Frozen Alaska

One of Alaska's natural wonders is found underfoot. It is permafrost, ground that remains frozen year after year. Made up of soil and rocks as well as frozen water, permafrost forms when the depth of winter freezing exceeds the depth of summer thawing.

Permafrost is thickest in arctic Alaska north of the Brooks Range, but it is found to some extent beneath nearly 85 percent of Alaska. On the arctic coastal plain it extends as much as 2,000 feet below the surface and is found virtually everywhere. From the Brooks Range southward its thickness gradually decreases and it becomes more and more discontinuous, broken by taliks, pockets of unfrozen ground. Near Anchorage, permafrost is found only in isolated patches, and in Southeast Alaska it is found only high in the mountains.

Much of the permafrost in Alaska is tens of thousands of years old. In arctic and interior Alaska, river erosion and gold mining have revealed the remains of now-extinct animals from the last great ice age 100,000 to 10,000 years ago, when animals such as woolly mammoths, mastodons, lions, and saber-toothed cats roamed what is now Alaska. Pingos and ice wedges are demonstrations of how permafrost has changed the landscape.

Many of the grasses, flowers, and berries of the arctic tundra owe their existence to the presence of permafrost. With only a few inches of precipitation a year, arctic Alaska could well be a barren desert. But permafrost forms a frozen floor beneath seasonally thawed ground, which can be from several inches to a few feet deep. Rainfall and snowmelt cannot percolate or drain off. Instead, water collects at surface, providing moisture to nourish plants and forming innumerable shallow lakes and ponds. Tundra plants, in turn, insulate the permafrost beneath them from thawing. They seal out the warm temperatures and sunlight of summer so the permafrost remains frozen.

Melting of permafrost can pose problems for humans and their activities. If overlying vegetation is removed or disturbed, its insulating qualities are lost and the permafrost begins to melt. Waterlogged ground becomes soft and collapses. Buildings and roads may slump or tilt, and vehicles bog down in mud.

Alaskans have developed innovative techniques for building on permafrost so it will not melt. Houses in permafrost areas are frequently built on pilings so they will not transfer heat to the ground. Floors may be insulated. Water and sewer pipes are installed above ground.

Engineering for the Trans Alaska Pipeline was complicated by the fact that three-fourths of the line, which carries oil at temperatures between 82 - 116 degrees Fahrenheit, would extend across land underlain by permafrost. To prevent melting of the permafrost, more than half the pipeline was built aboveground on elevated supports, some of which are refrigerated. In places where buried pipe extends across unstable permafrost, it is wrapped with insulation, and in a few locations the pipe is insulated and buried in refrigerated ditches.

spruce trees in a permafrost area
Permafrost Area With Spruce Trees USFWS

Is Alaska Melting?

Studies of permafrost in Alaska are providing valuable information about the potential effects of global warming. One project at the University of Alaska Fairbanks Geophysical Institute has been monitoring temperatures and depth of permafrost since 1976. Precise temperature measurements have been made in a series of holes bored 200 feet deep along a line running north to south down the middle of the state along the Trans-Alaska Pipeline.

Study results show that much of the undisturbed discontinuous permafrost south of the Yukon River has warmed significantly and some of it is thawing. That raises the possibility that roads, buildings, and other structures on thawed areas will collapse. Another problem could arise as well: As permafrost thaws it can release methane and carbon dioxide, gases that contribute to the green house effect and accelerate global warming.

Find more information on these studies.

Map of permafrost in Alaska.
Map of permafrost. NSIDC

Where to See Alaska's Permafrost

In Northern and Interior Alaska, permafrost is frequently visible along riverbanks or road cuts. It is most obvious where large wedges or lenses of ice have been cut perpendicular to the ground such as a river or road cutting through the soil. Where the Dalton Highway crosses the Yukon River, daily tourist boat trips give people a look at exposed permafrost along the riverbank.

Effects of permafrost melting can also be seen on many roads and highways in Interior Alaska. Watch for rough, wavy road surfaces and highway signs warning of "Dips." An area recommended by Tom Osterkamp of the Geophysical Institute can be seen along the Parks Highway from Nenana to Denali National Park.

Buildings tilted because of melting permafrost can be seen along Farmer's Loop Road near Fairbanks. You can see above-ground water and sewer pipes in Barrow and Bethel.

The map above illustrates where the permafrost is across the state.

What is a Pingo?

Note: This Embedded video resides on the official Alaska National Park YouTube channel

What are ice wedges and polygons?

Note: This Embedded video resides on the official Alaska National Park YouTube channel