| Summary: | Lemon Creek Glacier, a temperate valley glacier in the Juneau Icefield of Southeast Alaska, is the site of long running (>60 years) glaciological studies. However, the most recent published estimates of its thickness and subglacial topography come from two ∼50 years old sources that are not in agreement and do not account for the effects of years of negative mass balance. We collected a 1-km long active-source seismic line on the upper section of the glacier parallel and near to the centerline of the glacier, roughly straddling the equilibrium-line altitude. We used these data to perform joint reflection-refraction velocity modeling and reflection imaging of the glacier bed. We find that this upper section of Lemon Creek Glacier is as much as 150 m (∼65%) thicker than previously suggested with a large overdeepening in an area previously believed to have a uniform thickness. Our results lead us to reinterpret the impact of basal motion on ice flow and have a significant impact on expectations of subglacial hydrology. We suggest that further efforts to develop a whole-glacier model of subglacial topography are necessary to support studies that require accurate models of ice thickness and subglacial topography. We thank the Juneau Icefield Research Program (JIRP) for their support with facilities at Camp 17 and logistical planning for the field work. We thank Emily Graves, Joachim Schalk and Celeste Labedz for their participation in the field work. We thank the Incorporated Research Institutions for Seismology Seismic Source Facility at the University of Texas at El Paso for their assistance with the seismic sources. We thank two reviewers for their helpful commentary, and the Journal’s editorial volunteers and staff for their invaluable role in supporting this publication. This work was partially funded by Marianne Karplus’s startup funds at the University of Texas at El Paso. Yes
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