Climbing - Avalanches
Even in the 21st century, with over a hundred years of climbing experience and modern gear, avalanches still kill many each year. One of the reasons lies in something called, appropriately enough, catastrophe theory. The physics is complex, but the basic ideas are simple: avalanches occur abruptly and are extremely hard to predict.
Imagine an ordinary sandpile, on which you drop a few sand grains at a time. It builds up and up until, with the addition of only a few grains, the whole thing comes sliding down in... an avalanche. That scenario is even more true of huge rocks slides and snow collapses.
The reason is that the forces that keep layers of rock or snow together are generally hidden from view, and a small change can trigger a big reaction. Those changes are the result of millions of tiny adjustments as the pressure and temperature change. At a certain point, the ever present force of gravity overcomes forces keeping them in place and part of the mountain comes crashing down.
Those changes are more likely during transition periods, at daybreak or as the spring thaw arrives, for example. But they are occurring all the time and, since you never know what the status of the mountain and forces acting on it are, continual caution is called for.
Paranoia is not beneficial. For one thing, it muddies your thinking and slows your reactions. But be alert. Look for the signs of impending problems. And - most important of all - stay out of harms way as much as possible. Those are the keys to a safe climb.
When you're moving to a destination up a slope, maintain some lateral distance between members of the group. It's tragic when even one life is lost, but this technique has many times prevented one tragedy from becoming large scale and taking out an entire party. Also, the odds are much higher that someone trapped can be freed if others are able to react quickly. If everyone is buried, the result is almost certainly a disaster.
Avoid any snow covered area where heavy snowfall or rain has occurred recently. Avalanches are much more likely where a top layer is loose and rain acts to loosen the bonds underneath.
Convex slopes represent a greater risk than concave slopes. One that's concave could be a natural feature or it could be that combined with the fact that snow has already avalanched. But a concave area is a clear sign that there's less snow to fall, or it's already fallen.
Avalanches are much more likely on smooth ground. Try to move in areas with known useful ground cover and terrain. Grass, rock slabs and bushes help keep lower layers stable. Trees allow snow to pile up and take the impact of moving snow when it does slide. Boulders make very effective ground for lowering the odds of an avalanche.
The angle of the slope plays a large part. Flat ground may experience wind-driven snow drift, but can't avalanche. Very steep ground doesn't accumulate much snow. What falls on it falls easily away. But ground between 25-40 degrees represents a relatively much higher risk.
Knowing the terrain and conditions can't eliminate the possibility of rock slide or snow avalanche. But they help improve your chances of not being the next victim.
