Persistent overcut regions dominate the terminus morphology of a rapidly melting tidewater glacier

• Published in: Annals of Glaciology
• Main Authors: Nicole Abib, David A. Sutherland, Jason M. Amundson, Dan Duncan, Emily F. Eidam, Rebecca H. Jackson, Christian Kienholz, Mathieu Morlighem, Roman J. Motyka, Jonathan D. Nash, Bridget Ovall, Erin C. Pettit
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press 2023
• Subjects: Glacier ablation phenomena; ice/ocean interactions; iceberg calving; Meteorology. Climatology; QC851-999; Annals of Glaciology; glacier; Tidewater; Alaska
• Online Access: https://doi.org/10.1017/aog.2023.38; https://doaj.org/article/8a724f67bdcd4b6bb16595b09e827016

Frontal ablation, the combination of submarine melting and iceberg calving, changes the geometry of a glacier's terminus, influencing glacier dynamics, the fate of upwelling plumes and the distribution of submarine meltwater input into the ocean. Directly observing frontal ablation and terminus morphology below the waterline is difficult, however, limiting our understanding of these coupled ice–ocean processes. To investigate the evolution of a tidewater glacier's submarine terminus, we combine 3-D multibeam point clouds of the subsurface ice face at LeConte Glacier, Alaska, with concurrent observations of environmental conditions during three field campaigns between 2016 and 2018. We observe terminus morphology that was predominately overcut (52% in August 2016, 63% in May 2017 and 74% in September 2018), accompanied by high multibeam sonar-derived melt rates (4.84 m d−1 in 2016, 1.13 m d−1 in 2017 and 1.85 m d−1 in 2018). We find that periods of high subglacial discharge lead to localized undercut discharge outlets, but adjacent to these outlets the terminus maintains significantly overcut geometry, with an ice ramp that protrudes 75 m into the fjord in 2017 and 125 m in 2018. Our data challenge the assumption that tidewater glacier termini are largely undercut during periods of high submarine melting.