Shop Windows to the Universe

Warnings: The True Story of How Science Tamed the Weather by Mike Smith tells the story of our storm warning system. See our online store book collection.
The picture above shows how the shape of a tsunami wave changes as it moves into shallower water.
Click on image for full size
NOAA

What Is a Tsunami?

A tsunami (pronounced tsoo-NAH-mee) is a series of waves, generated in an ocean or other body of water by a disturbance such as an earthquake, landslide, volcanic eruption, or meteorite impact. Tsunamis can savagely attack coastlines, causing devastating property damage and loss of life. Some people call tsunamis “tidal waves”, but these monstrously large waves really have little to do with tides, so the term “tidal wave” is not really appropriate.

Tsunami waves are different from the waves you can find rolling into the coast of a lake or ocean. Those waves are generated by wind offshore. The wavelength of regular wind-generated waves, that is the distance between the crests or highest points of the waves, might a just a few meters for small waves or about 100 meters for large waves. But a tsunami in the open ocean can have a wavelength of more than 100 km. Tsunami waves have huge wavelengths, but they are typically less than a meter high in the open ocean. A tsunami can travel over the open ocean at about 700 km/hr.

As a tsunami travels into the shallower water near the coast, it transforms. As a tsunami approaches shore, it’s height increases and wavelength decreases. Therefore, even though a tsunami may be imperceptible at sea, it may grow to be several meters or more in height near the coast and have a tremendous amount of energy. When it finally reaches the coast, a tsunami may appear as a rapidly rising or falling tide or a series of waves with a maximum height of up to 30 meters above sea level.

A few minutes before a tsunami wave hits, the water near shore may recede, exposing the ocean floor. Often the first wave may not be the largest. Additional waves may arrive at the coast every 10 to 60 minutes and move much faster than a person can run. The danger from a tsunami can last for several hours after the arrival of the first wave. Unlike other waves, tsunami waves typically do not curl and break.

Coasts affected by a tsunami will be severely eroded. A tsunami can cause flooding hundreds of meters inland. The water moves with such force that it is capable of crushing homes and other buildings.

Last modified May 21, 2008 by Lisa Gardiner.

Shop Windows to the Universe Science Store!

Our online store includes issues of NESTA's quarterly journal, The Earth Scientist, full of classroom activities on different topics in Earth and space science, as well as books on science education!

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

What Is an Earthquake?

The expression "on solid ground" is often used to describe something as stable. But sometimes the solid ground underfoot is not stable. It moves as Earth’s tectonic plates move. Sometimes it moves gradually....more

Meteors

Meteors are streaks of light, usually lasting just a few seconds, which people occasionally see in the night sky. They are sometimes called "shooting stars" or "falling stars", though they are not stars...more

Ten Tsunami Safety Facts

1. Tsunamis that strike coastal locations in the Pacific Ocean Basin are almost always caused by earthquakes. These earthquakes might occur far away or near where you live. 2. Some tsunamis can be very...more

New Findings Indicate Sediment Composition Affected the Strength of Sumatran Earthquake

Sumatra experiences frequent seismic activity because it is located near the boundary of two of Earth's tectonic plates. Earthquakes occur at 'subduction zones,' such as the one west of Indonesia, when...more

What is a Supercomputer?

Some scientific problems and processes are so complex that you need SUPERCOMPUTING power to tackle them! Just what is a supercomputer? A supercomputer is a computer that is among the largest, fastest or...more

Earth Science Literacy - Big Idea 8

Natural hazards pose risks to humans. Big Idea 8.1 Natural hazards result from natural Earth processes. These hazards include earthquakes, tsunamis, hurricanes, floods, droughts, landslides, volcanic eruptions,...more

Ocean Literacy - Essential Principle 6

The ocean and humans are inextricably interconnected. Fundamental Concept 6a. The ocean affects every human life. It supplies freshwater (most rain comes from the ocean) and nearly all Earth’s oxygen....more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA