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

To characterize the spatiotemporal variations of glacier surface speed on the Kenai Peninsula, Alaska (similar to 3,900 km(2)), 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.

Automated summary

In this study, the spatiotemporal variations of glacier surface speed on the Kenai Peninsula, Alaska were analyzed. It was found that the speeds are 50% greater in spring than the annual mean, while winter speeds are close to the annual mean. Monthly variations over the 5-year period are synchronous, suggesting that regional-scale meteorological drivers govern the temporal variability. The impact of glacier lake outburst floods (GLOFs) and proglacial characteristics on glacier speed variations are highlighted.