Iceberg Calving Events Driven by Submarine Ice Morphology at LeConte Glacier, Alaska

Abstract:

Ongoing changes in mass loss from tidewater glaciers and the input of freshwater into glacial fjords are influenced by both submarine melting and iceberg calving. Observations of iceberg calving are largely made through remote sensing, which provides an incomplete picture of glacier calving events due to the inability to observe processes below the waterline. Historically, direct simultaneous observations of submarine melting and calving at tidewater glaciers have been difficult, resulting in a poor understanding of the relationship between these processes. Here we combine repeat multibeam sonar scans with concurrent time-lapse imagery obtained during a September 2018 field campaign at LeConte Glacier, Alaska, to investigate the controls of submarine melt on iceberg calving. We compare time series of subaerial and submarine calving events with observed multibeam-derived melt rates. We find that over 50% of the submarine terminus is overcut throughout the period of observation, most notably being a large ice ramp that extends 100m into the fjord located near a subglacial discharge outlet. Calving styles and rates are heterogeneous across the terminus, with large submarine calving events occurring near the ice ramp and smaller, more frequent subaerial events occurring where the slope of the terminus is closer to vertical. By constraining the relative importance and spatial patterns of these processes to frontal ablation, more accurate models of tidewater glacier evolution can be determined.