John Clague is a professor and Shrum Chair in Science at Simon Fraser University and Fellow of the Royal Society of Canada.
British Columbians learned about tsunamis in March, 1964. On the evening of March 27, a huge earthquake, the second-largest of the 20th century, rocked southern Alaska. It elevated the ocean floor off Alaska up to nine metres, along with the water above it, setting in motion a tsunami that ultimately travelled the length of the Pacific Ocean. As British Columbians slept, unaware of the disaster 1,700 kilometres away, the tsunami swept southward at a speed up to 800 kilometres per hour.
About three hours after the shaking stopped, it reached the west coast of Vancouver Island and struck community after community with high waves. Port Alberni was particularly hard hit. Three main waves swept into the town early on March 28. The second and most destructive wave surged one kilometre inland, forcing the RCMP to use boats to rescue guests from the upper floor of a local hotel. About 260 homes in Port Alberni were damaged, 60 extensively.
Miraculously, there were no fatalities. However, the damage to West Coast communities totalled about $10-million, equivalent to about $800-million today.
In 1964, computers were not accessible to the general public and there was no internet nor social media. This, coupled with government and public ignorance of tsunamis, resulted in a lack of warning of what was to come in the hours after the earthquake.
Fast-forward to the early morning of Jan. 23 this year. A magnitude 7.9 earthquake struck offshore of the Aleutian archipelago, south of Kodiak, Alaska.
The Aleutian Trench is one of the most earthquake-prone areas on Earth, the site of many large, tsunami-producing earthquakes in recent times. When the earthquake happened, seismologists and U.S. officials were concerned that it would trigger a damaging tsunami. They now have tools to deal with such a disaster.
The Pacific Tsunami Warning Center in Palmer, Alaska, established after a large Aleutian earthquake in 1949, issued a tsunami alert upon receiving information on the size and location of the 2018 earthquake from a network of computer-linked seismometers located around the Pacific basin. Government officials in British Columbia and at-risk U.S. states were notified. Coastal communities on Vancouver Island were then notified by the B.C. government, and planned emergency-evacuation measures were initiated.
While this was happening, staff at the Pacific Tsunami Warning Center closely monitored the situation, gathering data from tidal stations near the earthquake epicentre and records of ground motions at distant seismometer stations. Within one hour, it was apparent that the earthquake had not triggered a significant tsunami. Fortunately, it displaced the seafloor horizontally rather than vertically and had not disturbed the water column above. An hour later, the tsunami alert was cancelled.
The event proved to be a useful test of B.C.'s tsunami readiness. So how did we do? Not all that badly – although much work needs to be done.
Sirens in the most at-risk communities – Port Alberni, Tofino and Ucluelet – awakened people in the early morning hours of Jan. 23. Residents in low-lying parts of these communities were evacuated to refuge areas on high ground. Clearly the information cascade from Alaska through the B.C. government and down to the community level worked.
But on the other hand, residents were naturally anxious about what might happen and were not adequately informed following the evacuations. Remote, small communities on the coast were literally left in the dark, without cellphone coverage and reliant on land-based phones and radios.
In a time when we have remarkable communication technology, we can and must do better in informing our citizens about imminent threats.
But tsunamis that originate from Alaska, Kamchatka and Japan are not the full story. B.C. has its own seismic "elephant in the room" – the Cascadia subduction zone located off the West Coast of North America. Averaging every 500 years, a giant earthquake of magnitude 8 to 9-plus happens when the fault bordering the North America and Juan de Fuca plates slips. These earthquakes generate tsunamis similar to that from Alaska in 1964.
However, in contrast to tsunamis of distant North Pacific earthquakes, the Cascadia tsunami would reach communities on the west coast of Vancouver Island in as little as 20 to 30 minutes.
There would be little time to mount an effective evacuation of Tofino and Ucluelet. Residents in these communities, on experiencing three to five minutes of strong ground-shaking, must seek higher ground immediately rather than wait for a warning from provincial and local officials.
The most recent of these tsunamis happened in January, 1700, before the arrival of Europeans on the B.C. coast. It devastated coastal Indigenous communities and swept all the way across the Pacific, causing major damage on the east coast of Honshu, Japan.
Although we cannot predict when the next giant Cascadia earthquake will happen, we are more than 300 years out from the last one, and getting ever closer to the next. We cannot rest on our laurels and assume we are ready for the inevitable next tsunami.