MORPHOLOGY, DEPOSITIONAL PACE, AND ICE VOLUME CONTRIBUTION OF ICY DEBRIS FANS TO MCCARTHY CREEK GLACIER, WRANGELL MOUNTAINS, ALASKA (2013-2015): AN INTEGRATED APPROACH USING FIELD OBSERVATIONS, TIME-LAPSE AND DRONE IMAGERY, GROUND PENETRATING RADAR, AND TERRESTRIAL LASER SCANNING
Depositional events occurred throughout the year. Icy debris fans are exceptionally dynamic compared to alluvial fans, with resurfacing rates between 299–1,035% during the two year period. TLS-calibrated time-lapse imagery documented deposition of >2,000,000 m3 (mostly ice), ranging from ~ 3–34% of fan volumes. During this time, repeat TLS surveys showed variable response by the IDFs owing to catchment differences and icecap supply; East Fan grew by 3% while Middle and West Fans decreased by 22% and 25%, respectively. Although ice ablates from IDFs in summer months, significant ice is transferred to the valley glacier by surface and subsurface flow within IDFs. Estimates of glacier volume from integrated TLS-GPR data indicate that IDFs contribute 2.5%–5% of the volume of McCarthy Glacier annually. TLS surveys showed only minor thinning of McCarthy Glacier (< 1 m/yr) compared to significant thinning observed at three New Zealand IDF study sites (~5–10 m/yr). Supply of ice to valley glaciers via IDFs represents an important component of annual ice budgets for glaciers that are decoupled from high-level icecaps, slowing deglaciation of valley glaciers.