80-12 Subglacial hydrology insights from eskers developed atop soft beds of the Laurentide ice sheet

Session: Recent Advances in Glacial Geology, Geomorphology, and Chronology

Presenting Author:

Lucas Zoet

Authors:

Nunez Ferreira, Francisca Andrea¹, Zoet, Lucas², Rawling III, J. Elmo³, Haseloff, Marianne⁴, Rehwald, Matthew⁵, Ullman, David⁶

(1) University of Wisconsin- Madison, Madison, WI, USA, (2) University of Wisconsin-Madison Geoscience, Madison, WI, USA, (3) WI Geological & Natural History Survey, Madison, WI, USA, (4) University of Wisconsin-Madison, Madison, WI, USA, (5) Wisconsin Geological and Natural History Survey, Madison, WI, USA, (6) Northland College, Ashland, WI, USA,

Abstract:

Glacial landforms offer a valuable record of past ice sheets’ history and dynamics. Eskers, composed of sediment deposited by water flowing through subglacial channels, record paleo subglacial hydrologic and sediment transport conditions. Despite decades of study, debates persist about their formation mechanisms, particularly the differences between eskers formed over soft and hard beds. To address this complexity, we analyzed eskers formed over soft beds along the southern margin of the Laurentide Ice Sheet (LIS) in the Lake Superior region. To calculate the basal effective pressure gradient during esker formation along the subglacial channel, we developed a new method using grain size estimates from a 20 m tall esker exposure (Cable Esker). The sedimentology of the Cable Esker reveals a non-monotonic pattern in channel boundary shear stress, ranging from 10 to 300 Pa. Additionally, the basal effective pressure gradient fluctuates between -9 to -70 Pa m-1. Negative basal effective pressure gradients indicate esker formation in channels close to the glacier terminus, suggesting lower water pressure than previously assumed. This, coupled with dynamic water level fluctuations within the esker channel, supports the theory of esker formation near the ice margin.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7498

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