S.A.) .................................................................................... 47 4.6.1 Eruptions .......................................................................................... 47 4.6.2 Caldera unrest .................................................................................. 49 4.7 Aira Caldera and Sakurajima (Japan) ........................................................... 50 4.7.1 Eruptions .......................................................................................... 50 4.7.2 Caldera unrest .................................................................................. 51 4.8 Taal (Philippines) ......................................................................................... 52 4.9 Novarupta and Katmai (U.S.A) ..................................................................... 52 5.0 GLOSSARY ............................................................................................................ 53 6.0 REFERENCES ........................................................................................................ 58 FIGURES Figure ES1 Map of the eleven calderas in New Zealand. .................................................................................... v Figure ES2 An example of GeoNet monitoring data: earthquake epicentres at Taupo Caldera, April to September 2008................................................................................................................................ v Figure 1 Map of the geomorphic boundaries of the eight calderas within the Taupo Volcanic Zone (TVZ). Three additional calderas lie outside the old TVZ boundary, Mayor Island in the Bay of Plenty and Raoul and Macauley Islands on the Kermadec Ridge, shown in the inset map. Based on Wilson et al. (2009) and Nairn (2002). ..............................................................................2 Figure 2 St. Faith’s church (Rotorua) hydrothermal explosion deposits in 2011, caused by the leakage of a bore, seen below the window on the right-hand side. Photo by A. Somerville. .............8 Figure 3 An example of a volcanic eruption hazard map for the Okataina Volcanic Centre (Scott & Nairn, 1998). Areas with orange and red shading have a higher probability of damage, depending on vent location. ...........................................................................................................