What causes tsunamis?
A tsunami, a speeding wall of water, is one of the Earth's most terrifying natural disasters.
A wave from a tsunami crashes over a seawall in Miyako, Japan (© Miyako City Office/Reuters)
Who needs Nessie, the great mythical underwater monster of Scotland, when Mother Nature can conjure up her own dramatic and destructive fiend of the deep? It's no myth that tsunamis can reach dizzying heights of over 100 feet or race as fast as a jet plane with speeds up to 500 miles an hour. They can also retain their power over long distances, spanning entire oceans with limited energy reduction. In short, these oceanic terrors are one of the few natural disasters on the planet people don't think to take a picture of before seeking cover.
The name "tsunami" comes from the Japanese language, meaning "harbor wave." That sounds innocent enough, but the end result of these towering walls of water is much more than just a wave. Tsunamis can form in three primary ways: undersea seismic activity, undersea landslides or undersea volcanic eruptions. Additionally, while rare, tsunamis can also form due to asteroids and meteorites plunging into the ocean.
When an earthquake strikes under the ocean, usually occurring around the boundaries of the Earth's tectonic plates, a blast of energy shoots upward, the water becomes displaced and waves begin to form. In a sense, it's like dropping a large object into a pool of water and watching the waves ripple in all directions. The larger the tremors, the larger the waves become. On July 12, 1993, a magnitude 7.7 earthquake struck in the Sea of Japan near the islands of Hokkaido and Okushiri. Waves reaching as high as 104 feet (or 32 meters) barreled towards the islands, hitting Okushiri the hardest. Overall, 120 fatalities were attributed to the tsunami.
Undersea landslides and volcanic eruptions also serve to cause dramatic water displacement and transfers an overwhelming amount of energy upward into the water.
Forecasting these towering walls of water is still a relatively new concept, but scientists have developed what is called deep ocean tsunami detectors, which provides information necessary for issuing warnings before the wave materializes.
Tsunamis occur about once a year somewhere in the world, but most frequently plague the Pacific Ocean along the Ring of Fire, which includes Alaska, the U.S. West Coast and Hawaii.
5 facts about tsunamis
- About 80 percent of tsunamis happen in the Pacific Ocean's Ring of Fire.
- Hawaii is the U.S. state at greatest risk for a tsunami - they get about one per year and a damaging one every seven years.
- When tsunamis hit shallow water (often near the coast) they slow down but increase in height.
- Tsunamis are sometimes referred to as tidal waves but this term has fallen out of favor because tsunamis are not related to tides.
As a tsunami approaches the shore, water may recede from the coast, if it is shallow enough the water may be pulled back hundreds of meters. If you are in the area, observing this is a good indication that a tsunami is on the way.
Why do people see all the signs of a tsunami cioming, but fail to realise it walk down to watch the water recede even try to floundering fish, instead of heading to higher ground immediately?
Also, when discussing tsunamis and mention landslides can also cause them, why did not mention Latuya Bay in Alaska that recorded the largest tsunami ever. It was cause by an earthquake, which triggered a landslide that plunged into the head of the bay, on July 9, 1958. The initial was 1,720 feet high washing forest away and exposing bare rock. The effects can still be noticed today. A boat anchored in the bay at the time had a 300 foot anchor change played out and snapped in two. The father and son while on their boat was carried out toward the Pacific high above trees at the mouth of the bay and set back down in the bay. Two other boats were washed away and the people on them were killed, plus two people who were fishing in the bay at time.