If you have been reading about avalanches you have no doubt seen the terms 'weak layer', 'bed surface', and 'slab'. Fracture or fracture line is just refering to the spot where this 'slab' breaks off and starts sliding down the hill. The slab slides on the bed surface, and the tiny layer of snow btwn the slab and bed surface is the weak layer. So the portion of the slab above the fracture line stays in place while the portion of the slab below the fracture line tumbles down the hill wrecking all things in its path. You will also read about 'shooting cracks'. These are basically the beginnings of a fracture line and a very big warning signal to get the hell out of there, they can run anywhere from a few feet to 20-30 feet, any longer and they will probably completely fracture and the avalanche begins. This is what you need to be aware of and avoid, as its telling you there is a lot of unstable energy in the snowpack. There is no doubt in your mind when you see a shooting crack, it's very obvious what it is and the hair on your neck will stand straight up. However on a snowmobile you can easily miss these signals since we tend to move pretty fast and make lots of noise that masks any signals the snowpack is giving us. As a skier you have a much greater opportunity to see all of this stuff. Your best opportunity to see a shooting crack or even a full fracture without being in danger is to find a pocket of snow that has been windloaded, this snow will tend to be more cohesive and layered making it easier to see some cracks if you ride through it or walk around on it. Be sure to do this only in a safe area, 25 degree slope or less and not attached to steeper areas. Or better is to find a small windloaded test slope that you can cause to avalanche safely. Trust me, if the snow fractures you will recognize it immediately, the problem is it may already be too late at that point. Hope this helps.
