This is so cool (literally): NASA has just released satellite-view time-lapse videos of glaciers in Alaska and Yukon—each squeezing nearly 50 years' worth of changes into 6 seconds.

Mark Fahnestock, a glaciologist in the Geophysical Institute at the University of Alaska Fairbanks, stitched together satellite images from as far back as 1972. The videos cover every glacier in Alaska and the adjoining Canadian territory of Yukon.

Despite their brevity and sometimes-sketchy image quality, the videos are mesmerizing. They show many of the glaciers shrinking, some dramatically. A few actually grow.

The Malaspina Glacier in southeastern Alaska (photographed here from an airplane) is the world's largest piedmont glacier, meaning one that flows onto a lowland plain and spreads out in a fan shape. You can see its video history from 1972 through this year by clicking here. Photo by NASA/Operation IceBridge

"We now have this long, detailed record that allows us to look at what's happened in Alaska," Fahnestock said in a NASA news release about the videos. "When you play these movies, you get a sense of how dynamic these systems are and how unsteady the ice flow is."

Fahnestock talks about the glaciers and the images in a 4 minute 25 second NASA video. You can see (and download) it here, along with a dozen of the time-lapse glacier videos, on the NASA Goddard Media Studios website.

"The reaction I get from other people that study glaciers is that I watch these videos too fast," Fahnestock says in the explanatory video. "I like to see the fluid nature of the ice. It lets you see the ice on the land as sort of this very active participant in what's going on."