GULF OF ALASKA COASTAL DYNAMICS - THE RAPIDLY CHANGING COASTLINES OF WRANGELL - ST. ELIAS AND GLACIER BAY NATIONAL PARKS, ALASKA

The Gulf of Alaska coastline segment that is bounded by the coastal areas of Wrangell-St. Elias and Glacier Bay National Parks is one of the most active and unique coastlines on Earth. It is subject to high intensity coastal processes and natural hazards, and has changed rapidly, repeatedly, and radically on a variety of time scales. These time scales range from decadal to millennial. Located adjacent to the North American Plate-Pacific Plate boundary, this coastal segment is subject to active tectonic and isostatic uplift. Maximum post-Little Ice Age isostatic uplift rates are ~4 cm/yr. An instantaneous uplift associated with a large magnitude 1899 earthquake exceeded 15 m. Glaciers exist on all of the mountain ranges that are adjacent to this coastline. About half of the large advancing glaciers in Alaska (including Hubbard, Lituya, and North Crillon Glaciers) are located within this coastal segment. Most now have, or recently had a tidewater terminus. At times, ~20% of this ~500-km-long coastline has been made up of glacier ice.

Natural hazards affecting this coastline include: intense storms, storm surge, rapid coastal erosion, extreme seismicity, faulting, instantaneous uplifts, submarine and terrestrial mass wasting, giant waves and tsunamis, glacier advance and retreat, rapid sedimentation, and glacier outburst flooding. Four bays (Glacier Bay, Lituya Bay, Yakutat Bay, and Icy Bay) have evolved through large-scale, asynchronous, glacier retreats. Icy Bay, the most recent to form, is the product of ~50 km of 20th century glacial retreat. Several bays have rapidly filled with sediment (Taylor Bay, Dry Bay, and Vancouver's Icy Bay). All large bays are shoaling and have sedimentation rates of >1 m/yr. The perimeter of the piedmont lobe of the Malaspina Glacier makes up much of the western part of this coastline. At places it consists of a large area of forest-covered and debris-covered stagnant ice, associated with a foreland composed of glacial and glacial-fluvial sediment. During most of the 20th century, the non-surging, large valley glaciers of Icy Bay experienced extensive thinning and retreat, accentuated by calving. Separation into four distributary glaciers occurred in the early 1960s. Since then, although retreat generally continues, each glacier has demonstrated its own unique behavior.