Information on tsunamis
Tsunamis are large waves or series of waves generated by the rapid displacement of large volumes of water due to seismic events, volcanic eruptions, landslides, glacier calving, meteorite impacts, and other disturbances.
- If the earth starts to shake violently in an earthquake - head for higher ground immediately!
- If the ocean recedes to reveal seafloor usually underwater or rises to an abnormally high level - head for higher ground immediately!
- Do not linger by the shore until you can see it coming - a tsunami moves faster than a person can run.
- The first wave may not be the largest. Successive waves may be spaced minutes to hours apart and continue arriving for many hours.
|Alert Level||Potential Hazard(s)||Public Action|
|Warning||Dangerous coastal flooding and powerful currents||Move to high ground or island.|
|Advisory||Strong currents and waves dangerous to those in or very near water||Stay out of water, away from beaches and waterways|
|Watch||Not yet known||Stay tuned for more information. Be perpared to act.|
|Information Statement||No threat or very distant event for which hazard has not been determined||No action suggested at this time|
In deep water, tsunami waves may be less than a metre high, but can travel at speeds exceeding 800 kilometres per hour and cross entire ocean basins. When tsunami waves reach shallow water or narrow inlets the waves slow down and their height increases. Tsunamis cause devastation when they break on shore through mechanical force, flooding, and washing the resulting debris back into the water.
In areas where tsunami waves do not grow noticeably in height, currents become strong and erratic and can be especially threatening to marinas, beaches, and other low-lying areas.
Tsunamis in Canada
On January 26, 1700, one of the world's largest earthquakes occurred along the west coast of North America and created a tsunami, which destroyed the winter village of the Pachena Bay peoples with no survivors. First Nations on Vancouver Island recorded these events in their oral traditions. There is evidence of repeated tsunamis inundating our west coast following giant megathrust earthquakes along the Cascadia Subduction Zone.
A tsunami that struck Newfoundland’s Burin Peninsula killed 27 people on November 18, 1929. A magnitude 7.2 earthquake 250 km to the south triggered an underwater landslide that generated the tsunami.
Natural Resources Canada and the United States National Tsunami Warning Center
NRCan forwards selected seismic data from the CNSN to the United States’ National Oceanic and Atmospheric Administration (NOAA) National Tsunami Warning Center (NTWC) in Palmer, Alaska. The NTWC issues tsunami messages for all United States and Canadian coastlines and the British Virgin Islands including alerts and alert cancellations.
NTWC uses preset criteria based on preliminary seismic data from NRCan and other sources to produce and issue messages as early as possible, even before a tsunami is detected. Tsunamis caused by underwater landslides, moderate earthquakes, or other processes may not initiate NTWC alerting.
NTWC integrates additional seismic data analysis, water-level measurements, tsunami forecast model results, and historical tsunami information to estimate impact and produce and issue updates at 30 minute intervals.
A tsunami warning is issued when a potential tsunami with significant widespread inundation is imminent or expected. Warnings alert the public that widespread, dangerous coastal flooding accompanied by powerful currents is possible and may continue for several hours after arrival of the initial wave. Warnings also alert emergency management officials to take action for the entire tsunami hazard zone. Appropriate actions to be taken by local officials may include the evacuation of low-lying coastal areas, and the repositioning of ships to deep waters when there is time to safely do so. Warnings may be updated, adjusted geographically, downgraded, or canceled. To provide the earliest possible alert, initial warnings are normally based only on seismic information.
A tsunami watch is issued to alert emergency management officials and the public of an event which may later impact the watch area. The watch area may be upgraded to a warning or advisory - or canceled - based on updated information and analysis. Therefore, emergency management officials and the public should prepare to take action. Watches are normally issued based on seismic information without confirmation that a destructive tsunami is underway.
A tsunami advisory is issued due to the threat of a potential tsunami which may produce strong currents or waves dangerous to those in or near the water. Coastal regions historically prone to damage due to strong currents induced by tsunamis are at the greatest risk. The threat may continue for several hours after the arrival of the initial wave, but significant widespread inundation is not expected for areas under an advisory. Appropriate actions to be taken by local officials may include closing beaches, evacuating harbors and marinas, and the repositioning of ships to deep waters when there is time to safely do so. Advisories are normally updated to continue the advisory, expand/contract affected areas, upgrade to a warning, or cancel the advisory.
Tsunami Information Statement
A tsunami information statement is issued to inform emergency management officials and the public that an earthquake has occurred, or that a tsunami warning, watch or advisory has been issued for another section of the ocean. In most cases, information statements are issued to indicate there is no threat of a destructive tsunami and to prevent unnecessary evacuations as the earthquake may have been felt in coastal areas. An information statement may, in appropriate situations, caution about the possibility of destructive local tsunamis. Information statements may be re-issued with additional information, though normally these messages are not updated. However, a watch, advisory or warning may be issued for the area, if necessary, after analysis and/or updated information becomes available.
Tsunami Message Cancellation
A cancellation is issued after an evaluation of water-level data confirms that a destructive tsunami will not impact an area under a warning, advisory, or watch or that a tsunami has diminished to a level where additional damage is not expected.
- United States Tsunami Warning System and Tsunami Warning Centers (NOAA, Palmer, Alaska)
- From Emergency Management British Columbia(EMBC): British Columbia Tsunami Preparedness
- From the International Tsunami Information Centre: information about tsunamis and tsunami safety rules
- From UNESCO: Tsunami Preparedness: International Guide for Disaster Plannersfrom UNESCO (information for boaters in Section 2.2.3).