When a deadly avalanche broke loose from Mount Jumbo in 2014 and crashed into several Missoula homes, killing one person and temporarily burying two others, emergency responders learned a good deal from the conditions leading up to the disaster.
On Thursday, Travis Craft of the West Central Montana Avalanche Center said similar conditions have taken shape on the mountain this week. Heeding the advice of experts, the city issued an emergency alert for residents at the mountain’s base just before noon.
“It’s reminiscent of what happened in 2014,” Craft said. “My team assessed the east side and west slopes of Jumbo and we found a snowpack that is definitely able to produce avalanches. I would quote it as being dangerous avalanche conditions right now.”
Joined by the Missoula Fire Department and the local Office of Emergency Management, along with other city and county officials, Craft reflected on the deadly slide that erupted exactly five years ago Thursday.
In that instance, Missoula saw heavy snowfall on an existing snowpack. After Hellgate winds from the east loaded the snow near the mountain’s crest, a human trigger sent a slab racing down the slope, where it crushed several homes.
“From 2014, what we found out by looking at that incident, we have a recipe for when we should start being concerned about Mount Jumbo,” Craft said. “We have a snowpack that stays on Mount Jumbo and doesn’t melt out with significant Hellgate winds out of the east, and then we get a blizzard warning with a large amount of snow. If you look at the history of our weather, it almost matches where we are right now.”
With concerns about the unstable snowpack, and at the request of the city, Craft and his team visited the mountain on Wednesday and Thursday morning. During their last visit, they discovered a high-elevation slide triggered by an elk that nearly ran the length of the mountain.
“Before we even got on the slope, we saw an elk-triggered slide that was 75 feet across, two or three feet deep, and it ran about 800 vertical feet,” Craft said. “It didn’t reach the valley floor this time. We also found an unstable snowpack.”
Several snow events over the course of 2019 have slowly accumulated under freezing conditions around Missoula, including the surrounding hills and mountains.
But when a blizzard rolled in on Sunday, followed by several rounds of heavy snow, the dangerous conditions grew. And so did the city’s concerns.
“Since the weather event this weekend, we’ve continued to monitor the situation on the hill, and we closed public access on Tuesday,” said Jeff Brandt, chief of the Missoula Fire Department. “All access to Mount Jumbo has been closed and signed. Other than (Craft) and his team, there really should be no one up on that mountain.”
On Thursday, with the conditions mounting, Missoula International School closed its playground and removed students from its modular classrooms, which sit at the base of the mountain.
Residents who live nearby were also warned of the danger. Given the conditions, Craft said, any number of things could trigger a slide.
“We have the recipe for an avalanche, and what we’re looking for is a trigger,” he said. “That can be an artificial trigger or a natural trigger. A natural trigger could be another loading event of wind and snow. We’d work with the city to evaluate that.”
An artificial trigger could be a skier or hiker who illegally ascends the mountain during the closure. It’s suspected that a snowboarder or sledder, or both, triggered the fatal slide in 2014.
Dangerous conditions exist elsewhere around the Missoula Valley, one of only a few cities in the U.S. susceptible to urban avalanches, according to Craft. With more snow, wind and subzero temperatures forecast for the weekend, local officials will continue to monitor the danger.
Law enforcement will patrol the trailhead to ensure no one uses that access point.
“Any residents abutting Mount Jumbo, don’t play in your backyard, and don’t go out on those slopes,” Craft said. “Not only can it trigger an avalanche from above, but from below.”