In August 2018, Alex Normandeau was on a research cruise in the Southwind Fjord of Canada’s Baffin Island, attempting to study landslides on the seafloor. Normandeau, a research scientist at the Bedford Institute of Oceanography in Dartmouth, Nova Scotia, was aboard the CCGS Hudson collecting bathymetry data and core samples of the seafloor when the crew spotted an iceberg. “We took a bunch of photos and didn’t think anything of it at the time,” Normandeau remembered.
A year later, Normandeau and his colleagues determined that the same iceberg may have initiated a new submarine landslide. Scientists had never shown that icebergs could cause landslides before. Their findings were published in June in Nature Geoscience.
An Iceberg Aground
Submarine landslides can threaten sea life, cause tsunamis, and damage infrastructure such as subsea Internet cables.
Despite these risks, scientists don’t fully understand the causes of submarine landslides. In some cases, earthquakes are the culprits. But because most of the ocean floor is irregularly mapped, it is difficult to know when landslides occur and link them with a causal event.
When the researchers returned to Southwind Fjord in 2019, they learned a new landslide had occurred since their previous visit, providing a rare opportunity to look within a short time window and determine what might have caused it.
Because no earthquakes had occurred within 300 kilometers of Southwind Fjord, the researchers looked for other mechanisms. By comparing the bathymetry data from their two visits to the fjord, they found an intriguing piece of evidence. They noticed a characteristic pit left when an iceberg impacts the seafloor—right at the initiation point of the landslide, known as a head scarp. Using satellite images from Sentinel-2, they realized that the iceberg they saw the year before eventually ran aground. A few days later, it capsized and slammed into the ocean floor, regrounding several meters away.
NGeo: Iceberg gouging of continental slopes can initiate submarine landslides, potentially far from the iceberg source region@SediAlex; @GSC_CGC; @NRCan; @ClarkGRichards; @DCalvinCampbellhttps://t.co/TMZfbscUlc pic.twitter.com/bS9T7DQk6q
— Nature Geoscience (@NatureGeosci) June 24, 2021
“We interpret that it’s that impact that created the landslide because when you look at where the iceberg regrounded, that’s exactly where the landslide head scarp is,” said Normandeau. “We were hoping for something like this. But to see it happen? It was a lot of luck.”
For further evidence that the iceberg initiated the landslide, the researchers went back to the core samples they collected in 2018 near the landslide but before it occurred. By analyzing the sediment composition and the slope of the seafloor, they found that the sediment in the area was stable under gravitational load, but the estimated load of the iceberg would have been enough to initiate the slide.
Morelia Urlaub, a marine geoscientist at GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany, who wasn’t involved in the study, is researching ways to monitor the seafloor and identify new landslides. She said that when researching submarine landslides, researchers must be in the right place at the right time. “That’s what I found fascinating about this iceberg study. They basically caught one,” Urlaub said. “The study is important because it brings up a new mechanism and because the observation is good as it gets.”
Iceberg Impacts Run Deep
After discovering the landslide in Southwind Fjord, the researchers explored maps of the seafloor in other locations. They found several other iceberg pits at landslide head scarps. “The most surprising result was off the continental slope of Nova Scotia,” Normandeau said. “They’re much bigger [landslides] than what we see in the fjords.” Normandeau hypothesizes that when there was an ice sheet in the region around 20,000 years ago, big icebergs broke off and impacted the seabed, causing landslides. He’s hoping to address this hypothesis in future research.
As climate change causes more icebergs to break off the existing ice sheets, understanding the risks that icebergs pose could mitigate damage to new infrastructure projects. In Canada, there is a push to connect northern communities with subsea Internet cables, which would be especially at risk. But icebergs can also travel thousands of kilometers, potentially causing landslides far from the Arctic. “It’s important to be aware of the triggering mechanisms when we’re planning seafloor infrastructure,” Normandeau said. The gouges left when icebergs collide with the seafloor might be only the tip of the problem.
—Andrew Chapman (@andrew7chapman), Science Writer