Based on a recent study, a new research paper reveals that heavy downpours can boost the movement rate of an Alaskan glacier by as much as 251 percent when it is in its slow-flow phase.
Boise State University researchers analyzed GPS measurements from Turner Glacier, also known as Sít’ Kusá, in Alaska. The team compared rainfall-driven speed changes during a surge between 2020 and 2021 with a slower-flow period spanning 2022 to 2024.
Moving faster than their standard velocities, surge-type glaciers experience periodic velocity spikes that can increase by orders of magnitude. Researchers compared 10 GPS-derived glacier surface speed records with modeled rainfall estimates to track these shifts, according to the study.
GPS instruments installed around the glacier recorded its position every 15 seconds. Scientists also compared rainfall estimates with measurements from a weather station located at nearby Yakutat Airport.
During the 2020 to 2021 surge, nine out of 16 large rainfall events recorded speed anomalies. The glacier reached speeds of 24.6 feet per day, marking a 116 percent increase that lasted an average of 66.5 hours.
Between 2022 and 2024, rainfall-induced acceleration occurred less frequently. Out of 37 rainfall events, 17 showed speed-ups, producing smaller speed changes of approximately 4.9 feet per day over roughly 33 hours.
The percentage increase was considerably greater during this quiescent phase, reaching 251 percent. Roughly 12 hours after precipitation began, the glacier typically started speeding up during the surge, whereas speed increases during the quiet phase reached their maximum about 32 hours after the rain started.
The study examined these speed changes to understand how the glacier’s drainage system responds to rainfall. Glacier drainage efficiency influences how water moves beneath the ice, as inefficient drainage allows water pressure to build and reduces friction between the ice and the ground.
Differences in acceleration characteristics indicated more efficient drainage during quiescence. Yet, rain triggered speed increases during both periods, implying that a poorly functioning part of the drainage network remained active throughout the entire surge cycle.
Particularly large and prolonged rainfall events could temporarily slow the glacier during its surge. Within under two weeks, velocities dropped back to their baseline measurements as the drainage network transitioned back to its poorly draining condition.
GPS instruments installed around Turner Glacier recorded its position every 15 seconds. Researchers paired this high-frequency positional data with weather station measurements from Yakutat Airport.
According to the study, acceleration was greatest in the glacier’s lower sections during both the surge and quiescent phases, compared with areas higher in the valley.
Speeds returned to pre-event levels in less than two weeks as the subglacial drainage system reverted to its inefficient state following large rainfall events.
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