Are these crampons good for something such as crossing a 3 mile glacier in Alaska?

SteveH, I disagree with you. The Vasak Crampons by Petzl here are completely strong enough for serious ice climbing. Much depends on the boots. With a boot that has a stiff sole / Vibram type sole will work great with these cramons. Trying to climb serious ice (steep) with boots that are not stiff and fairly supportive won't work well NO MATTER WHAT CRAMPON you use. The key to a secure fit is to fit the crampons well to the boot (no slop) and tighten the straps firmly. This is done, once the proper length is determined, by pulling on the straps and holding them tight by putting pressure on the strap at the point where it rests on the Flexlock binding, then you can thread the strap with the other hand and tighten, then retighten it all again for a secure fit. I would not recommend climbing hard/steep ice with aluminum crampons. Hope this clarifies and helps.

As stated above, these are pretty light crampons and can help add safetey to mountaineering or slushy trails, but serious ice climbing they would not be strong enough.