Geologists confirm: Roan Plateau rock falls near Rifle caused by earthquake, freeze thaw
A visible black mark caused by a recent earthquake as well as weathering, seen on the face of Roan Plateau on Wednesday morning. Ray K. Erku / Post Independent
Geologists with the Bureau of Land Management have confirmed recent rock falls spotted on the eastern cliffs of Roan Plateau were caused by a combined force of a small magnitude earthquake and the natural freeze-thaw process.
“That’s kind of a common thing there; I think with the snow it’s a little more visible,” BLM Public Affairs Specialist Eric Coulter said. “And being faced toward town, it kind of caught a little more attention. But erosion happens all the time and (it’s) why Roan Plateau looks as it does.”
On Feb. 15, a 1.8-magnitude earthquake — the largest recorded history was 9.5, in Chile — occurred 11 miles northeast of Battlement Mesa, according to earthquaketrack.com. The reverberation would eventually cause two massive black marks on the plateau face, cliffs which range between 8,000-9,000 feet above sea level.
The two visible rock falls on the plateau are not exactly holes, Coulter said. Instead, the visible spots are the equivalent to chipped rock, with the combination of snow, earthy material and shadows causing the black marks.
With the nearby presence of the Anvil Points Oil Shale Facility, a mine that once encompassed nearly 400 acres and extracted millions of tons of oil shale between 1944 and 1956, Coulter said the natural freeze-thaw process could possibly cause further erosion.
“There’s the potential of collapses and rock falls,” he said. “A lot of times in that free-thaw process you have water that drains through cracks and when it freezes it, expands and moves the rocks. And when it thaws, it becomes loose.”
After the mine’s closure in 1956, authority to lease the facility was given to the U.S. Secretary of Interior in 1962. Throughout the 1960s, the property was then leased to the Colorado School of Mines Foundation to be used for improving mining technology.
By 1972, after six years of being unoccupied, the property was leased to the Development Engineering, Inc., a company that proposed to extract an additional 11 million tons of oil shale. Mining operations would ultimately last until 1982.
Kent Rose, 81, who grew up in the Rifle area, provided the Citizen Telegram a detailed moment in the facility’s history when one of the mine shaft ceilings caved in, in the winter of 1954. Rose, whose father, Charles Kenneth Rose, was the mine superintendent at the time, said massive icicles almost killed an entire crew of miners.
“That was kind of the sport there for a while,” he said. “The icicles would hang off the cliffs and they’d get out their hunting rifles and shoot ‘em down so they wouldn’t get too much bigger before they fell and hurt something.”
In the process of shooting the icicles, one miner went inside the mine to get something, Rose said. Moments later, the miner came out, covered in dirt and dust. Rose said the miner was speechless.
“Everybody else went back into the mine and part of the ceiling had fallen out of the room,” he said. “It was about 8 feet thick and crushed all of the equipment that the miners — including my dad — was working on. It would’ve killed every damn one of them.”
Rose said, despite the miners determining the icicles to have caused the cave-in, he doesn’t speculate any imminent or immediate danger for the future of Roan Plateau.
“I would assume maybe that a big pothole would form up there some day if the shale kept falling out into those areas,” he said. “But I don’t think that would ever happen in my lifetime or yours.”
Coulter said BLM geologists and hazardous materials and safety personnel continue to monitor seismic and weathering activity at Roan Plateau. They also intend to eventually fly an unmanned aerial vehicle closer to the material to estimate the amount of rock that was discharged during the falls.
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