January 4, 2016

Avalanche Observation

Front Range: Peak 3 to 4 ridge

Human triggered avalanche (presumably HS-ASu-D2-R2-O) and close call along the ridge line from Peak 3 to Peak 4 (~4100′, presumably SW aspect).

One human caught and carried briefly, but able to escape off the slab.  One dog caught and carried, but uninjured.

The involved party’s report: It whumphed deeply and then propagated across the entire bowl feature with a crown ~4′ in center and tapering to ~10″ near the flanks, estimated at ~150-200′ wide.  It was triggered from ~20 degree slope, but the slope angle at the crown was ~40 degree.  Seemed to be persistent slab that failed at faceted layer between old wind slabs.

Approximate location at yellow diamond in center of photo:P4avmap1:4:16

Looking up at the crown:

Some size perspective:peak-4-crown-2

Another view, looking towards Peak 4.  This avalanche start zone is a repeat offender.  It has been triggered multiple times unintentionally and intentionally; it releases relatively reliably when stressed from the typical thin and weak trigger point just to the looker’s left of the apex of the crown.1:3:16 p4 av view

This photo shows the trigger point (circle).  The party was practicing safe travel rituals, and only exposing one at a time.  The human trigger was booting from the X along the dashed line to the O trigger point.  The human trigger was able to crawl and roll off the slab back towards the rock outcrop near the X.1:3:16 p4 av trigger zone

The triggering party estimates the slide to have run ~1000′, possibly triggering another slide as it descended.