A scientific paper by the Geological Survey and the Department of Fisheries and Oceans says there were once two giant landslides on Douglas Channel that triggered major tsunamis and that the landslides were possibly caused by an earthquake on the fault line.
The Attorney General of Canada is asking the Northern Gateway Joint Review Panel for permission to file late-written evidence long after the panel’s original deadline of December 2011. The attorney general’s motion was filed on Aug. 17, but went unnoticed until the Kitimat environmental group, Douglas Channel Watch, brought the matter up with District of Kitimat Council on Sept. 17.
Appended to the attorney general’s motion is a copy of the October 2012 report titled: “Submarine slope failures and tsunami hazards in coast British Columbia: Douglas Channel and Kitimat Arm.” It says the scientists discovered “evidence of large submarine slope failures in southern Douglas Channel.”
The report goes on to say, “The failures comprise blocks of bedrock and related materials that appear to have been detached directly from the near shore off Hawkesbury Island.” Hawkesbury Island, which is just south of Kitimat, and many of the other islands in Douglas Channel are built up with material left over from the ice age glaciers and thus are vulnerable to displacement and landslides.
The research identified two slides, one estimated at 32 million cubic metres and a second of 31 million cubic metres. The report goes on to say that the discovery of an “apparently active fault presents the possibility that they may have been triggered by ground motion or surface rupture of the fault during past earthquake events.”
The slope failure landslides are covered with thick layers of mud, and that, the scientists say, could mean that the failures could be ancient, possibly occurring 5.000 to 10,000 years ago. Further research is needed to confirm the date of the giant slides.
What’s worrying about the discovery is the fact that there were two recent submarine slope failures near Kitimat on Douglas Channel. The first slope failure occurred on Oct. 17, 1974, triggering a 2.4-metre tsunami at low tide. Then on April 27, 1975 there was a second slope failure near low tide on the northeast slope of the Kitimat Arm that generated an 8.2-metre tsunami. The 1975 tsunami destroyed the Northland Navigation dock near Kitimat and damaged the Haisla First Nation docks at Kitamaat Village.
DETAILED MODELLING UNDERWAY
According to the attorney general’s filing, the DFO is using high-resolution scans of the Douglas Channel seafloor to create models of “potential wave heights and speeds that may have resulted from the two previously unrecognized submarine slope failures in the Douglas Channel.”
The scientific report says that evidence for a continuous fault was observed by a 2010 survey that tracked aligned stream beds and fractures on the south end of Hawkesbury Island, about four kilometers from the site of the second ancient slide.
The possible fault then appears to terminate far to the south near Aristazabal Island on the Inside Passage. The Geological Survey says that 11 small earthquakes, all less than magnitude 3.0, have occurred within 20 kilometres of the suspected fault over the past 25 years.
Scientists conclude that the slides appear to have left very steep slopes at or near the shoreline that could be susceptible to future failure events. According to the report:
The fault must be considered a potential trigger for the submarine failure events… The triggers for the failures have not been defined; however, their proximity to a potentially active fault represents one potential source. The failures probably generated tsunamis during emplacement and conditions exist for similar failures and associated tsunamis to occur along this segment of Douglas Channel in the future.
Natural Resources Canada sent this statement to me to underscore more research is required:
“Although the ancient large submarine slope failures which our scientists have identified may have caused tsunamis, this is not a certainty. It is important to note that Fisheries and Oceans Canada is currently studying this information to model potential wave heights and speeds.”
The attorney general’s filing offers to bring the scientists whose further research is expected to be completed by Nov. 1 to the Joint Review Panel to appear as witnesses sometime during the final hearings.
It also notes that the current evidence tendered to the panel by Enbridge and other parties does demonstrate the potential for marine geohazards. Enbridge has said it would undertake further geological survey during the detailed design phase for the terminal.
(A longer version of this report, with more technical details and maps appears on Northwest Coast Energy News.)