Glacier Surface Speed Variations on the Kenai Peninsula, Alaska, 2014–2019

Abstract

To characterize the spatiotemporal variations of glacier surface speed on the Kenai Peninsula, Alaska (∼3,900 km2), we derived 92 surface speed fields between October 2014 and December 2019 using intensity offset tracking on Sentinel-1 data. On average, speeds are 50% greater in spring (March-May) than the annual mean (69 m a−1) while winter speeds are close to the annual mean. While marine-terminating glaciers have their maximum speed near the terminus, both land- and lake-terminating glaciers flow fastest around the median glacier elevation. On average, the lake-terminating and tidewater glaciers flow 1.7 and 2.3 times faster than the land-terminating glaciers, respectively. Monthly variations over the 5-year period are strikingly synchronous regardless of terminus type suggesting that regional-scale meteorological drivers govern the temporal variability. Mean annual speeds fluctuate roughly ±10% of the period mean without an apparent trend. At lake-terminating Bear Glacier, a short-term tripling in ice speed in fall 2019 over the area below an ice-dammed lake coincides with an observed glacier lake outburst flood (GLOF). An earlier GLOF caused a persistent breach of the beach barrier between the proglacial lake and ocean which likely led to overall speed-up of the lower glacier part throughout 2019. A significant speedup was also observed at the lower part of the lake-terminating Ellsworth Glacier and attributed to rapid glacier retreat and lake expansion, probably further amplified by the terminus area becoming buoyant and a large tabular iceberg breaking off. Our results highlight the impact of GLOFs and proglacial characteristics in spatial and temporal glacier speed variations.