GLENWOOD SPRINGS, Colo. — The flash flood roared down Glenwood Canyon with such force that it changed the course of the Colorado River. Torrents of mud, boulders as big as cars and toppled trees plunged down towering walls of rock carved over millennia.
When it was over, the July 29 mudslide left a gaping hole in Interstate 70. The river of mud had breached a wall and swept across the highway, sending the eastbound deck crashing into the waterway and burying one of the most scenic drives in Colorado under 6 feet of debris.
"This is dirt the dinosaurs walked on, and it's all gone," said Tim Holbrook, a supervisor with the Colorado Transportation Department, who has seen all manner of blizzards, floods and wildfires in 19 years in highway maintenance but nothing like this summer's spectacle.
When the interstate through Glenwood Canyon was built it was considered an engineering marvel, an ambitious construction project that preserved the stunning environment. But the 12-mile corridor through the canyon in western Colorado leaves little room for maneuvering, and traffic is easily disrupted.
Experts say the situation is magnified by the changing climate and its cascade of crises this summer: drought, wildfires, monsoons and mudflows.
The physical alterations have led to road closures, hourslong detours, environmental disasters and economic displacement. And they have prompted hard questions about aging infrastructure designed decades before climate change moved to the forefront of public discourse.
"This should be a warning, the canary in the coal mine," said Paul Chinowsky, director of the environmental design department at the University of Colorado. "It's time to go back and look at where our critical transportation routes are, because most of them are probably pretty vulnerable to this type of situation."
"We cannot let the engineering hubris or arrogance overcome the science of saying what you design for no longer exists," he said.
Maintenance crews continue to repair a 1½-mile section of the interstate. Traffic is down to one lane in each direction where it was most damaged. Workers have been dogged by smaller slides and weather threats that have forced them to close the highway nine times. The slide also took out utilities and communication networks.
"We have this great confidence that this one thing will never fail. And then when it does fail, everyone runs around going, 'How did that happen?'" Chinowsky said. "All it takes is one disruption, and you really have economic damage."
The closures have profoundly affected Glenwood Springs, a tourism-dependent resort city whose renowned hot springs have drawn visitors for generations. Many people with reservations at hotels this summer who drove in from the Denver area were subjected to three- to four-hour detours. The historic Hotel Colorado was hit with $72,000 in cancellations in a single day. Workers in the hospitality industry could not get to their jobs, and some staffers at Valley View Hospital had to be flown in by helicopter from their homes on the other side of the slide.
"Our resiliency is being tested," Mayor Jonathan Godes said. "We will recover, but communities that can't, communities that don't have the ability, the finance, the tax base to be able to do projects, to provide a bit of resiliency, redundancy, are going to really struggle in the new paradigm."
When the interstate is closed, traffic is diverted through Steamboat Springs, a town of 13,000 people about a three-hour drive from Glenwood Springs that is a gateway to some of the best skiing and outdoor activities in Colorado. Hundreds of semitrucks and tractor-trailers rumble through the downtown corridor lined with shops and restaurants, braking at the eight stop lights and belching exhaust fumes.
"It's not how we want people to experience our beautiful place," said Kara Stoller, CEO of the Steamboat Springs Chamber of Commerce. "When I-70 is closed in Glenwood Canyon, the residents are not motivated or excited to even go through town."
Andrew Hoell, a research meteorologist with the National Oceanic and Atmospheric Administration, said "really extreme" weather events about a year apart led to the mudflow.
Record-low rainfall from January 2020 through May 2021, combined with historically high temperatures, created "a perfect storm," he said. A NOAA report said the phenomenon was "exceptional in the observational climate record since 1895."
"We call these compounding and cascading events, where they build on one another and they produce very bad consequences at the end," Hoell said.
Evidence that the mudslide was caused by climate change is "overwhelming," he said. "The higher temperatures are creating more demand of the land surface moisture, causing droughts to get that much worse."
Drought soon led to wildfire. Last year, the Grizzly Creek fire chewed up trees and other vegetation on both sides of the interstate. It burned for months, destroying over 32,000 acres and closing the interstate in Glenwood Canyon for two weeks. The fire was so intense that ash fell in Denver, 155 miles away.
Then came this year's seasonal monsoons, which typically cause intense mountain storms that pass quickly. This one dumped over 4 inches of rain in five days, double the average monthly rainfall, causing the ground to collapse on the burn scar and trapping over 100 people in vehicles below. The mudslide blew out the parapet wall on westbound I-70, ripped the road away on the eastbound interstate and crashed into the Colorado River.
Drone video revealed a gash in a mountain rising thousands of feet to what was once forestland. The collapse left 6 feet of mud and debris on the highway, which took 2½ weeks and 4,000 truckloads to clear.
"The problem that most people run into when they're looking at climate is they put it into silos, they compartmentalize it," Chinowsky said. "And that's not the way things work when it comes to a system. Anywhere you poke at it, somewhere else is going to get out of balance, and that's exactly what happened with Glenwood Canyon."
The Colorado River used to run wide through the passage, but it has narrowed with the accumulation of sediment, affecting the habitat and food supply of trout and other fish. Biologists are concerned that the fish that survived will not be able to build their nests, called redds, to lay eggs and that the insects they feed on will perish.
"We've had some reports from folks that have been on the river rafting and anglers that have noticed some fish that have been dead as a result of the mudslides," said Lori Martin, an aquatic biologist with Colorado Parks and Wildlife. "But we don't know what that means long-term in terms of impacts to the entire population and fish communities."
Today, massive sandbags weighing 3,000 pounds are the first line of defense against another slide. The state is working to fully reopen the most damaged part of I-70 through Glenwood Canyon by Thanksgiving.
"Who knows what the future will bring?" said Holbrook, of the Transportation Department, who is bracing for the next slide and more damage to the picturesque highway.
"You can pretty much engineer yourself out of anything," he said. "What's viable? Can it be built? Yeah, but at what cost?"
CORRECTION (Sept. 12, 2021, 11:48 p.m. ET): A previous version of this article misstated when Interstate 70 through Glenwood Canyon was built. Construction began in 1980, not 1963.