Avalanche Analysis- Craig Patterson Incident
With info provided by Bruce Tremper and Matt McKee
Photos by Bruce Tremper
Avalanche forecaster and instructor, friend and guide, Craig Patterson, perished in a small avalanche in a deadly place on the Northeast Ridge of Kessler Peak in Big Cottonwood Canyon, (BCC) Utah, on April 11, 2013. He paid a terrible price for a small mistake, if it could even be called that. Craig was assessing snowpack stability above Utah State Route 190 for his employer, the Utah Department of Transportation (UDOT.) He was working alone, a standard procedure in this profession. He had communicated to his co-workers around 1:30 pm, confirming that stability looked good on Kessler Peak, which has produced some of the largest avalanches to paste BCC road. Yet shortly thereafter he was surprised by this small, potent snowy torrent.
Patterson had ascended the standard route up the NE Ridge, which splits two big avalanche paths, Hanging Slab (East) and God’s Lawnmower (North.) The vast majority of this popular route is on wooded, protruding terrain exposed to little avalanche potential. The pocket that slid, is the only place on the climb that isn’t protected by the forest. Therefore, it is the only place that gets loaded by the northwest winds, which had averaged 34 mph at 11,000 feet during the previous night’s storm.
Storm total was 18.5 cm (4-8 inches) new snow and 19.5 mm snow water equivalent. Less than one inch of water and one foot of snow had fallen on a melt-freeze crust, meaning there was no pertinent weakness in the snowpack, except the new snow. Danger was rated as moderate by the the Utah Avalanche Center (UAC,) and UDOT did not deem it necessary to conduct avalanche mitigation measures that morning. Craig met with his superiors in Alta and all agreed the storm totals were considerably less in Big than in Little Cottonwood Canyon, as usual.
During the post-accident investigation, the party followed Craig’s skin trail to the crown at 9,940’. It’s impossible to know how far he went out on this slope before it fractured. No evidence of a slope test (aka ski cut) was found, probably because he still had skins on. Another party apparently ascended his skin trail after the slide, but before the investigation party arrived. If that party would contact the UAC, perhaps light could be shed on a mysterious tragedy.
The windslab, sitting on a 45-degree slope, broke out above Craig. Whether due to his stomping/jumping to test it, or stepping on to the slope we may never know, but once caught, it was bad. With climbing skins on, heel risers up and heels free, it was virtually impossible for him to ski or fight his way off the slab. The ride that ensued was brutal. The avalanche carried him over a cliff onto a rocky, sparsely treed slope below. The path then funnels through a narrow choke near the bottom. Craig wore an airbag pack, but it did not help.
The vertical fall was 1,380 feet, with an average slope angle of 49-degrees. The avalanche crown was 40 feet wide. Depth was 8-16 inches, averaging 12. Slab was fist-hard wind-deposit from the morning of the 11th. Bed surface was a pencil-hard melt-freeze crust formed on the 10th. The weak layer may have been facets near the surface, as traces of such crystals were found on the far side of the crown, or graupel that fell at the beginning of the relatively small storm. Stability tests performed at the site included a shovel shear and compression test, recorded as STM, Q2 and CT23, Q2*. These are not red flag scores, but snow can stabilize a lot in 24 hours, and no test can replicate conditions at the time and place of failure.
This was not a blatant error or a cataclysmic natural event. It was a small, late-season slide during a period of relative stability involving a professional known for good judgment and decision-making. Conclusions are difficult to draw. In comparing specifics of this avalanche to others, one is struck by how inobvious the weakness was; how subtle the change in aspect that enabled him to trigger it; and how improbable it is that a professional forecaster and strong skier was swept away by such a small slab.
What can we learn from it? Constant vigilance is one clear mandate. We can never let our guard down. Every decision has implications. Another take-home point is that consequences are critical. Craig knew the avalanche hazard was moderate, yet he stepped near enough to be caught to a slide path with extreme consequences on this last, tiny portion of the ascent.
It also emphasizes how incredibly vulnerable we are with skins on. We must try to climb terrain that is significantly safer than what we ski. I had a parallel accident while skinning to my home run on March 31, 2006. I stepped on a small windslab at the same altitude on the other (west) side of God’s Lawnmower. The carpet was ripped out from under me, and I had zero control over my destiny. Gravity tumbled me over a small cliff and then I slammed into a tree. But luckily, I hit the tree with the back of my legs. Waves of snow tried to rip me off the small fir, and I was bruised from calf to butt, but I hung on and lived to ski another day.
The similarities are eerie, and illustrate another reality of backcountry skiing: nature is random, and shit happens! If you choose to ski in high-consequence terrain, such as the upper flanks of Kessler, you must make wise choices and have good fortune. Sadly, on April 11th, 2013, 34-yo Craig Patterson was not lucky, and those who had the good fortune to know him must carry on without a person of great energy, integrity, compassion, charm, charisma and competence. Let us learn from his passing and tread carefully near the top of Kessler’s NE spur, aka “Patterson Ridge,” and every other slide path we must cross.
*STM=Shovel Shear Test, Medium difficulty in producing shear on isolated column, 30 x 30 cm.
Q2=Quality 2 shear. That is, planar shearing plane, but resistant, vis-à-vis Q1 (slab slides off weak layer with energy. Like its spring-loaded). Q3 is a rough or broken plane.
CT23=Compression Test failure after 23 hits to blade of shovel while its resting on top of snowpack. Mirrors the impact of a skier on snow surface. 10 hits each from wrist and elbow. Finally failed on 3rd drop with arm outstretched from shoulder.