Natural Hazards 2007 A review of the major hazard events of 2007, and the work of NIWA, GNS Science, and other organisations in their efforts to reduce the risks, and mitigate the effects, of natural hazards in New Zealand. More than a can of beans Disaster preparedness is a complicated business. There’s much more to it than stashing away a few cans of baked beans. Even an apparently simple matter like motivating people to create and maintain a household preparedness kit takes some smarts. The Ministry of Civil Defence & Emergency Management (MCDEM) demonstrated that last year in making the best use of heightened awareness after the Gisborne earthquake by rapidly implementing a public advertising campaign. This second annual Natural Hazards Review again highlights the range of natural hazards we experience in New Zealand: everything from lahars to coastal erosion. New Zealand scientists are working hard on answering fundamental questions about our natural hazards and taking this information all the way through to forecasting hazards and calculating likely risks. It’s smart science. An international expert review in October last year judged the NIWA weather and flood forecasting modelling systems now in use here (see pages 20–21) to be world class; and the same review panel stated that GNS Science’s Geological Hazard and Society programme (see pages 22–23) was a leading contributor to international best practice for science and application. We’re also using our expertise and knowledge to help develop science capacity internationally. I have seen first hand the valuable contribution GNS Science is making to developing Vietnam’s capacity to undertake tsunami hazard and risk assessment. And science can contribute still more to better understanding of the risks of natural hazards and to reducing the impact of these hazards on people and infrastructure. There’s a challenge here for central government: to maintain support for natural hazards research. But arguably the most vital link is getting the information to the people who need it in a clear and usable form. This review lists dozens of publications produced by scientists from the Natural Hazards Centre (GNS Science & NIWA) over the past year. I commend them for working closely with regional councils, MCDEM, the insurance industry, EQC, the Ministry for the Environment, and others across all of government and in the wider emergency management sector. This review is a great demonstration of their commitment to helping New Zealand get ready, get prepared and get thru. Hon Rick Barker, Minister of Civil Defence & Emergency Management 2 Natural Hazards 2007 Contents Hazards summary 2007 4–12 Volcanic activity 4 Landslides 4 Focus on …Mt Ruapehu’s lahars 5 Heavy rain & floods 6 Drought 6 Focus on …the Northland floods 7 Earthquakes 8 Tsunami 8 Focus on …the Gisborne earthquake 9 Wind & tornadoes 10 Coastal hazards 10 Focus on …the Taranaki tornadoes 11 Snow, hail, and electrical storms 12 Temperature 12 Insurance 13–14 2007 – an expensive year [Insurance Council] 13 The Earthquake Commission in 2007 [EQC] 14 Guidelines to assist natural hazards planning 15 Did you know …? 16–17 Government departments & hazard planning 18–19 Nine hundred civil defence events [MCDEM] 18 Developing a nationwide flood risk management policy [MFE] 19 Research in 2007 20–25 Validating our weather hazards forecasting model 20 Geological hazards and society 22 The Regional Riskscape Model 24 Publications in 2007 26–29 Selected hazard research publications 26 Selected hazard studies 28 Contributors 30 Acknowledgments 31 Natural Hazards Centre courses and conference in 2008 31 Resembling more a lake than a farm, Hikurangi Swamp soon after the July 2007 weather event in Northland. [Photo: Northland CDEM Group] Natural Hazards 2007 3 Volcanic activity New Zealand’s volcanoes were active in 2007, with a small eruption from Mt Ruapehu and signs of unrest at Mt Ngauruhoe and White Island. The largest volcanic event of 2007 was an eruption through the active crater lake at Mt Ruapehu on 25 September. This generated a blast to the north of the lake that bombarded much of the summit area with volcanic debris, and caused several small lahars. The much anticipated break-out lahar occurred earlier in the year on 18 March when the tephra dam blocking the natural outlet of the crater lake failed. There have been no eruptions at Mt Ngauruhoe since 1977, but the seismic unrest that began in 2006 continued. At Tongariro volcano, significant numbers of shallow volcanic earthquakes have been observed since 2000, but without any changes in monitored parameters and without an eruption. Hazards summary Hazards New Zealand’s other frequently active volcano, White Island, has not erupted since 2000. The water level in the crater