TsunamiA tsunami is a series of travelling ocean waves usually caused by a large EARTHQUAKE beneath or near the ocean. Volcanic eruptions, submarine landslides and coastal rockfalls can also generate one, as can a large meteorite impacting the ocean. The majority of tsunamis occur in the Pacific Ocean, however, people and property in all coastal areas are at risk. The 26 December 2004 tsunami in the Indian Ocean, which killed or displaced 230 000 people, was one of the largest tsunami events of the last 100 years. These very large tsunamis (called teletsunamis) can be destructive across entire ocean basins. This makes them the most far reaching of all natural DISASTERS.
In the deep ocean a tsunami travels at about the speed of a commercial jetliner and its length from crest to crest can be 100 km or more, but its height will be less than a metre and therefore it will not be noticed by ships at sea. As a tsunami enters shallow coastal areas it slows down and the wave height increases. In some instances, when the waves reach the shore their heights can be 30 m or more. Warning signs of an approaching tsunami may be strong and prolonged ground shaking, if the cause is a nearby earthquake, or the sea may suddenly recede along the shore.
A tsunami warning system was established for the Pacific region following a series of destructive tsunamis, that occurred between 1946 and 1964. Similar systems are being established for the Indian Ocean and for most other coastal regions. Warnings are initially provided based on an earthquake's magnitude and location, and the threat of a tsunami is then confirmed by water level measurements from networks of tide gauges. Once a warning has been issued nations are responsible for alerting communities at risk. The people living in these communities, through proper planning (mitigation) and education, would evacuate to safe areas until the threat has passed. Since a tsunami is a series of waves (and the first wave is frequently not the largest of the waves), no one should return to coastal areas until emergency officials deem it is safe to do so.
On 18 November 1929 an earthquake in the Grand Banks raised a 5 m high tsunami that hit the Burin Peninsula of Newfoundland; 26 people died. The Alaskan earthquake on 28 March 1964 raised a tsunami that caused property damage of several millions of dollars in the twin cities of Alberni and PORT ALBERNI, BC; there was no loss of life.