Skier Triggered Avalanche Lower Snowfields

On April 4th, 6 skiers went up Hillman’s Highway with the intent of skiing the Lower Snowfields.  The exact details of how the avalanche was triggered, and by who, is difficult to ascertain. However, whether it was the group of 5 above, or the skier below, both triggers were about 12 to 13 meters away from the fracture/crown line.  This is fairly consistent with what pencil hard slabs have the capability of doing, having the propensity to propagate long fractures.  Sometimes this initial fracture leads to: 1. a long shooting crack with no failure, 2. immediate failure under foot causing an avalanche, or 3. propagating until it finds enough stress and weakness to cause failure remotely leading to an avalanche.  It appears this last example is what caused the avalanche in this case.   From the apex, or center highest point, a 13meter long /2cm wide crack runs up to where the group had been standing.

It is plausible that as the second skier started to move the initial fracture occurred in the hard slab and propagated to the area of utmost convexity and highest stress causing the avalanche.   The slope faces close to due East at 80 degrees and has a 40 degree slope angle at its apex.

The crown was 150m long and had an average crown depth of 80 cm.  The upper surface 20cm had Pencil+ hardness while the next 60cm’s down to 80cm layer was softer at Pencil-.  The bed surface was a melt freeze crust <1cm thick from the previous weekend before the Monday-Tuesday storm.

The debris was probed down to between 4’-9’ deep.   The avalanche danger was posted at Moderate.