Earlier this month, on January 12, a persistent slab avalanche occurred at San Joaquin Ridge, resulting in a full burial of the avalanche’s trigger—a backcountry skier. The event was labeled as a “D2,” designating the avalanche as capable of burial, injury, or fatality.
But the skier’s recovery was fast—a self-rescue, and resulted in only minor injuries.
Following the event, which was published by the Eastern Sierra Avalanche Center (ESAC) on January 15, ESAC and the Mono County Sheriff Search and Rescue Team issued a warning to the public that hazardous avalanche conditions existed throughout the county, and the entirety of the Eastern Sierra. Winter recreators have been urged to exercise extreme caution when exploring backcountry terrain within avalanche zones.
“We use a technique in the search and rescue world called PSAR. Preventative Search and Rescue,” says John Pelichowski, a coordinator for the county’s search and rescue (SAR) outfit. “It’s just one of those awareness tools we use to keep people’s brains in the right headspace.”
As Pelichowski explained, with the record snowfall of last year’s season, avalanches earned more of a front-of-the-consciousness position in recreators’ psyche.
“Now, it seems to get lost,” said Pelichowski.
Pelichowski began to explain that the lack of snowfall this year, compared to last, does not negate the possibility of impactful avalanches. Actually, the opposite is true.
“This year’s base of the snowpack is an older snowpack. It’s what’s called fragile, or weak. So then when you get these other storms, especially El Niño type of heavy, wet, consolidated snow, it sits on top of those weak layers. Those weak layers become the breaking point—” said Pelichowski, before cutting himself off. “—you know what … you should talk to Steve. Your brain will hurt after talking to Steve.”
Steve Mace, Director and Lead Avalanche Forecaster at ESAC, has the typical pedigree of an elite forecaster—lifelong backcountry skier himself and a former ski patroller on the snow safety team at Mt. Hood Meadows.
As Mace acknowledged, the Eastern Sierra is an exciting place to study and monitor avalanche activity.
“It’s just kind of a unique geology,” said Mace. “We have very large vertical relief. The Sierra Nevada ramps up over 80, 90 miles from its west side, and then drops off in a matter of just a couple of miles from the crest. Mountain ranges outside of the northwest volcanoes don’t typically get that kind of relief … And I guess the consequence of that uniqueness is we have a lot of avalanche terrain because the mountains are so steep.”
And in a typical year, as explained by Mace, forecasting in the Sierra is more or less typical—as forecasting goes.
“We have a generally maritime climate. We tend to see less of these persistent slab avalanches than we are this year. But like I was saying, this year is atypical.”
What Mace is seeing, in terms of the Eastern Sierra’s current snowpack, is more typical of what you would see in a continental climate—think Colorado, or Montana.
Because of the lack of precipitation, this year’s snowpack is “meager” in general. And, said Mace, agreeing with Pelichowski, there are weak layers at the base of that snowpack.
“The weak layers will stick around for a long time so that instability is slow to rise, and it’s also slow to fall.”
This breeds potentiality for future persistent slab avalanches—defined as a kind of avalanche in which a slab forms over an integral weak layer—like the one on January 12.
“Persistent slabs are, as the name would suggest, persistent,” said Mace. They are also extremely difficult to manage and mitigate, and demonstrate surprising behavior.
The danger for recreators in the area, is that this is not a familiar phenomenon. The Eastern Sierra is used to seeing sizable storms that drop a lot of snow all at once, leading to the opposite kind of avalanche hazard—a quick to rise, quick to fall avalanche. But this year, the snowpack is being formed by what scientists like Mace call “incremental loading,” where small amounts of precipitation are added over time. With a strong base layer, incremental loading can add strength to a snowpack, and allow it time to adjust.
Weak snowpacks, however, will fail even with a small addition of weight.
“For backcountry users,” said Mace, “these incremental storms can have an outsized impact on stability … And with the state of our snowpack being so thin and weak, we’re just seeing that hazard [stay] elevated for a longer period of time.”
Mace draws one analogy. Tells me to think of it like building a house of cards: “That last card you put on is that one that knocks it all down.”
And looking ahead, while the next few weeks and months might hold the promise of increased snowfall, they also hold the possibility of increased risk.
Avalanche hazard consultant and highway patrol forecaster for Inyo and Mono County, Sue Burak, gave her report:
“A week from now, it looks favorable for the West Coast to get a series of atmospheric rivers. The jet stream is forecasted to be pointed straight across the Pacific.”
But unfortunately, more typical Mammoth snowfall today does not cancel out the atypical Mammoth snowfall of yesterday.
“If we start to see our typical snowfall—measured in feet and not inches—then that load to the existing snowpack will, in many places, cause it to fail,” said Burak.
Burak explained that she keeps a photo inventory of the avalanche paths, and analyzes the density and rates of snowfall that would be required to trigger a slope to slide. Based on what she has observed, the scientist is “pretty certain that there will be large avalanches, and that they could collapse closer to the ground … if you have avalanches failing near the ground, you have large, large avalanches occurring.”
So what is there to do, to remain cognizant in the backcountry?
“You need to be aware of the weather forecast and the avalanche forecast,” said Burak.
“In the backcountry, you have to remember that that’s a non-mitigated and non-patrolled area,” reminded Pelichowski. “That’s where your greatest risk of avalanches lie.”
Pelichowski, on behalf of Search and Rescue, urges anyone involved in backcountry recreating to take the tools, and have the training. The avalanche research and education organization AIARE, offers resources and course options for those interested in pursuing both basic and advanced avalanche safety training.
Importantly, Pelichowski, Mace, and Burak urge skiers and riders that, regardless of ability level, it’s never too early to be cautious.
“I’ve taught courses where people showed up with new skis still in the plastic,” said Burak. “And it’s just so eye-opening for people—to look around the terrain, and see it in a whole different way.”
Eastern Sierra Avalanche Center posts an avalanche forecast, daily at 7:00 a.m. on https://www.esavalanche.org/.
“Our forecast team is in the field, every day, monitoring and evaluating the snow conditions and verifying weather impacts,” said Mace. “We also have an observation page, with recent contributions from other forecasters, the public, and other professionals in the region.”
Like anything, education, adequate training, and remaining cognizant of the changing terrain go far in mitigating human-triggered avalanches, and the liability that results.
“But the fact is,” said Pelichowski, “We’re still dealing with mother nature, right? She’s still in control.”