Photograph from DigitalGlobe via Reuters
for National Geographic News
Published February 27, 2010
1. What can cause a tsunami?
b. Underwater earthquake
c. Volcanic eruption
d. All of the above
2. Do all undersea earthquakes trigger a tsunami?
3. What does the word "tsunami" mean in Japanese?
a. Tidal wave
b. Harbor wave
c. Killer wave
d. Century wave
4. Witnesses have said that an approaching tsunami sounds like what?
a. Firecrackers exploding
b. A freight train
c. Ice cracking
d. Nothing—there is absolute silence
5. What is the most active tsunami area?
a. Pacific Ocean
b. Caribbean Sea
c. Indian Ocean
d. North Atlantic Ocean
6. What is the deadliest tsunami ever recorded?
a. The 1782 South China Sea tsunami
b. The 1868 northern Chile tsunami
c. The 1883 South Java Sea tsunami
d. The 2004 Indian Ocean tsunami
7. How fast can a tsunami travel?
a. Up to 100 miles an hour (160 kilometers an hour)
b. Up to 200 miles an hour (320 kilometers an hour)
c. Up to 500 miles an hour (800 kilometers an hour
d. Up to 1,000 miles an hour (1,600 kilometers an hour)
8. Can you detect a tsunami in the open ocean?
9. Where was the largest tsunami in history recorded?
10. What is frequently a warning sign of an impending tsunami?
a. Winds suddenly change direction
b. The sky suddenly clears
c. Seawater suddenly retreats from the shore
d. All of the above
Tsunamis are usually generated by undersea earthquakes at tectonic plate boundaries, but they can also be triggered by underwater landslides, volcanic eruptions, or even a giant meteor impact with the ocean.
An undersea earthquake creates a tsunami only if it is of sufficient force and there is a violent enough movement of the seafloor to displace a massive amount of water.
Our English word "tsunami" comes from the Japanese term for "harbor wave." Tsunamis are not the same things as tidal waves and actually consist of a series of waves.
Many witnesses have described the sound of an approaching tsunami as being similar to a freight train's.
Most tsunamis, about 80 percent, happen within the Pacific Ocean’s Ring of Fire, a geologically active area where tectonic shifts make volcanoes and earthquakes common.
In 2004 more than 200,000 people—the most ever recorded—died in an Indian Ocean tsunami that was triggered by an earthquake off Sumatra, Indonesia.
Tsunamis race across the sea at up to 500 miles (805 kilometers) an hour—about as fast as a jet airplane. At that pace they can cross the entire expanse of the Pacific Ocean in less than a day.
No. In the open ocean, the wave length of a tsunami is hundreds of miles long and only a few feet high. Boaters are safer out at sea during a tsunami than close to shore or tied up at port.
In 1971 a wall of water 278 feet (84.7 meters) high surged past Ishigaki Island, Japan. It moved a 750-block of coral 1.5 miles (2.4 kilometers) closer to shore but did little other damage.
If the tsunami's trough reaches shore first, it sucks the water seaward, exposing the seafloor suddenly. The wave's crest usually hits shore about five minutes later. Recognizing this phenomenon—and getting to higher ground immediately—can save lives.
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