How to survive a tsunami

This story originally published on June 27, 2017 and has been updated.

On May 22, 1960, the largest earthquake ever measured struck off the coast of southern Chile. Once the shaking stopped, Denis García, a resident of the nearby port town Corral, noticed something odd. He was searching for his family, not realizing they were safe and on high ground, when he caught sight of Corral Bay. The waters had drawn back, leaving the seafloor bare. García went to investigate. He did not see the 40-foot-high tsunami barreling toward him until it was too late.

Caught in the swirling water, he clung to a piece of debris for hours before meeting another survivor and climbing onto the roof of a house as it floated by, he told interviewers decades later. Meanwhile, the tsunami swept across the Pacific. It’s estimated that the Great Chilean Earthquake and the tsunami that followed claimed more than 5,000 lives.

Around 80 percent of tsunamis begin along the Pacific Ocean’s seismically active “Ring of Fire.” In the United States, Hawaii, Alaska, and the west coast have the highest tsunami risk. But these mega waves can strike in any ocean, and travel across the sea to cause mayhem far from their source about twice per decade.

Denis García was lucky. Most people do not survive being swept into a tsunami. But there are a few ways you can protect yourself from these natural disasters. Your exact strategy will depend on where you are, and will go a lot more smoothly if you have planned in advance.

“It’s easy to say, ‘That’s not going to be my problem ever,’ and it’s also easy to throw up your hands and say, ‘It’s going to be so bad that there’s really nothing I can do,’” says Carrie Garrison-Laney, a tsunami and coastal hazard expert at the Washington Sea Grant office in Seattle. “Yes, it will be bad, but…there are some things you can do to be prepared in the event that it happens.”

Know the tsunami is coming

Most tsunamis are triggered when earthquakes near the seafloor displace a large amount of water. That water gets pushed out as a series of waves that move outwards in all directions. Undersea volcanic eruptions, landslides, and even meteorites can also spark tsunamis.

Out on the sea, these waves can be hundreds of miles long but no taller than a few feet and travel at the speed of a jet plane, up to 500 miles per hour. When the waves approach land, they will slow to about 20 or 30 miles an hour and begin to grow in height.

Most tsunamis are less than 10 feet high when they hit land, but they can reach more than 100 feet high. When a tsunami comes ashore, areas less than 25 feet above sea level and within a mile of the sea will be in the greatest danger. However, tsunamis can surge up to 10 miles inland. “It’s really just kind of relentless, the water just keeps on coming and coming and coming for a long time,” Garrison-Laney says.

The tsunami could resemble a wall of water or, more likely, a rapidly rising flood. “It’s not going to look like big, curling waves like you see at the beach,” Garrison-Laney says. “It’s really a very turbulent flow that is rising and flowing onto land pretty quickly.”

Before this happens, though, there may be a few warning signs.

First you’ll need to survive the earthquake, if there was one. After a strong coastal quake, make sure you get to high ground even if an official tsunami warning has not yet been issued. If a local tsunami has been generated it could be mere minutes away. “You cannot wait for the authorities if it’s a significant earthquake and you live along the coast,” says Denis Chang Seng, technical secretary for UNESCO’s Intergovernmental Coordination Group for the Tsunami Early Warning and Mitigation System in the North-eastern Atlantic, the Mediterranean, and connected seas.

As Denis García discovered in 1960, a tsunami can also cause the ocean to withdraw before it arrives, leaving sand and reefs bare. There may be a roaring noise like a train or jet plane as well. “You have to recognize the warning signs from nature itself,” Chang Seng says.

Meanwhile, tsunami tracking centers such as the Pacific Tsunami Warning Center in Hawaii or the National Tsunami Warning Center in Alaska will put out an alert. So be on the lookout for official warnings, sirens, and directions from your local authorities.

“You don’t want to hesitate if you know a warning’s been issued or you’ve felt the ground shaking,” says Laura Kong, director of the International Tsunami Information Center in Honolulu. “You want to get going.”

Get to high ground before the disaster arrives

If you happen to be on a boat in the open ocean, stay there. Otherwise, your best course of action depends on how much time you have before the tsunami arrives.

