The largest tsunami in 2012 was off the remote west coast of B.C.’s Haida Gwaii and created formidable waves up to 13 metres high, but it hardly left a trace.
Federal scientists have made repeated trips to the windswept, rocky and unpopulated west coast of Haida Gwaii to look for evidence of the tsunami that was triggered by a magnitude 7.7 earthquake, Canada’s second largest recorded quake, on October 28, 2012.
After scrambling up rocky beaches and into coastal forests Lucinda Leonard and Jan Bednarski, of Natural Resources Canada, did uncover telltale signs of the tsunami.
Dead salmon on the forest floor, seaweed dangling from tree branches metres off the ground, and Japanese fishing floats sitting beneath giant cedars revealed how huge waves hit the shore of Gwaii Haanas National Park Reserve and grew as they raced up inlets, inundating low-lying forests with up sea water.
“Western Haida Gwaii was impacted by significant tsunami waves that reached up to 13 metres above the state of the tide,” report the scientists, whose findings will be included in an upcoming report on the Haida Gwaii quake and tsunami in the Bulletin of the Seismological Society of America.
One large black fishing float stamped “Musashi” is identical to one discovered on a Washington beach and traced to an oyster farming area hit hard by the 2011 Japanese quake.
Bednarski said in an interview he was also stuck by the distinctive Japanese hard hats the sea tossed into the remote forest. And how campsites on seemingly protected beaches would have been hit with some of the biggest waves that funnelled up inlets.
Had the quake and tsunami struck in the summer — instead of an evening in October — it would have been a much different story as many people would have been fishing and kayaking in the region.
“It could have been a disaster,” says Garry Rogers, a senior scientist at NRCan, noting “it was not a small tsunami.” The scientists say it was the largest tsunami recorded globally in 2012.
But the tsunami was very focused, Rogers says, sending waves racing ashore along about 200 kilometres of Haida Gwaii and across the Pacific Ocean to Hawaii where it was picked up by tide gauges.
The Hawaiians evacuated coastal areas as a precaution but the tsunami was much smaller than expected — the waves were less than a metre high when they arrived. There was no damage, but the evacuations caused bumper-to-bumper traffic jams in Hawaii and calls for better tsunami forecasting.
There was also plenty of confusion and frustration in B.C. It took provincial emergency officials more than half an hour to issue a public tsunami warning, leaving many people in coastal communities wondering whether they were supposed to head for higher ground. Emergency Management B.C. says it is now working to improve earthquake/tsunami preparedness programs.
Scientists say the information gathered from the Haida Gwaii quake and tsunami have provided valuable insight into the geological forces at work off British Columbia’s north coast.
It also shows tsunamis do not always leave a lot of evidence behind, unlike the tsunamis generated by the giant quakes known to occur along the Cascadia subduction zone that runs from Vancouver Island south to California. Megaquakes rip down Cascadia about every 500 years — and the sand layers left by the tsunamis have been found up and down the coast providing evidence of 19 giant Cascadia quakes in the last 10,000 years.
The Haida Gwaii tsunami left “no sign of a sandy deposit,” Leonard and Bednarski report, “despite evidence that debris had been carried by a marine inundation up to 12 metres above mean sea level with flow depths up to 2.5 metres.“ The way the tsunami travelled up narrow steep fjords may help explain the absence of sand in the forests hit by the sea water, they say.
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