lake rose to reach within 1 m of overflow in February 2006. The lake temperature then rose to over 60 ºC and the level began to fall as the water evaporated. By March 2007 the water level had receded by 25 m, and remains low. Two small hydrothermal eruptions occurred in Rotorua during 2007. The first was on 27 May at the mouth of the Puarenga Stream, and a smaller one occurred in late June at the former site of Malfroy’s Geyser in the Government Gardens. Source: GNS Science Landslides GNS Science recorded over 100 significant landslides in 2007. These occurred throughout New Zealand and were triggered by rainstorms, earthquakes, and volcanic eruptions. In March a climber was killed in Mt Cook National Park by falling rocks. The most common trigger of landslides was rainstorms, particularly localised high-intensity rainfall. The most significant events were in the Buller region on 17 March and in Northland on 28–29 March and 10–11 July. Two earthquakes caused shaking strong enough to cause small rock falls – a magnitude 6.5 earthquake near Raoul Island on 30 January, and a magnitude 6.7 earthquake on 16 October near George Sound in Fiordland. There were no reports of rock falls or landslides attributable to the magnitude 6.8 Gisborne earthquake on 20 December. A number of landslides in 2007 were associated with volcanoes or volcanic activity, including the lahars on Mt Ruapehu in March and September. On 10–12 November a number of small landslides were reported from the crater area on White Island. The first and largest of these landslides entered the crater lake, resulting in a small landslide-generated tsunami. The upgraded GeoNet seismograph network in the Southern Alps is detecting 2–3 rock avalanches every year. In 2007 the network detected two landslides, the first on 5 March near Mt Cook and the second on 29 August in the Young River west of Makarora at the head of Lake Wanaka. Source: GNS Science 4 Natural Hazards 2007 2007 – the year of the lahar At 10:22 on 18 March 2007, one of the most anticipated geological events of the past decade finally happened – the fragile dam of rock and ash holding back Mt Ruapehu’s summit crater lake gave way. 1.3 million m3 of warm acidic water gushed out, forming a volcanic mudflow or lahar. The torrent rushed down the steep Whangaehu gorge on the eastern flank of Mt Ruapehu, entraining five times its weight in rock debris. Within 15 minutes, it had reached the Round-the-Mountain track, 7 km downstream. A sensor array, installed and operated by GNS Science and Massey University, measured the lahar’s peak depth at over 8 m, and the ground shaking associated with the flow. Further sensors and observation teams at multiple locations downstream were able to track the evolution of the lahar from its initiation right to the coast, 155 km away, where it arrived 16 hours later. This, and other parts of the comprehensive science programme developed by New Zealand researchers in the lead-up to the lahar, has captured arguably the world’s most complete dataset on a single lahar event. The possibility of a lahar was predicted a decade in advance, so a state-of-the-art early warning system (ERLAWS) was put into place by the Department of Conservation and a consortium of local government bodies, emergency services, and infrastructure agencies. A combination of pre-emptive engineering measures, including raising and strengthening the SH47 road bridge at Tangiwai, construction of a bund at the mouth of the lahars Ruapehu’s Mt on Focus Whangaehu gorge, and installation of gates and warning lights on roads crossing the river, coupled with flawless functioning of the warning system and the actions of responding agencies on the day, resulted in no casualties and minimal property damage. This was in direct contrast to the 1953 Tangiwai disaster, when a similar break-out lahar critically damaged a bridge minutes before arrival of the Wellington-Auckland express train, which plunged into the river with the loss of 151 lives. A blue sky eruption On 25 September, just as the mud from the March lahar was drying, Mt Ruapehu came back to life with an unforeseen or ‘blue-sky’ eruption through the crater lake. Lahars were triggered in two catchments by water thrown out of the lake basin landing on the snow-clad summit of the mountain and running down its flanks. A climber in Dome Shelter, which is about 700 m from the centre of the crater lake, was seriously injured when the shelter was hit by a boulder. A small snow- slurry lahar travelled about 1 km down the Whakapapa skifield near the Far West T-bar, while several larger flows occurred in the Whangaehu valley. These flows were radically different from the March lahar, consisting of 80% or more snow, with the balance being crater lake water and rock debris.