Highway Snow Mitigation
It is almost dark. Packs are loaded with explosives and the route teams clicks into their skis.
They would have preferred to have left by now but some things never go as quickly as planned. Four ski patrollers skate up and grab tow ropes behind two snowmobiles already idling, the driver ready to rip back up the mountain. Two skiers behind each snowmobile.
Through the darkening skies and the falling snow they look at each other and then nod to the driver of their snow machine. In a whine of a two stroke and pillow of blue smoke the day is still not over.
Five days of heavy snow had caused the Avalanche hazard to spike to “considerable” a forecast that indicates Avalanche activity is likely in Central Colorado. The weather had turned out the the biggest single snow event to impact the Sawatch Range in recent years and the highway department was struggling around the clock to keep the highway passable.
Attention turned to an ominous slope that looming over highway 50 on monarch Pass less than a mile south of Monarch Ski Area. It is known as Big Slide and it poses a big hazard. This particular stretch of highway has posed a problem in the past. As recently as 2004, three cars were buried when it released unexpectedly.
For this storm like every other major snow event along Monarch Pass, the Colorado Department of Transportation relies on the mountain’s ski patrol to access start zones that threaten the highway.
Monarch Pass, about 25 miles west of Salida, contains 19 avalanche slide paths that cross the road with a majority of them east of the Continental Divide.
CDOT partners with the Colorado Avalanche Information Center which provides daily avalanche forecasts from regional forecasters. “Their observations include some factors such as wind, drastic changes in temperature and large accumulations of snow” said Nancy Shanks, CDOT Region 5 Communications Manager. “CDOT follows their recommendations for avalanche mitigation on Monarch Pass.”
Even on big snow years U.S. 50 will be plowed. Shanks said that CDOT budgets $64 million each year with contingency funds if refills keep coming.
Big Slide is watched closely through every major storm cycle. It is a steep, rocky slope that reaches above the westbound lane of traffic. A slide there can bury the road for over a 100 yards in enough snow to bury a car completely.
“When there is a high risk of avalanche danger as determined by the CAIC, CDOT will close highways at the location of the avalanche path in order to conduct avalanche mitigation.” explained Shanks. By intentionally triggering avalanches the likelihood of large events that pose a threat to life and property are reduced. “We like to do it at first light to minimize disruption to travel but on Monarch Pass it is different. We work with the Monarch Ski Patrol so we do after the mountain closes,” said Shanks.
In order to perform the avalanche mitigation on Big Slide and other avalanche paths near Monarch ski area CDOT also partners with the Monarch Ski Patrol who are able access the top of the suspect slopes on skis.
A small team of three or four patrollers carry with them about a dozen explosive charges that are ignited and thrown onto the slopes by hand from above. “We use explosives from 2 to 10 pounds each depending on the conditions” said Gail Bindner, former patroller and long time director of Monarch Snowcat Tours. The team will stop at known troublesome locations to throw charges before advancing along the top of the avalanche path. Spotters from below help determine if the charges were effective.
CDOT also uses a truck-mounted “avalauncher” that uses pneumatic pressure to fire 2.2-pound round onto slopes.
Bindner was part of the first team of Monarch patrollers to work with CDOT to established routes used for mitigation work for the highway. “It had to have been about 1992,” she said “we went out and stood with signal mirrors to identify where to put the shots.” The shots were well placed. “It was massive,” said Bindner of the avalanche caused by their first highway route. “It had to have been 20 feet deep. Luckily we parked our cars below the slide path on the road and we were able to ski out and drive home.”
Once the mitigation work is complete crews begin to clear the road of debris. The length of the closure depends on how much debris was on the road and how many lanes were affected. According to CDOT during the 2013-2014 winter there 616 hours of road closures due to avalanche control.