Tsunamis: Killer Waves
[Excerpted from National Geographic online.]
The Indian Ocean tsunami generated by the most powerful earthquake in decades [occurred] on December 26[. It] is believed to have killed more than 150,000 people and made millions homeless, making it perhaps the most destructive tsunami in history.
The epicenter of the 9.0 magnitude quake was under the Indian Ocean near the … Indonesian island of Sumatra…. Within hours killer waves … slammed into [coastlines] …snatching people out to sea, drowning others in their homes or on beaches, and demolishing property from Africa to Thailand. …
What Causes A Tsunami?
• A tsunami is a … great sea wave…caused by an underwater earthquake, landslide, or volcanic eruption. More rarely, a tsunami can be generated by a giant meteor impact with the ocean. Scientists have found traces of an asteroid-collision [3.5 billion years ago] that they say would have created a giant tsunami that swept around the Earth several times [and covered] everything except the mountains …
• Tsunami (pronounced soo-NAH-mee) is a Japanese word. Tsunamis are fairly common in Japan and many thousands of Japanese have been killed by them in recent centuries.
• A tsunami is not a single wave but a series of waves, also known as a wave train. The first wave in a tsunami is not necessarily the most destructive….
• Tsunami waves can be very long (as much as 60 miles, or 100 kilometers) and be as far as one hour apart. They are able to cross entire oceans without great loss of energy. The Indian Ocean tsunami traveled as much as 3,000 miles (nearly 5,000 kilometers) to Africa, arriving with sufficient force to kill people and destroy property.
• A tsunami may be less than a foot (30 centimeters) in height on the surface of the open ocean, which is why they are not noticed by sailors. … Once a tsunami reaches shallow water near the coast …the top of the wave moves faster than the bottom, causing the sea to rise dramatically.
• … In some places a tsunami may cause the sea to rise vertically only a few inches or feet. In other places tsunamis have been known to surge vertically as high as 100 feet (30 meters). Most tsunamis cause the sea to rise no more than 10 feet (3 meters).
• The Pacific is by far the most active tsunami zone, according to the U.S. National Oceanic and Atmospheric Administration (NOAA) …tsunamis have [also] been generated in … the Caribbean and Mediterranean Seas, and the Indian and Atlantic Oceans.
How Fast Can A Tsunami Travel?
As Fast as a Commercial Jet! When the ocean is deep tsunamis can travel unnoticed on the surface at speeds up to 500 miles per hour (800 kilometers per hour), crossing the entire ocean in a day or less. Scientists are able to calculate arrival times of tsunamis in different parts of the world based on their knowledge of when the event that generated them occurred…
What Are The Warning Signs of A Tsunami?
• An earthquake is a natural tsunami warning. If you feel a strong quake do not stay in a place where you are exposed to a tsunami….
• Witnesses have reported that an approaching tsunami [can cause] a noticeable fall or rise in the water level. If you see the ocean receding unusually rapidly or far it’s a good sign that a big wave is on its way. Go to high ground immediately.
Many people were killed by the Indian Ocean tsunami because they went down to the beach to view the retreating ocean exposing the seafloor. Apparently they were unaware that this phenomenon precedes a killer wave…Because tsunamis can approach the shore as fast as 100 miles per hour (160 kilometers per hour) it is often too late to get away if you see one.
Anyone ever seen the destruction of a tsunami? I’d like to hear about it. You can post your comments below.