A hillside in Provo Canyon where several tons of mud and large rocks broke loose Wednesday is still unstable and U.S. 189 will likely remain closed through Thursday and possibly longer.
Engineers for a construction firm working in the canyon flew in from California Thursday morning to evaluate the stability of the slide area. Utah Department of Transportation officials said fractures on the steep hillside that were 2 inches wide Wednesday, were more than 8 inches wide Thursday."That indicates there's still some potential for more to come down," UDOT spokeswoman Andrea Packer said.
If engineers determine the hillside is unsafe, UDOT will decide if it can stabilize the mountain and reopen the road. The road is closed at Wallsburg in Wasatch County and at the Sundance turnoff in Utah County.
The large slide came crashing down on the highway at about 1:30 p.m. Wednesday about one mile east of the Sundance turnoff. Byron Day, of Midway, was traveling to Provo when he saw a few small rocks come down on the road ahead of him. Suddenly, his vehicle was stopped in its tracks by a boulder more than two times the size of his full-size pickup truck.
"He saw some of the smaller stuff on the road, but he never saw the big rock that crushed his truck," Utah Highway Patrol Lt. Bardell Hamilton said.
The rock smashed everything but the driver's side cab of Day's truck. Miraculously, he walked away with a few scrapes and bruises. Had a passenger been in truck he or she likely wouldn't have been so lucky. Traveling a few vehicles behind Day was a large propane tanker.
"If the rock would have hit that truck it really would have been messy," Hamilton said.
Crews spent most of Wednesday afternoon removing the debris. Most of the rocks had to be blasted with dynamite. Many large trucks were unable to turn around on the narrow canyon road and waited more than five hours before a path was cleared.
The slide was one of many that broke loose Wednesday in Provo Canyon. Most were smaller and only a few reached the highway. However, after crews removed the large slide, another one came down across the road a few miles toward Deer Creek Reservoir. It too had to be cleared before workers could leave the canyon.
While the large slide occurred in an area of construction, UDOT officials say it was weather-related and not caused by the construction work. They say the soil basically thawed out to quickly and the ground didn't have a chance to stabilize.
"This is very typical activity for sudden changes in weather, especially after the cold temperatures we had a few weeks ago," Packer said.
The slide area is part of an ancient landslide that is well-known to Utah geologists. Called the Hoover Slide, geologists say the slide is creeping a few inches every year, causing slippage in the highway. However, as long as the highway runs on the north side of the Provo River it will always cross the slide's toe.
Though not as big as the ancient slide near Thistle that moved in April 1983 and blocked the Spanish Fork River, the Hoover slide has the potential to break loose and move uncontrollably if sufficiently saturated. However, state geologists say a Thistle-type slide in Provo Canyon is unlikely.
"The Thistle slide was a rare case where the whole thing started moving," said Gary Christensen, a geologist with the Utah Department of Geological Survey. "It's hard to tell how much water this slide would take for it to begin moving faster."
In 1983, Utah had more than 2,000 landslides. Christensen said geologists are comparing data from 1983 to this year, but don't know whether this spring will be as bad.
"I think this slide is an indication that we might expect a little more activity this spring than normal," he said.
Christensen said the high-hazard areas for landslides are Provo, Spanish Fork, Ephraim and Fairview canyons. Several areas in Davis County have high potential for mud slides.