5.1.3 Gravity
Gravity causes avalanches to occur on sloped but not flat terrain. We'll use these graphics to see why.
Like all forces, gravity can be described in terms of vectors, with the gravity vector drawn to indicate the direction of its pull. The total gravity vector remains constant.
In flat terrain (A), gravity pulls the snowpack straight downwards towards the ground.
When a slope is introduced (B, C, D), the total force of gravity remains the same but the gravity vector can be represented by two components:
- One that's parallel to the slope (that runs along it), g1
- One's that's perpendicular to the slope, g2
There are several important relationships between the two components.
- The component that's parallel to the slope increases as the slope steepens. Conversely, the component that's perpendicular to the slope decreases as the slope steepens.
- When the slope is vertical (E), the slope-perpendicular vector is reduced to zero so all of the gravitational force is directed parallel to the slope.