Glaciology 101

THE EXQUISITE ART AND SUBTLE SCIENCE OF GLACIERS

When you're standing on a glacier, the ice is so blue that it hurts. Crampons squeak on brittle névé. There might be wind in your face, or rain or sun or snow. You can’t help but let your eyes sweep the landscape, tracing that undulating curve of relentless frozen power. There’s no denying it: they’re dangerous, beautiful, dynamic beings.

Scientists currently estimate that 10% of the land area on Earth is covered with ice, storing 75% of the world’s fresh water. That’s down from a high of 32% during the last ice age, but it still equates to more than 15 million square miles. Like huge rivers of ice, those glaciers carve valleys, sculpt mountains, and reshape every landscape they touch.

Each glacier is unique, of course. There are ice sheets, like those found in Greenland, which are permanent layers of ice covering extensive tracts of land. There are ice shelves, which are slabs of ice that float on the sea—including the famous Ross Ice Shelf in Antarctica, which is roughly the size of France. And there are the glaciers that form in the mountains, which are varied, dynamic, and plentiful. Mountain glaciers are on every continent, but in the United States alone they cover more than 30,000 square miles. You can find them in state parks, national monuments, and other public lands. They’re yours to hike, ski, climb, and explore, so here’s what you need to know.

ANATOMY OF A GLACIER

THE ACCUMULATION ZONE is where a glacier gains snow and ice through snowfall and compression. Ice begins to flow like a conveyor belt, driven by gravity and ever-mounting snows.

THE ABLATION ZONE is where the glacier loses ice through melting and evaporation.

THE FIRN LINE is a line across a glacier— usually visible from edge to edge—that marks the transition between exposed glacier ice (below) and the snow-covered surface of a glacier (above). During the summer melt season, this line migrates up-glacier; at the end of the melt season, the firn line separates the accumulation zone from the ablation zone.

CREVASSES are a crack (or series of cracks) that open in the surface of a moving glacier. They can be linear or arcuate, and they vary dramatically in both length and depth. Their orientation can be in any direction relative to the glacier’s flow.

COMPRESSION ZONES can be found where the underlying bedrock flattens out, which forces the glacier ice to compress. Crevasses often narrow or disappear.

LATERAL AND TERMINAL MORAINES are formed on the sides and tongue of the glacier respectively as ice recedes, scraping and grinding the bedrock and leaving boulders, gravel, and sand. Be careful if you travel on glaciers near these zones; the ice can be brittle, cracked, and unstable.

A BERGSHRUND is a single large crevasse that develops at the top (or “head”) of a glacier as the ice pulls away from the bedrock wall.

MOULINS are narrow, tubular chutes through which water enters a glacier from the surface. These are dangerous, as they’re often very deep.

A NUNATUK is an Inuit word that has come to refer to an exposed, rocky peak or ridge that pokes through the surface of an ice field or glacier.

CLIMATE CHANGE

Because they grow shrink in response to snowfall and snowmelt, glaciers are sensitive indicators of changes in regional and global climate. To grow, a glacier must receive more snow in winter than melts or evaporates the following summer. If more melts than accumulates, a glacier will shrink.

Case in point: in a recent National Geographic article titled “The Big Thaw,” Daniel Glick wrote that “the famed snows of Kilimanjaro have melted more than 80% since 1912. Glaciers in the [Himalaya] are retreating so fast that researchers believe that [they] could virtually disappear by 2035.” In a recent study conducted in the Olympic National Park, the 266 glaciers recorded in 1982 had been reduced to 184 in 2009. And the United States Environmental Protection Agency uses glacial mass as a key climate change measurement, stating that “glaciers worldwide have been losing mass since at least the 1970s, which in turn has contributed to observed changes in sea level.”

The effects of climate change on glacial ice will be felt around the world; sea levels will change, drinking water may become less available, and glaciers themselves may become less and less stable. As one geologist said, “If you want to explore these frozen treasures, don’t wait. Go now.”

IF YOU’RE ON OR NEAR A GLACIER…

1 LOOK FOR COMPRESSION ZONES.

They're often less crevasse-riddled than other parts of the glacier, making them good places to camp, travel, or rest. On Mount Rainier, for example, many climbers choose to camp in the compression zone of the Ingraham Glacier, which is colloquially known as “Ingraham Flats.”

2 WHEN YOU'RE PLANNING YOUR TRIP, ALWAYS CONSIDER HOW CONDITIONS WILL BE AFFECTED BY THE DIFFERENT TIMES OF DAY.

At night and in the early morning, for example, colder temperatures often make ice easier to navigate—crevasse bridges are more solid, you won't get baked by the sun, and icefall is less likely before the full heat of the day. If you’re on a boat hoping to see a glacier calve into the ocean, though, you’ll want to schedule your adventure in the mid-to-late afternoon.

3 KEEP AN EYE OUT FOR WORMS!

Iceworms—which are also called Mesenchytraeus solifugus, or “sun-avoiders”—hide deep in some glaciers during bright sunny days, then emerge to the surface of the snow and ice at dusk. Scientists believe that these tiny worms feed on algae and pollen grains, and are eaten in turn by birds and bats. They’re not on every glacier, but if you look closely you’ll find them in many places around North America.

4 DON'T EXPECT MAPS TO REFLECT WHAT YOU SEE IN REAL LIFE.

Climate change has dramatically affected glaciers, snowfields, and other ice formations, and many navigational aids haven't been updated to reflect new terrain. Double-, triple-, and quadruple-check all navigational and terrain management decisions—and whenever possible, assess conditions from above, where you’ll have a better perspective on the terrain.

5 IF YOU GET A CHANCE, CHECK OUT SOME OF THE ICE CAVES IN NORTH AMERICA!

They’re disappearing fast, but adventurous spelunkers can still find these chilly caverns in Washington, Idaho, Iowa, New York, and Alaska.

6 WATCH OUT FOR THE SUN.

Because snow and ice both have a very high albedo (meaning that they reflect a very high percentage of the solar radiation that hits their surface), glacier travelers are notoriously prone to terrible sunburns—even when it’s cloudy, overcast, or even precipitating. Use sunscreen with a high SPF, wear a hat, and always protect your eyes.

7 IF YOU SEE SOMETHING INTERESTING, DOCUMENT IT!

Glaciologists always want to know about current conditions, unique findings, and other phenomena that they may not have noticed (or have the resources to go see). If you see anything that strikes you as unique, snap some photos, note the GPS coordinates, and contact the National Snow & Ice Data Center at nsidc.org.

Words by CHARLOTTE AUSTIN

Illustrations by NIKKI FRUMKIN