Heavy rainfall can rapidly accelerate an Alaska glacier, according to GPS observations from Sít’ Kusá, also known as Turner Glacier. The finding matters because short-lived glacier surges can reshape valleys, fracture ice, create temporary lakes and increase risks downstream.
Glaciers are often pictured as slow, steady rivers of ice. Their movement is driven by gravity, but their speed is not constant. At times, a glacier can enter a surge-like state and move far faster than its usual pace. Researchers studying Sít’ Kusá found that rain is closely associated with many of those abrupt accelerations.
Tracking a glacier in near real time
Parker Wilkerson of Boise State University and colleagues installed GPS instruments around the steep, heavily crevassed glacier to record its position every 15 seconds. That unusually detailed record allowed the team to compare short-term changes in ice motion with rainfall estimates.
The rainfall estimates were checked against observations from the weather station at nearby Yakutat Airport. The researchers then examined whether rain events aligned with increases in the glacier’s speed during two contrasting periods: a surge period in 2020 and 2021, and a slower-flowing period from 2022 through 2024.
The analysis, published in The Cryosphere, found that more than half of the rainfall events during the study were followed by speed-ups. The largest recorded response reached 7.5 metres in a day, a 116% increase in speed compared with the glacier’s preceding movement.
Rainfall was linked to stronger, longer motion
The fastest event was not simply a brief jolt. It lasted 66 hours, twice as long as any event observed during the later quiescent-flow period. The pattern suggests that rain can affect how water moves through and beneath the glacier, altering conditions that govern how readily the ice slides or deforms.
The team found that the strongest responses tended to begin about 12 hours after rainfall started, once precipitation had reached at least 20 millimetres. That delay is important: it indicates that monitoring rainfall totals and timing could offer useful warning information rather than merely explaining a speed-up after it has occurred.
The study does not mean every rainy period will produce a glacier surge. But it shows that precipitation can be a significant trigger when the glacier is in a susceptible state. The contrast between the 2020–2021 surge period and the quieter 2022–2024 period also points to the importance of the glacier’s underlying condition, not rainfall alone.
Why sudden glacier motion matters
Rapid glacier advances can have effects well beyond the ice itself. A moving glacier can erode a valley floor and sides with exceptional force, open deep crevasses and push into side valleys. If it blocks a tributary valley, it can form an ice dam and impound water behind it. When such a dam fails, the resulting release can cause destructive flooding.
For glaciers that flow toward the ocean, changes in speed can also influence calving and melting. Those processes are relevant to the broader question of how land ice contributes to sea-level rise. The relationship is complex and varies from glacier to glacier, but the work at Sít’ Kusá underscores that weather events can affect glacier dynamics on timescales as short as hours and days.
That makes detailed field measurements valuable. Satellite imagery is essential for observing remote ice, but the GPS record used in this research captures rapid movement that can be difficult to resolve with less frequent observations. Pairing high-temporal-resolution ice measurements with weather data gives scientists a clearer view of the conditions surrounding a surge.
A monitoring challenge in a wetter world
The research adds a practical variable to glacier-hazard assessment: heavy precipitation. Scientists and managers monitoring unstable glaciers may need to consider not only longer-term warming and melt, but also individual rainstorms capable of delivering substantial water over a short period.
At Sít’ Kusá, the threshold-like pattern observed by the researchers offers a starting point for that work. Rainfall of at least 20 millimetres and a delay of roughly half a day were associated with the stronger speed-ups recorded in the study. Those figures should not be treated as a universal rule for all glaciers, but they demonstrate the kind of measurable signal that site-specific monitoring can uncover.
The central result is a reminder that glaciers are dynamic systems. A storm can do more than wet the surface of an ice mass: under the right circumstances, it can help set a glacier moving at more than twice its earlier speed. Understanding when that happens is increasingly important for anticipating landscape change and hazards in mountain and coastal glacier regions.
This article is based on reporting by Phys.org. Read the original article.
Originally published on phys.org
