I understand that sun needs to hit a mountain side of snow and that creates a slick surface. But, there must be more to this because that doesn’t sound like it’s ACTUALLY it.
In: Physics
To understand avalanches you need to understand another phenomenon in physics. Any pile of aggregate material, like gravel, has a maximum possible slope. This is simply due to physics if the slope is too steep, gravity acts on the individual particle enough to overcome the friction and have it roll down until friction stops it.
However aggregate materials like snow and sand where the particles are so small, can reach a “super critical state” where the pile can go beyond the maximum natural steepness because the individual particles have some extra force attracting them to one another. In the case of snow, it is the fact that snow flakes have those tiny feathery crystal structures that get tangled.
When this happens it is not stable. Adding enough energy to this super critical area will cause a chain reaction where one particle overcomes friction and adds energy to the next which overcomes friction, so on and so forth. In the case of an avalanche that energy can be as little as a simple echoing yell.
There are different kinds of avalanches
But generally spoken snow has different layers. The deeper layers are compressed, really hard snow/ice. If this type of snow is exposed to heat, from the ground or the sun, it gets really, really slippery. It’s why Ice is so slippery when you step on it.
Ice at very cold temperatures isn’t slippery even when walking on it. But if you step on it, and it’s warm enough so your weight is enough to melt the upper layer of the ice, it’s super slippery.
That’s by the way the principle of ice skates, because all your weight rests on those narrow skids, which causes the ice under the skids to melt which provides a slippery sliding layer between metal and ice.
The same happens with the compressed snow/ice in avalanches. The layers of snow lying on a compressed layer that’s now super slippery looses grip and starts moving. Once snow is moving snow causes more snow to do the same.
If a skier causes an avalanche, it’s usually because everytime it snows, a different layer of snow results. They don’t grip on each other that good, so a skier shatters the weak connection between the layers and kicks of an avalanche.
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