Your goal, assuming you’re on land, is to evacuate away from the coast. Try to reach someplace 100 feet above sea level or two miles away from the ocean.

If you’re lucky, the tsunami will have been caused by an earthquake far away and won’t arrive for several hours. Take a disaster kit if you have one on hand, and bring your pets with you. If you aren’t sure where to go, there may be evacuation signs you can follow. But pay attention to any instructions from emergency personnel, since they may recommend a different evacuation route than you were planning to take.

[Related: 300 years of tree rings show just how badly hurricanes have soaked the Carolinas.]

If you aren’t certain how far to evacuate, keep going. “If you’re at 20 feet [above sea level] don’t stop, just keep moving uphill,” says Ian Miller, a coastal hazards specialist at Washington Sea Grant who is based in Port Angeles.

As you head for high ground, stay away from rivers and streams. “A tsunami can move up the river very fast, and many people have been caught by surprise,” Chang Seng says.

And plan to evacuate on foot. “If everyone jumps in their car in the same time it’ll just be traffic and no one will get out,” Garrison-Laney says.

If there has already been an earthquake in the area, watch out for downed power lines. Stay clear of buildings and bridges that could shed heavy debris if there’s an aftershock.

You can also buy survival pods intended to protect you from a tsunami, although they are pricey and have yet to prove their mettle.

Take shelter

You may not have enough time to reach high ground before the tsunami arrives. The Seattle Times once asked cross-country athlete Ben Brownlee to run the evacuation route from Long Beach Elementary in Washington State, a particularly vulnerable peninsula in a region due for a massive earthquake. Brownlee can run a mile in under 6 minutes, and he cleared the hazard zone in 15 minutes. With no injuries or earthquake rubble to struggle through, he might have escaped an oncoming tsunami—but just barely. If you can see the wave, you should assume you’re too close to outrun it. Many folks faced with a tsunami have to make do with whatever shelter they’ve got.

That’s where vertical tsunami shelters will come in handy. Ideally, these structures are sturdy enough to withstand the onslaught of water, tall enough to clear the danger zone, and placed in locations where as many people as possible can reach them. Last year, Ocosta Elementary School in Westport, Washington unveiled the nation’s first tsunami evacuation structure. The school’s gymnasium is engineered to withstand an earthquake and tsunami and shelter more than 1,000 people on its roof.

The city of Long Beach is planning to build a tsunami shelter that will resemble an armored hill. Other cities are designing tsunami sanctuaries as well; Newport, Oregon, is turning a forested hill into a refuge that can accommodate 2,300 people.

If you are fleeing from a tsunami and no such havens are available, try to find a sturdy, reinforced concrete building. Climb as high as possible—at least to the third floor—and head for the roof.

“If there’s a large hotel with several stories, that would probably be your best bet rather than any of the vacation homes,” Garrison-Laney says. “It would need to be a building that had a pretty substantial concrete foundation, and even then there’s no guarantee.” After all, most buildings weren’t constructed to withstand the kinds of forces a tsunami will throw at them.

If there are no buildings, try to scramble up a tree.

Hang on tight when the wave hits

If everything else fails, grab a piece of floating debris. Some people have survived by climbing aboard roofs and using them as makeshift life rafts.

If you are caught up in the wave, you’ll face turbulent water filled with rubble. Survival, at this point, is a matter of luck. “A person will be just swept up in it and carried along as debris; there’s no swimming out of a tsunami,” Garrison-Laney says. “There’s so much debris in the water that you’ll probably get crushed.”

Eventually, the wave will pull back, dragging cars, trees, and buildings with it. But even if you’ve made it this far, you’re not totally safe yet. A tsunami is actually a series of waves, and the first one might not be the largest. The coasts are often inundated with several waves over a period of hours.

“People have perished by assuming that the first wave was the extent of the disaster,” Miller says. “There’s always follow-on waves…in the same way that when you throw a pebble into a rain puddle there’s never just one wave.”

