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April 2011 Issue
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Survival skill #2 – Backcountry earthquakes

Avalanches and rockfall can be caused by earthquakes. Photo: Geoff Spearpoint
Get off the slopes, check bridges, be extra careful around waterways and inspect gas lines and stoves in huts

Most earthquake-related injuries and deaths result from falling debris, flying glass and collapsing structures such as buildings and bridges. Earthquakes can also trigger landslides, avalanches, flash floods, falling trees, fires and tsunami.

On a slope: If your group is on a slope exposed to rockfall or avalanche, spread out to reduce the risk of the whole team being buried at once. “Steep slopes can be particularly hazardous during and after earthquakes,” says Mountain Safety Council bushcraft programme manager Chris Owens. “In the long rainy season of winter and spring, soils can become saturated and quakes can produce rapidly moving landslides. In dry areas, rock fall can be an issue and in winter above the snowline, consider the avalanche risk.”
Waterways: Earthquakes can turn soil to quicksand, a process called liquefaction, particularly along current or former river channels. Be vigilant near riverside tracks where bank undercuts may be created or enlarged.

“Due to rockfall, rivers may change course or disappear and flash floods may now be an issue even without heavy rainfall,” says Owens.

Huts: An earthquake may compromise the foundations of backcountry huts or they could be in a rockslide/avalanche pathway. “If you’re at a hut, check for damage around any gas bottles and pipes,” advises Owens. “When entering a hut beware of broken glass, strewn objects on the floor and loose articles stored overhead. Water tanks may also be damaged. Before lighting stoves, check for damage to the stove and chimney.”

Bridges Assess all bridges thoroughly prior to using. If in doubt, don’t use them and consider an alternative crossing option.

Report all damage to the DOC Hotline (0800 362 468).

Caught in a quake

In 1994 John Corcoran was running an instructor training course for Mountain Safety Council in a high basin in Arthur’s Pass when a 6.7 magnitude earthquake struck.

“I remember dropping to my hands and knees and seeing the mountain coming at me like a wave,” recalls Corcoran. “You could hear a lot of rumbling and not far from where we were there was a huge rock fall that blocked the river for a while.”

At the time, the earthquake was the largest land-based quake in New Zealand since 1968. In Christchurch it was reported buildings swayed and people fled into the streets. Corcoran’s group of eight were not injured by the quake so they set up their camp in the basin. However, that night a powerful storm ripped open two of the group’s tents and Corcoran and the other instructor decided they had to get off the mountain. “Some of them were very frightened because they were on a training course and were probably out of their comfort zone already,” he says. He guided the group down to a swamp behind Castle Hill where they set up a second camp only to be hit by a strong aftershock.

“A bloody great wave action came through the swamp,” says Corcoran. “Everyone was very shocked.”

The next day the group got out safely with no injuries and found damage at Castle Hill and in Arthur’s Pass. “We had been sitting on the epicentre of the damn thing,” says Corcoran.

In the 45 hours after the initial earthquake there were 71 aftershocks measuring over four on the Richter scale.

Corcoran says staying calm and making good decisions is the key to surviving dangerous situations. “I’m a great believer in stopping to have a brew to think about it,” he says. “But then again there’s some cases you need to move fast.”