Kinematics of the exceptionally-short surge cycles of Sít’ Kusá (Turner Glacier), Alaska, from 1983 to 2013

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.

Complementary Approaches Towards a Universal Model of Glacier Surges

“…Kamb et al, 1985) logically imply that the stress balance plays a consequent role in the spatial propagation of zones with high basal sliding rates. This is further supported by areas of the glacier being isolated from draw down by the kinematic barrier provided by an ice fall (Echelmeyer et al, 1987;Nolan et al, 2021). Down-glacier surge propagation is then simply driven by the increase in compressive longitudinal stress induced by fast upstream motion, and up-glacier propagation is caused by longitudinal stretching (e.g.…”

“…The resulting gradual surge build-up does reflect the multi-year activation of certain Svalbard surges but is less representative of sudden onsets of the active phase that characterise Alaskantype surges (e.g. Nolan et al, 2021). Here, the non monotonic response of basal drag to increasing sliding rates caused by a regime change towards low basal friction in Thøgersen et al (2019) and by till failure at yield strength in Minchew and Meyer (2020) could provide specific thresholds above which initial acceleration starts to occur.…”

The Evolution of the Glacier Surges in the Tuanjie Peak, the Qilian Mountains

“…Sentinel-2 Level 1C products include orthoimages containing radiometrically corrected top reflectance values of the atmosphere. These orthoimages are geometrically corrected based on an accurate geometric model [39]. The processing of Landsat and ASTER products is similar to the processing of Sentinel-2 data for radiometric and geometric correction, orthorectification, and resampling to the map grid [40].…”

“…Surface elevation changes were documented using four ASTERs, one Shuttle Radar Topography Mission (SRTM), and four 1:50,000 topographic (TOPO) maps. We used MMAS-TER [49] to create ASTER DEMs with ∼10 m vertical uncertainty [39] and 30 m spatial resolution using stereo imagery data from 02 November 2002 (ASD02), 16 November 2007 (ASD07), 28 October 2012 (ASD12), and 10 March 2018 (ASD18). The SRTM mission collected near-global data at 30 m-resolution from 11 to 22 February 2000 using C-band radar [50].…”

“…Two principal, broadly recognized hypotheses of surge triggering mechanisms have been proposed: hydraulic and thermal [39]. The hydraulic mechanism consists of an event that causes the base water pressure to increase, reduces bed resistance, and causes a rapid slip to occur; this trigger type is expected to produce more sudden behavior [16].…”