There has to be some final nudge, some force or combination of forces, to account for the release of these masses of snow at a particular time and place. The engine of your car may be rated at 200 horsepower, but it cannot deliver an erg of energy until you press the starter. Such a fracture usually occurs at the sharpest part of a convex slope. The plane of cleavage of the fracture is characteristically perpendicular to the snow surface. How overloading operates to trigger an avalanche is fairly obvious.
Weight simply piles up until it overcomes cohesion-a final straw breaks the camel's back.
Vibration is related to shearing, but it is treated separately because, unlike the other triggers, it can operate at long range. They may also be started by vibrations transmitted through the earth and snow from heavy machinery or blasts. Avalanche control work with ex plosives frequently starts secondary avalanches at some distance from the detonation point. The most common triggers are overloading and temperature. There is nothing, of course, to prevent any of them from working in combination.