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On the evening of Saturday, August 11, lightning struck nine miles north of West Glacier, Montana and hit Glacier National Park’s Howe Ridge. A fire began.
By the following day, the Howe Ridge Fire began to expand rapidly, with windy and dry conditions acting as the perfect fuel.
As the fire grew, officials closed surrounding roads and issued an evacuation order for nearby campgrounds as well as Lake McDonald Lodge and North Lake McDonald Road, due east of the fire’s point of origin, reports the National Park Service. Management crews plan to establish point protection around structures and evaluate the areas in which they can construct control lines, but they face a major concern: Uneven terrain and the risk of falling trees prevent crews from safely establishing a direct fire line, the Park Service reports. About 250 personnel are assigned to the four fires burning within Glacier National Park, according to its Howe Ridge Fire hotline. Crew members assigned to Howe Ridge are using fire engines or taking to the sky in CL-215 ‘Superscooper’ airplanes and a K-Max helicopter to control the inferno, which currently spans about 3,500 acres.
The Howe Ridge Fire’s estimated containment date, reads its InciWeb (Incident Information System) page, is approximately 12:00 a.m. on Thursday, November 1. But unfortunately, the embers could affect the landscape even after its last plume of smoke is distinguished, Jason Kean a U.S. Geological Survey research hydrologist who works with USGS’ Landslide Hazards Program, warns. Usually attributed to interactions between heavy rains, loose bedrock and gravity, landslides can be an all-too-real consequence of forest fires.
“You can look on Google Earth and see these scars from shallow landscapes all around,” he says.
Fire primes a landscape for a slide in a few ways. When a fire strikes, some trees––sometimes many––are felled. The vegetation is like a “blanket on the soil,” Kean explains, with trees functioning as an anchor, securing soils in place. “When you remove the vegetation, raindrops can directly hit the soil and make those particles move.”
But fire also chars the earth, transforming the hydrology, or water content, of its soil. As the soil burns, precipitation is less able to penetrate below the soil’s surface level. The ground’s surface could become unstable, and instability is a key ingredient for a landslide. Thanks to gravity, soil on a slope is most at risk.
Most of Glacier National Park’s precipitation falls as snow, the National Park Service’s National Parks Fire Programs Coordinator Richard Schwab explains, but the Park is also home to powerful thunderstorms––the very cause of the Howe Ridge Fire. “It’s the summer thunderstorms that can trigger the kind of event that we’re concerned about,” Schwab says.
“Particularly right after the fire, when the earth doesn’t have that blanket of vegetation, an intense storm can cause a real problem,” Kean adds. “Then in the spring, if you were to get rain on top of snow, the rain could melt the snow and essentially cause double the amount of water.”
In the first year or two after the fire, the roots of trees it destroyed will still be intact, effectively creating support for the soil. But in time, the tree roots start to decay, and a shallow landslide–– one where the surface layers of soil slough off––can occur. Surface landslides can occur up to 10 years after a fire, Kean warns.
Already, the Howe Ridge Fire has destroyed numerous private summer residences, park-owned boathouses, a camp house and its outbuildings. Tourists are being encouraged to stay on Glacier’s east side. Throughout Tuesday night, fire management crews heard noises that resembled gunfire, Montana’s Great Falls Tribune reports––sounds made by trees collapsing to the ground.
When rain finally falls again upon Howe Ridge, having fewer trees could cause its terrain to more readily slurp up moisture.
Working with the NPS’ Burned Area Emergency Response and other fire response teams, the USGS will conduct a debris-flow hazard assessment for the region scorched by the Howe Ridge Fire. This assessment entails using satellite imagery to generate a map of the burned area, finding the slope of the terrain within that area, and applying rainstorm models that are low, moderate, and severe in intensity to gauge the range of potential for a landslide, among “a whole suite” of other conditions, Schwab says, including at-risk “critical cultural resources, erosion, natural resources, invasive species and endangered species.”
The Howe Ridge assessment will have to wait until its fire gets close to containment, USGS researchers say, but last year, the Sprague Fire, which burned on the other side of Lake McDonald from the Howe Ridge Fire, was one of 96 different fires across the country that the USGS conducted an assessment for in 2017.
“Fortunately, that fire didn’t become problematic, unlike the others I’ve worked on,” Schwab, who’s currently stationed at California’s nearly 200,000-acre Carr Fire, says of the Sprague. He cautiously adds: “The Sprague fire has the potential to create a problem if you get the right rain event.”
Responsible for the deaths of 21 people, California’s 2017 Thomas Fire caused some of the worst debris flows that Kean had ever seen. “People need to plan for these events as soon as possible,” he says.
The intensity of the Thomas Fire’s landslides makes Kean worry about the repercussions of California’s Mendocino Complex Fire––the state’s largest in recorded history––most. But he stresses that landslides are a very real repercussion within Montana’s Glacier National Park, too.
“It’s definitely a possibility,” he says of landslides occurring as a result of the Howe Ridge Fire. “In 2003 and 2006, there were a bunch of debris flows that were associated with fires that aren’t too far from Howe Ridge. When you have intense slopes like these, there’s always the possibility.”