GLACIER BAY'S NEOGLACIAL LANDSCAPE HISTORY 5000 TO 250 YEARS AGO, SOUTHEASTERN ALASKA

In the West Arm and Muir Inlet regions of Glacier Bay National Park we reconstructed the Neoglacial advance and transition from dominance by marine tidewater glaciers to a progressive building and preponderance of outwash sediments infilling over-deepened fjord basins. These changes created a terrestrial landscape in the lower bay by valley glacier complexes between 5,000 to 250 years ago. In the lower bay the Beardslee Formation provides important stratigraphic evidence from glacial, fluvial, and marine sediments. Forty radiocarbon ages, from previous work in Muir Inlet and from this study, provided the geochronologic foundation to link stratigraphic data for compilation of five paleo-maps showing glacier terminal positions. These maps depict the gradual infilling by outwash of a former marine embayment between the Brady Glacier and Excursion Inlet spanning the lower Glacier Bay region from west to east. At least one period of glacial reversal was noted. Data support the persistence of a large outwash complex for most or all this time, located in front of the ice terminus, and occupying much of the lower bay. During the Neoglacial, ancestors of Huna Tlingit people living on the outwash plain would have faced conditions that become increasingly difficult as the climate deteriorated and landscape dynamism altered the land surface, especially at times when glacial Lakes Muir and Adams may have drained catastrophically across it from the Muir Inlet region. The final Little Ice Age advance into Icy Strait was very abrupt, followed by an equally abrupt post-Little Ice Age calving retreat.