Tuesday, August 4, 2009

On the Road Again - Post 10: Glaciers

Borders, like time, have always seemed a little silly to me. They're merely constructs, real only because we agree to consider them so. At the Waterton-Glacier International Peace Park, established in 1932, Canada and the United States decided to agree otherwise for one segment of the line on the map dividing them. Marked only by a couple of white markers, one on the ground, one high atop a ridge, and a swath cut in the forest at the 49th Parallel, that segment is the longest undefended border in the world.

The peace and trust signified by the decision to ignore the border seem utterly at home in serene Upper Waterton Lake (pictured above) and the rest of this magnificent park. There's a super-abundance of beauty here: craggy peaks; gentle slopes; sheer drops; deep chasms carpeted in green and taupe; thick forests; glittering waterfalls; vast pristine lakes hundreds of feet deep, most of them astonishingly clear, others tinted turquoise by suspended glacial silt; even the engineering marvel that is the Going-to-the-Sun Road.

I've written about these beauties before and barely scratched the surface. It's tempting to go over that territory again or to mention cool facts I left out the first time, such as Triple Divide Peak. The Continental Divide winds its way through the Northern Rockies; at Triple Divide Peak, not two, but three watersheds intersect. Depending on exactly where it falls on the Peak, a raindrop will ultimately end up in the Hudson Bay, the Pacific Ocean or the Gulf of Mexico. An area only as big as the span of a hand determines which direction the drop will travel.

Instead, though, I'm going to write about glaciers, my absolute favorite geological phenomenon and the reason Waterton-Glacier looks the way it does. Its topography is a textbook illustration of the effects of glaciation - if the textbook were the educational equivalent of an illuminated manuscript.

Glaciers cover about five million square miles of Earth's surface, four million over Antarctica, 750,000 over Greenland and the other quarter-million scattered around the rest of the world. Glacial ice is the largest reservoir of fresh water on the planet, and is second only to the oceans as the largest reservoir of total water. As such, glaciers are crucial to both world water resources and variations in sea level.

And they are fast disappearing. In Glacier NP, for example, there were 150 at the end of the cooling trend known as the Little Ice Age (1550-1850). By the middle of the 20th century, there were 50; in 2005, there were 27. If global warming continues at current levels, all the glaciers in the park will be gone by 2030.

That will be very sad, not only for aesthetic, fresh water or sea level reasons, but also because glaciers are an extraordinary phenomenon and the sculptors of some of the most striking landscapes on Earth. Glacial ice comes in second to streams as an agent of erosion, but what a glorious second.

Glaciers are the beautiful ice-blue result of climates cold enough to permit snow and ice to survive year-round. When over time the amount of snow that falls is greater than the amount that melts, a remarkable transformation takes place. Delicate snowflakes are converted by a process called sublimation into vapor that instantly recrystallizes into a granular ice called firn or névé. The sand-sized crystals then bump into each other and melt at their points of contact. The resulting water flows into the spaces between the grains and instantly refreezes, creating a mass of glacial ice.


Once the mass reaches a thickness of 150 feet, the weight of the top ice causes the bottom ice to become plastic and flow. Remember, in geology "plastic" means neither a liquid nor a solid. The rocks in the asthenosphere portion of the mantle are likewise plastic and for the same reason: the weight of the overlying rocks in the lithosphere. Plastic flow occurs because the ice (or, in the case of the asthenosphere, the rock) is composed of layers of molecules stacked on top of one another with relatively weak bonds between the layers. When the stress caused by the weight of a higher layer exceeds the strength of the bonds between the layers, the top layer moves faster than the layer below. Voil
à
! Plasticity.

I understand plastic flow and I can explain it, but it seems magical to me anyway and it's one of the big reasons I love glaciers. Another is the way they operate. As glaciers advance (which means grow in size), they erode the rock under them spectacularly. They're very workmanlike about this, despite the dramatic results. Glaciers physically remove chunks from the underlying bedrock and pull them up into the ice. (This process, called quarrying or plucking, is accomplished by the very same eons-long freeze-thaw process that carved Bryce Canyon's eye-popping rock formations.) The rocks so taken up in the ice abrade the bedrock over which the glacier moves, effectively turning the flowing ice into a colossal piece of sandpaper that scours, polishes and stripes the surface below.


