Coastal Erosion at Two Arctic Alaska Parks: What Images From 1950 to 2014 Show

A comparison of images taken between 1950 and 2014 shows that the coastlines of Bering Land Bridge National Preserve and Cape Krusenstern National Monument have eroded in most areas, while in some places the shore has advanced seaward, a process called accretion. The two parks are among the five Arctic parks collectively referred to as the Arctic Network.

The 5 Arctic parks collectively referred to as the Arctic Network: Bering Land Bridge National Preserve, Cape Krusenstern National Monument, Noatak National Preserve, Kobuk Valley National Park, and Gates of the Arctic National Park and Preserve. Image from the National Park Service’s page.

What the images show

Long-term erosion rates are generally higher in Bering Land Bridge than in Cape Krusenstern, and average rates of erosion have not changed much over time. The variation from place to place has recently increased, though, meaning locally both more erosion and more accretion than before. The brief says this is probably because the ice-free open water lasts longer, leaving more time for wave action.

Erosion at rates of over 1 meter per year continues in many areas and could threaten archeological sites. Vegetation cover on the barrier islands has held steady or increased, and the Park Service did not observe an increase in breaches of the barriers. Barrier islands and spits face the ocean over much of the two parks, with grass-covered dunes behind the beach and salt marshes behind those, next to lagoons, and the pristine condition of these barriers helps protect the land from erosion.

The shoreline has moved inland because of erosion over most of the two parks. In some areas it moved more than 164 feet (50 meters) inland between 1950 and 2014. Image from the National Park Service’s page.

Why it matters

Coastal environments in the two parks are changing rapidly through coastal erosion, bluff retreat, beach accretion, sediment deposition and permafrost thaw. The coastal zone may change quickly as Arctic warming lengthens the ice-free season, raises sea level, warms seawater and alters the frequency and severity of storms.

A variety of near-shore habitats are threatened by erosion: sandy shores, barrier spits and islands, lagoons, bays and inlets, tundra bluffs, dunes, estuaries and salt marshes. They provide habitat for unique plants, fish, birds and marine mammals, including migratory stopover sites. Coastal changes will also affect human activities and cultural resources such as travel routes, fishing and hunting, and many of the important archeological sites in these parks lie on the coast and could be threatened by erosion.

How the coast is monitored

Every 10 years the Park Service acquires and analyzes aerial photographs or satellite images. Staff trace the position of the shoreline on a computer screen and use specialized software to calculate erosion and accretion rates from the digitized shorelines.

How it helps park managers

The coastal zone harbors many kinds of wildlife, including fish, migratory birds and mammals. Tracking coastal change over time and space will let park managers better understand changes in wildlife habitat, including habitat of important subsistence species. By identifying areas of rapid erosion, managers can target them for special management of archeological resources.

Sources

• National Park Service, Coastal Erosion Resource Brief for the Arctic Network; the two coastline photographs credited to ShoreZone, the photograph of a person on the shore and the contact details are left out; rewritten in hubnx's own words.