Tundra polygons are flooded with seawater near the mouth of Fish Creek in Harrison Bay, Alaska. Fish Creek is a stream that flows northeast through the Arctic Coastal Plain for about 110 miles (177 km) to Harrison Bay, west of the Colville River Delta. The local name was first reported in 1951 by the U.S. Coast and Geodetic Survey. Harrison Bay is about 57 miles (92 km) across, on the coast of the Beaufort Sea between Cape Halkett and Oliktok Point. On July 26, 1837, Dease and Simpson named the bay after Benjamin Harrison who at the time was a director of the Hudson’s Bay Company.
Polygons can form in permafrost areas when thermal contraction of the tundra during the winter forms cracks. In the spring when the snow melts the cracks fill with water that refreezes and eventually forms an ice wedge that can extend for several meters below the surface. During the summer months, the permafrost expands and horizontal compression deforms the frozen sediment resulting in ridge formations. The mean annual air temperature needed to form ice wedges is −6° to −8° C or colder.
Coastal tundra in some areas is being inundated by rising sea levels. The coastal topography along the Arctic Plain is very flat so that small changes in sea level can inundate vast areas of low lying tundra. The ridges surrounding tundra polygons facilitate the ponding of water that exacerbates thawing and subsidence allowing more frequent flooding by the ocean. Logs stranded on the ridges show that this entire area can be submerged during storm surges. Read more here and here. Explore more of the tundra polygons at the mouth of Fish Creek here: