Holocene history of Hubbard Glacier in Yakutat Bay and Russell Fiord,southern Alaska

摘要

Stratigraphic and geomorphic data de-fined by radiocarbon ages, tree-ring dates, and historical observations provide evi-dence of three major Holocene expansions of Hubbard Glacier. Early in each advance the Hubbard Glacier margin blocked Rus-sell Fiord to create Russell lake, raising base level and causing stream beds and fan deltas throughout the Russell drainage ba-sin to aggrade. Each Hubbard Glacier ex-pansion continued with an ice lobe advanc-ing through Disenchantment and Yakutat Bays in the west, and an eastern lobe ad-vancing into Russell Fiord.The earlier two Holocene expansions were, respectively, under way at 7690 and 5600 calibrated yr B.P., and each advance culminated more than 1 k.y. later. The late Holocene advance was under way by 3100 yr ago and reached —13 km farther south in Russell Fiord than the preceding two ex-pansions. Late Holocene deglaciation of Yakutat and Disenchantment Bays was complete before A.D. 1791; Nunatak Gla-cier flowing from n~v& east of Russell Fiord became the primary ice source to the Russell Fiord lobe at or before this date. Ice retreat from the southern end of Russell Fiord began in the late eighteenth century and the penultimate Russell lake drained ca. A.D. 1860.The relatively slow advances and more rapid retreats of Hubbard Glacier are con-sistent with the model of the iceberg-calving glacier cycle. Hubbard Glacier is currently advancing and will likely reestablish Rus-sell lake in the near future, affecting local fisheries. However, glacier lobes are unlike-ly to reach the area of the town of Yakutat, built on late Holocene glacial deposits, in the next 1 k.y.