The Coastal Plain of the Arctic National Wildlife Refuge [ANWR], which comprises about 8 percent of the Refuge area, extends about 100 miles from the Aichiik River in the east to the Canning River in the west and 15 to 20 miles inland from the coast. The western boundary lies about 50 miles east of Prudhoe Bay. The only permanent community in ANWR is Kaktovik with a population of 210, mainly Inupiat Eskimos. Also located at Kaktovik is a radar station of the Distant Early Warning (DEW Line) syatem.
The ANWR Coastal Plain covered by the ANILCA-mandated study lies entirely within the White Hills section of the arctic coastal plain. With the exception of a few small areas of flat plains nesr the coast, the terrain is rolling and merges gradually with t he foothills to the south. The entire study area is underlain by continuous permafrost believed to be up to 2,000 feet thick; the upper two to three feet or 'active' layer freezes and thaws with the seasons. Permafrost is a condition of the earth's surfa ce in which a temperature below 32 degrees F has existed for two or more years. It is not implicit in this definition that ice be present, although it commonly is. When ice is present it frequently takes the form of ice wedges or lenses.
In many locations, seasonal thawing of the surface has resulted in the formation of polygonally patterned ground. The polygons develop in response to intense winter cooling and subsequent contraction of the fine-grained sediments. The thermal contraction cracks are subsequently filled by ice. The process of freezing and thawing, repeated over many centuries, results in vertical, wedge-shaped masses of ice that penetrate several feet into the soil. The result is a mosaic of polygons on the tundra, ranging up to twenty feet in diameter.
At the surface, the tundra serves to insulate the soils, limiting the depth of thaw during the summer months to no more than two or three feet in most areas. If the tundra is disturbed, deeper seasonal thawing may occur. Once the thermal balance is destro yed, it may take years to stabilize again. During that time, ponds may develop as ice wedges melt and soils subside, altering t errain, changing the vetetative cover, or in extreme cases, resulting in erosion.