Subsurface architecture of alpine icy debris fans: Integration of ground-penetrating radar and surface observations in Alaska and New Zealand

Icy debris fans (IDFs) are extremely dynamic supraglacial landforms at the mouths of bedrock catchments between valley glaciers and icecaps. Recent studies quantified nature, pace, volume mass flow processes contributing ice sediment to IDFs by integrating field observations, drone time-lapse imagery, terrestrial laser scanning. New geophysical data presented herein characterize subsurface architecture along McCarthy Glacier in Alaska Douglas, La Perouse, Mueller Glaciers Zealand. Ground Penetrating Radar (GPR) profiles soundings from surveys during 2013–2015 provide stratigraphic evidence following important delivery ice/sediment through glaciers: (1) transitional merging fan IDF deposits with glacier cirque settings, (2) progressive rotation (slumping) preserved hanging walls downfan-dipping crevasses/faults, (3) progradation onto glaciers, (4) buttressing margins glaciers. The GPR-based variations architecture/processes attributable previously documented supply overlying icecaps/nevés topographic interaction junctions. GPR document major depositional units separated prominent reflectors, interpreted as annual ablation lag surfaces where lithic sediments relatively concentrated. Most contain less than five units, which may reflect transitory nature these landforms. uppermost package on revealed is deposition year preceding survey because it appears unconsolidated lacks diffractions common imaged older (lower) units. thickness upper typically or equal new recorded cameras spread evenly over surfaces, expected accounting for compaction ablation. datasets, together previous surface bear directly managing hazards evaluating glacial budgets alpine regions. In particular, documentation rotation, buttressing, stratigraphies indicates protracted episodes landform instability deglaciation, consistent observations documenting exceptionally high rates resurfacing slumping. deformation suggests transferred IDFs. This interpretation supported visual evidence, including sliding/glacial coeval little change size. Integrating role budget models result forecasting a lower rate deglaciation traditionally recognized some decoupled • icy (IDF) subsurface. Supply/accommodation dynamics prompt variable syndepositional Ice/sediment be exceedingly – <5 years most cases. transfer significant adjacent Hazard assessment requires integration processes.