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updated: 11/9/2010 1:15 PM

Kids ask: How does a tsunami form?

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  • Tidal waves wash through houses at Maddampegama, about 38 miles south of Colombo, Sri Lanka, in 2004. Massive waves triggered by earthquakes crashed into villages along a wide stretch of the Sri Lankan coastline.

      Tidal waves wash through houses at Maddampegama, about 38 miles south of Colombo, Sri Lanka, in 2004. Massive waves triggered by earthquakes crashed into villages along a wide stretch of the Sri Lankan coastline.
    Associated Press

 

Kate Crawford's fifth-graders from West Oak Middle School in Mundelein wanted to know, "How does a tsunami form?"

Tsunami is the Japanese word that means harbor and wave.

But that's deceiving because tsunamis can occur in an ocean or a large lake.

Second Lieutenant Blake Hamilton, U.S. Air Force meteorologist, said, "Tsunamis are caused by a large displacement of water. This is generally from an underwater earthquake, but can also be from an avalanche, volcanic eruption or, rarely, a meteorite impact."

Last month, 10-foot waves forming a tsunami struck 10 islands in western Indonesia when a 7.7 magnitude earthquake rocked the coastal region.

"In this case, a portion of the land slides deep under the ocean," Hamilton said.

When the land shifts, the water wants to find balance, and a series of waves are set into motion.

"This is the start of the tsunami, as the wave will crash back and spreads out in all directions from this particular point. Over the deep water of the ocean tsunamis are barely noticed, as the majority of the waves are just a couple of feet high at most," he said.

Tsunamis are fast they can clock in at 500 mph. When they reach the shoreline, the result is an instant disaster.

"Here, it encounters friction and slows the wave down," Hamilton said. "The slowing of the wave will cause the wave to compress and, at this point, the wave will grow significantly just as it hits land.

"Tsunamis are rarely one wave, but a series of waves that can spread across a great distance. The 2004 Indian Ocean tsunami actually had impacts, although only noticeable with instruments, in parts of Hawaii and San Diego."

Indonesia is made up of 17,000 islands. The epicenter of the earthquake that caused the October tsunami was along the same fault line that triggered the massive 2004 Indian Ocean tsunami.

Just one day after the Indonesian tsunami struck land on Oct. 25, Mt. Merapi Indonesia's most active volcano erupted. The volcano has continued to erupt since that first rock and ash explosion, only with even greater force.

Indonesia lies atop the "ring of fire," the faults that cause earthquakes and volcanic activity around the perimeter of the Pacific Ocean. Scientists believe the multiple volcanic blasts and earthquakes could mean the Earth's tectonic plates are realigning.

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