Taku and Le Conte Glaciers, Alaska: Calving-Speed Control of Late-Holocene Asynchronous Advances and Retreats

Post, Austin; Motyka, R. J.

doi:10.1080/02723646.1995.10642543

Cited by 58 publications

(105 citation statements)

References 26 publications

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“…1). The glacier is approximately 35 km long, covers an area of 469 km 2 and has an accumulationâ rea ratio of nearly 0.90 (Post and Motyka, 1995). It underwent a 2 km calving retreat between 1994 and 1998 after a 32 year period of stability.…”

Section: Settingmentioning

confidence: 99%

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Short-term variations in calving of a tidewater glacier: LeConte Glacier, Alaska, U.S.A.

2003

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ABSTRACT. Knowledge of iceberg calving is important for understanding instabilities of tidewater glaciers and ice sheets. Since 1995 the terminus of LeConte Glacier, Alaska, U.S.A., has retreated about 2 km and the glacier has thinned approximately 120 m at its 1999 terminus position. Our focus is short-term (hours to weeks) variability of the frequency and magnitude of calving events and calving flux. Both photogrammetric and visual observations are employed in a temporal analysis over a several-week period. We combined these data with measurements of ice speed, tide level, surface water input and water-storage estimates in an attempt to better understand the calving process. Contrary to results obtained over longer time-scales on other glaciers, our results show no correlation between ice speed and the frequency of calving. However, calving events do not appear to occur randomly; often they are a response to measurable changes in other parameters within the terminus region. Caclving can often be attributed to buoyancy perturbations and possibly flexure of the nearly floating terminus. Given the multiple possibilities for buoyancy perturbations, we have found no simple relationship between any specific forcing parameter and calving at short time-scales.

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Section: Settingmentioning

confidence: 99%

“…Post, 1975;Mann, 1986;Post and Motyka, 1995). Rapid retreat may be the expression of an unstable response to negative mass balance (Clarke, 1987;Vieli and others, 2001), and often results in the disintegration of a significant portion of the ablation area via iceberg calving.…”

Section: Introductionmentioning

confidence: 99%

Short-term variations in calving of a tidewater glacier: LeConte Glacier, Alaska, U.S.A.

2003

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“…It has an interesting history, with an advance/retreat pattern that is largely out of phase with regional glacier change (Arendt and others, 2002;Larsen and others, 2007). The glacier reached a maximum extent around AD 1750, at which time it blocked the Taku River and created a glacierdammed lake extending into modern-day Canada (Post and Motyka, 1995;Motyka and Begét, 1996). Thereafter, a rapid tidewater glacier retreat (e.g.…”

Section: Introductionmentioning

confidence: 99%

Terminus dynamics at an advancing glacier: Taku Glacier, Alaska

Truffer

Motyka²,

Hekkers³

et al. 2009

J. Glaciol.

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ABSTRACT. Taku Glacier, Alaska, USA, is currently in the advance stage of the tidewater glacier cycle. We investigated the near-terminus dynamics by measuring surface velocities, surface elevation changes, ice thickness and ablation. Velocities vary on sub-daily, diurnal, seasonal and interannual timescales. Flowline modeling shows that the modeled surface velocities are sensitive to changes in till yield strength and thus effective basal pressures. The glacier bed deepens in the up-glacier direction and this imposes a minimum subglacial water pressure necessary for water to drain along the bed. In a simple model we impose water-pressure gradients based on phreatic surfaces of constant slopes to simulate the wintersummer transitions. This proves sufficient to explain an observed early-season switch from compressional to block flow. Velocities also vary between years. Changing basal conditions can result in lower horizontal velocities, which decrease the ice supply to the terminus and result in temporary surface lowering. But a decrease in ice flux to the terminus must lead to ice storage further upstream, and that ice mass will eventually reach the terminus. This can explain the observed episodic nature of terminus advance.

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“…Therefore, sometime between 1794 and 1880 the terminus evolved from a calving margin into a noncalving margin. Post and Motyka (1995) As Taku Glacier continued to advance onto the tidal flat, its terminus spread out and became convex in map view (Post and Motyka, 1995). Brady Glacier's calving margin was probably similar to that of the Taku Glacier in the late 1800s and other present tidewater glacier margins,…”

Section: Subsequent Maps Frommentioning

confidence: 99%

“…To dam the lake to this elevation, the glacier would need to be at least 92 m in elevation at the southern ice-margin of the basin at that time. 1929-1937(Post and Motyka, 1995 and had a less steep front, several years could have passed between the initial damming of the lake and it eventually reaching 83 m a.s.l. We know from observations cited in the introduction that the glacier was calving in 1794 but not in 1880.…”

Section: Chronology Of Last Glacier Advance and Lake Dammingmentioning

confidence: 99%

Evolution of glacier-dammed lakes through space and time; Brady Glacier, Alaska, USA

Capps

Clague

2014

Geomorphology

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Glacier-dammed lakes and their associated jökulhlaups cause severe flooding in downstream areas and substantially influence glacier dynamics. The goal of this dissertation is to identify and characterize the evolution of glacier-dammed lakes in order to predict their future behaviour using ground-truthed remote sensing techniques and dendrochronology. Brady Glacier in southeast Alaska is particularly well suited for a study of these phenomena because it presently dams ten large (> 1 km 2 ) lakes and many smaller ones. This dissertation comprises three studies. First, I used interferometric synthetic aperture radar (InSAR) to identify and characterize three previously unknown subglacial lakes. InSAR allowed me to quantify the vertical displacement and volume of water discharged from the three lakes through time. From the fall of 1995 to the spring of 1996, subsidence ranged from 4 to 26 cm/day and the volume of water discharged ranged from 22,000 ± 2000 to 243,000 ± 14,000 m 3 /day. Subsidence and discharge rates declined significantly during the winter and continued at a lesser rate through March. Second, I used dendrochronology and precise elevation-constrained mapping to date glacially overridden and drowned trees at the glacier margin. Brady Glacier impounded Spur Lake to an elevation of 83 m a.s.l. around AD 1830 and 121 m a.s.l. around 1839. The glacier continued to advance, thickening by at least 77 m between ca. 1844 and 1859 at a site down-glacier of Spur Lake on the opposite glacier margin. Farther down-glacier, North Trick Lake began to form by 1861 and reached its highest elevation at approximately 130 m a.s.l. when Brady Glacier reached its maximum extent around 1880. Third, I georeferenced a variety of maps, airphotos, and optical satellite imagery to characterize the evolution of the glacier and lakes and also created five bathymetric maps. The main terminus of Brady Glacier has changed little since 1880. However, it downwasted at rates of 2-3 m/yr between 1948 and 2000, more than the regional average. The most dramatic retreat (2 km) and downwasting (123 m) occurred adjacent to glacierdammed lakes. These lakes will continue to evolve and play a pivotal role in the evolution of Brady Glacier. If downwasting and retreat continue at rates comparable to the past, the glacier may return to a tidewater regimen and retreat catastrophically until it stabilizes in shallow water.

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Taku and Le Conte Glaciers, Alaska: Calving-Speed Control of Late-Holocene Asynchronous Advances and Retreats

Cited by 58 publications

References 26 publications

Short-term variations in calving of a tidewater glacier: LeConte Glacier, Alaska, U.S.A.

Short-term variations in calving of a tidewater glacier: LeConte Glacier, Alaska, U.S.A.

Terminus dynamics at an advancing glacier: Taku Glacier, Alaska

Evolution of glacier-dammed lakes through space and time; Brady Glacier, Alaska, USA

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