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The tsunami risk in Canada

Beneath our feet, Canada is constantly atremble. Earthquakes shake the country about 2,500 times per year, most too small to feel. But occasionally, and without warning, the earth's crust below Canada buckles and spasms to frightening effect. More dangerous are the tsunamis that such quakes can cause. CBC Archives looks back at notable Canadian quakes, fears about "the big one" predicted for the West Coast and scientists' efforts to better understand the threat from below.

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In the Indian Ocean the biggest earthquake in 40 years has spawned a tsunami that devastated swaths of south Asia. Whole communities were wiped out. Beaches were littered with corpses. A viewer of CBC Television's The National wants to know, if such giant waves ever hit the B.C. coast, what parts would be hardest hit? In this clip, national science columnist Bob McDonald answers by first describing the "ring of fire" -- the earthquake and volcano zone that surrounds the Pacific Ocean.

The "ring" -- a crack in the earth's crust -- is responsible for most of the world's quakes, McDonald says. At highest risk are southern B.C. and the northern U.S. near the Juan de Fuca tectonic plate, where a major quake is expected in the future. But not all quakes produce tsunami waves so it's far from certain that B.C. will ever be swamped like south Asia.

Canada's Atlantic coast is also at some risk from tsunami, McDonald adds. A giant wave struck Newfoundland in 1929. But there is far less earthquake activity at the bottom of the Atlantic than the Pacific with its "violent geography," he says.
• The south Asian tsunami, one of the world's worst disasters, began on the morning of Dec. 26, 2004. Along a 1,000-kilometre fault line at the bottom of the Indian Ocean, about 150 kilometres off the Indonesian island of Sumatra, the Australian and Eurasian tectonic plates heaved. The collision of the plates pushed a section of seabed up about 10 metres, displacing hundreds of cubic metres of water.

• The sudden displacement created a series of waves rolling out in different directions from the earthquake's epicentre. In deep water, the waves moved at speeds up to 800 km/h. Approaching land they slowed, but grew in size. Waves slammed into the coasts of Indonesia, Thailand, Malaysia, Myanmar, Bangladesh, Sri Lanka, India and, thousands of kilometres away, Somalia on Africa's east coast.

• The first waves slammed into the coastline within minutes of the earthquake, leaving no time for warnings. The only signal that something was amiss came just before the tsunami hit, when the waterline suddenly retreated, exposing hundreds of metres of beach and seabed. Several waves struck in intervals of between five and 40 minutes and penetrated as far as one kilometre inland.

• British Columbia gets tsunami warnings from the Alaska centre. The centre processes seismic information from around the Pacific Rim, including tidal gauges on the west coast of Vancouver Island and the north end of the Queen Charlottes. The system has, however, been prone to false alarms.

• In January 2005, world leaders pledged to set up an Indian Ocean tsunami early-warning system like the one that exists in the Pacific Ocean. Experts said such a system could have dramatically reduced the death toll of well over 100,000 caused by the Boxing Day disaster.
Medium: Television
Program: The National
Broadcast Date: Jan. 3, 2005
Guest(s): Bob McDonald
Host: Peter Mansbridge
Duration: 3:59

Last updated: April 25, 2014

Page consulted on September 10, 2014

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