Glaciers come in two varieties: the stodgy-seeming continental (like Antarctica and Greenland) and the flamboyant alpine (like the rest). What they do is identical: form, advance, retreat, and erode the landscape. How they do it and what it looks like when they're done are very different.


Continental glaciers form only in polar regions and they sit on huge horizontal surfaces. Constantly falling snow causes the ice to collapse under its own weight, which moves the whole mass. The movement is very slow, only
15 feet or so per year. When they eventually retreat, continental glaciers leave landscapes that look like Canada east of the Rockies or the Finger Lakes region of upstate New York. This topography may seem boring, but it is, in fact, the result of ultra-dramatic glacial activity. Advancing continental glaciers actually increase the relief of the bedrock over which they move. But when they retreat (think "melt"), they deposit gigantic loads of glacial till (the stuff they've quarried along the way over eons). The till piles up and piles up, and eventually it reaches and buries the high-relief peaks, turning the landscape into flat or very gently rolling plains dotted with depressions where water collects into lakes.

Alpine glaciers are the showboats, much flashier in terms of how they move and the landscape they leave behind. They form in the headwaters of V-shaped mountain stream valleys. First, the growing mass of ice digs a bowl into the mountainside called a cirque. Eventually, the ice overflows its cirque and goes careening down the mountain (well, geologically speaking - the rate of movement is typically a foot or so a day). The glacier spills into the stream valley below and transforms the existing V-shape into the tranquil, soothing U-shape characteristic of glacially created valleys.


Alpine glaciers indulge in a bunch of other acrobatics as well. They can form in adjacent valleys on two sides of a mountain and eventually sculpt knife-sharp ridges (aretes). They can tunnel through ridges and create high mountain passes (cols). They can get together and gang up on all sides of a mountain peak to create a horn (think of the Matterhorn or the Grand Tetons).


The forces of gravity that caused alpine glaciers to spill down mountainsides in the first place are still at work when these glaciers retreat. They deposit their quarried loads in moraines below and sometimes astride the cirques, filling up valleys (remember Jackson Hole?), but leaving the highest ground craggy, the cirque basins filled with glacier remnants or cold clearwater lakes (called tarns), and the slopes down which they flowed polished, striped and spectacular. The sculpting effected by alpine glaciers is superimposed on topography already carved by streams, and the combination is what we have to thank for scenery as incredible as the Northern Rockies and the Alps.


Although they, too, are in retreat, the Mendenhall Glacier in the Juneau icefield and especially the Hubbard Glacier in Alaska's Yakutat Bay retain miens of power. It is possible to look at them and see as well as comprehend the gargantuan work they've done and still do.


By contrast, the glaciers in Waterton-Glacier NP are small, outwardly inert, sad even. They seem to be clinging by their metaphorical fingernails to their cirque basins and mountainsides as if for dear life. If you know nothing about how glaciers work, you might find them pathetic. Armed with knowledge, however, you have to be impressed. With their dazzling handiwork spread out around and below them, Glacier's glaciers are like proud great-grandparents at the head of the table - aware that their work is done and content in the realization that they did a superlative job.


We saw a veritable wildlife jamboree on this visit: a black bear; a perfectly posed ring of bighorn sheep; a more independent, but equally picturesque, lone bighorn; a deer wandering through the Logan Pass parking lot looking for all the world like a prospective car buyer checking out the inventory; three mountain goats, including the baby pictured below; a stag that sauntered up to a hedge, sat, stretched his elegant neck, posed thusly for 15 minutes, then rose and sauntered off, his shift apparently over; and another black bear.

2 comments:

Hiro Boga said...

Debra, thanks for this fascinating article on glaciers, and for sharing your beautiful photographs of the mountains, and the wildlife that lives in them.

When I first moved to Canada, the mountains drew me into their gorgeous, glaciated hearts, as mountains always have. I've had a love affair with the Rockies ever since.

Raul Ramos y Sanchez said...

Hi Debra,

Thanks once again for a fantastic post about your travels with its rich geological narrative. You have introduced me to Triple Divide Peak which I never knew about and now hope to visit some day. Kathy and I have been enjoying -- and learning from -- your blog series. Thanks for keeping us posted on your posts. They are fascinating.