by Mary Caperton Morton Friday, August 3, 2018
The Caribbean is famous for clear blue waters and serene white sand beaches, and infamous for destructive hurricanes — but another type of natural disaster can also strike: tsunamis. On Aug. 4, 1946, a magnitude-8.1 earthquake shook the Dominican Republic and set off a tsunami across the Caribbean that killed as many as 1,800 people and registered on tide gages as far away as Atlantic City, N.J. At the village of Julia Molina on the northern coast, the waves reached 5 meters. In the decades since, smaller waves have caused flooding and injuries. Now, geoscientists are helping the region prepare by modeling worst-case scenarios for the annual CARIBE WAVE tsunami drill.
Today, more than 40 million people live in the Caribbean, with tourism driving population numbers far higher. Enough time has passed since the last big tsunami in the Caribbean “that many people have forgotten all about the threat,” says Christa von Hillebrandt-Andrade, manager of NOAA’s Caribbean Tsunami Warning Program, based in Puerto Rico. “During that time, the populations living along the coasts have increased dramatically, so if a wave were to strike, the impact could be unprecedented.”
The Caribbean region is made up of more than 700 islands, many of which sit atop or alongside the Caribbean Plate. The northern and southern edges of the plate form transform fault boundaries with the North American and South American plates. To the east, at the Puerto Rico Trench — home to the greatest depth in the Atlantic Ocean at 8,648 meters — the boundary dives deep into the Lesser Antilles Subduction Zone, which produced large earthquakes in 1839, 1843 and 1918. Several active submarine volcanoes also dot the seafloor of the eastern Caribbean, with the potential to trigger tsunamis through underwater eruptions or large-scale marine landslides.
In May, von Hillebrandt-Andrade gave a presentation at the Seismological Society of America annual meeting in Miami entitled “Megathrusts and tsunamis in the Caribbean.” We used to think a roughly “magnitude-8 earthquake was the largest we might see in the Caribbean, based on the history of earthquakes there and the length and motion of the faults,” she says. “But now some scientists think that several faults in the region could be capable of producing earthquakes of magnitude 8.6, and the catastrophe planning by our emergency management community is now considering 8.5 and 9 earthquakes as the worst-case scenarios.”
To remind people about the dangers of tsunamis and help them prepare for potentially deadly events, von Hillebrandt-Andrade and colleagues spearhead the CARIBE WAVE tsunami exercise, an annual event held in March that offers different wave scenarios, generated by different ruptures, and encourages emergency response agencies, communities and individuals across the Caribbean to update and practice evacuation drills. In 2018, more than 680,000 people participated in the drill, with 46 out of 48 countries and territories involved.
This year’s CARIBE WAVE recreated the 1918 Puerto Rico Trench earthquake and subsequent tsunami. The magnitude-7.1 quake triggered a 6-meter-high wave that destroyed villages on the west side of Puerto Rico. “It can be very motivating for people to respond to a historical event that they have heard stories about,” Hillebrandt-Andrade says. “We want people to do an actual evacuation, so if a tsunami strikes, they’ve already practiced their evacuation route to higher ground.”
In 2019, the CARIBE WAVE exercise will feature a new scenario not based on a specific past event: a flank collapse at the Kick ‘em Jenny Volcano, an active submarine volcano 8 kilometers north of the island of Grenada, which could displace enough water to trigger a tsunami.
Practicing such drills is important because the emergency response to a tsunami differs from the more commonly deployed response to a hurricane due to the different lead-times involved, says Ronald Jackson, executive director of the Caribbean Disaster Emergency Management Agency. “When dealing with storms you often have days to prepare, but in the event of a tsunami we’re always going to be racing against time. We have to get the word out and get everybody moving to higher ground in a matter of minutes. It’s a very daunting task and one that needs to be practiced.”
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