What Are Tsunami Waves?

Causes

• The Earth's crust is made up of large, moving plates. Tsunamis can occur anywhere but are more common in the Pacific Ocean where the oceanic plates slide under the continental plates. When these plates fracture, a powerful vertical movement shifts energy from the Earth's crust to the ocean. Tsunamis typically occur during earthquakes greater than 7.0 on the Richter scale. For example,the tsunami that struck Indonesia in 2004 was caused by an earthquake measuring 9.3 on the Richter scale. Tsunamis are also caused by landslides. The tsunami that struck Papua New Guinea in 1998 was caused by a landslide during an earthquake measuring 7.0 on the Richter scale.

Warning System

• The Tsunami Warning System has been providing warnings of potential tsunami danger in the Pacific Basin since 1946. It monitors the size and location of underwater earthquakes and estimates the likelihood that a tsunami will occur. Tide gauges can measure the size of the tsunami, however, tsunamis are affected by local factors such as the nature of local waves and tides, ocean floor characteristics and coastline shape. According to NOAA, 15 of the 20 warnings issued since 1946 were considered false alarms because the tsunami was too weak to cause harm.

Reducing Impact

• According to NOAA, the combination of new tsunami predicting technologies and education can potentially prevent 25 percent of tsunami deaths. For example, the tsunami that hit Aonae, Japan, in 1993, only killed 15 percent of the people in the affected area because a warning system was in place, and the well-informed populace had made ample evacuation plans. When a tsunami hit Warapa, Papua New Guinea, in 1998, 40 percent of people in the area died because there wasn't a warning system. The populace was not properly informed and no evacuation plans were made.

Characteristics

• A tsunami's initial impact is sometimes preceded by the water receding from the shore, exposing the ocean floor. Tsunamis typically consist of a series of waves that crest every 10 to 60 minutes. They can be between 32 and 98 feet high. Later waves are often full of debris picked up by the first waves. The debris often consists of rocks weighing several tons, boats and smashed buildings that the waves often carry hundreds of feet.

Safety Measures

• According to the Intergovernmental Oceanographic Commission, coastal residents should take a few precautions. When a tsunami warning is issued, make sure your family members are informed. Have an evacuation plan and leave the evacuation area in a calm and orderly fashion. If an earthquake strikes while you are at the beach, do not wait for the tsunami warning, and calmly move towards higher ground. Many low-lying coastal areas have multi-story, reinforced concrete hotels that can withstand tsunamis. If it is allowed, take shelter in the upper floors of one of these hotels.