Avalanche warning on sunny slopes
JOHN EDENS IN QUEENSTOWN
Skiers and boarders venturing off piste at Southern Lakes ski fields or into the back country have been warned of considerable avalanche risks on sunny slopes this weekend.
An avalanche on Thursday outside the Remarkables ski area boundary in a steep section below Double Cone was probably triggered by a smaller avalanche and upgraded from an estimated 1.5 to a 2-grade size slip, large enough to bury, injure or kill.
No-one was caught in the 200m-long, 80m-wide avalanche but a full-scale search was mounted by helicopter, 40 patrollers from three skifields - the Remarkables, Coronet Peak and Cardrona - and three dog teams.
The New Zealand Mountain Safety Council danger rating for the Southern Lakes region yesterday was "considerable" - the third highest of a 5-point scale.
The rating means northerly facing aspects at sub-alpine and alpine altitudes, about 1000 metres and above, risk loosing avalanches.
Wind, rain, late-season snow and increasingly warmer temperatures increase the risk.
Mountain Safety Council avalanche programme manager Andrew Hobman said the considerable rating meant the back country should be attempted only by experts.
Despite the rating the back country was still accessible but people should be aware of the risk, he said. "Stay off suspect spots where the sun is really affecting the snowpack.
"Natural avalanches are occurring, they can run out on to much flatter terrain.
"We're definitely not saying "do not go" but be aware. We can say there's considerable danger of avalanches releasing and probably on those (high northerly facing) slopes throughout the weekend."
The search response team did not hesitate, using probe searches in a grid pattern over the debris field, a transceiver search and a search for RECCO reflectors, Mr Hobman said.
The reflectors bounce signals back to a receiver and are in many brands of ski and snowboarding gear.
Combined with dog-team searches and grid probing the search yielded a high probability of detection if anyone was buried.
Avalanche programme assistant manager Gordon Smith mapped the debris field below Double Cone yesterday morning.
He conducted a crown wall profile digging into the snowpack at the point where the avalanche started, about 30m to 40m below where the chutes fanned out.
The avalanche ran along a firm base and the council believed a smaller wet snow avalanche triggered the larger event, which was 30 to 40cm deep at the crown and about 50m wide.
"We can easily say it's a solid size two. A size two is when it's big enough to injure or bury somebody."
- © Fairfax NZ News
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