Wildfires burning away trees and shrubs along the Interstate 70 corridor through Glenwood Canyon, perennially plagued by falling rocks, have raised risks of catastrophic landslides — prompting federal geologists to install more monitoring sensors.
Barren slopes above I-70 have become so unstable that modest rain could set off sediment catapulting far beyond flames, a U.S. Geological Survey assessment has found.
And federal authorities aim to improve early warning capabilities — even by a couple minutes — and minimize false alarms, to protect the growing population drawn by residential and commercial development around Glenwood Springs.
U.S. Geological Survey director Jim Reilly joined a team of federal hydrologists in Colorado on Thursday assessing the impacts of the 32,302-acre Grizzly Creek fire in Glenwood Canyon and the 139,006-acre Pine Gulch fire near Grand Junction in the broader context of climate change.
Adapting to landscapes where warming temperatures accelerate changes — rising sea levels, flooding, shifts to aridity — will require increased monitoring, Reilly and a team of agency scientists said in an interview.
And residents also must think carefully about how they are building and relating to the natural environment, Reilly said. This summer’s wildfires, which forced a shutdown of I-70 through Glenwood Canyon for two weeks, stood out as a cause of potentially cascading impacts.
“The binding characteristics of the biomass from trees down to the soil itself, those are all things that got changed. You lose that binding. It’s going to increase the likelihood of seeing mass failures, slope failures, particularly on the steeper parts of that topography,” Reilly said as firefighting commanders faced flash flood warnings.
Among danger zones prone to post-fire slides in Glenwood Canyon were slopes that drain directly toward I-70, the delicate Hanging Lake site that tourism industry boosters have promoted, and the rocky walls east of Glenwood Springs around the Shoshone power plant above the highway, an adjacent bicycling trail and headwaters of the Colorado River.
The sensors include cameras, automatic water samplers that can show changes in sediment movement, and devices that measure water temperature, acidity and turbidity. USGS scientists have the ability to quickly install radar systems on bridges to watch water levels nationwide, Denver-based hydrologist John Fulton said. Flash floods and landslides, or debris flows, can start within minutes of intense rainfall and, often, surges of water and sediment signal what may follow.
Next week, federal crews planned to install new instruments at four existing water-measuring gauges in the area, including gauges along the Colorado River above and below Glenwood Springs in an effort to anticipate trouble.
“You can certainly say the probability is enhanced, or greatly enhanced by the fire. … We obviously have a very high potential for significant impacts,” Reilly said, referring to post-fire hazard maps that the USGS put out this week. “The flow may not necessarily be a catastrophic debris flow at Hanging Lake, but there’s the potential for increased sediment and ash that could affect the quality of the ecosystem at Hanging Lake.”
Warnings would be conveyed, as at present, by meteorologists with the National Oceanic and Atmospheric Administration and National Weather Service — largely triggered by rates of rainfall. Two-tenths of an inch in 15 minutes has been identified as a threshold around Glenwood Canyon for setting off slides.
That’s less than half an inch per hour and not an unusual rainstorm even in semi-arid Colorado, yet it could set off what the hydrologists described as significant debris flows that typically gain momentum leading to larger rock-ripping torrents downstream.
The scientists said more monitoring using precise instruments, combined with detailed mapping from aerial surveys, will help reduce the false alarms that authorities issued after the 2012 Waldo Canyon fire that destabilized the already crumbly, pinkish granite foothills west of Colorado Springs.
For decades, the U.S. Geological Survey has served as one of the nation’s main hubs for hard climate science, from investigations of Antarctic ice that provided context for current atmospheric concentrations of heat-trapping greenhouse gases (currently at 412 parts per million, the highest level in human history) to measuring the global average rate of sea level rise (about 3 millimeters a year).
Monitoring instruments also help assess water quality, and after recent wildfires led to advance warning for water providers to close intake systems to prevent clogging as sediments thickened.
Wildfires that burn off vegetation typically lead to increased organic carbon material and sediment, higher water temperatures and “flashier” stream flow, Grand Junction-based hydrologist Cory Williams said. And the runoff in coming weeks from the Pine Gulch wildfire, now the largest in Colorado’s recorded history, likely will measure high in salinity and selenium, he said.
The USGS budget around $1 billion a year ranks less than other federal agencies — the Department of Defense receives more than $680 billion — despite growing evidence and concerns about climate warming impacts on people and the economy. A 2018 federal assessment of climate change found that people moving away from coastlines would be unavoidable.
More funding for the USGS would help, Reilly said Thursday, but added that’s not likely to happen. A former astronaut and exploration geologist, he has focused on “force multiplier” collaboration with other federal and state agencies and on re-organizing within the USGS to encourage “integrated science” related to immediate challenges.
Climate warming impacts vary around the country. Drought conditions and insect infestations in forests rank among the multiple drivers of landscape changes in Colorado and the West. And past suppression of wildfires has loaded forests so that wildfires, when they ignite, tend to burn big.
Changing landscapes mean Americans must think carefully about their own position in the nature, Reilly said.
“You have to be aware of your surroundings wherever you are building,” he said. “You have to do what you can do to reduce the threat. In Colorado’s rural areas, we tend to build pretty big houses and we love to have trees around our houses. … Those can have an immediate impact on fire intensity. We can do a lot better in how we manage our forests right now, removing as much of that loading as possible.
“We also have to recognize that fire is part of a natural process. Are we doing the best we can in not adding risk to situations in how we build?”
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