Tsunami waves aren’t just caused by earthquakes or landslides—they can be triggered by weather, too.
These meteotsunamis, which are generally smaller and more localized than their seismic brethren, are prevalent along the East Coast of the United States, new research shows. Scientists found that, on average, 25 meteotsunamis rolled up on shorelines each year from 1996 to 2017, according to a recent paper published in the Bulletin of the American Meteorological Society.
Potentially destructive waves—those topping about 60 centimeters in height—occur only about once a year, the data revealed, but such events can cause injuries and significantly contribute to flooding, the researchers concluded.
Meteotsunamis, as their name suggests, are similar to seismically induced tsunamis, said Gregory Dusek, a physical oceanographer at the National Oceanic and Atmospheric Administration’s (NOAA) National Ocean Service in Silver Spring, Md., who led the new study. “They’re meteorologically driven tsunami waves.”
An abrupt change in air pressure or high wind speeds, often associated with storms, can cause meteotsunamis to form in shallow waters. If the waves move at the same speed as the storm system, they receive periodic injections of energy, which cause them to grow in size.
Dusek and his colleagues collected data from 125 tide gauges between Maine and Puerto Rico. These roughly football sized instruments, mounted on piers or bulkheads, measure water height by bouncing microwaves or sound waves off the water’s surface. After subtracting out the signal caused by the tide, researchers looked for signatures of passing meteotsunamis. They flagged energetic waves taller than 20 centimeters that were detected by at least two tide gauges. Dusek and his collaborators also looked for certain meteorological conditions: a wind speed above 10 meters per second or a change in air pressure of at least 0.9 millibar over 6 minutes.
Many Small Ones
The scientists identified 548 meteotsunamis over the 22-year time span, which averages to roughly 25 per year.
“I certainly didn’t expect to see that number,” said Dusek.
However, other recent studies that focused on the Great Lakes and the Gulf of Mexico have corroborated these findings, making the results less surprising, said Dusek.
Most of the meteotsunamis on the East Coast probably didn’t cause damage, researchers found: Over 90% had a peak-to-trough height of less than 40 centimeters. Thirty events had a wave height of more than 60 centimeters, and three were larger than 1 meter. Meter-size waves can injure beachgoers and also contribute to coastal inundation during a storm surge, said Dusek.
This study provides insights into the timing and severity of meteotsunamis along a highly populated shoreline, said Eric Anderson, an oceanographer at the NOAA Great Lakes Environmental Research Laboratory in Ann Arbor, Mich., not involved in the research. “[It] supports the notion that meteotsunamis are a frequent occurrence along the Earth’s coastlines.”
A few of the larger meteotsunamis found by Dusek and his colleagues were also detected by Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys. These instruments, designed to measure seismically induced tsunamis, are complementary to tide gauges, said Dusek.
Researchers are planning to combine their tide gauge detections of meteotsunamis with DART data to determine what kinds of events trigger both types of sensors.
Correction, 4 April 2019: This article has been updated to describe accurately how tide gauges measure water height.