Juneau Icefield

Trip Through Time

Embark on a trip back in time during a visit to the Juneau Icefield. Located in the Coast Mountain Range, North America's fifth largest icefield blankets over 1,500 square miles of land, and stretches nearly 85 miles north to south and 45 miles east to west. It feeds 38 large glaciers, including the Mendenhall, on the road system just north of Alaska's capital city, Juneau, and the Taku, the largest, visible only by boat or plane.

Proceed up any valley and observe the transformation. Watch the temperate rainforest diminish as the ice spreads like tentacles among the jagged mountain peaks.

What ancient process fashioned this stark landscape? How will it be transformed in the centuries yet to come?

Step back two million years to the Pleistocene when mammoths roamed the West and a cooling period locked moisture into ice. During this Great Ice Age several climate fluctuations nourished glacial advance and retreat, and vast sheets of ice enshrouded nearly a third of the Earth's land mass and one half of Alaska. Ten thousand years ago, as the climate warmed at the dawning of the Holocene, the ice released its hold on the land and retreated. In Alaska, ice remained at only the highest elevations. Continuing variations in climate prompted four smaller scale glacial advances and retreats. The most recent period of glaciation to shape the Juneau Icefield began 3,000 years ago and ended in the mid-1700s. During this time, many glaciers in Alaska, including those which flow from the Juneau Icefield, fluctuated with the climate, advanced, and again retreated after reaching their glacial maximum in the mid-1700s.

Although the Juneau Icefield is at least 3,000 years old, the ice itself remains relatively young because it is perpetually renewed through snowfall at upper elevations as it flows downhill in its glaciers. Glacial ice at the terminus of Mendenhall Glacier has flowed for 200-250 years on its 13-mile (21-km) trek to Mendenhall Lake across from the visitor center.

Big Daddy - The Juneau Icefield

The Juneau Icefield is a massive accumulation of ice and snow stretching from upper Taku Inlet north to Skagway. Scientists estimate the icefield's snow and ice depth to be from 800 to over 4,500 feet (245 to 1371 meters). It lies around peaks called nunataks which push through the ice. Devil's Paw, the icefield's highest peak, straddles the Alaska-Canada border and stands 8,584 feet (2616 m) tall. Like a parent, the Juneau Icefield sends its offspring down from the heights to find their way inexorably down between the peaks in the many glaciers it feeds.

Glacier in Retreat?

The Mendenhall Glacier reached its point of maximum advance in the mid-1700s, and its terminus rested almost 2.5 miles (4 km) down the valley from its present position. It started retreating in the mid-1700s because its annual rate of melt began to exceed its annual total accumulation. The glacier's terminus currently calves into Mendenhall Lake, where the water is 220 feet (67 m) deep. The ice is retreating at a rate of 100 to 150 feet (30 to 46 m) a year. At this rate, the glacier would take several centuries to completely disappear.

For Mendenhall Glacier to advance, the icefield's snowfall needs to increase, the glacier's rate of melt needs to decrease, or both. Glacial advance would require a reversal of the current warming trends.

Taku Glacier Marches to its Own Drummer

Stretching to ocean tidewater, the Taku is the Juneau Icefield's largest glacier. The climate changes that caused the advance and retreat of glaciers from the icefield also affected the Taku, which retreated in the mid-1700s with many of the icefield's other glaciers. However, the very nature of this tidewater glacier may cause separate advances and retreats unrelated to climate change. Fed by its substantial accumulation area, the Taku began to advance again in the late 1800s pushing forward over four miles, while other glaciers on the Juneau Icefield continued to retreat.

Today the Taku's melt almost equals its accumulation, and its terminus remains relatively stable, separated from tidewater by glacial debris. If its advance begins again, it may eventually block the Taku River as it has several times in the past. However, this transformation in the landscape may not come to pass for a century or more.

Juneau Icefield Research Project

Studying Climatic Change Through Clues in the Ice
The American Geographic Society established the Juneau Icefield Research Project in the late 1940s to study glacial formation, botany, geology and many other related topics. Presently, the Foundation for Glacier and Environmental Research manages this project, continuing research while providing combined academic and field training for educators, university students and high school students. Evolving from Dr. Maynard Miller's search to find a prototype area to study Alaska's coastal glaciers and trends in climatic change, the foundation encourages young scientists to integrate academic learning with field experience.

Every summer students and scientists pursue research on the Juneau Icefield at several of the fifteen permanent icefield camps, some of which are visible from flights over the icefield. Aided by skis and crampons, participants cross the icefield from Juneau to Atlin, British Columbia, and conduct field investigations focusing on the effects of climate change on the icefield. Many of the program's alumni have pursued careers related to research in the natural sciences.

The Mark of the Glacier

The base of a glacier works like a giant piece of sandpaper. As the ice flows downhill, the glacier plucks rocks from the valley floor, rocks that become imbedded in the ice. The glacier scrapes these rocks across the bedrock creating grooves and striations. The glacier's erosive power changes the landscape and scrapes much of the soil and rock from valley walls. Rocks scoured from the surrounding valley walls create dark debris lines called moraines on the edges and down the center of the glacier. As the glacier continues its path, it grinds rock to a fine powder called rock flour. Mendenhall Glacier's rock flour escapes with glacial melt water and creates the Mendenhall Lake's murky color. The glacier's retreat exposes its trimlines, slightly sloping changes in vegetation on the valley walls that indicate the glacier's height at its point of maximum advance. As the glacial ice melts or calves icebergs, the glacier drops geologically misfit rocks called erratics that its ice either quarried farther up the valley or that fell onto the ice from rock walls above the glacier. These granitic boulders can be seen lying on the metamorphic rock around the visitor center.

Life Around the Icefield

Plants Return
As Mendenhall Glacier retreats and uncovers bare rock, the wind carries seeds and spores of moss and lichen onto barren land. Alder, willow and cottonwood systematically grow in deglaciated landscapes. Glacial debris, poor in nutrients, depends on flowing lupine and alder to fix nitrogen in the soil, and all species add organic matter to the soil as they are overtopped and shaded out by other species. Spruce and hemlock ultimately rise to close the forest canopy, eventually creating an old growth forest. Encompassing almost 350 years, this sequence of plant succession provides habitat for an increasing number of plant and animal species.

Rocky Homes
Coyote, porcupine, squirrel, snowshoe hare, and short-tailed weasel build homes on the valley floor, and migrating songbirds build nests in the deciduous shrubs in the young forest. In Steep Creek, beavers work to create ponds while spawning sockeye and coho salmon provide a food source for black bears and eagles. Loons, gulls, and Arctic terns nest around Mendenhall Lake. And mountain goats use the rocky slopes and alpine meadows above and around the Mendenhall Glacier. The terrain protects the goats from predators who need more secure footing. The sparse vegetation is high quality, enriched by the nutrient-laden soil left by the glacier. Visitors to the Mendenhall Glacier Visitor Center have a good chance to see some of these awesome animals through the spotting scopes in the center's viewing room or through their own binoculars or telephoto lenses.

 How to Enjoy the Juneau Icefield

Flightseeing and helicopter tours, some of which offer a dogsled ride on the glacier, are among the options available to the visitor wishing to see the icefields. Trails around Mendenhall Lake bring fabulous views of the glacier and the surrounding area to the casual visitor and give the more adventurous a chance to get closer to the glacier, skirting the face to climb above the ice mass. Walking on the glacier is dangerous and shouldn't be tried without proper equipment and training.

Updated March 10, 2003

Contact us: mjjones@fs.fed.us

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