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Abstract Glacier speedups occur on daily to centennial timescales. While basal water and subglacial drainage configuration are thought to drive glacier speedups across these timescales, it remains unclear whether this forcing always occurs through the same mechanisms. Here, we explore whether the enthalpy model of glacier surging can explain speedups over a broader range of timescales if modified to account for seasonality in surface melt and continuous water supply to the glacier bed. We simulate velocity oscillations that range from seasonal to years. Our model results more closely resemble observations of surges than previous model versions because ice flow variability at seasonal and multi‐year timescales is reproduced simultaneously through hydrological forcing. Under favorable conditions, seasonal water delivery to the bed gradually accumulates in a poorly‐connected basal drainage system, priming the glacier to surge. Surges themselves are marked by high water fluxes and enthalpy drainage from the glacier base. 

Abstract Glacier surges are opportunities to study large amplitude changes in ice velocities and accompanying links to subglacial hydrology. Although the surge phase is generally explained as a disruption in the glacier's ability to drain water from the bed, the extent and duration of this disruption remain difficult to observe. Here we present a combination of in situ and remotely sensed observations of subglacial water discharge and evacuation during the latter half of an active surge and subsequent quiescent period. Our data reveal intermittently efficient subglacial drainage prior to surge termination, showing that glacier surges can persist in the presence of channel-like subglacial drainage and that successive changes in subglacial drainage efficiency can modulate active phase ice dynamics at timescales shorter than the surge cycle. Our observations favor an explanation of fast ice flow sustained through an out-of-equilibrium drainage system and a basal water surplus rather than binary switching between states in drainage efficiency. 

Abstract We use satellite image processing techniques to measure surface elevation and velocity changes on a temperate surging glacier, Sít’ Kusá, throughout its entire 2013–2021 surge cycle. We present detailed records of its dynamic changes during quiescence (2013–2019) and its surge progression (2020–2021). Throughout quiescence, we observe order-of-magnitude speedups that propagate down-glacier seasonally from the glacier's upper northern tributary, above a steep icefall, into the reservoir zone for the surging portion of the glacier. The speedups initiate in fall and gradually accelerate through winter until they peak in late spring, ~1 − 2 months after the onset of melt. Propagation distance of the speedups controls the distribution of mass accumulation in the reservoir zone prior to the surge. Furthermore, the intensity and propagation distance of each year's speedup is correlated with the positive degree day sum from the preceding melt season, suggesting that winter melt storage drives the seasonal speedups. We demonstrate that the speedups are kinematically similar to the 2020–2021 surge, differing mainly in that the surge propagates past the dynamic balance line at the lower limit of the reservoir zone, likely triggered by the exceedance of a tipping point in mass accumulation and basal enthalpy in the reservoir zone. 

Abstract. En masse application of feature tracking algorithms to satellite image pairs has produced records of glacier surface velocities with global coverage, revolutionizing the understanding of global glacier change. However, glacier velocity records are sometimes incomplete due to gaps in the cloud-free satellite image record (for optical images) and failure of standard feature tracking parameters, e.g., search range, chip size, or estimated displacement, to capture rapid changes in glacier velocity. Here, we present a pipeline for pre-processing commercial high-resolution daily PlanetScope surface reflectance images and for generating georeferenced glacier velocity maps using NASA's autonomous Repeat Image Feature Tracking (autoRIFT) algorithm with customized parameters. We compare our velocity time series to the NASA Inter-Mission Time Series of Land Ice Velocity and Elevation (ITS_LIVE) global glacier velocity dataset, which is produced using autoRIFT, with regional-scale feature tracking parameters. Using five surge-type glaciers as test sites, we demonstrate that the use of customized feature tracking parameters for each glacier improves upon the velocity record provided by ITS_LIVE during periods of rapid glacier acceleration (i.e., changes greater than several meters per day over 2–3 months). We show that ITS_LIVE can fail to capture velocities during glacier surges but that both the use of custom autoRIFT parameters and the inclusion of PlanetScope imagery can capture the progression of order-of-magnitude changes in flow speed with median uncertainties of <0.5 m d−1. Additionally, the PlanetScope image record approximately doubles the amount of optical cloud-free imagery available for each glacier and the number of velocity maps produced outside of the months affected by darkness (i.e., polar night), augmenting the ITS_LIVE record. We demonstrate that these pipelines provide additional insights into speedup behavior for the test glaciers and recommend that they are used for studies that aim to capture glacier velocity change at sub-monthly timescales and with greater spatial detail. 

Abstract Glacier surges are periodic episodes of mass redistribution characterized by dramatic increases in ice flow velocity and, sometimes, terminus advance. We use optical satellite imagery to document five previously unexamined surge events of Sít’ Kusá (Turner Glacier) in the St. Elias Mountains of Alaska from 1983 to 2013. Surge events had an average recurrence interval of ~5 years, making it the shortest known regular recurrence interval in the world. Surge events appear to initiate in the winter, with speeds reaching up to ~25 m d −1 . The surges propagate down-glacier over ~2 years, resulting in maximum thinning of ~100 m in the reservoir zone and comparable thickening at the terminus. Collectively, the rapid recurrence interval, winter initiation and down-glacier propagation suggest Sít’ Kusá's surges are driven by periodic changes in subglacial hydrology and glacier sliding. Elevation change observations from the northern tributary show a kinematic disconnect above and below an icefall located 23 km from the terminus. We suggest the kinematic disconnect inhibits drawdown from the accumulation zone above the icefall, which leads to a steady flux of ice into the reservoir zone, and contributes to the glacier's exceptionally short recurrence interval.