The response of Black Rapids Glacier, Alaska, to the Denali earthquake rock avalanches

Shugar, Dan H.; Rabus, Bernhard; Clague, John J.; Capps, Denny M.

doi:10.1029/2011jf002011

Cited by 50 publications

(48 citation statements)

References 56 publications

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“…The effect of temporal and spatial changes in debris deposition must be addressed through both empirical and theoretical approaches. Isolated, large landslides have been shown to suppress melt rates, change glacier surface slopes and perturb glacier surface velocity fields (Gardner and Hewitt, 1990;Reznichenko et al, 2011;Shugar et al, 2012). If debris inputs are allowed to vary in space and time, a complex glacier length history will likely result even with a steady climate.…”

Section: Potential Model Improvements and Future Researchmentioning

confidence: 99%

Modeling debris-covered glaciers: response to steady debris deposition

2016

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Abstract. Debris-covered glaciers are common in rapidly eroding alpine landscapes. When thicker than a few centimeters, surface debris suppresses melt rates. If continuous debris cover is present, ablation rates can be significantly reduced leading to increases in glacier length. In order to quantify feedbacks in the debris-glacier-climate system, we developed a 2-D long-valley numerical glacier model that includes englacial and supraglacial debris advection. We ran 120 simulations on a linear bed profile in which a hypothetical steady state debris-free glacier responds to a step increase of surface debris deposition. Simulated glaciers advance to steady states in which ice accumulation equals ice ablation, and debris input equals debris loss from the glacier terminus. Our model and parameter selections can produce 2-fold increases in glacier length. Debris flux onto the glacier and the relationship between debris thickness and melt rate strongly control glacier length. Debris deposited near the equilibriumline altitude, where ice discharge is high, results in the greatest glacier extension when other debris-related variables are held constant. Debris deposited near the equilibrium-line altitude re-emerges high in the ablation zone and therefore impacts melt rate over a greater fraction of the glacier surface. Continuous debris cover reduces ice discharge gradients, ice thickness gradients, and velocity gradients relative to initial debris-free glaciers. Debris-forced glacier extension decreases the ratio of accumulation zone to total glacier area (AAR). Our simulations reproduce the "general trends" between debris cover, AARs, and glacier surface velocity patterns from modern debris-covered glaciers. We provide a quantitative, theoretical foundation to interpret the effect of debris cover on the moraine record, and to assess the effects of climate change on debris-covered glaciers.

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Section: Potential Model Improvements and Future Researchmentioning

confidence: 99%

Modeling debris-covered glaciers: response to steady debris deposition

2016

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“…Neglecting flux divergence most likely leads to missed emergent flow early in the modeling period and missed submergent flow later on (the increasing elevation difference between the rockslide deposits and neighboring clean ice causes the switch from emergent to submergent flow). Shugar et al (2012) describe a more sophisticated approach that considers flux divergence under Black Rapids' rockslide deposits, however, this model is too computationally expensive for our Monte Carlo simulations.…”

Section: Glacier Geometrymentioning

confidence: 99%

Mass Balance Evolution of Black Rapids Glacier, Alaska, 1980–2100, and Its Implications for Surge Recurrence

et al. 2017

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Surge-type Black Rapids Glacier, Alaska, has undergone strong retreat since it last surged in [1936][1937]. To assess its evolution during the late Twentieth and Twenty-first centuries and determine potential implications for surge likelihood, we run a simplified glacier model over the periods 1980-2015 (hindcasting) and 2015-2100 (forecasting). The model is forced by daily temperature and precipitation fields, with downscaled reanalysis data used for the hindcasting. A constant climate scenario and an RCP 8.5 scenario based on the GFDL-CM3 climate model are employed for the forecasting. Debris evolution is accounted for by a debris layer time series derived from satellite imagery (hindcasting) and a parametrized debris evolution model (forecasting). A retreat model accounts for the evolution of the glacier geometry. Model calibration, validation and parametrization rely on an extensive set of in situ and remotely sensed observations. To explore uncertainties in our projections, we run the glacier model in a Monte Carlo fashion, varying key model parameters and input data within plausible ranges. Our results for the hindcasting period indicate a negative mass balance trend, caused by atmospheric warming in the summer, precipitation decrease in the winter and surface elevation lowering (climate-elevation feedback), which exceed the moderating effects from increasing debris cover and glacier retreat. Without the 2002 rockslide deposits on Black Rapids' lower reaches, the mass balances would be more negative, by ∼ 20% between the 2003 and 2015 mass-balance years. Despite its retreat, Black Rapids Glacier is substantially out of balance with the current climate. By 2100, ∼ 8% of Black Rapids' 1980 area are projected to vanish under the constant climate scenario and ∼ 73% under the RCP 8.5 scenario. For both scenarios, the remaining glacier portions are out of balance, suggesting continued retreat after 2100. Due to mass starvation, a surge in the Twenty-first century is unlikely. The projected retreat will affect the glacier's runoff and change the landscape in the Black Rapids area markedly.

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“…The landslide also caused the glacier to begin advancing (Figure 9.10). At Black Rapids Glacier, Shugar et al (2012) used satellite radar and ground surveying to measure surface ice velocity in the vicinity of the three 2002 rock avalanche deposits. At Black Rapids Glacier, Shugar et al (2012) used satellite radar and ground surveying to measure surface ice velocity in the vicinity of the three 2002 rock avalanche deposits.…”

Section: Glacier Advance and Velocity Change Due To Rock Avalanchesmentioning

confidence: 99%