Modelling historical and recent mass loss of McCall Glacier, Alaska, USA

摘要

Volume loss of valley glaciers is now considered to be a significantcontribution to sea level rise. Understanding and identifying the processesinvolved in accelerated mass loss are necessary to determine their impact onthe global system. Here we present results from a series of model experimentswith a higher-order thermomechanically coupled flowline model(Pattyn, 2002). Boundary conditions to the model are parameterizations ofsurface mass balance, geothermal heating, observed surface and 10 m ice depthtemperatures. The time-dependent experiments aim at simulating the glacierretreat from its LIA expansion to present according to different scenariosand model parameters. Model output was validated against measurements of icevelocity, ice surface elevation and terminus position at different stages.Results demonstrate that a key factor in determining the glacier retreathistory is the importance of internal accumulation (>50%) in the totalmass balance. The persistence of a basal temperate zone characteristic forthis polythermal glacier depends largely on its contribution. Acceleratedglacier retreat since the early nineties seems directly related to theincrease in ELA and the sudden reduction in AAR due to the fact that a largelower elevation cirque – previously an important accumulation area – becamepart of the ablation zone.