What could cause a tsunami along the Grand Strand?


MYRTLE BEACH, SC (WMBF) – Devastating tsunamis have struck around the world, leaving those along the Grand Strand to wonder if the area is at risk, too.

The Grand Strand knows its vulnerability from tropical storms and hurricanes, but buried deep in the area’s past is evidence tsunamis have also impacted the region.

There are records from the not-too-distant past to show that tsunamis have impacted the East Coast.

“Yeah, you might not think that having a tsunami on the East Coast is something that could happen, but there have been records of past tsunamis along the Carolinas,” said Steven Pfaff, with the National Weather Service. “As recently as 1929, there was a tsunami that impacted Nova Scotia and Newfoundland.”

Research shows a few likely areas where a tsunami could be generated that could reach the Grand Strand.

An underwater landslide off the North African coast, or an earthquake or landslide in the northern Atlantic could both send tsunamis toward the Grand Strand, but the greater and most likely threats lie a bit closer to home.

“Yeah, the deepest part in the Atlantic basin is the Puerto Rico Trench and that has a history of tsunamis in the past causing submarine landslides and causing a tsunami like Indonesia, where there’s plate tectonics involved,” Pfaff said.

The Puerto Rico Trench is 1,200 miles away and an area where two of earth’s plates are pushing against each other. It’s a hotbed of earthquake activity.

Most of those earthquakes are weak, but scientists believe that a magnitude 9 quake in that area would be large enough to send a tsunami toward the Grand Strand.

An earthquake that large would displace tremendous amounts of ocean water and send large waves quickly out into the Atlantic. Like a ripple on a pond, those waves would travel outward until eventually reaching the Carolina coast in a fairly short amount of time.

Something coming from the Puerto Rico Trench would take us a few, maybe six hours, before it reaches parts of the Southeast United States,” Pfaff said.

The waves generated by an earthquake in the Puerto Rico Trench could be as small as 2 feet, or as large as 10, but tsunami waves don’t act like regular waves that crash on local beaches every day. They move fast and carry a tremendous amount of energy.

Even if it’s just a small tsunami, a 2- or 3-foot run up from that, with it moving so fast, anyone that was caught on the beach, they’d be knocked down, potentially carried out into the ocean or slammed into piers and other things,” Pfaff said. “It’s a hazard that is real.”

However, there’s another threat area that is just offshore.

“The one that concerns me the most is something that would be a submarine landslide off the continental shelf and slope just off our coast,” Pfaff said.

A submarine landslide, or a landslide that occurs under water, has happened many times before and right offshore. Once past the shallow waters of local beaches, the ocean bottom drops off very fast.

It’s along that slope and into the depths of the open ocean where these landslides can occur.

“All it’s going to take is a little earthquake in the continental slope offshore and that might trigger the next submarine landslide and now we’re going to be dealing with a tsunami warning as a result,” Pfaff said.

Recent studies from the U.S. Geological Survey modeled a large underwater landslide off the Outer Banks of North Carolina.

The simulations revealed waves as high as 18 feet on much of the North Carolina coast, and over 10 feet on the South Carolina coast. A tsunami generated that close to home would arrive in a short amount of time.

“If it’s a submarine landslide just offshore, it would be about one to two hours before it moves in, so we have time to issue the warnings,” Pfaff said.

One of these landslides would most likely be triggered by an earthquake nearby or just offshore.

“I think any earthquake we have in the coastal areas, especially just off the coast, that’s one we’re going to have to pause and make sure and listen for watches and warnings in case we need to take action,” Pfaff said.

The Charleston Earthquake of 1886, a magnitude 7.3, likely generated a landslide just off the Florida coast that resulted in a small tsunami there. As recently as 2002, magnitude 4.3 and 3.8 earthquakes occurred just 15 miles offshore of Charleston.

While the threat of a tsunami off the Grand Strand’s coast is low, it is one that does not go unnoticed.

“If we prepare for a terrorist attack in Myrtle Beach, we need to be preparing for a tsunami event in Myrtle Beach,” Pfaff said. “They’re both very low-probability scenarios, but when it does happen, it could be high impact. “So, we can’t disregard tsunamis.”

The threat is real enough that local and state governments have a plan in place.

“We had a tsunami drill last year and the year before, where we tested communications from the state level down through the counties and the coastal communities that was very successful,” Pfaff said. “So having that plan in place that has everybody going in the same direction when that event does occur, and the main intent of that is to keep everyone safe and off the beaches when a tsunami does threaten.”

All the cities along the Grand Strand are certified tsunami ready, meaning they have a comprehensive plan in place for when a tsunami may strike.

“We just don’t know. Is it going to be two days, two hours from now or 2,000 years from now? Pfaff said.

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