Colorado interstate closed indefinitely following mudslides

After a mudslide stranded over 100 motorists overnight and indefinitely shutdown a major interstate in Colorado on Thursday, the state is preparing to issue a state and federal disaster declaration.

Crews are still cleaning up the impacted area of I-70 near the Hanging Lake Tunnel in Glenwood Canyon where the mudslides occurred, and there is currently no estimate as to when the section of the interstate will reopen.

"The monsoon weather patterns means this threat is ongoing," Colorado Gov. Jared Polis said during a press conference on Monday. "Today's hail and rain could potentially do additional slides and we're not out of the woods yet with regards to additional damage."

He added that they won't know the extent of the damage until the debris is cleared and that there were some areas that were under 10 feet or more of mud. Due to the extent of the damage, the state would also be seeking aid at a federal level.

"We are also readying a state disaster declaration and a request for a federal declaration with the Biden administration," Polis announced on Monday in an update on the damage. "Glenwood Canyon is majestic, but its majestic nature makes for challenges when it comes to infrastructure, especially in the face of catastrophic climate change affecting states across the West. We have extensive damage to I-70 in multiple locations in Glenwood Canyon, and the monsoon weather pattern means this threat is ongoing."

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The mudslide occurred on Thursday night amid heavy rainfall and thunderstorms. A flash flood warning had previously been issued for the area earlier in the evening, closing the interstate. However, it reopened when the warning expired at 6 p.m., local time, according to an operational report from the Colorado Department of Transportation (CDOT).

Crews work on clearing the road after a heavy rain hit the area, sending debris cascading down the canyon side. (Facebook/Governor Jared Polis)

Around 9 p.m. that night, another flash flood warning went into effect for the area, and the update said that storm cells had quickly formed in the area. Not long after, debris from the burn scar of the Grizzly Creek Fire spilled over onto I-70 in Glenwood Canyon, according to the CDOT.

"Mudslides and debris reached I-70 within a few minutes," the update noted.

"Given the historic wildfires that we experienced last summer, the three largest in the history of our state, we knew that we would see the severe impact that burn scars and debris could have on a landscape," Polis said during a press conference on Monday.

A wildfire's impact on an area can last for years after the flames have burned away the vegetation, creating a burn scar. Grass, trees, shrubs -- all of it typically keeps soil in place during periods of heavy rain. But with the vegetation burned away, flooding and debris flows can happen frequently in and around the scars.

Locations downhill or downstream from burned areas are particularly susceptible to these debris flows and mudslides, such as the area downhill from the Grizzly Creek Fire, a wildfire that had burned during the challenging fire season of 2020. The greatest time of risk for this in the West is during the monsoon season.

"Just to put it into perspective the amount of rain that we've been having, average monthly rainfall is 2.4 inches in July, for the entire month," Polis said. "We had 4 inches drop in five days. So unusual monsoon rains on top of the burn scars and debris from the fires is the recipe that has led to the extensive damage and closures."

"The Grizzly Creek Fire also burned in 2020 but was not nearly as big as others, only burning around 32,500 acres," AccuWeather Meteorologist Brian Lada said. "However, it is a prime example of how a fire does not need to be significant in size to cause major disruptions."

He added that one of the factors that had played into the active fire season during 2020 was the lack of moisture from the monsoon, which was "virtually non-existent" in the Four Corners in 2020.

This is not the first time this summer that I-70 through Glenwood Canyon has been closed due to mudslides.

On June 28, all lanes on the interstate through Glenwood Canyon were reopened after crews had cleaned up from two mudslides within two days, according to the CDOT.

Over the last five weeks there have been intermittent closures across the state due to debris slides, Polis added during the press conference.

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