GEOMORPHOLOGY OF THE SOUTHERN COAST OF ALASKA

Abstract

The shoreline of southern Alaska is a narrow coastal plain dominated by large glaciers, periodic earthquake activity, and strong extratropical cyclones. Studies on the coastal geomorphology and sediments carried out in 1969-71 and in the summer of 1975 were directed at defining geological hazards with respect to developing shore facilities for OCS oil exploration activities. Most of the shoreline was found to undergo rapid changes and experience a variety of serious environmental hazards. The safest potential port areas are located inside Icy Bay and Yakutat Bay. The coastal areas in the vicinity of the Malaspina Glacier and the Copper River delta are examples of the two principal shoreline types (glacial outwash plain and deltaic). The coastal area surrounding the Malaspina Glacier, the largest piedmont glacier in the world, was classified into 5 categories on the basis of its geomorphology, sediments, and local glacial history: 1. Regional retreating coast: This area, which is located at the mouth of Icy Bay, is eroding rapidly (approximately 1.5 km since 1900) as a result of retreat of a glacier (up the bay) a distance of over 40 km since 1900. Consequently, it should not be developed. 2. Prograding spits: Sandy spits that have built into either side of Icy Bay since the retreat of the glacier are also unstable because of the general recession of the shoreline as a result of erosion at the mouth of the bay. 3. Abandoned glacial coasts: These areas, located on the inner eastern shores of Icy Bay and Yakutat Bay, are coastlines of relatively low wave energy composed of. abandoned glacial tills, kame terraces, and outwash sediments. These are the most stable and least hazardous areas on the southern Alaska coast. 4. Actively eroding glacial margins: This area, located at Sitkagi Bluffs on the southernmost terminus of the Malaspina Glacier, is an eroding scarp of glacial till jutting into the Gulf of Alaska. 5. Glacial outwash coasts: These shorelines are highly variable and are usually dominated by prograding spits composed of sand and gravel.