Not All Iceberg-Generated Tsunamis Are Alike. Here’s How They Differ

Many people are familiar with ocean tsunamis caused by earthquakes, such as the devastating Japan 2011 tsunami, but fewer know they can also be caused by iceberg calving. As glaciers and ice sheets undergo intensified melting, we can expect to see more frequent tsunamis triggered by icebergs dropping off the face of the world’s glaciers. These events threaten the lives of people in nearby coastal settlements, whether residents or tourists, and infrastructure as well.

In a recent study published in the journal Scientific Reports, lead researcher Valentin Heller and colleagues investigate the potential for five different calving mechanisms in producing tsunami waves. They knew that iceberg calving, also known as glacier calving, accounted for most of the mass loss from the Antarctic Ice Sheet and about a third for the Greenland Ice Sheet between 2009-2012. Their research could not only contribute to science but have practical effects. Identifying the impacts of  different calving scenarios is beneficial for implementing disaster management strategies and strengthening disaster resilience in coastal regions.

Scientists observed that iceberg calving events in polar regions interact differently with the surrounding waters through distinct calving mechanisms. They investigated five types of calving events: capsizing, gravity-dominated fall, buoyancy-dominated fall, gravity-dominated overturning, and buoyancy-dominated overturning.

To test the tsunami energy potential of each type of calving event, large-scale experiments were conducted in a 50 by 50 meter wave basin at Deltares in Delft, Netherlands. Sixty-six experiments were conducted , at depths of 1 or 0.75 meters. The researchers used PPH blocks, a thermoplastic material with similar density to ice, as a proxy for icebergs.

The researchers implemented various methods of control to simulate the five types of calving events. To represent capsizing, for example, the researchers  fed a wooden rod through the centers of the blocks in order to control the rotation. They simulated buoyancy-dominated fall by pulling the blocks underwater with rope and stabilizing them with a steel beam from above.

Falling and overturning icebergs, and sketches of calving mechanisms (Source: Heller et al.)

They then quantified the maximum heights and energies of the iceberg-tsunamis and found the relative energy releases of the iceberg calvings. They then  analyzed and compared the results with the predictive methods of landslide-tsunamis. By doing this, researchers aimed to transfer knowledge from a well-established research field to the relatively new field of iceberg-tsunamis.

The team found large differences in tsunami height between the mechanisms. The two gravity-dominated mechanisms were found to be better predicted by landslide-tsunami models than the others. These results are significant in understanding the relative impact and prediction capabilities of specific calving events, which is vital to disaster management. Yet the results will be of most use for cases of gravity-dominated calving events. More research will need to be done to better analyze the other calving mechanisms.

One thing not considered in the comparison was the movement of icebergs along coastal locations such as harbours. Researchers noted that even significantly smaller iceberg-tsunamis from capsizing can cause large destruction. They team also scrutinized the existing landslide-tsunami models for failing to capture the physics of the capsizing and buoyancy-driven mechanisms of A, C, and E, which are important iceberg events.

Calving at the Hubbard glacier in eastern Alaska (Source: Navin Rajagopalan/Flickr)

Lead author Valentin Heller, who’s an assistant professor of hydraulics at the University of Nottingham, said the experiments showed that icebergs falling into water were about 10 times larger than those breaking off underwater and moving to the surface, as well as capsizing icebergs. He said the researchers were surprised that this large difference has never been quantified before.

“The overall aim of the study is to be able to predict the tsunami magnitude in function of the size of the iceberg, its initial position relative to the water surface, and on how it interacts with the surrounding water,” Heller said. “This helps to predict the iceberg-tsunami height at any location in front of the glacier front to provide guidelines for tourist boats on how close they can safely approach a glacier front.”  

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