stu

Salt Lake » Mill Creek Canyon » Porter Fork » Main Porter

Main Porter Fork

9,500'

East

35°

Skier

Remotely Triggered

Soft Slab

New Snow

Density Change

10"

60'

300'

We started up Main Porter Fork. It was raining bellow about 7600'. Lots of cornice building and wind loading on the ridge from Sox's to Ice Box. We noted evidence of one natural avalanche from the ridge on a NE facing slope. We picked our way into Ice Box through low angle terrain. Hand pits away from ridge line at 11:00 AM did not indicate propagation through the slab. However ski cuts on a somewhat loaded test slope off of the ridge line produced a long running 12" deep x 15' wide SS on the 4th ski cut. Winds off the ridge line were variable and decreased in the afternoon. We noted increasing PI throughout the day and the skinner was filling back in rapidly. No collapsing or shooting cracks. Hand pits showed increasing sensitivity and slab formation through the afternoon. We picked our way up Main Porter Fork on low angle terrain to drop into West Porter Fork. Just past the saddle with West Porter Fork person breaking trail initiated a kick turn to avoid a steeper open slope. The slope collapsed and cracks shot out and propagated up the adjacent slope 100' above him. The slab was about 10" deep and 60' wide and slid right past his ski tips. The slab ran with considerable energy about 300' down into small trees. Measured slope of skin track where initiated was 33* (steeper than we thought). Adjacent avalanche path was estimated at 35* steepening to 38*. Phone was dead so no pictures.

RED FLAGS: Heavy precipitation intensity Poor snow pack structure: buried near surface facets with dense slab on top. Also basal facets Ridge top wind loading Natural Avalanches Increasing slab formation