| A Japanese word that means "harbour wave", tsunamis are huge ocean waves caused by an undersea
disturbance generating a vertical motion to the water column. These distrubances are triggered by
volcanoes that erupt under water or by earthquakes and landslides that occur underwater.
The waves of the tsunami spread in a circular manner from the point of disturbance and can move large
distances without a great loss of energy. Their speed can reach more than 800 kilometres per hour. In
deep waters, tsunamis are less than a metre high. However, when they reach shallow waters or narrow
bays, the waves slow down and pile up into a tall wall of water which causes devastation to things on
shore. The first wave of a tsunami is often preceded by a lowering of the water level. When the tsunami
hits the coast, it appears like a rapid rise in water level instead of a breaking wave. Earthquakes outside
Canada have caused tsunamis which have damaged the Canadian coastline.
Descriptions for each of the tsunamis shown on the map are found
in the document Tsunamis.
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