At around 10:30 a.m. on September 19, two climbers triggered an avalanche on the Silverhorn route. The weather was clear, with light winds, and the temperature was near 0° Celsius. The leader described the snow as being “Styrofoam-like.” They had seen no signs of instability. The team was at an altitude of 3,200 meters, about 200 meters below the top, on a northern aspect, when the avalanche occurred. The party heard and felt a “whumph” underfoot, and an avalanche swept the roped pair down the mountain for 600 meters before they came to a stop.

One member was partially buried, with head and one arm exposed. Both climbers were carrying shovels, probes, and beacons, and the partner was able to excavate the partially buried climber. ACMG guides witnessed the avalanche, reported it, and assisted the two climbers. The team was transported by helicopter to Jasper, where one of the climbers was diagnosed with a fractured ankle.

ANALYSIS

Moderate winds and warming temperatures had created consolidated wind slabs over older faceted snow lying on ice. The top of this face transitions from 50° to 25° slopes, and the slab on this broad convexity was thinner and more prone to collapse. The avalanche was estimated to measure 500 meters by 750 meters and 0.4 meters thick (size 2.5). The team was prepared with the appropriate emergency equipment.