Exploring North American glaciers

Glaciers appear to be as lifeless and immovable as the mountains from which many flow. But there’s much more to one than a casual look might suggest.

Ice covers about one-tenth of the earth today. It buries Antarctica and the Arctic Ocean. Almost all of Greenland lies under ice. And glacial ice streams down mountainsides around the world, even on the equator.

Some 20,000 years ago an age began that would eventually cover almost a third of the earth with ice. Bulldozing down from the north, ice reached what are today the suburbs of New York City. The ice carved out the Great Lakes, scooped out Scotland’s lochs and gouged out Norway’s fjords. Around Canada’s Hudson Bay the ice was almost two miles thick.

By about 10,000 years ago, though, the ice had retreated and the age ended. But the ice hasn’t completely disappeared. Most — but not all — of the hundreds of glaciers around the world today are ice-age leftovers.

How glaciers form

Glaciers typically develop in mountain heights. The glacier-forming process usually starts in snow-filled depressions, called cirques, whenever one year’s snow does not melt away before the next year’s arrives.

Fresh snow consists of about 10 percent delicate flakes and 90 percent air. So small are the individual flakes that some 50 million make up an average snowball. Under a microscope you would see that each flake has a six-pointed shape. The points keep the flakes apart, giving snow its fluffiness.

As the water composing the flakes evaporates the points become rounded. Gravity pulls them closer together, forcing out some of the air. When additional snow falls its weight packs the underlying flakes still closer. Some individual flakes even begin to merge.

Over the years new snow accumulations continue packing the snow beneath. (The face of a glacier may reveal these accumulations through thin ribbons of dirt separating the annual layers.)

Alternating winter freezing and summer thawing coupled with the compression from the accumulated snow mass eventually squeezes molecules together, forming ice crystals. The bonding molecules squeeze out practically all remaining air except for bubbles trapped here and there in what has now become glacier ice. These bubbles make a glacier appear white when viewed from a distance.

You can test a small piece of glacier to see if it has transformed into ice or is still in the process. Blow hard through a piece — but don’t let it touch your lips. If your breath bounces off it, it’s probably glacier ice. Should your breath flow through, it’s still snow in the transformation process. At this stage the snow is called firn.

Glaciers thrive in areas where cold, wet winters nourish them with snow and cool, cloudy summers help sustain them by cutting down on snow loss due to melting and evaporation.

As additional snow accumulations turn to ice, the glacier builds. Eventually, it completely fills the depression — the cirque — and begins to flow out. Regardless of how far from the cirque it travels, though, it still depends on snow falling over the filled depression — the accumulation zone — for its growth.

Life in a glacier

Even in such a harsh and barren environment as a glacier, you’ll find life. A red algae and small ice worms up to an inch long make glaciers their home.

The ice worms, ranging from yellow-brown to red-brown to almost black, move among the tiny air pockets, feeding on algae and pollen. You may be able to see them on cloudy days or when a glacier is shaded. The worms thrive at temperatures just about freezing. When sun warms a glacier’s surface the worms burrow deeper. If you spot a patch of red algae, check there for them.

Glacier types

Scientists categorize glaciers according to easily distinguishable characteristics. The two main types are ice sheets and mountain glaciers. Each also has sub-categories.

Also called alpine glaciers, mountain glaciers are constrained by the underlying topography which controls and directs their flow. Sub-types include:

• Cirques - Circular-shaped glaciers that have formed in depressions, basins or amphitheaters. When a cirque glacier fills its containing structure and flows out, its classification changes.

• Icefields - These glaciers flow out in all directions. But they are not entirely free flowing like an ice cap. The shape of the land does confine and control them.

• Valley - As the name implies, these glaciers flow through mountain valleys. The term river of ice derives from these glaciers. They may even have tributary glaciers flowing into them. The following are valley glacier sub-types:

— Branched Valley - A main valley glacier with tributary glaciers.

