BLM officials analysing whether seismic activity, weathering behind rockfall on Roan Plateau

Ray K. Erku
Glenwood Springs Post Independent
A black mark on the rock face of Roan Plateau near Rifle on Friday morning. Ray K. Erku / Post Independent

Experts are saying a natural freeze-thaw process is the likely culprit behind a large rockfall that created two large black marks on the rock face of Roan Plateau late this week.

The natural freeze-thaw process occurs when water seeps into cracks, freezes and over time expands, causing rock and sediment to eventually corrode.

“What happens a lot of time through the winter is you have the thaw process that happens,” Bureau of Land Management Public Affairs Specialist Eric Coulter said. “Rocks can fracture and create a fall.”

Coulter said the black marks are located near — but not directly on — Anvil Points Mine, a massive subterranean naval oil shale mine that saw high productivity in the 1970s. In addition, the plateau, a feature of the Piceance Basin, was the focal point of producing billions of dollars in energy development revenue.

But weathering isn’t the only possible cause behind the black marks. BLM officials are also analyzing the possibility of a recent small-magnitude earthquake causing the rockfall.

“We are aware of the earthquake,” Coulter said. “We’re not sure how much of an effect it had on (the rockfall) or if it was a result from the earthquake.”

According to an online earthquake tracker, the tremor occurred Monday.

“I had my filters set up for magnitude 2.5 or bigger,” Hazard Management and Resource Restoration Specialist Jessica Lopez Pearce said in an email. “This was a tiny one… magnitude 1.8.”

BLM officials continue to analyze and study the size of the black marks, the amount of tonnage produced from the fall and whether future hazards are possible, among other analyses.

“Until we’re able to kind of assess the current situation, we won’t know exactly,” Coulter said.