Tuesday, April 7, 2009

Sliding into spring — Avalanche hazard in Turnagain Pass


By Jenny Neyman
Redoubt Reporter

Snowmachiners, backcountry skiers and climbers beware: the January hurricane crust could come back to bury you.

That’s the message from Carl Skustad, with the Chugach National Forest Avalanche Information Center. The center issued an advisory of extreme avalanche danger in the Turnagain Pass area on Friday.

“The current hazard is out there due to the large amounts of new snow. We’ve actually gotten about one-third of our total snow in the last three weeks, and that is sitting on top of a weak layer that was formed mid-January,” Skustad said Friday.

Conditions formed what Skustad calls a hurricane crust. Winds gusting up to 120 mph on ridge tops and rain up to 3,000 feet in January created an icy layer on top of the snowpack. Subsequent snowfalls, which have gotten heavier as temperatures warm, are sitting on top of that slick surface.

“Now we’ve reached this point where there’s this much stress on top of a weak layer and it’s exceeding the strength of this weak layer. That’s why any additional load could tip the balance, or any skier or snowmobile or climber,” Skustad said.

In these conditions, a slide could be triggered by as little as the warming rays of the sun. On steep slopes, any snowmachining, skiing, climbing or snowshoeing could trigger an avalanche, and risky activities like high marking pose a distinct threat.

“No, that’s definitely not a good idea right now,” Skustad said.

Most avalanches happen on slopes with a 38-degree or higher angle.

“But that’s just another indication of how tender our snowpack is now, that we’re seeing avalanches as low as 25 degrees,” Skustad said.

“I do not have a good feeling for the rest of the season,” he said. “We’re in April, so, really, we’re looking at a month. Once the snowpack has a chance to go through the whole avalanche cycle, which it does every spring, and it gets to what is called isothermal — when the snowpack is all the same temperature. Past that we’re golden, but until that point this weak layer will live under there.”

The hazard was issued for the Turnagain Arm area, but Skustad cautions that the same conditions probably exist throughout the highway backcountry corridor.

“It’s confirmed all the way through Summit Lake, and I expect all the way into the Lost Lake area. There’s nothing to think that it’s not at Lost Lake. I think it’s safe to assume this hazard does exist all the way down to there,” he said.

The death of 35-year-old Yancy Flair, of Anchorage, who was buried in a slide in Johnson Pass while snowmachining March 28, and a slide that closed the Seward Highway between Girdwood and Portage on March 27 has punctuated the avalanche danger in the Turnagain Arm region recently. It took searchers until Saturday to recover Flair’s body.

Skustad said conditions are hazardous, but not extremely unusual.

“It’s something that we can expect every few years. It’s the persistent weak layer that happens midwinter that determines how significant our spring instability is going to be. We had a couple really large events midwinter that have now come back to haunt us in the snowpack,” he said.

That doesn’t mean the mountains should be off-limits, just approached with caution and the proper gear — including avalanche beacons.

“I always tell people they should go out and recreate out of doors somehow. You need to keep the slope angle low and have experience, or travel with someone who has experience with avalanche awareness,” Skustad said.

1 comment:

muhammad amir said...

It wasn’t that big and didn’t go that far and, luckily, there was a big alder patch. sliding doors