A massive 2014 landslide in western Colorado was caused by a rainstorm over melting snowpack that triggered a series of earth movements that began 10 hours before the fatal disaster, a report released Monday shows.
"Our results revealed that the rock avalanche was a cascade of landslide events, rather than a single massive failure," said the study led by Jeffrey Coe, a research geologist with the U.S. Geological Survey.
The 2.8-mile long West Salt Creek landslide on the Grand Mesa killed three men on May 25, 2014, and was the longest such slide in Colorado history.
The report found the sequence that eventually led to the massive slide began with an early morning rockfall event that combined with a later earth failure.
The slide near the town of Collbran lasted about 3.5 minutes and sent a wall of debris rocketing down from the Grand Mesa.
"If precursor events, such as the one at West Salt Creek that occurred (before) the main avalanche, could be seismically detected and placed in the proper context, they could possibly be used for avalanche warnings," the report said.
The men who died in the slide had gone up to find out why irrigation water below the slope that gave way had stopped running.
Coe says that irrigation ditch had likely been plugged by the rockfall 10 hours before the main slide.
"To really be able to use that precursor event for warnings, we'd need a much more detailed seismic network than we have in the U.S.," Coe told The Denver Post.
Coe explained there are proposals for such systems in some landslide prone areas, but not on the scale needed to provide universal coverage.
"I think we're a ways off from any kind of dense network," he said. "That kind of infrastructure just isn't currently available and the cost would be very substantial."
In October, the Colorado Geological Survey said conditions remain at the West Salt Creek area that could prompt another disaster of comparable magnitude.
Worries of another catastrophe have persisted in the slide's wake, particularly in June, 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 prompt fears among geologists of another catastrophe.