In the last decade, we’ve seen two catastrophic tsunami events: the infamous Indian ocean tsunami, and the recent one that struck Japan. In part because of these disasters, and in part because of other published data, scientists are beginning to realize that tsunamis are much more common than was previously thought.
What causes a tsunami?
The most common trigger for a tsunami is a subduction-zone quake over the ocean that suddenly causes a large swath of the ocean floor to shift upward, thus displacing a large amount of water. Tsunamis can also be triggered by a landslide underneath the ocean or rock falling into the ocean.
How fast does a tsunami travel?
Out on the open ocean, a tsunami can travel up to several hundred miles per hour. Once inland, a tsunami moves at a speed of around 11 mph, which means that you’d have to run at least a 5:30 mile in order to outpace it. So it’s important that you get a head start.
Basic Tsunami Safety Tips
- Teach kids the tsunami warning sign: If you see the ocean suddenly withdraw and go out really far, exposing shoreline that was underwater just a minute ago, it means a tsunami is on its way and about to hit shore. Turn and start running for higher ground immediately.
- If there is no high ground available, look for shelter inside a commercially built concrete building that is several stories high, such as a hotel. Such structures should survive a tsunami.
- Stay away from estuaries and waterways. These often channel the water several miles inland, and can see some of the highest water levels. Bays are also more dangerous, because their bowl-like shape tends to result in higher waves.
- Recognize and teach kids that a tsunami is not one wave, but many. During the 2004 tsunami, many people were killed because they wandered back out after the first wave seemed to recede. When water is disturbed, it doesn’t just produce one uniform ripple, but many. A tsunami is the same way. It comes in waves, and often times the latter surges are more severe than the first, so stay put in a safe place until you’re sure the danger has passed.
- If you’re out on the open water or in a boat, the safest place to be is in the open ocean, where a tsunami is harmless. Boats in the open ocean will ride right over a tsunami wave, and divers in the open ocean may feel the pulse or get pulled off course by the current, but otherwise won’t suffer devastating consequences. The danger of a tsunami occurs as it approaches land. As the ocean landscape becomes hollowed, the water has nowhere to go but up. A wave that might have only been 1 to 3 meters high on the open ocean gets stacked up, and can reach heights of 20 to 30 meters.