The sinkhole that suddenly swallowed part of a Colorado highway is not a sinkhole, it's an old railroad tunnel, highway officials clarified on Tuesday.
The hole opened up on Highway 24 between Leadville and Minturn near mile marker 165 on Monday.
A variety of engineers, maintenance supervisors, and geological experts were called in and they determined the sinkhole is actually a century-old railroad tunnel, according to the Colorado Department of Transportation.
The tunnel was built sometime between 1900 and 1910, according to CDOT spokeswoman Ashley Mohr.
Mohr explained that the tunnel's wooden supports collapsed decades ago. CDOT thought the tunnel had settled and built over it many years ago.
However, with the warmer weather this year, the frozen soil deep in the tunnel thawed and the hole was exposed.
CDOT said the hole is currently estimated to be about 100 feet. Officials said the tunnel is so deep, engineers still found some ice inside.
"We've had problems in that area in the past and this may be the cause of it," said Mohr.
The collapsed tunnel was the first tunnel built under Tennessee Pass. Union Pacific replaced the tunnel with another one about 600 yards away. It is re-enforced with concrete.
CDOT has marked the hole and barricaded it from the highway, but only one lane of US 24 is open to traffic.
Right now, CDOT flaggers are directing traffic in one direction at a time.
This evening, a portable traffic signal will be in place to direct motorists until the tunnel is filled in and repaired.
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