Development of a semi-persistent floating terminus at San Quintín Glacier (Northern Patagonia Icefield), the last piedmont glacier in the Andes

Abstract

The piedmont lobe of San Quintín Glacier, the largest outlet of the Northern Patagonia Icefield, has recently entered a phase of rapid frontal retreat. We present results from a helicopter-borne ground-penetrating radar (GPR) survey conducted in May 2019 in the terminal zone of the glacier, combined with satellite-derived ice velocity, frontal position and surface elevation change data. GPR measurements along the flowline indicate ice thicknesses of 215–240 m in the lowermost 1400 m of the glacier. The inferred grounding line is located approximately 1500 m upstream from the 2019 calving front. Analysis of surface elevation change in 2017–19 shows mean thinning rates of -5.43

1.58 m a

minus 1 $^{-1}$ − 1

upstream and -1.08

plus or minus $\pm$ ±

1.39 m a

minus 1 $^{-1}$ − 1

near the terminus. Satellite-derived velocities reach up to 1050 m a

minus 1 $^{-1}$ − 1

in the lower glacier, with higher values observed in the later part of the observation period. Residual bed reflection power derived from the GPR profiles indicates the presence of water at the glacier bed in the terminal zone. Taken together, these observations are consistent with the development of a semi-persistent floating terminus, where basal water and buoyancy modulate surface elevation change and control frontal stability and calving style. The results provide new observational constraints on the transient behaviour of floating termini at fast-flowing outlet glaciers in lacustrine settings.