Freezing, expanding, thawing, and repeating: that is what the water from the heavy fall rain and snow has been doing along the Hardscrabble deep inside the tiny and invisible cracks in the granite layers that define the mountain range for the past few months. Unseasonably warm temperatures and high winds finally allowed a weak rock face at the intersection of Highway 96 and 165, known as Mackenzie Junction, to collapse in a large landside Sunday afternoon that has closed the highways indefinitely.
Drivers started to notice a dusting of small rocks around 1 p.m. By 2 p.m., motorists were forced to work around large rocks that had tumbled into the road. One video sent to the Tribune by Mariah Raymond showed large cracks forming in the granite wall that stands well over 100 feet overlooking the intersection.
Shortly before 3 p.m., locals Sierra Wright and Quin Rasmussen were returning from a hike near San Isabel and noticed the hillside was collapsing. The rockslide was called in, and Rasmussen directed traffic away from the area. Shortly afterward, the entire face of the cliff collapsed, covering both lanes of the highway. Wright captured video on her cellphone at a safe distance.
At 4:25 p.m., the Custer County Sheriff’s Office stated that the Colorado Department of Transportation (CDOT) had assessed the situation and had called in a geologist to examine the hillside further to see if more might collapse. Because of the size of the rockslide and the uncertainty of the stability of the rest of the cliff face, crews will not be able to start cleaning up the highway until more information is gathered Monday.
CDOT stated Sunday evening that it anticipates a multi-day highway closure to allow rockfall mitigation to make sure the area is safe for crews to start the cleanup and repair.
The Wet Mountain Fire Protection District was able to get a drone to inspect the extent of the rockfall before nightfall, and the size of the rockslide is considerable.
The scientific name for the process of water freezing and thawing in cracks of rocks that can cause landslides is frost weathering or cryofracturing. Further, the Wet Mountains are made out of a metasedimentary with granite metamorphic rock and composite rocks that are multilayered. This type of geology is particularly prone to frost weathering as the layers are not bound together very well, and water easily works its way into the endless cracks. Highway 96 is no stranger to large landslides and rockslides that close the highway for days or weeks.
The wet weather this past fall, with the relatively warm temperatures the past several weeks, caused the thawing that often proceeds large landsides and rockslides in winter and spring. Highway 145 in Dolores closed for several days right after Christmas due to a large rockslide caused by the same weather pattern that is being experienced here.
The primary detour is to take Highway 69 north to Highway 50, which takes drivers to Canon City.
The Tribune will continue to provide updates as they become available.
Jordan Hedberg