Natural Hazards 2009 Natural Hazards 2009 A review of New Zealand’s major hazard events of 2009, 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. They thought ‘it won’t happen here’, but it did Many New Zealanders were directly and tragically affected by the Samoan earthquake and subsequent tsunami on 29 September 2009, which killed 226 people. It took only 10 to 20 minutes for the waves to reach the Samoan coast. Filomena Nelson, Principal Disaster Manager in Apia, Samoa, describes that terrible day (p 16, 17). She tells of how villagers who had taken heed of drills and warnings felt that their lives had been saved as a result; those who thought ‘it won’t happen here’ may have been slower to react. Closer to home, New Zealanders were lucky that the massive (magnitude 7.8) Fiordland earthquake in July 2009 was so remote. This earthquake was the biggest to strike New Zealand since the 1931 Hawke’s Bay quake, when 256 people were killed. These events remind us of how vulnerable we are to natural hazards, and how important it is to be prepared. The better we understand why and how natural hazards happen, the better we can forecast them and the safer we will be. That’s where science is so critical. The new Natural Hazards Research Platform (p18) is a bold initiative, introducing a more stable, long-term, and productive research structure. Natural hazards researchers have long been recognised as a cohesive group, with strong links to end users, including the civil defence and emergency management community, the Earthquake Commission, policy makers, planners and engineers. The Platform will encourage collaboration, rather than competition, between those scientists and end users to the benefit of all New Zealanders. The need for a stable, long-term research environment is a recurring plea from scientists, so it’s no surprise that the value of accurate long-term data sets is a theme of a number of the articles in this fourth Natural Hazards Review. All this data collection is not an ‘academic’ exercise; it’s fundamental to reducing property damage and saving lives. By looking back we can look forward, and begin to predict the impacts of long-term environmental changes on hazard probability and scope. NIWA’s new and growing Snow and Ice Monitoring Network is a good example of an innovative data-collection system which will increase understanding of alpine hazards and could ultimately save lives. Congratulations again to NIWA and GNS Science for bringing together Natural Hazards 2009, and to the Ministry of Civil Defence and Emergency Management, the Earthquake Commission, and the Insurance Council for working closely with scientists. It’s a valuable reference, outlining the great work researchers and end users do together. Hon John Carter Minister of Civil Defence Contents Hazard summary 2009 4-12 Earthquakes 4 Tsunami 4 Focus on … the Samoan tsunami 5 Landslides 6 Heavy rain & floods 6 Focus on … Waihi landslides 7 Snow, hail, & electrical storms 8 Temperature 8 Focus on … avalanches 9 Wind & tornadoes 10 Drought 10 Focus on … tornadoes 11 Volcanic activity 12 Coastal hazards 12 Insurance, EQC, and civil defence in 2009 13–15 A benign year for natural disaster claims (Insurance Council) 13 The Earthquake Commission in 2009 (EQC) 14 Hazard notifications & the National Warning System (MCDEM) 15 The deadly day of the tsunami 16–17 A new structure for natural hazards research 18 Encapsulating historic weather events 19 Research in 2009 20–25 The value of sustained observations in hazard forecasting 20 Geological hazards and society 22 RiskScape – putting science into practice 24 Communicating and applying our science 26–29 Research publications 26 Popular articles 27 Hazard studies 28 Contributors 30 Acknowledgments 31 Australasian natural hazards conference 31 The Steaming Cliffs above Waihi village, Hipaua geothermal area. Photo: Graham Hancox, GNS Science Earthquakes On 15 July the largest earthquake since the 1931 Napier earthquake struck remote Dusky Sound in Fiordland. The magnitude 7.8 earthquake was felt throughout the South Island and mainly on the western side of the lower North Island. Luckily damage was limited. The largest aftershock was magnitude 6.1 and occurred 20 minutes after the main shock. Two deep earthquakes of magnitude 6.1 were the other largest earthquakes of the year. The first was on 21 March at a depth of 160 km and centred 30 km northwest of Whakatane; the second, on 1 September, was at a depth 280 km and centred Hazards summary Hazards 120 km north of Whakatane. On 27 June, two shallow earthquakes (magnitude 4.3 and 4.4) centred about 5 km northwest of Turangi were felt at the southern end of Lake Taupo. These were the largest of a swarm of several hundred earthquakes that commenced in late May; Waihi village was evacuated because of landslide risk. Five earthquakes outside the New Zealand region were felt. On 20 March a shallow magnitude 7.6 quake centred in the Tonga Islands, about 2000 km northeast of Auckland, was felt on the eastern side of the North Island and in Nelson. The magnitude 8.1 Samoan earthquake on 30 September was not felt here. In 2009, a total of 42 earthquakes of magnitude 5.0 or greater occurred. 