Causes

• Tsunamis are generated by submarine earthquakes. These are earthquakes that occur under the sea. An earthquake can cause the ocean floor to slip and rise up, raising the water and setting off seismic waves across the ocean. At first, these waves are invisible due to the deep water. However, once the tsunami reaches land, a lot of water will recede quickly, followed by a massive wave that hits the shore, resulting in catastrophic damage. To a lesser extent, tsunamis can be the result of volcanic eruptions, landslides and large meteorites.
  
  

Tsunami Properties

• Seismic ocean waves consist of a massive train of tsunamis. The first wave is not always the largest, either. Tsunamis have been as far as 60 miles long, with each wave being up to one hour apart. Seismic waves can reach speeds of up to 500 mph. To put it into perspective, this is about as fast as a passenger jet. Luckily, most tsunamis are benign and only rise up to 10 feet.
  
  

Notable Tsunamis

• The most destructive tsunami recorded was the Indian Ocean tsunami of 2004. Waves reached heights of 30 feet, killing 200,000 people. In second place was the 1782 tsunami triggered by an earthquake in the South China Sea. This seismic wave caused the deaths of 40,000 people. In 1868, a tsunami in Chile killed over 25,000 people.
  
  

Tsunami Safety

• If you live in an area prone to seismic waves, it is important to know the warning signs and safety measures. First, be aware of earthquakes; these are telltale signs of a potential tsunami. Check the TV or radio for updates. If the ocean water level changes dramatically, this is a major sign of a seismic wave. At this point, you have up to five minutes to reach higher ground. Do not forget that tsunamis come in groups that can be a few minutes to an hour apart. Never assume you are safe after the first wave. Any body of water that leads to the ocean can be affected by a tsunami, so stay away from rivers and streams. Finally, keep some emergency supplies of medication, food and water that can last at least 72 hours.