From The Grand Junction Daily Sentinel (Gary Harmon):
Authorities are monitoring the pond atop the land that tipped in toward Grand Mesa in a major landslide two years ago, watching for signs that it could spill over as the high country snowmelt increases.
Mesa County and other officials went to a level of heightened awareness a week ago, as what is known as the “sag pond” filled with snowmelt, said Pete Baier, the county’s deputy administrator for operations.
“We’re entering into uncharted territory here for the next few days,” Baier said on Thursday.
The pond is filling to the point that it is as high as it was last year, when there was concern it might spill, “and there’s still snow up there to melt,” Baier said.
The nearly 3-mile-long landslide of 39 million cubic feet of rock and debris slid down the West Salt Creek drainage on May 25, 2014, engulfing three men — father and son Clancy and Dan Nichols and Wes Hawkins — who were working to clear an irrigation ditch in the drainage.
The water in the sag pond passed the 20-foot depth mark and the question isn’t so much whether it grows higher, but whether it suddenly falls, Baier said.
With that possibility in mind, the county alerted Collbran and Plateau Valley officials, as well as state and federal authorities, about the status of the pond.
The next step — alerting residents that they should be prepared to move — will depend on a variety of factors, such as a shift in the block still clinging to the side of the mesa, a new source of water running into the pond, or a large thunderstorm headed toward the slide, Baier said.
A shift or break could result in an evacuation of downstream residences.
The pond holds about 400 acre-feet of water and no one knows how long it can be contained, or what might happen should it suddenly release, carrying with it tons of mud, rock and debris.
Heavy rains two years ago soaked the soils as the snowmelt geared up, setting the stage for the slide.
There’s no prediction of rain, but there is more snow atop the mesa than there was two years ago, Baier said.
From The Denver Post (Jesse Paul):
Mesa County authorities have raised the alert level at the site of the massive West Salt Creek landslide near Collbran because of increased spring runoff.
The county said Friday it has initiated a Level Two response to its emergency preparedness action plan, advising residents in the area to be prepared to evacuate.
A pond at the landslide area released water and cut a new drainage channel Thursday evening.
“Mesa County Sheriff deputies are contacting people who live nearby in addition to reverse 911 notifications,” the county said in a news release. “Road and Bridge equipment is being staged in Collbran as well as thousands of sand bags in the event flooding becomes an issue.”
The 2.8-mile-long West Salt Creek landslide on the Grand Mesa on May 25, 2014, was the longest such slide in Colorado history. It killed three men.
Worries of another catastrophe have persisted in the slide’s wake, particularly last spring, when heavy rains prompted warnings. The main risk, officials say, is in early spring as snowmelt travels down the slide area.
Water that has collected in a depression near the top of the slide has created a “sag pond,” which continues to spark fears among geologists of another catastrophe.
In October 2015, the Colorado Geological Survey said conditions remain at the West Salt Creek area that could prompt another disaster of comparable magnitude.
The highest alert level for the landslide area is Level Three.
“The alert level was raised because the pond spilled over the slump block at the head of West Salt Creek early (last Friday) morning,” said Jeffrey Coe, a research geologist with the U.S. Geological Survey who has studied the slide. “There was some local flooding near the toe of the landslide. A flood watch was issued for areas downstream. But from everything that I have heard so far, the impact to downstream areas has been minimal.”
Coe’s research showed the initial deadly slide was caused by a rainstorm over melting snowpack in the area, triggering a series of events that led to the disaster.
The county said Friday that an initial water surge made it through Collbran without overflowing the banks of Plateau Creek. There have been no signs of land movement.
“Right now the landslide is doing what we want and expect it to do,” the county said. “However, if Mother Nature decides to take more land down, we want residents to be ready to evacuate.”
Officials say they have a team flying over the area that will monitor the conditions.