Iceberg tsunamis can be dramatic and violent events. A recent paper used large-scale experiments to better understand tsunamis generated by iceberg calving. The team of scientists set up a large tank and used heavy blocks to create waves under controlled conditions. The different iterations of the experiments revealed some of the differences that can be found when icebergs fall into water or rise to the surface in various ways.
The findings were published at the 38th International Association for Hydro-Environmental Engineering and Research World Congress (IAHR 2019) in Panama City. The researchers sought to better understand the different features of iceberg-tsunamis that result when icebergs of different sizes calve. They aimed to expand their research by comparing the new findings to the features of tsunamis caused by landslides. The team hopes that their work will serve to create benchmark test cases that future research can benefit from.
Lead author Valentin Heller, a professor of environmental fluid mechanics at the University of Nottingham, highlighted the work’s immediate and future impacts. “The research enables the efficient systematic prediction of iceberg-tsunamis for a wide range of calving mechanisms for the first time,” Heller told GlacierHub. “In the longer term, this is likely to impact the design of coastal infrastructure and disaster risk assessment in areas where iceberg-tsunamis occur.”
The process through which blocks of ice break off the terminus (end) or margins (sides) of glaciers, ice shelves, or ice sheets and fall into a body of water, typically an ocean, is called iceberg calving. Calving events range from rarer instances in which very large chunks of ice break off, like in the video above, to more frequent events with much smaller pieces of ice separating, like in the video below. Calving events can cause iceberg-tsunamis, examples of which can be seen in both videos.
Though glacier melt is increasing worldwide due to the climate emergency, Heller said an increase in ice loss will not automatically bring about an increase in number or strength of iceberg-tsunamis. This is because other melting mechanisms are playing a role as well. “Ice mass loss is primarily driven by two main components; (i) melting of ice and runoff in the form of water from the ice sheet surface and (ii) discharge through glaciers terminating in the sea in the form of iceberg calving.” He continued, saying that “an acceleration of ice mass loss through (ii) does not necessarily result in larger iceberg-tsunamis.”
Iceberg-tsunamis are dangerous to coastal communities, tourists, and the fishing and shipping industries. Greenland has been the site of multiple significant iceberg-tsunamis; one tsunami at the Eqip Sermia glacier in 2013 produced waves so substantial a tourist boat landing was destroyed. The inhabitants of the village Innaarsuit, located in Greenland, were on high alert in 2018 when a 330-foot tall iceberg drifted into the waters near their homes, bringing with it the threat of flooding.
The research team conducted 66 unique, large-scale experiments in a 50 by 50 meter basin with heavy blocks of up to 187 kilograms each with different variations of iceberg volume, geometry, kinematics, and initial position relative to the water surface. They looked at five iceberg calving mechanisms; capsizing, gravity-dominated fall, buoyancy-dominated fall, gravity-dominated overturning, and buoyancy-dominated overturning. The researchers wrote that “gravity-dominated icebergs essentially fall into the water body whereas buoyancy-dominated icebergs essentially rise to the water surface,” distinguishing the two categories.
The researchers looked at nine parameters influencing iceberg-tsunamis that could impact wave heights and their decay. The parameters monitored were released energy, water depth, iceberg velocity, iceberg thickness, iceberg width, iceberg volume, iceberg density, water density, and gravitational acceleration.
The data showed that tsunami heights caused by gravity-dominated fall and gravity-dominated overturning are approximately an order of magnitude larger than those generated by capsizing, buoyancy-dominated fall, and buoyancy-dominated overturning. In other words, icebergs that fall into the water from above are much more hazardous than icebergs released underwater. Heller told GlacierHub that the researchers were surprised about this large difference because it had not been quantified before.
Diving deeper into the researchers’ analysis reveals that the wave magnitudes generated by the gravity-dominated overturning mechanism created the largest tsunamis, the gravity-dominated fall mechanism created the second largest tsunamis, and the three other mechanisms had waves that were up to a factor of 27 smaller. In other words, the two processes that result from icebergs essentially falling into the water created much larger tsunamis than the mechanisms where icebergs rise to the water surface.
A further difference between the two largest wave producers and the three smaller is that for the gravity-dominated mechanisms the largest wave amplitude was observed earlier in the wave train. For the three processes that resulted in smaller waves, the largest wave amplitude was found in the middle of the wave train.
The results of the study will be useful to both scientists and policy-makers. Heller told GlacierHub that the “results [will] help scientists looking into wave runup at shorelines and wave impact on infrastructures, such as coastal buildings, by providing the necessary offshore wave parameters to support their work.” He elaborated, saying that predicting the heights of iceberg-tsunamis “helps to make decisions on how close to a glacier front ships can safely navigate or if evacuations are necessary, as in the case of the village Innaarsuit on Greenland.”
“Iceberg-tsunamis is a relatively new field of research and people are just starting to realize the significance of such waves for coastal infrastructure, tourists and coastal communities,” Heller said. As the body of research grows, we will have a better understanding of how iceberg-tsunamis function. Once more information is available, impacted communities will be better able to prepare for such events.