Where do tsunamis originate from, and what makes them so dangerous?
Tsunamis can be triggered by earthquakes, volcanic eruptions or landslides in the sea. In the case of the violent tsunami that originated off the west coast of Indonesia on December 26, 2004, the cause was one of the three strongest earthquakes to have ever been measured, with a magnitude of 9.3. The Indo-Australian continental plate meets the Eurasian plate off the coast of Indonesia. The danger lies in both the speed and the height of the tsunami, which is difficult to predict. The tidal wave unleashed in 2004 raced towards the coast at a speed of 800 kilometers per hour, reaching land in just 20 minutes. In practice there was virtually no time to flee. This is in addition to the fact that tsunamis are rarely formed of just one wave – in 2004, Indonesia was hit by at least three. At heights of up to ten meters, they devoured miles and miles of the island's interior.
What have we learnt from that catastrophic event 10 years ago?
In 2004 there was no early warning system in Indonesia. The number of victims and the extent of the devastation, which reached as far as Africa, led to the development of one of world’s most modern tsunami early warning systems, the German Indonesian Tsunami Early Warning System (GITEWS). Systems like this, including for example those set up in Japan and Hawaii, measure seismic activity. Buoys also measure the water pressure on the sea floor. The data is reported via satellite to the tsunami warning stations, where it's evaluated. The time factor and the accuracy of the prediction naturally play a crucial role in the success of the early warning. Carrying out emergency exercises with authorities and the general population is also a significant aspect of prevention. Yet, training and rapid evacuation still represent a considerable challenge, particularly in developing countries.
How high do you judge the risk of tsunamis nowadays?
Viewed on a global scale, we should expect severe tsunamis every 30 years. The early warning systems do indeed help to save lives, but material properties continue to be at the mercy of natural forces. This is compounded by the fact that more and more people are moving to coastal areas, accompanied by infrastructure and industries that can be destroyed by a tsunami. Despite modern technology, higher population density in coastal areas means we have become more vulnerable.