The biggest US state is full of superlatives. Denali, the highest peak in North America at 20,320 feet, is still rising, pushed upward as a tectonic plate collides from the south. The collision has also created huge mountains along Alaska's Gulf Coast, where humid coastal air has produced the largest subpolar icefield in North America. The exceptional heights of Alaska's mountains are mirrored below sea level by the 22,377-foot-deep trench of the...