Northland Civil Defence Emergency Management Plan, 2010

VOLCANOOverviewHazardLikelihood (E)HazardConsequence(3/4)How do wemanage thisrisk?What moreshould we bedoing?What is thefuture risk?Most of New Zealand’s volcanic activity is associated with the subduction of the PacificPlate under the Australian Plate which produces many small volcanoes (0.1-1.0km3), whicherupt only once, every hundreds to thousands of years apart.Although there are no currently active volcanoes, there has been volcanic activity inNorthlands geological past with the most recent being at the Puhipuhi-Whangarei andKaihohe-Bay of Islands volcanic fields.Northland could be affected by either local or distant volcanic activity:1. Locally with a new volcanic eruption within the region, most likely within the Kaikohe-Bay of Islands volcanic field, causing ejection of basalt scoria, lava flows, acid rain, gasemission, volcanic seismicity and lightning strikes.2. A volcanic eruption outside the region causing ashfall and potentially an indirecteffect on the region if evacuees need to be accommodated.An Auckland volcano may also have other impacts such as disruption to electricity and fueldistribution in Northland.Determining recurrence intervals for renewed volcanic activity from the local fields isdifficult. A local Bay of Islands eruption recurrence interval is expected to be >1000 yearsand Whangarei much less frequent (the most recent Whangarei eruption was estimated atover 250,000 years ago).The more likely event is ash from a central North Island eruption, potentially every 50-300years. Ash volumes will depend on eruption size, duration and wind directions.SocialLocal eruption could cause loss of life/injury and displacement for prolonged periods.Ash cover may damage infrastructure and cause road and airport closures. Transportroute closures in a volcanic event may result in social impacts. Health impactsparticularly for at-risk (elderly, asthmatic, etc).Built and EconomicLocal eruption: Devastation of any buildings or infrastructure within a 1-3 km radius,or within 10km if in the path of lava flow. Volcanic activity in the higher developedtourist areas of the Bay of Islands would have a significant and long term impact ontourism in the area.Distant eruptions can impact Northland with ash cover causing widespread loss ofservices and disruption to most commercial and farming activities. Road and air travelcan be impacted and ash can also cause electrical tripping and water supplycontamination.Environmental:In a local eruption, a permanent alteration of the landscape may result. Ash may alterthe chemistry of soils and water, having a long term effect on habitats.Most events have precursor activity (e.g. seismicity; ground deformation), howeverthere is no warning system in place for local volcanism in Northland.Generally low awareness of how to respond as not perceived as a high threat inNorthland.Determine the frequency of distal ash (e.g. from TVZ; Taranaki) and its impacts.Improve the age/dating of Northland volcanic fields. Uncertainty in this area makesrecurrence intervals difficult to estimate and contentious.Assess the extent/impact of explosive volcanism in Northland.Raise awareness of potential risk and response actions.No known effects that might cause change, other than general increase in communitysize.Northland Civil Defence Emergency Management Plan, 2010-2015 Page 76