So if you are perched in a sturdy tree or on a building and haven’t received the all clear from emergency personnel, don’t come down right away. “I would probably stay up in the tree for three or four hours,” Garrison-Laney says.

If you have made it to secure terrain, wait for the authorities to tell you it is safe to return to low-lying areas. “The coastline could be devastated with flooding and damaged homes and debris fires,” Chang Seng says.

And the tsunami may have weakened structures that it did not sweep away. Several hours after the 2004 Indian Ocean tsunami, Chang Seng drove over a bridge in his home country, the island nation of Seychelles, which is located off the eastern coast of Africa. “I’d just crossed the bridge in a car, then a couple of seconds after that the same bridge collapsed,” Chang Seng says.

Be ready and know your region’s risk

Tsunamis can hoist boulders and sweep buildings right off their foundations. Unlike the ones you normally sea at the beach, these monster waves span the entire water column from seafloor to surface. “It’s very powerful, there’s a lot of energy because when a tsunami comes it’s not just a surface wave,” Chang Seng says. “It’s the whole ocean that moves and comes and sweeps over the coast.”

And it’s hard to have a wave slam into the coastline without threatening people. Over one third of the world’s population lives within 60 miles of the ocean. In 2010, 39 percent of the population of the United States lived in counties directly on the shoreline, and the coast is only expected to become more crowded.

Tsunamis are uncommon in the Mediterranean. “It’s the busiest area in the world in terms of shipping and tourism, so there’s a big risk [from] tsunamis even if it’s rare,” says Denis Chang Seng of UNESCO’s Tsunami Unit & Ocean Observation Services Section.

[Related: The average hurricane season is officially more intense.]

That’s why you need to be prepared in case one of these rare but devastating waves comes to a beach near you. “You must have a plan for your family if you are living along the coast,” Chang Seng says. If your home or office is near the sea, know the tsunami evacuation zone. Map out and practice an evacuation route, and have a kit ready for emergencies. Know your community’s disaster plans. “Every tsunami-prone area should have a tsunami evacuation map where they’ve worked out where the unsafe zones are,” Kong says.

You may also find yourself in a hazard zone when you are visiting the shore. Tourists are especially likely to be caught off-guard. “If you’re on vacation you don’t necessarily want to worry about something like that,” Miller says. But if you are in tsunami territory, it’s best to make a plan for what you would do if disaster did strike. Miller also advises bringing a flashlight if you’re vacationing on the coast. “Just that one thing may make a big difference if you have to do an evacuation at night,” he says.

When a devastating tsunami strikes, scientists review footage from the event to see what they can learn. These videos leave a sobering impression. “In the course of tens of seconds you go from dry land, everything’s normal, to a foot, two feet, several meters, ten feet of water and everything is floating including cars with people in them,” Kong says. “You hear the crunch of buildings getting broken in half by the water.”

Scientists also prepare for tsunamis by running computer simulations to predict which parts of a coastline are most vulnerable and how much time its inhabitants will have before the first wave hits. They can then come up with a plan for different scenarios and plot out evacuation routes.

One reason that the 2004 Indian Ocean Tsunami, which killed 230,000 people, was so devastating is that people were unaware of the danger. They did not realize a tsunami was rushing towards them because there were no regional warning systems. But the tsunami inspired advances in detection and readiness and today, the nations bordering the Indian Ocean are better prepared.

“Now that we’ve had a couple of those big, devastating tsunamis people have a much better idea of what to do,” Garrison-Laney says. Even so, tsunamis can be unpredictable. Earlier this month, a rare tsunami hit the west coast of Greenland. And Japan, the best-prepared nation in the world when it comes to earthquakes, was still devastated by the 2011 quake and tsunami, which reached up to 133 feet. An estimated 16,000 people died, the majority killed by the waves.

So coastal communities should prepare for the worst-case scenario. This can be tricky in areas that haven’t seen a tsunami in some time, like the Pacific Northwest, which was last ravaged by a tsunami in 1700.

“The main thing we don’t know…is where the next tsunami will happen,” Garrison-Laney says. “It’s really just up to coastal communities to make sure that they’re ready, and hopefully it won’t happen before everyone’s ready.”