The hard crust provided a slick base for the snow mass to ride down the mountain, moving like a lethal toboggan. The layer below the crust was softer than fist. He's referring to the hand test used to quantify snow hardness. If you can push your fist fully into a layer of snow with about the same force you feel comfortable tolerating against your nose, the snow is considered to be very soft. From there you progress up the hardness scale using four fingers, then one, then a pencil, and then a knife to penetrate the snow.
Depth hoar occurs because snow insulates the earth's surface.
Buried under a shallow snowpack, the ground acts as a heat source. When colder snow settles on top, a temperature gradient forms between the warm layers and cold ones, and a metamorphosis begins. The lovely stellar snow crystals that would normally bond easily are transformed into angular facets that will have nothing to do with each other. For want of a beacon This deep, weak layer could not hold the weight of a man and a snowmobile and it released, carrying them both into a gully and burying the man four feet below the surface. Unfortunately, the three friends he was traveling with were not wearing beacons.