A review of natural hazards information for Northland Region by R. D. Beetham, M. McSaveney, G. Dellow, M. Rosenberg, D. Johnston & W. Smith Institute of Geological & Nuclear Sciences science report 2004/06 Institute of Geological & Nuclear Sciences Limited Lower Hutt, New Zealand May 2004 BIBLIOGRAPHIC REFERENCE Beetham, R. D., McSaveney, M., Dellow, G., N., Rosenberg, M., Johnston, D. & Smith, W., 2004. A review of natural hazards information for Northland Region, Institute of Geological & Nuclear Sciences science report 2004/06 25 p. R. D. Beetham, Institute of Geological & Nuclear Sciences Limited, Lower Hutt M. McSaveney, Institute of Geological & Nuclear Sciences Limited, Lower Hutt G. Dellow, Institute of Geological & Nuclear Sciences Limited, Lower Hutt M. Rosenberg, Institute of Geological & Nuclear Sciences Limited, Lower Hutt D. Johnston, Institute of Geological & Nuclear Sciences Limited, Lower Hutt W. Smith, Institute of Geological & Nuclear Sciences Limited, Lower Hutt © Institute of Geological & Nuclear Sciences Limited, 2004 ISSN 1171-9184 ISBN 0-478-09841-3 CONTENTS ABSTRACT.........................................................................................................................................................III KEYWORDS.......................................................................................................................................................III 1.0 INTRODUCTION ......................................................................................................................................1 2.0 SEISMIC HAZARD ...................................................................................................................................1 2.1 Identified gaps .....................................................................................................................2 3.0 LANDSLIDING ..........................................................................................................................................6 3.1 Introduction..........................................................................................................................6 3.2 Current knowledge...............................................................................................................6 3.3 Future development .............................................................................................................7 4.0 TSUNAMI ...................................................................................................................................................9 4.1 Identified gaps ...................................................................................................................11 5.0 VOLCANIC HAZARDS ..........................................................................................................................11 5.1 Background........................................................................................................................11 5.1.1 The Puhipuhi-Whangarei volcanic field............................................................ 11 5.1.2 The nature of volcanoes in the Kaikohe- Bay of Islands field .......................... 11 5.2 The nature of volcanic hazard............................................................................................11 5.3 Previous risk and hazards assessment................................................................................11 5.4 Suggestions for future work to improve volcanic hazard assessment ...............................11 5.5 Identified gaps ...................................................................................................................11 6.0 MINE SUBSIDENCE...............................................................................................................................11 6.1 Background........................................................................................................................11 6.2 Subsidence occurrence.......................................................................................................11 6.3 Subsidence hazard assessment...........................................................................................11 6.4 Conclusions........................................................................................................................11 7.0 RECOMMENDATIONS..........................................................................................................................11 7.1 Seismic hazard ...................................................................................................................11 7.2 Landslide hazard................................................................................................................11 7.3 Tsunami hazard..................................................................................................................11 7.4 Volcanic hazard .................................................................................................................11 7.5 Mine subsidence hazard.....................................................................................................11 8.0 ACKNOWLEDGMENTS........................................................................................................................11 9.0 REFERENCES .........................................................................................................................................11 ©Institute of Geological & A review of natural hazards information Nuclear Sciences Limited 2004 i For Northland Region FIGURES Figure 2.1 Examples of damage caused by the 1963 Peria earthquakes .......................................................3 Figure 2.2 A Modified Mercalli (MM) Intensity recurrence map for New Zealand .....................................4 Figure 2.3 A brief summary of Modified Mercalli Intensity descriptions.....................................................5 Figure 3.1 Large landslides mapped from aerial photos in the Waimamaku Valley SE of Hokianga inlet where weak silt and mudstones are overlain by strong basalt rock......................................8 Figure 4.1 Occurrence of tsunami in New Zealand since 1820.....................................................................9 Figure 4.2 Estimated tsunami-height probability-density distribution for New Zealand from the Tsunami Risks Project of the UK Tsunami initiative ................................................................10 Figure 5.1 Location of late Cenozoic basalts and associated volcanics in Northland .................................12 Figure 6.1 Coalfields in the Northland region.............................................................................................18 TABLE Table 3 Impacts of ash falls ....................................................................................................................17 ©Institute of Geological & A review of natural hazards information Nuclear Sciences Limited 2004 ii For Northland Region ABSTRACT The levels of Natural Hazards that Northland Region is exposed to, excluding floods and climatic events, are relatively low. Of the landslide, volcanic, seismic, tsunami, and mine subsidence hazards considered, the landslide hazard is assessed to be the most significant. Slope instability is common in the region and there are large areas of creeping slope failures in some rock types. However, these areas can be readily and clearly identified and action taken if required. A brief summary is shown below. Hazard Occurrence Notes Landslide Common in some rock types Affected and potentially unstable areas can be readily identified. Volcanic Two potential sources are identified Are the local centres still active? 1. local centres There is ash fall from distant 2. ash fall from distant eruptions in NZ sources in NZ, such as Taupo Region (TVZ) and Taranaki. Further study is need for both. Partially funded student theses may be a practical option for getting studies done. Seismic MM6 shaking occurs every ~1,000 years. Low hazard and small MM7 shaking every ~7,000. earthquakes <M5. No active faults known. Small earthquakes will give short duration shaking that may not have enough cycles to cause liquefaction. Microzoning studies probably not required as hazard is low. Tsunami Local and tele-tsunami sources. Local Most hazardous areas could be tsunami may be large but is a probable long readily identified. Low hazard. recurrence interval (~4,000 year) event. Tele- tsunami have been small. Mine Subsidence Localised hazard above underground coal Areas of hazard are known and mines. clearly identified for Kamo and Hikurangi. Other mines at Kiripaka, Whareora and Whauwhau may need evaluation. Mine shafts and adits are shown at Hikurangi but may need consideration at the other mines. KEYWORDS Natural hazards, Northland Region, landslide, volcanic, seismic, tsunami, mine subsidence. ©Institute of Geological & A review of natural hazards information Nuclear Sciences Limited 2004 iii For Northland Region 1.0 INTRODUCTION The Northland Region is subject to a range of natural hazards. The aim of this report is to assemble and present a review of existing information on natural hazards and their effects in the region for earthquake, tsunami, volcanic hazards, mine subsidence and landslides, and to identify “gaps” that may require additional work. The work has been undertaken by staff from GNS, Northland Region and Whangarei District Councils. 2.0 SEISMIC HAZARD Earthquake risk in Northland