Science may give answers at A-Basin |

Science may give answers at A-Basin

Ryan Slabaugh
Special to the DailyThe red area on this illustrated map of Arapahoe Basin shows where an inbounds slide on the expert Pallavicini area slid Friday. The avalanche claimed the life of one man.

ARAPAHOE BASIN – For Scott Toepfer, an avalanche forecaster for almost 30 years, last week’s slide at Arapahoe Basin was a call to arms.Toepfer’s job is to forecast snow cPhoto:7042572,left;onditions in hopes of preventing fatalities. Each day during the winter, the Colorado Avalanche Information Center – Toepfer’s employer – posts warnings on its phone system and by e-mail letting people know the possibilities for avalanches.However, the May 20 slide, which killed David Conway a 53-year-old stay-at-home dad from Boulder, is a learning experience for everyone involved, Toepfer said.

Despite huge advances in technology and knowledge about snow in the last 30 years, the Toepfer, who lives in Breckenridge, said it doesn’t mean forecasters will ever master the science.”I know what the patrollers at Arapahoe Basin are going through, and it’s horrible,” he said. “From a scientist’s perspective, we’re probably the only ones not suffering.”Toepfer, another member of the avalanche center and the A-Basin ski patrol surveyed the site on Sunday with probes and scanners, but found no more victims. They also looked at the fracture line profile – the layers of snow – and found a few unique occurrences that could have contributed Friday’s avalanche:

• The run was north facing which, according to this year’s patterns, are the type that have experienced slab avalanches in the northern mountains. Weak, sugary (and now wet) layers found near the ground are more abundant on north aspects, as well, Toepfer said.• The run was too small for snow cats. Although ski resorts do not groom every run, snow cats can pack down the snow, breaking up the layers and providing a more cohesive base. The run at A-Basin was too narrow and steep for a snow cat, Toepfer said, although the thousands of skiers who trekked on it this winter should have helped. “It’s not the same as running a multi-ton snowcat up it,” Toepfer said.• The snowpack was so complex, it was tough to read. Toepfer said the usual hoar frost at the base of snow (a weak layer that’s usually the culprit for avalanches) wasn’t that big, and the recent weather pattern wasn’t that different from previous years.• A hardened mid-layer could have been the culprit instead of the base, because the slide was only 18 inches deep. “We may never know, but it was a factor,” Toepfer said. This could have been caused by an early thaw in January or the thaw in mid-March, when the snow melted and refroze several times over several days. And when the winter conditions came, the layer remained frozen and sat on top of older snow, and under new snow.

“There’s a lot of rules of thumb we try to live by, but the first rule of thumb is there’s no rule of thumb,” Toepfer said.All this is speculation, Toepfer said, because snow science is “wonderfully complex.” And the fact that avalanches destroy most of the evidence of what caused the slide won’t help the scientists.While rare, inbounds avalanches do happen. Earlier this year at the Las Vegas Ski and Snowboard Resort in Nevada, a 13-year-old boy was killed after an avalanche swept him off a ski lift. The resort had received huge amounts of snow – almost 78 inches in two weeks – before the fatal slide occurred, according to the Las Vegas Review-Journal.

The last inbounds fatal slide in Colorado – in 1975 in Crested Butte – occurred in the trees between open runs.”You have to look at every accident as a learning experience,” Toepfer said. “I want to know what caused (this slide), so we can prevent this in the future. This is very unusual.”Vail, Colorado

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