392 earthquakes were reported felt on the GeoNet website. Apart from the Dusky Sound earthquake and its aftershocks, this was a relatively quiet year for earthquakes in New Zealand. Source: GNS Science Tsunami Four tsunamis were recorded by coastal sea-level gauges around New Zealand in 2009, but no reported damage occurred. In order of wave-height size in New Zealand these tsunamis were: 1. On 15 July a tsunami originated from Dusky Sound in Fiordland, the result of a magnitude 7.8 earthquake. The highest wave was 0.97 m, recorded at Jackson Bay 2.5 hours after the earthquake. A wave of 0.5 m was recorded at Charleston. Fortunately the largest waves occurred soon after low tide. 2. On 30 September (29 September local Samoan time) a magnitude 8.1 earthquake to the south of Samoa caused the devastating Samoan tsunami. The first waves reached the Chatham Islands and the North Island (East Cape) at 4.2 and 5 hours after the earthquake respectively. The largest wave recorded here was 0.9 m at Kaingaroa (Chatham Islands), nearly 2 hours after the first wave. Wave heights over 0.5 m were recorded at East Cape, Mt Maunganui and Timaru and on the west coast at Jackson Bay and Charleston. Peak waves at Christchurch (Sumner) and Port Taranaki occurred more than 12–13 hours after the first waves. 3. On 8 October a magnitude 7.3 earthquake in northern 2009 Vanuatu caused a small tsunami that was recorded at four sites on the west coast from New Plymouth to Jackson Bay and on the Chatham Islands. 4. On 20 March a magnitude 7.3 earthquake south of Tonga caused a small tsunami that was directed mainly eastwards and Sources: NIWA, PrimePort Timaru, Environment Waikato, Northland Regional Council, Port Taranaki Ltd., Lyttelton Port Co. Ltd., GeoNet/LINZ, Natural Hazards Natural Hazards sideswiped the Chatham Islands (peak wave height of around 0.2 m, 9 hours after the first waves arrived). Bureau of Meteorology (Australia) 4 The Samoan tsunami – what can we learn? On 29 September 2009 a shallow magnitude 8.1 earthquake caused a catastrophic tsunami which hit Samoa, American Samoa, and northern Tonga. Two hundred and twenty six people died as two to three waves of up to five metres high swept in from the Pacific. Water travelled inland for over 500 metres in some places. The Pacific community responded immediately with aid; a joint NIWA/GNS Science team was deployed to bring longer-term lessons home to help New Zealand and other Pacific Islands become better prepared for future tsunami. Looking beyond the human suffering Trees or dense vegetation afforded some protection by One of our roles was to look beyond the immediate reducing the energy of incoming waves. But when the the Samoan tsunami human suffering and objectively assess damage to shielding or ‘protection’ itself became debris, damage buildings. Building construction in American Samoa and, was much worse. Some debris originated from the to a lesser extent, Samoa, is similar to New Zealand, as natural environment, but more damaging were parts of timber-framed and masonry or concrete-block buildings collapsed buildings or objects such as unanchored water are common. Most shoreline tsunami wave heights were tanks which became missiles and were swept into people in the order of between three to five metres above sea and structures in their path. Focus on level: these are the estimated 500-year wave heights for Natural physical factors, such as reef morphology, coastal some of New Zealand’s most populated coastal areas. topography, and the existence of offshore islands also Factors affecting the level of damage affected the damage wrought by the tsunami. Coral-reef to buildings size influenced the flow depth and consequently the We surveyed over 150 damaged buildings, including degree of damage; wider reefs reduced wave height or homes and tourism-based buildings and traditional fales, energy, and areas with extensive reefs seemed to have and found some consistent factors affecting the level of lower wave depths so sustained less damage. damage to buildings. Traditional light timber buildings were essentially totally destroyed at an inundation depth The poorly-constructed concrete foundations of this building of over 1.5 metres or higher. were undermined by the water.