— Hanging - A cirque or valley glacier that ends at a cliff top. Hanging glaciers are dangerous to walk under. Large chunks of ice breaking off their face — a process known as calving — crash to the valley below.

— Remanié - Rather than growing from accumulated snow layers, these form from glacial ice that has fallen from hanging glaciers. Remanié is the French word for altered or transformed.

—Tidewater - Valley glaciers that flow into the sea. Calving tidewaters produce icebergs.

— Piedmont - Valley glaciers that flow out onto a plain, usually in a lobe shape.

— Rock - A glacier that has become covered with rocks and debris. Gray or black in color, it resembles a lava flow more than a river of ice.

1) A glacier's ice forms in the accumulation zone, but it is lost — or ablated — primarily at its face or terminus. If snow piles up faster in the accumulation zone than any melting, evaporating or calving, the glacier grows and moves forward, or advances. If not, it shrinks and retreats.

A general rule will help you tell if a glacier is advancing or retreating. An advancing glacier tends to have a steep face, a retreating one a sloping face.

2) Regardless of whether a glacier is advancing or retreating, ice within and on it is always moving. This bulk ice always moves forward, somewhat like a super-slow, semi conveyor belt. A glacier’s surface ice moves forward, pulled by gravity and pushed by the weight of accumulating snow. The conveyor movement transports relatively new ice from where it forms in the accumulation zone to the terminus. Ice at the bottom also moves forward but at a slower rate than the upper ice.

Even if the terminus is pulling back — retreating — the glacier’s conveyor effect is still transporting ice to the terminus. But the amount of ice conveyed is not enough to replace that lost. So the glacier retreats and the terminus gradually withdraws.

Some glaciers are stable, neither advancing nor retreating. The conveyor effect is then transporting just enough ice to the terminus to offset any loss.

The natural slipperiness of ice also aids a glacier’s movement. The slower-moving bottom ice of many glaciers actually slides over the ground lubricated by water. Geothermal heating — the heat coming from the earth — can produce sufficient warmth to melt enough water at the bottom of a glacier to minimize friction.

A glacier whose underbelly is frozen solid to the ground still moves forward, but at a slower rate because of the high friction between the ice and the bedrock.

Nature’s landscape modifiers

As a glacier moves it erodes and transports rock and debris. Rock — from small pebbles to huge boulders — becomes frozen into the bottom of a glacier. When it moves the embedded rock acts like a rasp to grate and scrape away the landscape. This new rocky debris can also become frozen into the glacier, adding to its eroding power.

Rock also freezes into a glacier’s sides. This rock, too, scrapes and tears away at the valley. In a process called plucking, an advancing or retreating glacier can actually pull rock frozen into it from the valley walls. Some glaciers erode so much of the lower walls that the upper portions collapse, falling onto the glacier. It’s then on its way to becoming a rock glacier.

Testing for glacier movement

Glaciers grind and pulverize some rock into a fine powder called glacier flour. Collect some water running directly off a glacier, and you can use this flour to get a rough idea of its movement.

You’ll need a two-liter plastic soft drink bottle and a coffee filter. Collect five bottlefuls — 10 liters — of runoff and pour them through the filter. The amount of flour captured by the filter depends on the rate of water draining from the glacier, how fast it’s moving and the composition of the underlying bedrock.

The typical glacier will leave less than a half-ounce of flour in the filter. But some relatively fast-moving ones grinding much material will deposit up to 18 ounces.

Moraines

The rocky debris that a glacier transports is called a moraine. Every glacier has some type of moraine. Debris pushed ahead is called a push or terminal moraine. A fairly high terminal moraine indicates a stable glacier — neither advancing nor retreating. The conveyor effect still transports rock and debris forward to the face where melting and evaporation allow it to pile up.

Moraines can also appear at a glacier’s sides, a lateral moraine, or as a stripe running down the glacier, a medial moraine. If tributaries merge their lateral moraines become a medial moraine for the now single ice flow. Spot a medial moraine and you can be sure you’re looking at a branched valley glacier.

