A giant sinkhole that caused part of a highway near the top of a Colorado mountain pass to be shut down earlier this week was caused by thawing soil in an abandoned, century-old railroad tunnel, engineers there said:
The Colorado Department of Transportation was forced to close part of U.S. 24 between Red Cliff and Leadville after the 100-foot-deep, 20-foot-wide sinkhole was discovered near the top of Tennessee Pass.
From the DOT's release:
After thorough examinations of the sinkhole yesterday involving a variety of engineers, maintenance supervisors, and geological experts, it was determined that the sinkhole is actually a century-old railroad tunnel that collapsed decades ago. The depth of the hole is currently estimated to be about 100 feet, and since the depths reach so far into the earth, much of the soil was still frozen until very recently. When the soil thawed, the hole was exposed
The tunnel—part of the Royal Gorge Railroad route—appears to have been constructed in 1880, authorities said.
[Slideshow: Massive sinkholes wreak havoc]
It's unknown when the highway will be reopened. But according to VailDaily.com, the closure, to this point, has not affected local tourism. Camp Hale, established in 1942 to provide winter and mountain warfare training during World War II and now a popular tourist destination, is still reachable via a 60-mile detour.