GLENWOOD CANYON – A gigantic granite rock the size of a passenger van broke off a cliff wall in Glenwood Canyon at 10:15 p.m. Tuesday, crashing into several sections of Interstate 70.

No vehicles were damaged and no one was harmed due to the rock fall.

“We’re extremely happy no one was injured,” said Joe Elsen, a program engineer for the Colorado Department of Transportation.

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However, Elsen said it will take “several months” of lane closures and repair work before the highway is back to normal.

The rockfall occurred just west of the Hanging Lake Tunnel, and the rock ended up on the Hanging Lake exit ramp.

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Eric Langford, a maintenance worker at CDOT’s Hanging Lake Tunnel control station, said the first person from CDOT on the scene was Richie Drew. He was driving west when the rock fell 300 feet in from of his truck.

“He saw everything,” Langford said.

He said the rock, 8 feet tall, 10 feet wide and close to 22 tons, came off the canyon wall about 600 feet above. The rock barreled down the wall, clearing a swath of vegetation, and rolled right between the legs of a sign bridge that arched over the road.

“Think of a sign bridge as a huge 18-foot high croquet wicket,” said Elsen. “I went out there today and I couldn’t believe it. From the angle the rock came down, it was an expert shot. The rock didn’t even touch the legs of that sign bridge.”

The rock cleared the sign bridge, but “smoked the guard rail,” according to Elsen, and dinged up the elevated westbound lanes.

Bridge engineer Pete Mertes was called to the site Wednesday to assess the damage. Mertes is the project engineer in Snowmass Canyon on Highway 82.

“Portions of the cantilevered overhang are trashed, and the decks on both east and westbound lanes have similar damage,” Elsen said, adding that CDOT has already closed off any lanes that have structural damage.

The rock hit portions of pavement and concrete, crushed sections of the median guard rails, dinged up more pavement on the eastbound lanes, and came to rest on the concrete rail on the eastbound Hanging Lake off ramp.

“When you think in terms of energy relationships, it’s amazing to think of that rock stopping short like that,” he said. “The rock had to release all that energy before coming to rest.”

Over the next few months, maintenance workers will keep at least one lane of traffic flowing both east and west near the Hanging Lake tunnel while CDOT receives bids and oversees the repair work needed on the interstate.

“We’ve got a top notch maintenance staff at Hanging Lake,” said Elsen.

That staff was in charge of removing the big rock Wednesday. The rock became many small rocks, CDOT’s Langford said, when workers blasted the boulder by drilling three-quarters into its center, using a combination of gunpowder and water.

“We had five different drilling points,” he said of the rock’s demise, “and a 50-foot cord.”

Elsen said it’s difficult to predict when and where rockfalls will occur.

He said inspectors periodically review the canyon, and workers have put up rockfall fences in high problem areas.

Typically, during freezing and thawing weather, water creeps in between the cracks in the canyon rock. When the water freezes and thaws it contracts and expands, slowly working the rock free.

“I worked on the Glenwood Canyon project between 1983 and 1994. Back then, geo-techs made every effort to scale off the most likely candidates,” Elsen said of the rocks workers brought down before they dislodged on their own. “There’s a risk assessment with this canyon, and unfortunately, we can’t make it zero percent.

“We’ve had some warm days and clear cold nights,” he said. “That could have contributed to this rock coming loose. Hopefully, this rock is the last one.”

Contact Carrie Click: 945-8515, ext. 518

cclick@postindependent.com