Weather 101: Tsunami

Weather 101

On Boxing Day 2004 (December 26), a catastrophic earthquake and tsunami struck the Indian Ocean and caused massive destruction to 14 countries.

Hat Rai Lay Beach in southern Thailand as water moves out right before the tsunami hits. Image: AFP/Getty Images

275,000 people lost their lives and the damage is estimated to total around U.S. $9.9 billion. With a speed over 300 miles per hour, the wall of water destroyed 141,000 houses and reached heights up to 100 feet.

What Is A Tsunami?

A tsunami, also known as a tidal wave or harbor wave or seismic wave, is caused by a sudden shift in the seafloor in the ocean by an earthquake, landslide, or volcanic activity.

In the case of the 2004 Indian Ocean Tsunami, an earthquake along a fault line caused the seafloor to shift suddenly. Ocean water was forced up vertically to the surface and spread out in all directions.

As you move closure to shore, the continental shelf (seafloor) rises and becomes more shallow. When a tsunami moves over this shallower water, it grows in height until it hits the coast, destroying everything in its path.

A direct result of the 2004 Tsunami disaster was the creation of the Indian Ocean Tsunami Warning System. The Pacific Ocean already had the Pacific Ocean Tsunami Warning Center, operated by the U.S. in Hawaii.

Warning Signs From Mother Nature

A common sign a tsunami may be imminent is water from the ocean receding farther out than normal low-tide. Other signs include feeling a strong and long earthquake near the shoreline and hearing a loud roar from the ocean.

Natural warning signs a tsunami may be approaching. Image: Honolulu Government

Tsunami Advisory Vs. Watch Vs. Warning

If one of these waves is triggered by an earthquake, landslide, or volcanic eruption, one of three bulletins may be issued for areas along the affected coastlines.

Chart from the Pacific Tsunami Warning Center showing the the different warning bulletins that may be issued for an area.

Tsunami Watch – a tsunami may later impact the area. People within the area should continue to monitor the situation for future updates, including an upgrade to a warning or watch cancellation.

Tsunami Advisory – a tsunami with the potential to generate strong currents or waves dangerous to those in or around the water is imminent, expected, occurring. May last for several hours by significant inundation/flooding is not expected for the advisory area. People should stay away from beaches, harbors, and marinas.

Tsunami Warning – a tsunami with the potential to generate widespread inundation is imminent, expected, or occurring. Dangerous coastal flooding with very strong currents is possible and may continue for several hours after arriving. Anyone in low-lying areas need to evacuate and move to higher ground immediately.

What To Do If You Are Under A Tsunami Threat?

While we won’t have to deal with tsunamis in Northwest Arkansas and the River Valley, you may find yourself traveling to an area where a tsunami may strike. Here is what to do if you are ever under a tsunami threat.

If threatened by a tsunami, move to higher ground and away from the water as soon as possible. Follow all
instructions from local authorities and emergency management officials. Help those you know may have trouble evacuating and leave all possessions behind. Photo Credit: Federal Emergency Management Agency (FEMA)

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