To understand a tidewater glacier in Alaska – to picture its movement and how it sheds ice, or how it merges fresh water with salt water and shoots out the front – the first step is to remove it.

"Picture a valley without any glacier," said Roman Motyka, a glaciologist and professor at the University of Alaska Fairbanks. "You have all these streams feeding into the main river that drain through the valley and into the ocean. The same thing is happening, except it's happening underneath the glacier and it's exiting underneath the submerged face in the front."

Motyka is the self-proclaim...