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Further reflection PAGE 3
Nuts about trees PAGE 5
Twelve-year-old Oban Hansen at Cardrona Alpine Resort during the school holidays.Snow Farm, Cardrona Alpine Resort and Treble Cone report high numbers during the past two weeks. Story page 6.
Earthquake could cause seiche Tim Brewster Wanaka Sun
Representative hockey PAGE12
sunviews PAGE 13
League winners PAGE 16
PHOTO: WANAKA.TV
Nature, not structures, could be Wanaka’s most serious potential hazard in a large earthquake event with rockfalls, collapsed bridges, lake surges and subsequent flooding possible in a big shake. “It is worth being aware that earthquakes can cause landslides into or within large bodies of water, such as lakes and rivers. It is a good idea to avoid these immediately after an earthquake. Some who live close to the shores of Lake Wanaka, for example, [should] have a plan to move to high ground in the event of a significant earthquake, just in case the level of the lake is affected. This effect is referred to as a ‘seiche’ and behaves similarly to tsunami,” QLDC Emergency Management Officer Jon Mitchell said. GeoNet Seismologist, John Ristau said it was difficult to pinpoint what magnitude or location of an earthquake would be required to cause a seiche
large enough to be considered a hazard. “The Fiordland region has one of the highest rates of seismic activity in New Zealand and a number of large earthquakes (M > 6.5) have occurred there in the last 25 years. The biggest were the July 15 2009 M 7.8 Dusky Sound earthquake at the southern end of Fiordland, and the August 22 2003 M 7.2 Fiordland earthquake which occurred at the northern end of the national park. Both of these earthquakes generated numerous landslides and small tsunamis. Earthquakes of this size should be capable of generating a seiche in lakes in the Wanaka area. They could also generate landslides in the mountains around the lakes which could potentially cause large seiches in the lakes. In addition to Fiordland earthquakes, the Alpine Fault runs along the west coast of the South Island and very close to the Wanaka region. The Alpine Fault produces earthquakes with M > 7.5 and would almost certainly generate a large seiche in lakes in the region.”
Road and bridge damage could also restrict movement around the area following a large earthquake. “Skifield access roads, in particular, are vulnerable to earthquake damage, as any roads cut into or below hillsides are. Rockfall or landslides on roads in the gorges and valleys within and to and from the district is an ever-present hazard that would be triggered by any significant earthquake. This became an issue after some protracted and heavy rain recently, when the Kawarau Gorge and the highway between Hawea and Makarora were affected,” Jon Mitchell said. Jon spent a decade based in Christchurch in emergency management and was heavily involved in the aftermath of the Canterbury Earthquakes in both emergency response and transition to recovery. He was chief of staff for a composite headquarters of eight local and regional bodies following the earthquake and has also been involved in emergency management in Britain during the foot
and mouth outbreak and flooding incidents. Jon also suggests residents consider carrying a small readiness kit in their car along with preparations at home. “Readiness at home includes having emergency supplies in convenient locations, such as water, easy to store and prepare food, torches and a small radio (either with batteries or self-charging), a car charger for your cell phone, a simple landline phone that doesn’t need a power supply, first aid kit and any special medication, important papers (insurance, property papers, etc.).” Communicating with neighbours, workmates and classmates in readiness for an event is also crucial, he said. “One of the things we’ve found [following the Christchurch earthquake] is that communities are a lot more resilient than previously thought. They respond together and assist their neighbours. We’re working on developing and building that resiliency,” Jon said.