While the ocean is beautiful, it can also be a source of natural hazards that impact the coastline. This week we will take a dive beneath the waves to learn about the most perilous ocean phenomena – tsunamis. “Tsunami” is Japanese for harbor (tsu) wave (nami). These gigantic waves are a silent natural force, but when they strike, they can have drastic and devastating effects. It has been 16 years since one of the world's deadliest natural disasters, the 2004 Indian Ocean tsunami and earthquake, which devastated parts of Indonesia, Sri Lanka, India and Thailand, killing at least 225,000 people1.
A tsunami is a series of waves in a water body, generally in an ocean or a large lake, which results from the displacement of a large volume of water, usually triggered by an earthquake, a landslide or a pyroclastic flow from a volcanic eruption. The velocity of the tsunami waves depends on the depth of the water body. Over deep waters, they can travel as fast as jet planes. However, when they travel inland and reach shallower waters, the waves slow down but instead dramatically increase in height, reaching up to 10 meter high. Three types of tsunamis can be distinguished: local, regional and distant. A local tsunami can reach coastlines up to 100 kilometres from its source and can reach a nearby shore in less than ten minutes. A regional tsunami can cause damage anywhere from 100 to 1000 kilometer from its source, taking between 1 to 3 hours before making landfall. Originating from a faraway source (more than 1000 kilometres), a distant tsunami may take more than 3 hours to arrive on an affected coasts.
Local tsunamis are often the most deadly since there is not sufficient time for coastal residents to take life-saving action. However, is there any way to know if a regional or distant tsunami is about to occur? Since the 2004 disaster, governments and scientific communities have sprung into action. By observing sudden changes in the ocean, warning systems can alert people about an impending tsunami and many of these warning systems have been developed to protect coastal areas worldwide. They maintain a network of detectors, which can track quakes that may trigger a tsunami. UNESCO’s Intergovernmental Oceanographic Commission (IOC-UNESCO) took the lead in establishing a Tsunami Warning System in the Indian Ocean2 and continued working on:
Our map of the week features historic tsunami origin points in European waters. On the European atlas of the seas, you can also check out a map with the coasts that were affected by these tsunamis.
The data in this map were provided by EMODnet Geology.