What caused crystal blue iceberg in Alaska park? It could be very old, experts say

A striking crystal blue iceberg was photographed in Alaska’s Glacier Bay National Park and Preserve, prompting the U.S. Department of Interior to offer an explanation.

The jagged block of ice appeared April 22 (Earth Day) on the park’s Facebook page, but the image didn’t get attention until the Department of Interior shared it Tuesday.

“Why is this glacier ice at Glacier Bay National Park and Preserve blue?” the department asked.

The question has gotten nearly 8,000 reactions this week, including an observation that the scaly-backed monstrosity “looks like a Godzilla ice sculpture.” The Department of Interior agreed; it does resemble Godzilla climbing out of the water.

None among the nearly 100 commenters has offered a sensible explanation, though one person guessed it might be due to the ice being salt free.

So what caused the phenomenon?

Experts say it’s largely due to intense compression, suggesting the chunk of ice might be very old. Variations of blue ice are often seen in Alaska, but this iceberg was more intense than most, park service photos showed.

“Glacial ice often appears blue when it has become very dense,” the Department of Interior reported. “Years of compression gradually make the ice denser over time, forcing out the tiny air pockets between crystals. So really, the key word here is compression.”

That’s the simple answer. A more complicated explanation notes long wavelengths of light are absorbed by ice, leaving shorter wavelengths that turn “more blue” as they travel deeper through the ice, the department said.

The bluer the look, the more “pure” the ice, experts say.

The U.S. Geological Service reports the oldest glacier ice ever found in Alaska was about 30,000 years old, “from a basin between Mt. Bona and Mt. Churchill.”

“Glacial ice mostly looks white, since it is typically jagged and worn from exposure,” the National Park Service says. “Glacial ice can also look black and brown from the rock and debris plucked up by the ice in its journey down the mountainside and incorporated into the flowing glacier.”

Park officials didn’t say when or where the crystal blue iceberg was seen. Glacier Bay National Park covers “3.3 million acres of rugged mountains, dynamic glaciers, temperate rain forest, wild coastlines and deep sheltered fjords,” according to the park’s website.

This story was originally published May 5, 2021 at 11:49 AM with the headline "What caused crystal blue iceberg in Alaska park? It could be very old, experts say."