The reality of most crevasse falls where an individual goes in over his or her head, is that they tend to take place when a person slips above a crevasse and falls in. But occasionally someone will fall through a hidden bridge and drop deeply into a crevasse.
It's really hard to find videos of accidental crevasse falls on the internet. But the following video is an absolutely stunning look at a catastrophic snow bridge collapse:
And while this next video isn't as scary to watch, it was taken shortly after an unroped skier nearly fell to his death in a hidden crevasse. He is still slightly in shock as he talks about the incident. All that saved him from the bottomless pit was a single ski binding attached to a ski jammed at the top of the crevasse.
Sometimes it is completely impossible to detect crevasses buried under the snow. Every now and then your foot will blow through a thin spot, but you won't go all the way in. In many ways a field of crevasses where you occasionally punch a foot through is a very safe field. When you know your moving through a minefield, you tend to take more precautions. So if you do go all the way through, it's unlikely that you'll go over your head.
Of the many thousands of days our guides and climbers spend in the mountains, we only see someone go in over their head once every two or three years. It's far more likely that this will happen in a spot where it is completely unexpected.
The best way to avoid a serious crevasse fall is to always be on guard. Unless an area has been heavily probed, assume that there are thin and dangerous crevasses beneath you. Avoid areas where it looks like the snow is sagging. And always make sure that there isn't too much slack in the rope between the climbers.
If an area looks dangerous, make the rope between the climbers tighter. You might even allow it to come up off the ground. If someone starts to go through, everybody should self-arrest.
Using good judgment and being on guard all the time is the best way to avoid the danger of a crevasse fall.
--Jason D. Martin
