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

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