Skied first run from main ridge on a east aspect.  Some pockets of surface hoar 4-6" deep which didn't fail.  This slope had wind damaged surface hoar last weekend.  Dense fog moved in for second run.  Poor visibility led to an alteration of our intended route down a generally safe sub ridge onto a steeper slope which was a protected NNE aspect.  The first skier ski cut our alternate route without failure and skied to a relative island of safety.  The second skier then entered the slope which fractured at his feet (6-16" deep crown) and ran downslope just catching the first skier knocking him off his feet, but not carrying him.  Voice contact was made with all 3 skiers and the third skier entered the slope to the right of the second skier releasing another slide of similar depth which ran past the first skier who had moved to a safer position.

This slope was more wind protected and had a more defined layer of surface hoar which was buried by deeper snow.  This combined with a steeper slope angle was the difference between the first slope we skied and the second which failed. I think as we get more snow load the danger will rise substantially in the areas with this buried surface hoar layer.