More information: Wet slab was human triggered at 11:45am by snowboarder. Person reported "barely crust" conditions at the top. Descended down slope, triggered wet loose, continued down slope as snow softened to 6" depth. Got to bottom and looked up to see LARGE slow moving wet slab, large enough to bury, injure, or kill. Likely scenario: small wet loose triggered large wet slab. Don't underestimate the solar heating and rapidly rising temps early in the day on southerly aspects.