23.04.2025 | Jiahui Kang | WSL News
When frozen rivers break up in spring, the sudden release of ice and water can reshape river channels and pose serious risks to nearby infrastructure. These events potentially influence sediment transport, erosion patterns, and bank stability. In collaboration with Umeå University, a team from WSL laid a fiber-optic cable on river ice in northern Sweden to find out whether the ice breakup event could be predicted. In the WSL Logbook, WSL doctoral student Jiahui Kang reports on how that worked – and how things sometimes happen faster than expected.
We arrived on the banks of the Sävarån River near Umeå on March 25. Our goal was to use Distributed Acoustic Sensing (DAS) to capture the process of river ice breaking apart in spring. For this method, researchers use a standard fiber-optic cable as a dense array of seismic sensors. It can detect slight deformations caused by elastic waves, pushes or pulls (i.e., quasi-static deformation) along the entire length of the cable. It was an ambitious idea: laying a fiber-optic cable directly onto the ice surface as nature takes its course. We weren’t entirely sure what would happen when the ice began to melt. What we didn’t anticipate was just how quickly it all occurred.
Since the start of the year, northern Sweden had seen its warmest winter in over a decade. This raised concerns that the usual late April breakup might come early. But to our relief, when we arrived, the river was still frozen solid. That was perfect!
Cozy headquarters ¶
With the help from our colleagues in Umeå University, we rented a little red hut nearby, which quickly became our field HQ: warm, cozy, and, crucially, the power source for our DAS system. We spent two days installing the cable on the ice and running tap tests – we walked along the fiber and stepped on the ice next to it about ten times at set intervals along its length to check the data quality. By March 27, everything was set.
The next two days were spent doing something surprisingly exhausting: shoveling snow. We tried to cover as much of the cable which laid on the bare ice as possible with snow from the surrounding regions to insulate it from the sun and help it stay frozen in place. During data recording, we visited the site daily to check conditions, hoping the ice would hold long enough for a longer recording period.
Then things got dramatic.
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Shoveling with safety ropes — doing our best to protect both the cable and ourselves! (Photo: Sophia Laporte, University of Umeå)
Rapid melting and cable rescue ¶
By March 31, we noticed that one section of the cable was already floating in a ponded «lake» on the river ice surface. On 1 April, we found most of the upper part of the cable had sunk into the river. It was hanging there, held up only by a piece of ice connected to the bank, just barely keeping it from being swept away.
From that point on, the melt accelerated like a time-lapse movie. Within two days, cracks widened, edges thinned, and soon we could see multiple ice floes drifting downstream. It had only been a week…
By the time we retrieved the cable, most of it was already swimming in the flowing river water. Some sections had been torn clean off by the force of the current. Luckily, we’d tied each cable end to a tree. That saved us from losing many parts of the cable. In the end, we recovered most of it.
Success! ¶
Despite the early finale, the experiment was a success. We captured a first-of-its-kind, high-resolution Distributed Acoustic Sensing recording of river ice break-up process which was compressed into just a few days. Beyond the data, it was beautiful to witness such a transformation of nature up close. We also saw moose, reindeer and even the northern lights!
To sum it up: We spent one week of setup and daily visits in the cold Nordic region, followed by one intense week of rapid melting and cable rescue. Along the way, we gathered valuable data, witnessed the river’s transformation firsthand, and collected more stories than we ever expected.
Copyright ¶
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