Looking for weak layers in snowpack

Monarch Ski Patroller Charlie McGrail looks for weak layers in a snowpack above Monarch Pass by using an extended column test. Avalanche mitigation professionals use these tests to assess the overall stability of a snowpack.

As snow accumulates on the slopes above U.S. 50 on Monarch Pass, Colorado Department of Transportation works with a team of avalanche mitigation experts to keep the roads clear.

Monarch Pass, about 25 miles west of Salida, contains 19 avalanche slide paths that threaten 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.”

Shanks said, “We are well above average for the year; we have had a huge year.” When asked about the impact of a big snow year on CDOT, she said, “Budgets are set at around $64 million, but we have contingency funds so that roads will always be plowed.”

The largest slide path on Monarch Pass is less than a mile north of Monarch Mountain ski area and is called “Big Slide.” It is a steep, rocky slope that extends above the westbound lane of U.S. 50 and has been the site of a large avalanche as recently as Dec. 22.

That event left a debris pile 100 yards wide and 7 feet deep across all three lanes, and the highway was impassable for several hours.

“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 it at night,” said Shanks.

To perform the avalanche mitigation on “Big Slide” and other avalanche paths near Monarch ski area, CDOT partners with the Monarch Ski Patrol, who are able to access the top of the suspect slopes on skis.

A small team of three or four patrollers carries 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 Bidner, former patroller and now director of Monarch Cat 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 rounds onto slopes.

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.

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