Experts detail March 2019 avalanche cycle at Colorado Snow and Avalanche Workshop in Breckenridge
BRECKENRIDGE – At Friday’s 18th annual Colorado Snow and Avalanche Workshop in Breckenridge, Art Mears shared a story that spoke to the core of this past March’s historic avalanche cycle.
Mears, an experienced avalanche consultant based in Gunnison, told of how his wife once looked up at an avalanche slide path near Avery Peak in Crested Butte. She turned to her husband and asked him why couldn’t an avalanche in the path they were looking at run all the way to where their car was currently located on the road.
“‘I don’t think the conditions will ever be quite right for it to run that big,’” Mears remembers saying. “This year, it did exactly that.”
“It’s certainly nothing like we’ve ever seen,” CAIC Deputy Director Brian Lazar said of the March 2019 avalanche cycle. “Anyone on staff was unanimous that we’ve never seen anything like this in our careers.”
At Friday’s Colorado Avalanche Information Center event at the Riverwalk Center in Breckenridge, Mears, Lazar and other speakers contextualized how and why this past March was an unprecedented year for snow and avalanches in Summit County and elsewhere in the state.
Lazar began the day taking the audience through a chronology of what set last March up to be unprecedented. He explained how last October’s early snowfall set the initial stage for the March cycle, as deposited snowpack layers weren’t as weak as many other years. The subsequent snowfall until March, Lazar said, created a relatively deep and strong snowpack across the state, which was already more than four meters in the deepest areas.
“And in these really deep snowpack areas,” Lazar said, “three to four meters on the ground, we weren’t worried about them at all unless we got a massive loading event. “…we did realize the potential for unlikely, very large persistent slab avalanches to occur. But, again, we thought we’d need something of epic proportions to get these things to break.”
March 2019 turned out to be epic.
In the first week, between two-and-a-half and seven feet of snow dumped on most mountain areas. But, more importantly, Lazar explained, the snow water equivalent of the new snowfall manifested ideal conditions for big, powerful slides. Snow water equivalent measures the amount of water contained within the snowpack.
Come March 3, as slides began to run onto open highways – including two in Tenmile Canyon between Frisco and Copper Mountain – Lazar said increases approaching 20% in snow water equivalent at heavy-snowfall locations helped CAIC experts like him to understand the uniqueness of the storm cycle. Considering the heavy, wet and copious nature of the maritime snowfall combining with the pre-existing strong snowpack that had yet to slide in many paths, avalanches on aspects of all kinds, slopes facing in all different directions, were possible.
March 7 spoke directly to that. The day — known to many in Summit County as “Black Thursday” as four backcountry zones went to extreme “black” danger levels — resulted in tremendously energetic slides on state Highway 91 just outside of Copper Mountain, rupturing gas lines.
“These are clear illustrations that this avalanche cycle was not aspect dependent,” Lazar said. “This was running on all sides of the compass, on all elevations.”
Fast forward to March 9, where, on the other end of Summit County, transmission lines and towers in the Peru Creek basin near Montezuma were taken out. The nearby SNOTEL sensor measured a 38% increase in total snow water equivalent since the start of the month.
Outside of Summit County, a handful of mega slides registered D5 on the United States Avalanche Rating Code, which measures destructive force. A D5, the highest rating, is defined as a slide so strong it can “gouge” the landscape. That’s precisely what deposited into Conundrum Creek in the Maroon Bells-Snowmass Wilderness, a slide more than a mile wide and 3,200-feet long. It was one of several slides across the state in March that shocked experts by running up valleys, sheering rarely-touched landscape in the process.
“This thing was a monster,” Lazar said.
How monstrous was last March? In terms of mere numbers, more than 1,000 avalanches were reported to the CAIC over two weeks, including 87 rated D4 or larger. None of these mega slides were triggered by humans, though.
“These took inches and inches of water and feet and feet of snow or large (human-launched avalanche mitigation) explosives,” Lazar said.
Lazar also said the cycle opened CAIC’s eyes to classifying more slides as D5 in the future. He said many more slides in March actually fit two to three characteristics of a D5 slide. In terms of total slides, Lazar said CAIC estimates only 25% of March’s total avalanches were reported.
Pointing to the jaw-dropping Peak 1 slide, Lazar showed a photo indicating that the path had previously slid much the same way about 120 years ago, perhaps in the big snow year of 1898-99. Other historical photos show slides like this year’s in Tenmile Canyon likely occurred during that same time frame, including images of early settlers clearing railways lines in the canyon in 1898-99.
Mears’ presentation subsequently spoke to the raw power of the avalanches. He said many of this year’s avalanches were noteworthy because they were destructive in the total length of their paths. That variable speaks to just how much kinetic energy was loaded up and bonded together on slopes during March’s cycle.
“Theoretically,” Mears said, “I knew a lot of these things could happen, but I never thought I’d actually see it happen.”
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