Cardiac Ridge Avalanche: Part 1

I'm going to present this in two parts.  Part 1 will be my best shot at presenting the objective facts -- 3rd person account, no wishing this or that, and no swear words.  Part 2, which might come later after I process it, will be my own subjective analysis.

A group of 4 skiers (Skier 1, Skier 2, Skier 3, and Skier 4) gathered the morning of December 12, 2009 in Big Cottonwood Canyon at Mill D.  They headed south, hoping to ski in the Cardiac Bowl/Ridge vicinity.

From December 12, 2009

Snow Conditions
About 5 inches of snow had fallen during the night (the "New Snow").  Winds were blowing from the southwest and had done so throughout the night.  On Cardiac Ridge, the New Snow had fallen on a layer of hard windblown snow.  A very cold period of 2-3 days had created likely created a layer of facets on top of the windblown layer.  There was some wind loading on the east facing slopes.  The snowpack was relatively shallow.

The Avalanche
The avalanche was triggered near the top of Cardiac Ridge.  Cardiac Ridge runs north and south and connects Mt. Superior and Mr. Kessler.  The skiers were working their way up the north end of the east facing slopes along a rock band and less than 200 feet from the ridge top when the avalanche was triggered.  An illustration of the skiers relative positions follows:

From December 12, 2009

Skier 1 triggered the avalanche from the position shown in the picture above.  Skier 1 and Skier 2 heard a "whumpf" and felt a collapse.  Skier 1 felt a slab under him move a few inches and stop.  A few seconds later, a soft  slab above and to the climber's left pulled out and began sliding down the slope.  The soft slab consisted of wind blown and fallen New Snow.  The soft slab most likely failed on the thin December 8-11 facets and ran on a hard wind blown crust.

The soft slab was about 10-12 inches deep and 40 to 50 feet across.  The total area is unknown since it quickly turned into a big powdery sluff. Here is a picture of the crown:

From December 12, 2009

The avalanche ran approximately 300 to 400 feet.  Here is a picture taken 100 feet above the burial site.

From December 12, 2009

The Burial
Skiers 1, 2, and 3 were sheltered by the rock band above them and generally out of the way of the avalanche path.  Skier 4 was directly in the avalanche path and was swept away.  Skier 4 was carried approximately 200 to 300 feet.  A portion of the avalanche ran down a gully.  Another portion of the avalanche piled up before a roll over.  Skier 4 was deposited in a low spot before a roll over and buried perpendicular to slope. His head was about 2 feet under. He was lying face up. He lost one pole, but held on to the other one.  Both skis were on -- dynafit toe pieces locked.

Skier 4 was located within 1 minute after the burial.  By wiggling his one pole, the basket created a disturbance on the surface and then exposed the tip of the pole, which was observed by Skier 1.  Skier 1 used hands to dig down to expose Skier 4's face.  Skiers 2 and 3 used shovels to dig out Skier 4.  Skier 4's face was exposed within 3 to 4 minutes after the burial.  Skier 4 was fully conscious and took a big breath when airway was cleared.  Skier 4 was uninjured.

Below is a photo of the burial site:

From December 12, 2009