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A tsunami is not one wave but a series of waves, caused by a large and sudden disturbance of the sea. This Ready.gov kids page explains what causes them, who is at risk and what to do.
What a tsunami is
Tsunami waves move outward in all directions from where they start and can cross entire oceans. As they approach shallow water along the coast they grow to a great height, as high as 100 feet, and smash into the shore. Most are caused by undersea earthquakes, though landslides, volcanic activity and even meteorites can cause them, and not every earthquake causes one. On the open ocean a fast-moving tsunami may be only a few feet high, with 100 miles between crests. Few "break" like surfers' waves; they are more often strong currents and walls of water that do not retreat like normal tidal waves. "Tsunami" is a Japanese word: tsu means "harbor" and nami means "wave." Another term for tsunamis is seismic sea waves.
Who is at risk
Tsunamis generally appear in the Pacific Ocean and coastal areas but can strike any U.S. coastline. Areas within a mile of the shoreline and less than 25 feet above sea level are at greater risk.
| Place | Frequency |
|---|---|
| Hawaii, the state at greatest risk | About one a year, with a damaging tsunami about every seven years |
| Alaska | High risk |
| California, Oregon and Washington | A damaging tsunami about every 18 years |
Hawaii, Alaska, Washington, Oregon, California and the U.S. Caribbean islands are at greatest risk.
Alert levels
The tsunami warning centers issue four levels of alert for U.S. and Canadian coastlines:
| Level | Meaning |
|---|---|
| Warning: Take Action, Danger! | Follow local officials; evacuation is recommended; move to high ground or inland |
| Advisory: Take Action | Stay out of the water and away from beaches and waterways; follow local officials |
| Watch: Be Aware | A distant earthquake has occurred and a tsunami is possible; stay tuned and be ready to act |
| Information Statement: Relax | An earthquake or an alert elsewhere; most statements mean no threat of a destructive tsunami |
What to do
Illustration from Ready.gov's page.
- Before: build an emergency kit and make a family communications plan with evacuation routes. If you see the water pull back from shore very quickly, get away immediately.
- During: obey evacuation orders and leave at once, with pets; move inland and uphill; stay away from the beach and never go down to watch, since if you can see the wave you are too close to escape. A noticeable retreat of the water is nature's warning. Move to an upper level of a tall, fortified building if needed.
- After: do not go home until officials say it is safe; waves can continue for hours and the next may be more dangerous than the first. Stay away from debris in the water, which can hold harmful chemicals or be electrified by downed power lines, and out of buildings with water around them, since water can crack floors and collapse walls. Text rather than call, so emergency workers keep the phone lines, and be careful entering buildings, with a parent or adult. It is normal to feel anxious or stressed, and kids should talk to a parent or trusted adult.
Illustration from Ready.gov's page.
Words to know
Debris is rubble, trash or random material such as large pieces of wood, metal or plastic. Inland means away from the coastline. Evacuation means leaving an area declared unsafe.
Sources
- FEMA, Ready.gov kids page on tsunamis (https://www.ready.gov/kids/disaster-facts/tsunamis); rewritten in hubnx's own words.
Licenza: CC0 1.0 (pubblico dominio) · Tratto da www.ready.gov
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