Bute Inlet landslide a rare research opportunity for geologists
COURTENAY, B.C. -- Researchers say a large landslide and tsunami that occurred in the Bute Inlet area back in November has provided them with a once-in-a-lifetime opportunity.
Natural Resources Canada researcher Gwyn Lintern says an international team has been focusing on the Bute area for the past five years, but was surprised by the November incident.
“We see these outburst floods in the sediment record from when the glaciers receded from this area 10,000 years ago and it’s pretty rare that we would actually have one occur, that we could go out and measure and compare the sediment deposits to what we see in the geological record,” Lintern says.
Part of their efforts has been looking at sedimentation deposits at the bottom of the inlet and determining how thick deposits are in various parts of the delta and dating them.
Lintern and other researchers used the Canadian Coast Guard ship Sir Wilfrid Laurier for their research, while a smaller vessel was used to do repeated multi-beam mapping of the sea floor. They finished their mapping in October, but are now doing it again after a tsunami dumped fresh sediment in the area.
“There’s a big international team that’s interested in Bute, looking at sedimentation and carbon burial and these things, so when this event occurred, it was like the cream on the top, that we have a sedimentation event of a lifetime occurring right in the midst of our project,” he says.
Research scientist Andrew Schaeffer of the Geological Survey of Canada says the Nov. 28 event was preceded by three earthquakes near a glacier at the top of the inlet. Research is being conducted as to whether these events could have triggered the landslide which led to a domino effect that included the tsunami and a forest being destroyed.
“There were three earthquakes that all locate within about three kilometres of where this slide happened,” Schaeffer says.
He says they occurred on Nov. 27 and 28, with the final quake – a 2.2-magnitude shaker – taking place just 40 seconds before the start of the slide.
“Traditionally, we consider that an earthquake has to be a magnitude 4.0 or higher before it triggers a landslide, but there could be some mitigating factors here that essentially allowed everything to be stressed right on the edge,” Schaeffer says.
“It’s kind of a new method for us in science to understand what we call source-to-sync, that is from the top of the mountains to the bottom of the ocean, rather than just keeping these separate all the time,” Lintern says.
The research project is co-led by Geological Survey of Canada, Durham University and National Oceanography Centre in the United Kingdom, and Calgary University.
Lintern says underwater landslides occur in the area every 25 years, with major events taking place every century and a half.
“So we’re interested to find out is this the 25-year event or is this the 150-year event or does this show up at all in the geological record?”