Tonga eruption and tsunami: University of Michigan experts available to discuss
Written by Jim Erickson
University of Michigan experts are available to discuss Saturday’s undersea volcanic eruption near the Pacific island nation of Tonga and the tsunami that followed.
Zack Spica is a seismologist and assistant professor of geophysics in the Department of Earth and Environmental Sciences. He studies volcanoes using seismic and acoustic waves to learn about their underground magmatic architecture and to monitor their activity. He has worked on several active volcanoes around the world.
“The Hunga Tonga volcano eruption is a one-in-a-century event with a plume of ash that went up to 30 kilometers (about 19 miles) into the stratosphere. Like the Pinatubo eruption in the Philippines in 1991, this eruption was not well anticipated and surprised the international volcano community,” he said.
“However, what has changed since then is that today, the global network of sensors to monitor the eruption is much more advanced than before, and the volcano community was able to quickly assess the importance of this event. Satellites, seismometers and barometric stations (pressure measurements) recorded the blast of the eruption on all continents.
“The air-pressure blast seemed to have revolved the globe at least twice. The umbrella, which is the top of the ash cloud and expands sideways, was comparable in size to Michigan’s Lower Peninsula. The tsunami generated by the eruption was observed everywhere around the Pacific and affected the U.S. West Coast.”
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Jeremy Bricker is an associate professor of civil and environmental engineering at the College of Engineering studying hydraulic and coastal engineering.
“The reach of the Tonga tsunami across the entire Pacific Ocean basin surprised tsunami researchers, because eruption-type tsunamis are usually devastating locally, but disperse rapidly as they move away from the source,” he said. “We need to better understand the way a volcanic tsunami can generate waves, including by induced landslides and meteo-tsunamis from atmospheric disturbances.
“Worryingly, the presence of noticeable waves incident on Japan and the Americas portends that the waves that struck communities near the volcano itself must have been absolutely monstrous. With Tonga’s communications still out and reconnaissance flights yet to report due to ash obscuring the skies, I fear the damage that will be found in unsheltered communities closest to the source.
“Unlike the 2004 and 2011 tsunamis that struck along the Indian Ocean and in Japan, the Tonga tsunami is not expected to have traveled as far inland. The earlier tsunamis were both generated by undersea seismic faults, which caused vertical movement of the seafloor over an area of thousands of square kilometers, leading to very long tsunami waves lasting 10 minutes or more. However, the Tonga tsunami is likely to have caused extensive damage on the coast. Furthermore, the Tonga tsunami did not provide local communities with any warning in the form of retreat of the ocean, again due to the difference in behavior between seismic subduction and volcanic eruption sources.”
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Brian Arbic is a physical oceanographer and professor in the Department of Earth and Environmental Sciences who models oceanic tides and currents on supercomputers. His research group has written a small number of papers on tsunamis, including the 2004 Indian Ocean tsunami and the megatsunami caused by the Chicxulub asteroid impact that killed the dinosaurs 66 million years ago.
“Tsunamis are an ever-present danger for coastal areas,” he said. “They can be caused by earthquakes, volcanic eruptions, and even asteroid impacts.”
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Sue Anne Bell is an assistant professor in the School of Nursing and nurse scientist with expertise in disaster preparedness and response, community health and health care in emergency response settings. She is active in multiple emergency response activities, including the Federal Emergency Management Agency’s National Advisory Council and the U.S. Department of Health and Human Services’ National Disaster Medical System, with recent deployments to the COVID-19 response, Hurricane Maria and the California wildfires.
“The accepted definition of a disaster is when a hazard and a vulnerability combine to exceed the capacity of the community. There is a much more real definition of what a disaster is, one that involves the impact of a volcano and associated tsunami on people and the communities who live in harm’s way and the very real experience of recovering from these events,” she said.
“Efforts should focus on the immediate and long-term needs of Tongan communities, centering on those who will most be affected by the disaster events within these communities, such as older adults. After all, disasters start and end locally. By equipping those who are on the front lines at the local level with the tools to respond, there will be a cadre of responders who share the knowledge and values of the community.
Ben van der Pluijm is a professor in the Department of Earth and Environmental Sciences and an expert on the societal impacts of geohazards and environmental change.
“The Tonga eruption caused an atmospheric boom that was widely heard, a stratospheric ash cloud, damaging flooding in the region, and a tsunami that crossed the Pacific Ocean,” he said. “The explosion was heard and felt around the world, similar to but smaller than the late 19th century Krakatoa explosion in the Indonesian region. It was among the larger volcanic events in recent decades, with an explosivity magnitude of 4-5. For comparison, the 1991 Pinatubo eruption had an explosivity magnitude of 6.
“The sudden water displacement from the underwater volcanic explosion created a tsunami wave, much like an oceanic earthquake does. The explosive volcanism is characteristic for the region’s tectonic setting, where the Pacific plate moves under the Australian Plate. The ash plume is not big enough to create significant solar shielding and cooling.”
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Seth Guikema, a professor of industrial and operations engineering, co-directs the Center for Risk Analysis Informed Decision Engineering and has studied how communities change over time in response to repeated hazard events spaced years apart.
“Working in collaboration with Jeremy Bricker, we found that tsunamis can have a substantial impact on the development patterns in a coastal community over time after the event. In particular, hard protective measures such as levees must be carefully weighed against ‘soft’ measures such as nature-based solutions and land use change, evaluating the differences in how these approaches impact community development over time and risk from future tsunamis. In some cases, hard measures such as levees can induce additional development in hazard zones, potentially increasing future tsunami risk.”
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