Why tsunamis are so dangerous

A combination of plate tectonic in the region, the shape of the coastline, vulnerable communities and a less-than-robust early warning system all combine to make Indonesian tsunamis especially dangerous.

Read more: Would a better tsunami warning system have saved lives in Sulawesi? Indonesia covers many complex tectonic environments. Many details of these are still poorly understood, which hampers our ability to predict earthquake and tsunami risks.

In December and March , there were a pair of subduction zone earthquakes along the Sunda Trench offshore of the west coast of Sumatra. In particular, the magnitude But only looking out for these kinds of earthquakes can blind us to other dangers. Eastern Indonesia has many small microplates, which are jostled around by the motion of the large Australia, Sunda, Pacific and Philippine Sea plates. It is rare — although not unknown — for these kinds of quakes to create tsunamis.

The fault systems are rather large, and through erosion processes have created broad river valleys and estuaries. The valley of the Palu river, and its estuary in which the regional capital Palu is located, have been formed by this complex fault system. Studies of prehistoric earthquakes along this fault system suggests this fault produces magnitude earthquakes roughly every years. COUNT how long the earthquake lasts. If you feel more than 20 seconds of very strong ground shaking and are in a tsunami hazard zone, evacuate as soon as it is safe to do so.

If you are on the beach or in a harbor and feel an earthquake - no matter how small - immediately move inland or to high ground. Roads and bridges may be damaged. Avoid downed power lines. If evacuation is impossible, go to the third or higher floor of a sturdy building or climb a tree.

This should only be used as a last resort. If you hear that a tsunami warning has been issued but did not feel an earthquake, get more information. Listen to the radio, television or other information sources and follow the instructions of emergency personnel.

If you are outside of a tsunami hazard zone, take no action. You are safer staying where you are. There are two ways to find out if a tsunami may be coming. These natural and official warnings are equally important. The recent tsunami in Japan is the most powerful since Japan started keeping records years ago and literally thousands of people are feared dead.

Hopefully, with each tragedy scientists can learn more about early detection and warning systems. There is no doubt about it; when mother nature shakes her stuff, we are at her mercy. Why are Tsunamis so dangerous? Why are Tsunamis so deadly? But as they approach shoreline and enter shallower water they slow down and begin to grow in energy and height.

The tops of the waves move faster than their bottoms do, which causes them to rise precipitously. When it does, it produces a vacuum effect that sucks coastal water seaward and exposes harbor and sea floors. Recognizing this phenomenon can save lives. A tsunami is usually composed of a series of waves, called a wave train, so its destructive force may be compounded as successive waves reach shore.

People experiencing a tsunami should remember that the danger may not have passed with the first wave and should await official word that it is safe to return to vulnerable locations. Some tsunamis do not appear on shore as massive breaking waves but instead resemble a quickly surging tide that inundates coastal areas.

The best defense against any tsunami is early warning that allows people to seek higher ground. The Pacific Tsunami Warning System, a coalition of 26 nations headquartered in Hawaii, maintains a web of seismic equipment and water level gauges to identify tsunamis at sea. Similar systems are proposed to protect coastal areas worldwide.

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