LATE HOLOCENE EVOLUTION OF THE COASTLINE OF THE GLACIER BAY NATIONAL PARK AND WRANGELL - ST. ELIAS NATIONAL PARK AREA, ALASKA

The coastline of the Glacier Bay National Park and Wrangell - St. Elias National Park area is one of the most active and unique coastlines on Earth. It has changed radically and repeatedly since the start of the Little Ice Age. Located adjacent to the North American Plate - Pacific Plate boundary, this coastline is undergoing both tectonic and isostatic uplift, with maximum isostatic uplift rates in the easternmost part of Glacier Bay of ~4 cm/yr. However, most of the large-scale modifications affecting this coastal segment are related to regional climate, especially glacier advances and retreats, and to glacier-erosion-produced sedimentation. More than half of the currently advancing glaciers in Alaska are within this coastal segment. All of them now have, or recently had tidewater termini. At times, glacier termini have made up ~20% of this ~500-km-long coastline.

Four bays evolved through large-scale, asynchronous, glacier retreats [Glacier Bay (mid-18th century - present), Lituya Bay (18th century), Yakutat Bay (15th century - late 19th century, and Icy Bay (early 20th century - present)]. In two (Lituya and Yakutat Bays), glaciers are currently advancing. In the other two, retreat continues although three of the remaining tidewater termini in Glacier Bay are advancing, Three bays, Taylor Bay, Bering’s Bay (mouth of the Alsek River), and Vancouver’s Icy Bay, filled with sediment during the 19th and/or 20th centuries. All of the other bays are shoaling and have sedimentation rates of > 1 m/yr. On the west side of the Alsek River, a 10-km-wide sequence of more than a dozen ridges and swales has developed. The ridges range in age from > 3,000 yr at the foot of the mountains, to modern at the coastline.

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, surrounded by a foreland composed of glacial and glacial-fluvial sediment. At Sitkagi Bluffs, only a lag of widely-spaced boulders separates the stagnant glacier terminus from Pacific Ocean surf. During extreme high tide and storm conditions, ocean waves undercut the stagnant ice resulting in mature trees falling into the surf zone. Continued retreat of the Malaspina and other large glaciers may expose additional large embayments in this coastline.