Heavy rain can more than double glacier speeds in Alaska

November 7, 2026 feature Heavy rain can more than double glacier speeds in Alaska Hannah Bird Author Sadie Harley Scientific Editor Robert Egan Senior Editor Glaciers are often thought of as unyielding blocks of ice that slowly carve out the landscape as they move downhill by gravity. But sometimes their slow crawl becomes a surge that sees them move orders of magnitude faster than their usual speed. Such events can have dramatic effects on the environment, acting like a bulldozer to erode valleys, shattering the glacier's surface into crevasses, blocking side valleys to create ice dams with temporary lakes behind, or causing catastrophic flooding when these ice dams burst. And as glaciers move toward the sea, increased ice calving and melting have considerable impacts on rising sea levels. Understanding the mechanisms behind these aggressive advances is therefore vital for scientists to monitor instabilities in the world's glaciers and their wider implications for climate change conversations. Surging states Parker Wilkerson, of Boise State University, and colleagues turned to the steep, highly crevassed Sít' Kusá (Turner Glacier) in Alaska to explore how rain can induce glacier surges. Using GPS measurements from instruments installed around the glacier, the researchers recorded its position every 15 seconds to monitor speed changes in the short term compared to the glacier's longer-term movement. These were then associated with rain estimates validated by measurements taken at the weather station of the nearby Yakutat Airport to identify if there was a correlation between rainfall events and glacier surges. The results, published in The Cryosphere, show that there is. Comparing a period of surge (2020–2021) to slow flow (2022–2024), the team found that over half of the rainfall events caused speed-ups, with the maximum reaching 7.5 meters (24.6 feet) in a single day—that's equivalent to a 116% increase in speed, or more than double. This surge also lasted twice as long (66 hours) as any occurring during the quiescent flow period and tended to begin 12 hours after the start of the rainfall event when precipitation reached at least 20 mm (0.79 inches). The glacier returned to a stable state three days later. However, while rain-induced speed-ups were less frequent during quiescence, when they did occur, they required 60 mm (2.4 inches) of rain since the start of the event and resulted in a much bigger percentage increase (251%) in speed, peaking on average 32 hours later. Despite this speed increase only being 1.5 meters (4.9 feet) per day, it is proportionately larger given the glacier is moving at such a slow background speed. And during both phases, glacier acceleration was greatest in the downhill parts compared to those higher in the valley, likely a combination of landscape topography, gravity and meltwater aiding movement. Dynamic drainage The researchers explain that the surge phenomenon is a consequence of the efficiency of the glacier's drainage system. An efficient one has linked channels running on top of, through and beneath the glacier that allow rainwater and meltwater to drain away quickly, meaning the glacier sits on the underlying bedrock and continues its slow, steady advance. But an inefficient one creates issues. Water gets trapped in isolated pockets under the ice or in the sediment directly beneath the glacier (known as till) with nowhere to drain away. This causes pressure to build up as more water continues to enter these pockets and counteract the weight of the overlying ice, reducing friction and creating a lubricating layer for the glacier to slide quickly over the underlying ground. Known as basal sliding, in other scenarios this can also be caused when the weight of ice reaches a critical point and the high pressure changes the temperature at which it melts to create a water layer between the glacier and bedrock. A future outlook These insights into the relationship between drainage efficiency and glacier speeds are vital for scientists to refine model projections for ice loss into the future. Shifting weather patterns leading to more rain could be an important driving factor in the frequency and duration of surges in years to come. Coupled with increased melting in a warmer world, we are likely to see continued glacier ice loss and need to understand the implications of that for sea levels, especially for coastal and island communities at risk of flooding. While useful, models are complicated by the fact glaciers are ever-evolving and their drainage systems can change on decadal, yearly and even daily timescales. So as much as scientists can try to predict how glaciers may behave in a warmer world, their enigmatic nature means there are some components that may always remain unpredictable. Written for you by our author Hannah Bird, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you. Publication details More information: Wilkerson et al., Rain-induced speed up events of a temperate surging glacier, AK, inferred from GPS measurements, The Cryosphere (2026). DOI: 10.5194/egusphere-2026-6232 Journal information: The Cryosphere © 2026 Science X Network