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Kopczynski, S.E., 2009

Satellite predictions of subglacial hydrology, and final collapse of twinned terrestrial-tidewater glaciers, Anchorage lowland, Alaska

Bibliographic Reference

Kopczynski, S.E., 2009, Satellite predictions of subglacial hydrology, and final collapse of twinned terrestrial-tidewater glaciers, Anchorage lowland, Alaska: Bethlehem, Pennsylvania, Lehigh University, Ph.D. dissertation, 247 p.

Abstract

Investigations of snow and ice processes underpin broader portability and predictability of cryospheric processes. This research is motivated by two driving questions: (1) 'Are glacial spring events remotely predictable?' and (2) 'How would a twinned terrestrial-tidewater glacier collapse?' The first phase was the first to discover a link between satellite detected supraglacial snowmelt and subglacial flooding leading to plumbing transitions. The space born algorithm uses 37 GHz vertically polarized brightness temperatures (Tb) from the Special Sensor Microwave Imager (SSM/I) to detect snowmelt indicators quantitatively linked to subglacial floods (+/-5 days, R2=0.61). Concurrent transitions glacier velocity and subglacial suspended sediment support major ice-plumbing evolutions catalyzed by flood events. Remote prediction of these events underpins broader works to assess subglacial erosion, flooding, and glacial ice stability possibly linked to surges and ice collapses. The second phase evaluated a very unique example of the collapse of a twinned pair of tidewater and terrestrial glaciers. This deglacial record of the Matanuska-Knik Lobe, Anchorage Lowland is the first to document retreat of two paired glaciers governed by contrasting ice flow processes. Drift provenance, terrain geomorphological interpretations, and radiocarbon chronologies unravel final ice retreat following advance between 18,800 and 16,700 yrs BP. The Matanuska segment was thinner, covering two-thirds of the lowland, while the remaining one-third was occupied by the thicker Knik ice. Knik ice primarily flowed in the Knik Arm fjord as tidewater ice and retreated rapidly, establishing ice-free conditions just prior to 16,400 yrs BP. In contrast, stagnating Matanuska ice persisted for 1,200 to 1,800 years. This new retreat chronology establishes retreat onset in southern Alaska between 1,000 and 2,000 years earlier than prior estimations. Other concordant well-document chronologies in Alaska are limited, though speculative evidence exists in the Kenai Lowland and Chuilnuk Mountains. Available Alaska chronologies are too sparse to permit sound arguments of global climate versus local Alaska phenomenon driving retreat, but this work should motivate other Alaska studies to broaden understanding of glacial responses during this time.

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