Holocene Sea Levels in Southeast Alaska: Preliminary Results

Abstract

Natural raised marine deposits and archaeological sites recently discovered in southeastern Alaska have been measured relative to mean sea level and radiocarbon dated. Plots of sites on Heceta and Prince of Wales islands are compared to those developed for British Columbia. The Heceta Island curve is comparable to that of the Queen Charlotte Islands, in which pre-Holocene shorelines were lower than present until about 10,000 B.P. and then rose to a maximum of 15 m asl by 8500 B.P., when gradual emergence began to bring the sea level down to its present position. In contrast, the Prince of Wales Islands data indicate that sea level remained a few metres above its present position between 10,000 and 7000 B.P. - a time when the shores of mainland British Columbia were as much as 15 m below present sea level. Because Holocene sea levels are a function of isostatic rebound due to removal of glacial ice, as well as global sea level changes and tectonic activity, the implication is that whereas Heceta Island underwent processes and magnitudes of glaciation and isostatic rebound similar to the Queen Charlotte Islands, Prince of Wales Island was subjected to a pattern of glaciation and isostatic rebound different from that of the Queen Charlotte Islands and mainland of British Columbia.

Key words: Alaska, Alexander Archipelago, archaeology, eustacy, geomorphology, glaciation, Holocene, isostacy, sea level, Quaternary