University of Michigan: University of Michigan experts available to discuss

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.”

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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