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What's a Glacier, Anyways?

Daniel F
5 min read

You no doubt have heard glaciers mentioned a great deal, especially recently in the context of climate change. Moreover, if you’re planning an Alaskan cruise, you’ll soon be seeing some stunning examples of glacier ice up close and personal!

But have you ever wondered: What exactly are glaciers? Or, how do they form? In this article, I’ll be teaching you some Glaciology 101 so you can observe Alaska’s gorgeous glacier ice like the experts!

Glacier Basics

Perhaps you’ve heard a glacier referred to as a “river of ice.” It turns out that this definition isn’t too far from reality!

Glaciers can be defined in a few ways. Some of these might look overwhelming at first glance. Geologists, for example, might describe a glacier as a large, persistent body of ice that features a distinct accumulation and ablation area.

Luckily, though, it’s actually not too complicated! One easy way to think about a glacier is simply as a body of snow and ice that, instead of melting out in the summer, sticks around from year to year. Because it stays put, that snow and ice gets compacted under more and more layers until this dense material has nowhere to go but downhill! Thus a “river of ice” that flows downhill, carving into the surrounding land as it passes.

Glaciers are usually grouped into two categories. Continental glaciers, like the one that covers most of Greenland, dominate massive swaths of land and spread outward as new snow and ice accumulate. Alpine glaciers, sometimes called valley glaciers, are small in comparison. These are the glaciers you likely are most familiar with. They move downhill, usually at a rate of hundreds or thousands of feet per year, and develop deep cracks called crevasses. Continental glaciers may branch out into a series of smaller alpine glaciers at their edges. Several alpine glaciers converge in a large valley glacier. Notice the moraines (long black lines) from rock that was scraped off and transported by the moving ice.

Why Are Glaciers Important?

I’ll tell you why: Because they’re ridiculously cool!

Besides their exceptional coolness, though, glacier ice is responsible for many of the structures that define the world’s great landscapes.

Maybe you’ve seen pictures of the Alps’ iconic Matterhorn? This “horned peak,” as geologists would refer to it, was carved by glaciers that plucked rock off of its sides, sharpening it to the jagged point that it is today. Indeed, without glaciers, the Grand Teton and many of the Rocky Mountains’ most stunning peaks would be, well, less stunning.

Or perhaps you’ve visited Yosemite? Again, we owe glaciers for the millennia-long work they did in sculpting out these gorgeous U-shaped valleys. They also helped accentuate hard-to-believe natural features like Half Dome and El Capitan. Not to mention that they’re responsible for a number of other unique geologic structures!

Many important geologic features, such as Yosemite’s Half Dome, would look quite different if it weren’t for the slow-and-steady work of glaciers.

The Swiss Alps’ iconic Matterhorn owes its extraordinary sharpness to glaciers that plucked away at its sides. Notice the massive body of glacier ice at bottom-right!

Alaska Glaciers: A Geologist’s Dream

The Last Frontier is a special place for anyone with a penchant for glaciers. From the grand Columbia Glacier in the Prince William Sound to Matanuska Glacier north of Anchorage, Alaska glaciers are far more numerous and more massive than any other state. With 665 (!) named glaciers and thousands of smaller ones, there are more Alaska glaciers than anyone could hope to see in a lifetime.

Importantly, Alaska is home to an especially high concentration of tidewater glaciers, which flow all the way to the ocean. Keep an eye peeled if you find yourself face-to-face with Mendenhall Glacier, outside of Juneau, or with one of the massive glacier ice flows in Glacier Bay National Park, as you’re likely to see what’s referred to as a “calving” event: as the front ends of tidewater glaciers reach the sea and melt, they often break into massive bodies of ice that cascade down, often explosively, into the ocean!

Are The Glaciers Really Melting?

Sadly, yes. And at a very fast rate due to climate change.

I used to be skeptical, too. Could the situation really be as dramatic as it’s made out to be? When I visited the Last Frontier for the first time, though, I was blown away: I spoke with a number of locals who’d watched local glacier ice get substantially smaller even since a few years ago!

The point was further driven home for me when a lifetime Alaska resident drove me to a series of dwindling Alaska glaciers. He stopped at Portage Glacier, near Anchorage, and pointed out the spot where the now-dwindling glacier ice used to extend. It had withdrawn hundreds of yards in only a few decades!

Portage Glacier, between Anchorage and Whittier, has retreated hundreds of yards in the past century. Notice its 1914 position as compared to its extent in 1999.

Can you believe that’s the same glacier!? When I saw it a few summers ago, it had shrunk even more!

There’s not much doubt among scientists that most of the world’s glaciers are retreating. There are a handful of oddball glaciers that are actually advancing, possibly because they’re now sliding on a base that’s been lubricated by meltwater, but a typical glacier’s surface area has decreased each year for at least the past several decades. In other words, things are getting warmer.

In any case, you’ve chosen the right time to visit Alaska! No one’s entirely sure how exactly the Last Frontier’s tidewater and alpine glaciers will fare over the next few decades. For now, though, Alaska glaciers, representing a truly extraordinary array of glorious deep-blue ice, remains, in a word, unparalleled.

Pro tip: The famous Mendenhall Glacier in Juneau Alaska is receeding incredibly quickly in recent years, so much so that many tours can no longer guarantee that you'll be able to walk on the glacier. Your best bet for walking on a glacier in Juneau is with a helicopter tour. Check out these Juneau glacier helicopter tours. Or, explore all Juneau glacier tours.

A Few More Glacier Facts…

Glacier ice is blue because the super-dense ice that makes them up absorbs longer-wavelength light, like reds and yellows, while scattering short-wavelength blue light back toward your eyes.

The Laurentide Ice Sheet, a massive continental glacier that covered much of North America until around 20,000 years ago, stretched further south than present-day New York and Chicago!

Cape Cod, along the eastern coast of Massachusetts, is made up mostly of sediment that was reworked by ocean waves after a massive North American glacier melted out. For evidence of New England’s glacial past, look around for hills rounded by prehistoric glaciers the next time you fly into the Boston airport!

Check out some of these resources to learn more about the future of Alaska’s glaciers.

(1) & (2): USGS Fact Sheet 2006-3141; Retrieved 3 Jan 2017 from https://pubs.usgs.gov/fs/2006/3141/figure2.html

Daniel F
Travel Guru
Daniel first saw Alaska at age nine, after a weeks-long drive up the Alaska highway in a weathered RV. He's been in love with the Last Frontier ever since, and he's spent several months guiding teenagers in the wilderness around the Talkeetna Mountains north of Anchorage.

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