As a glacier retreats the former terminal moraines remain put and become known as dump moraines.

Exploring North America’s accessible glaciers

While you can explore glaciers around the world, North America has dozens of accessible glaciers, many of which offer spectacular viewing. You’ll find them in Alaska, Western Canada, Montana, Oregon and Washington State.

• Glacier Bay - Located at the northern end of the Inland Passage some 55 miles northwest of Juneau. Numerous tidewater glaciers spill out of the St. Elias and Fairweather mountains. Often they calve small icebergs into the bay. Among the largest tidewaters are Muir and McBride glaciers. Both are almost two miles wide. Muir’s sheer face rises 265 feet above the water. McBride’s about 150 feet.

Best views are by sea or air. A sea kayak will let you get an up-close look. You can find local outfitters, tour boats, scenic flights and float plane taxis in both Gustavus and Juneau.

Among the outfits arranging sea kayak trips are:
Glacier Bay Tours and Cruises — http://www.glacierbaytours.com
Alaska Discovery — http://www.akdiscovery.com

Some cruise lines include Glacier Bay on their itineraries:
Cruise West — http://www.smallship.com
Cunard — http://www.cunardline.com
Holland America Westours — http://www.hollandamerica.com
Princess Cruises — http://www.princess.com
World Explorer Cruises — http://www.wecruise.com

Information:
Glacier Bay National Park and Preserve — http://www.nps.gov/glba

• Portage - The valley glaciers Byron and Portage and the hanging glaciers Explorer and Middle occupy the Portage Valley. To get there, follow the Seward Highway out of Anchorage for about 50 miles to the Portage Glacier road. About five miles down you’ll reach the Begich-Boggs Visitor Center where guided tours are available.

Information: http://www.alaska.net/~design/scenes/portage/portage.html

• Prince William Sound - Some 20 tidewater glaciers, including the Columbia, flow into Prince William Sound from the Chugach Mountains. Best viewing is by boat or air. You’ll find boat and air tours offered in Whittier and Valdez.

Among the outfits offering kayak trips are:
Prince William Sound Cruises and Tours — http://www.princewilliamsound.com
Pangaea Adventures — http://www.pangaeaadventures.com
Anadyr Adventures —
http://www.alaska.net/~anadyr/anadyr.index.html

• Juneau - Just outside the city sit the Juneau Icefield and Mendenhall Glacier. You can reach the visitor center for this calving valley glacier by heading north for about 12 miles from downtown Juneau. Public buses run between the center and downtown. The Mendenhall is a tributary of the Juneau Icefield.

Companies in Juneau operating Mendenhall tours include:
Alaska Icefield Expeditions — http://www.akdogtour.com
Alaska Travel Adventures —
http://www.alaskaadventures.com/flttrip.htm

Information:
http://www.snowcrest.net/geography/field/mendenhall

• Banff National Park - Among the park’s glaciers you’ll find: Horseshoe, a remanié glacier fed by avalanching snow and ice; Saskatchewan, a branched valley glacier with a prominent medial moraine; and Wenkchemna, a rock glacier.

Information:
http://www.banffview.com/parkscanada/index.html
Travel Alberta tourist office — http://www.discoveralberta.com

• Jasper National Park - Among Jasper’s glaciers: Angel, a spectacular hanging cirque glacier; the Columbia Icefield and Athabasca, a valley glacier you can visit on a ranger-guided tour.

Information:
http://www.worldweb.com/ParksCanada-Jasper
Travel Alberta tourist office — http://www.discoveralberta.com

• Glacier National Park - Rangers conduct guided tours of Grinnel, a cirque glacier.

Information: http://www.nps.gov/glac

• Mount Hood - You’ll find nine major valley glaciers all offering easy access via hiking trails.

Information: http://www.fs.fed.us/r6/mthood

• Mt. Rainier National Park - From the park’s Paradise Visitors Center you can follow trails to several valley glaciers.

Information: http://www.nps.gov/mora