Just over 320 years ago, on Jan. 26, 1700, many coastal areas of Vancouver Island experienced a significant tsunami following a major earthquake along the Cascadia Subduction Zone. The event has been captured in Indigenous oral histories and was measured and dated as far away as Japan.
More recently, in January 2018, a 7.9 magnitude earthquake in Alaska triggered an early-morning tsunami warning for Greater Victoria. While the warning was eventually called off, it gave local emergency personnel a chance to practise emergency response plans with residents evacuated in some low lying areas such as the Esquimalt Lagoon. April 11 to 17 marks Emergency Management BC’s Tsunami Preparedness Week.
A tsunami is a series of long waves caused by a sudden shift in water triggered by an event such as an earthquake. The speed in which a tsunami travels is dependent on the depth of water. In deep oceans, a tsunami is barely noticeable but can travel at speeds upwards of 800 km/h. The closer it gets to shore, the higher the waves get and they begin to slow to speeds of 30 to 50 km/h.
“Tsunami Preparedness Week provides a great opportunity for Saanich residents to develop or update their emergency plan,” said Saanich Deputy Fire Chief Frank Macdonald. “The primary tsunami risk in our region is from a Cascadia Subduction Zone earthquake, and the strong shaking from this event is nature’s warning to move to higher ground or inland, four metres vertical from the high tide line.”
In 2013, the Capital Regional District (CRD) conducted tsunami modelling, but it was based on an almost worst-case scenario, explained Tanya Patterson, the City of Victoria’s emergency program coordinator. Teams are working to update the modelling to include lesser threats, such as the 2018 earthquake which turned out to be of minimal risk to Greater Victoria.
In the event of a magnitude 9 earthquake along the Cascadia Subduction Zone, the CRD predicts a tsunami would reach Port Renfrew in approximately 35 minutes with wave heights of up to 11.5 feet (3.5 metres), followed by Sooke Harbour within 60 minutes with waves of over eight feet (2.5 metres) and the Esquimalt and Victoria harbours in 76 minutes with respective wave heights of nearly nine feet (2.7 metres) and eight feet (2.5 metres). It will then reach Cadboro Bay within 90 minutes and Sidney within 110 minutes, with both expected to see waves up to 6.6 feet (two metres).
The CRD considers four metres – 13 feet – above sea level to be a safe distance.
Different areas also offer alert systems for residents to subscribe to. Colwood, Langford, View Royal and Highlands have partnered on a system called Westshore Alert. The CRD and Township of Esquimalt also offer alert systems for residents. The Saanich Peninsula recently relaunched an alert app to include Sidney, North Saanich and Central Saanich.
Saanich is among the communities participating in Emergency Management BC’s Tsunami Preparedness Week by encouraging residents to develop personal emergency preparedness plans. The district hosts a virtual online presentation for residents on April 27 at 7 p.m. register by emailing email@example.com or call 250-475-7140. Learn more about tsunami preparedness and the Saanich Emergency Program on Saanich.ca/prepare.
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