SOUTH KINGSTOWN — Tsunamis, some more devastating than others, occur around the world and the coast of southern New England is not safe from these destructive waves.
One of the lesser-known types of tsunami, called a meteotsunami, is caused not by seismic activity, but by weather. After a line of severe thunderstorms passed through southern New England on May 15, the Federal Emergency Management Agency and the National Weather Service issued tsunami warnings for the coast.
While not nearly as dramatic as the immense waves that swallow entire towns, meteotsunamis can reach heights of 6 meters, or approximately 19 feet. They are created by severe weather disturbances that cause dramatic differences in atmospheric pressure. Fortunately, most meteotsunamis are too small to even notice.
Just two days after the local meteotsunami warning, Ph.D. candidates at the University of Rhode Island’s Graduate School of Oceanography presented a talk on tsunamis and meteotsunamis in particular.
Part of the ongoing Bay Informed series of public lectures by graduate students, Thursday’s talk by Christina Wertman and Lauren Schambach described the different types of tsunamis, their causes and where they are likely to occur.
Wertman explained that all tsunamis (the word “tsunami” is harbor wave in Japanese) are long waves created by the vertical displacement of water.
They are caused by earthquakes, volcanoes, underwater landslides, and even meteors hitting the water. Tsunamis start off small, but they undergo a dramatic increase in height when they reach shallow coastal waters.
“In the deep ocean, we’re talking 3,000 to 4,000 meters, these tsunamis are very small waves, on the order of meters high, so when when you look at the total water column, that’s not a very large percent,” Wertman said. “The problem with tsunamis is, when they enter shallow water, they end up doing what we call ‘shoaling’, so they get really short and really tall, and that’s where the problem lies.”
Meteotsunamis are generated by pressure changes caused by severe storm systems moving quickly over the water. Wertman pointed to a series of dots on a map of the East Coast, each one indicating that a meteotsunami had been recorded there. In 2008, a large meteotsunami, 4 meters tall, was recorded in Boothbay Harbor, Maine, and a smaller one was recorded a few years later in Rhode Island.
“In 2013, there was actually a tsunami that entered Narragansett Bay,” she said. “It was picked up by the local news … and the government also picked up and detected the tsunami, so the National Oceanographic and Atmospheric Administration, NOAA, classified this event as a tsunami”
The Deep-water Assessment and Reporting of Tsunamis warning system, known as DART, consists of 39 buoys in oceans throughout the world,. The buoys, which are anchored in very deep water, detect tsunamis and transmit the data to NOAA. One of the buoys, off the coast of New Jersey, picked up a meteotsunami in June, 2013, during severe thunderstorms.
“What caused this is the displacement of water at the surface that’s created by a storm,” Wertman said. “This isn’t just any little storm. This is a really strong, severe storm. This one in particular was called a squall line, a straight line windstorm. These are organized groups of thunderstorms, hundreds of kilometers long and wide.
“A great example of one of these storms is the one that passed by on the 15th, two days ago,” she continued. That was a perfect example of a storm that could have generated a meteotsunami. It just died offshore, so it didn’t really generate anything.”
Wertman said meteotsunamis, while interesting phenomena, were not something Rhode Islanders needed to worry about.
“Is it going to wipe out all of Narragansett Bay? Probably not,” she said.
The first thing to know about tsunamis, Lauren Schambach said, is that they are not tidal waves. “We know our tides come about every six and a half hours here and that is a tidal wave,” she explained.
The most destructive tsunami in history occurred in the Indian Ocean in 2004. Caused by a 9.1 magnitude earthquake near Sumatra, it killed between 230,000 and 280,000 people in Indonesia, Sri Lanka, India and Thailand.
In 2011, another earthquake in Japan caused the Tohoku tsunami that killed 16,000 people and damaged the Fukushima nuclear power plant, causing a meltdown.
There are also records of tsunamis reaching the East Coast. An earthquake in 1929 off the Grand Banks triggered a landslide which resulted in a tsunami that killed 28 people in Newfoundland. That event prompted American researchers to begin investigating tsunami-generating earthquake faults and underwater landslides.
“It led researchers to go out and they actually found evidence that the earthquake caused an underwater landslide, and that’s what caused the tsunami,” she said.
Researchers who are mapping the underwater shelf have determined that landslides had also occurred off the U.S. coast.
Schambach said that all the underwater hazards that might cause tsunamis were being mapped and that the initiative was still in the early stages.
“We’ve modeled all of them, figured out what the run-up is on the coastline, what areas are affected, and we’re coming up with hazard maps to let people know where the hazard is,” she said.
A NOAA-National Weather Service website shows the current locations of earthquakes and tsunami warnings. The site can be accessed at https://tsunami.gov/