A tsunami (Japanese for “harbor wave”) happens when something displaces water vertically in the sea or another large body of water. These big waves can be deadly, and they happen with little warning. Preparation for one involves advance planning as well as knowledge of what to do as the tsunami approaches and what to expect and do in its immediate aftermath.
♦ Causes of tsunamis
The Honshu tsunami on March 11, 2011, happened when a huge earthquake suddenly deformed the sea floor in the subduction zone that sits some 80 miles offshore from Japan, displacing the sea above it vertically and with great force. A similar temblor at another type of tectonic plate margin near Sumatra on December 26, 2004, caused the Boxing Day tsunami that devastated the coastal populations of many countries around the Indian Ocean, killing almost 228,000 people.
Other events besides earthquakes can cause tsunamis, including volcanoes, landslides, and underwater mudslides, although tsunamis from these don’t last as long as those generated from earthquakes, which can be powerful enough to cross the Pacific Ocean without losing much of their initial energy.
For example, everybody has heard of Krakatoa (“Krakatau” in Indonesian), the volcano that “blew up” back in the 19th century, but few know that the volcano itself didn’t directly cause the tens of thousands of fatalities that happened. Most of those people died in the huge tsunamis (up to 151 feet) that were generated during the eruption’s final four catastrophic explosions.
♦ Plan ahead for a tsunami
You need to find out now if the area you live in or will be visiting is prone to these big waves. This includes not only the obvious coastal areas that have previously experienced tsunamis but also any steep surface in an earthquake-prone region, especially if there has been heavy rain recently that has saturated the ground, making it more likely to slip into a nearby lake or bay during a sudden earthquake. Tsunamis happen in surprising places sometimes. In 1959, a rare magnitude 7.5 earthquake in Yellowstone Park caused a landslide that fell into Hebgen Lake and caused a tsunami, killing 28 people who were camping along the shore.
As you would for a hurricane or other emergency, keep a pack handy with supplies of food, water, and medicines for at least 3 days, as well as copies of important papers and other things, like flashlights and batteries. Smart phones, cell phones, and NOAA weather radios with EAS-programmable features all can deliver tsunami alerts and other information; make sure you have charged batteries for those, too.
Identify safe shelters near your home and place of work, or hotel, if you are on vacation, and learn the routes to these well enough to be able to get there even in the dark, through crowds of panicked people. Designate somebody who lives out of the danger zone to take calls from everyone with you so that you can all stay in touch, even if you get separated during the tsunami.
♦ When a tsunami is on the way
A few places have tsunami sirens. Head for a shelter at once, if one goes off, or if authorities broadcast a tsunami warning through the media. If you are on a vessel in a harbor, head out to sea—the tsunami is much smaller away from land. Be aware of your fuel, though, and any alternate ports you could head for, because your harbor may be closed for several hours, longer if there is a lot of damage.
Sometimes an earthquake or landslide is your only warning. That’s close, and the wave will arrive in seconds, so don’t stand around wondering. Immediately get away from the water and head to high ground.
If you are in an isolated area and out of the range of a cell tower or wireless Internet connection, recognize the warning signs of an approaching tsunami. You may not feel the ground move or witness the landslide, but if you are near a body of water and the water level suddenly drops, get away from the shore line and up as far as you can on high ground. If trapped in a city, get up as high as you can in the most sturdy building around. If absolutely nothing else is available, climb a tree or try to find something that floats and hang on to it.
♦ The aftermath
When it is all over, wait for the official all-clear. Tsunamis come in waves that can have long periods in between arrivals, and the first wave is often not the biggest. Too, the water sometimes doesn’t recede like ordinary waves; there is a force out in the ocean behind it that keeps it coming in. It will persist for hours. Be patient.
When the flooding does recede, there will be a lot of debris, dirt and sewage, and possibly also bodies around. This is very disorienting as well as disturbing. Expect it, and keep your courage up: one of the best ways to do that is by taking action. Get yourself to a safe shelter or evacuation center and help others along the way. Do, and if you must think, think about what to do next. Don’t try to erase the stressful stuff or bury it, but save it until later, when you are safe and have friends and family around to help you deal with it.
If you were very lucky and still have a house, prepare to shelter your neighbors. Always listen for instructions from the authorities, and do what they say.
Your property may have been out of the damage zone but still was flooded. In this case, of course, you would just do the same things you would after any flood or storm. However, the scale of the tsunami event may cause regional power outages, traffic congestion, and other hazards. This is when a battery or hand-cranked radio and extra food and water will prove their worth. It may be a few days or longer before communication and transportation lines open up again.
♦ Preparation, not luck
Seneca, a Roman philosopher in the 1st century A.D., once said, “Luck is what happens when preparation meets opportunity.”
No one can know ahead of time exactly what deadly dangers and life-saving opportunities they may face during a tsunami. However, we can all make our own luck, and thereby boost our chances for survival, by preparing for a tsunami before it happens, knowing what to do during the emergency, and also what to expect, where to go, and what to do after it’s all over.
West Coast and Alaska Tsunami Warning Center (n.d.) “Tsunami Safety Advice.” Retrieved on March 11, 2011, from http://wcatwc.arh.noaa.gov/tsunamiready/safety1.pdf (Note: Requires Adobe Reader.)
Royal Society (Great Britain) (1888). “The eruption of Krakatoa, and subsequent phenomena.” Retrieved (date unknown) from http://www.archive.org/details/eruptionkrakato00whipgoog
U.S. Geological Survey, Circular 1187, Version 1.1 (2005). “Surviving a Tsunami—Lessons from Chile, Hawaii, and Japan.” Retrieved March 11, 2011, from http://pubs.usgs.gov/circ/c1187/