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Syverson, K.M., 1992

Glacial geology of the southeastern Burroughs Glacier, Glacier Bay National Park and Preserve, Alaska

Bibliographic Reference

Syverson, K.M., 1992, Glacial geology of the southeastern Burroughs Glacier, Glacier Bay National Park and Preserve, Alaska: University of Wisconsin, Madison, Ph.D. dissertation, 212 p.


The Burroughs Glacier is a stagnating remnant of a large Neoglacial ice mass that completely covered much of what is now Glacier Bay, southeastern Alaska. Ice-surface lowering has taken place at rates up to 8 m/yr during the past 100 years. Cross-cutting striations with included angles up to 107 degrees indicate that emerging nunataks changed ice-flow directions markedly. Striations formed on an easily-striated substrate. Fine striations from late stages of ice flow may not have formed on a less suitable substrate. Till crag-and-tail features and long axes of bullet boulders reflect the final ice-flow direction. Marginal channels formed as the ice thinned. Rates of marginal channel formation range from 2.1 to 3.1 channels/yr over a 19-year period. Ice ablation was measured beneath debris cones and medial moraine sediment. Ablation rates beneath debris less than 2 cm thick were approximately the same as rates for clean ice. Ice-surface lowering beneath deltaic sand 1.1 - 2.1 m thick was negligible over a 44-day period. Slope retreat at this ice-cored delta averaged 21.6 m/yr over a 23-month observation period. Subglacial and englacial eskers in the region are sharp-crested, 1 - 4 m high, sinuous, contain poorly-sorted, poorly-stratified sandy gravel, and lack 'anticlinal' bedding. An englacial esker melting out of the ice displayed numerous angular unconformities and one spectacular example of primary 'anticlinal' bedding. Esker paths were compared to Burroughs Glacier hydraulic head maps from Gaffield (1991). Esker paths and sedimentology agree reasonably well with the concepts presented by Shreve (1985b). Sediment characteristics in ice-marginal lake basins in the region are a function of the water source (meltwater versus non-meltwater), proximity to the ice margin, lake duration, and the amount of supraglacial debris. Most inflow to Calving Lake has come from non-meltwater sources, so overflow and interflow sedimentation has dominated. Approximately 80 - 90% of the lacustrine sediment by volume has been deposited in nearshore deltas and fan-deltas. Offshore sediment generally is composed of massive silt, although non-annual rhythmites are observed in one region. Iceberg gravity craters 2 - 4 m long and displaying rims up to 0.2 m high are located on the former lake plain. Coarsening-upward sequences and thick lacustrine sediment are deposited in a river lake where abundant supraglacial sediment is present.

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