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Analysis of a Historic Avalanche Cycle: The Spring of 2019

Colorado Mountain School Guide, Jason Maurer, inspects a piece of equipment that had been buried by avalanche debris at Mosquito Gulch, Colorado.

As we prepare for another season recreating in the backcountry, it’s hard not to reflect upon how last season ended. I, for one, feel lucky to have witnessed the historic avalanche cycle that the state of Colorado experienced in March of 2019.

On the weekend of March 8th, what ended up being the height of the avalanche cycle, my fiancée and I had made plans to ski up near Frisco – only to change them last minute after not wanting to accept the risk of driving up I-70 with our beacons turned on, or the risk of being stranded on the interstate for an unknown number of hours. Instead, we opted to ski super low-angle pow up in Rocky Mountain National Park and play it ultra-conservative. Overall, I think that’s what it took to manage the dangerous conditions that we were experiencing in the backcountry during early March, and skiing 2 feet of powder in the Banana Bowls did not disappoint.

Skinning up Banana Bowls, Rocky Mountain National Park: March 8, 2019

As a guide and avalanche educator, my preparation for the upcoming season is to continue with my professional development and analyze the past season’s conditions, decisions, and near misses. Pursuing this, I attended this year’s Colorado Snow Science Workshop hosted by the Friends of CAIC. This was an opportunity for professionals as well as recreationalists to get together and recap the historic avalanche cycle that greatly affected the state. Speakers such as Brian Lazar, Deputy Director of the Colorado Avalanche Information Center (CAIC), and Art Mears, a professional avalanche consultant out of Gunnison, among many others, spoke to a full house up in Breckenridge and laid out the framework for how such a historic event transpired.

In retrospect, looking at the details now available, such as weather and snow totals, it’s easy to see that there was no way our Colorado continental snowpack could withstand such a large loading event. Before the record-setting snowfall that we had in March, our snowpack up to that point had been relatively strong, measuring on average 3 to 4 meters deep throughout most of the state. On February 28, 2019, the avalanche problem was Persistent Slab and most areas in the state were at a Moderate avalanche danger rating. We did have a buried persistent weak layer, but it was buried so deep that a skier’s weight alone was unlikely to trigger a slide. What our snowpack needed to induce failure was a large rapid loading event, which is exactly what happened in the first 2 weeks of March. On March 7th, during the height of the historic loading event, 4 backcountry zones went to Black or “Extreme” danger. Now called “Black Thursday”, this was just the start of a record-breaking March.

North American Public Avalanche Danger Scale
Avalanche Forecast for March 7, 2019

Looking a little deeper into how this loading event affected our snowpack, we have to talk about water. How much water is in the snowpack? Being Colorado skiers, we all think of snow as light and fluffy. And most of the time when it snows up in the mountains at high altitude that’s the type of snow we get—dry powder. But the snow Colorado received from these March storms was not so dry and powdery. It was more like that Sierra cement you may have experienced if you’ve been skiing in the Pacific Northwest. It was wet and heavy, more akin to snow that falls in a maritime snow climate. In other words, the snow that we were receiving during the early March storms had a high SWE or Snow Water Equivalent. The SWE associated with the March storms just kept increasing with each incoming storm surge.

A snow pit shows the various prominent historic avalanche cycle of the 2019 season.
Deep snowpack at Berthoud Pass, 2nd Creek: Feb 9, 2019

Essentially, what we ended up having from this historic avalanche cycle was strong over weak snowpack. Not just an isolated layer of strong over weak somewhere in the snowpack, but the whole dang enchilada. We had a Maritime storm slab over a Continental snowpack that was harboring a persistent weak layer. The energy alone that was stored up in these maritime storm slabs with high SWE was all that was needed to rip out our full season’s snowpack, all the way to the ground.

An isolated column of snow shows a large slab falling off of a buried layer of near-surface facets during the historic avalanche cycle of 2019.
Berthoud Pass 2nd Creek: A large slab falls off of a buried layer of near-surface facets: March 12, 2019

The numbers from this historic avalanche cycle speak for themselves. CAIC reported 855 artificially triggered avalanches with 380 of those impacting the highway. 108 natural avalanches impacted the highway. 47 avalanches were classified as large or very large. Avalanches that had not released in over 60 years were running full track and most of those were jumping the road or making a whole new path altogether. Two examples include the Disney slide path near Berthoud Pass that last went in 1957, and the Peak 1 avalanche near Frisco that surprisingly hadn’t ripped since then 1898, 120 years ago.

 Buried excavator at Mosquito Gulch: March 15, 2019

For me, the true scale of the March avalanche cycle really came to light while Spring skiing up in Summit county in April and May. I can’t recall ever walking over so much avalanche debris! Entire slopes of aspen trees resembled a pile of Pixi sticks, with large old-growth pine trees ripped out by their roots. It was a humbling experience to say the least. Even with a backcountry float pack, I doubt anyone would survive getting caught in an avalanche with that much destructive force. In light of such destruction, CAIC has issued a preliminary count of three “D5” avalanches last season (knowing there may have been more), when usually Colorado has none.

A forest that has been wiped out by an avalanche on Independence Pass during the historic avalanche cycle of 2019.
Avalanche damage at Monitor Gulch, Independence Pass
Avalanche damage at Monitor Gulch, Independence Pass

So, what’s next? How can we take what we’ve learned about this past season’s avalanche cycle and apply it to how we approach the backcountry this season? As backcountry travelers should be doing anyway, tracking the season’s snowpack as it develops will give you a good overall picture of our depth and layering preceding a large loading event. This is in addition to paying close attention to the daily weather and avalanche forecast that is posted by CAIC, and especially applying it to planning before a day in the backcountry. In addition, for those really looking to geek out on snow conditions, paying close attention to the SWE (snow water equivalent) within the snowpack is a great tool in predicting upcoming avalanche cycles before they occur. At the heart of safety in the backcountry is avalanche training, open communication, and good decision-making with trusted and skilled partners. Get out there, have fun, and more than anything, be safe.

Author, Jason Maurer, taking snowpack observations on March 8, 2019

Jason Maurer
– AIARE Course Leader
– AMGA Apprentice Rock Guide
– AMGA Apprentice Alpine Guide
– AMGA Assistant Ski Guide
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