Ocean Alive! Tsunamis


Here on the West Coast we hear a lot about
tsunamis. As we know from recent events in Japan and southeast Asia, tsunamis can be
incredibly destructive. So, what exactly are tsunamis and where do
they come from? A tsunami is what we refer to as a body wave.
It affects the entire water column in an ocean or a lake. It is essentially is a wave phenomenon
in that energy is propagated away from a source. I kind of, because they’ve been so destructive,
refer to them as stealth killers. The seismic ones generated by earthquakes
when you displace the bottom. Off Sumatra in 2004, that huge tsunami that
was generated there, was displacements of five to ten metres in the bottom where suddenly
the bottom goes up on one side and down on the other and all that water, two thousand
metres of water, is displaced. Huge waves are generated. So that’s earthquake generated tsunamis, seismically
generated tsunamis. They happen everywhere in the world. The other kind are landslide generated tsunamis. So a failure of the coast line or some kind
of big slump that fails and it pushes the water ahead of it as it fails or a mountain
falls into the water. But about eighty percent of the big tsunamis
in the world are generated in the Pacific Ocean and the reason that tsunamis occur in
these environments is that’s where big earthquakes occur, along the Pacific Ring of Fire. It’s called that because these earthquakes
are also associated with active volcanoes. We get these very explosive, fiery eruptions
that occur because these plates are in contact with one another and generating the forces
that can create both earthquakes and volcanic eruptions. The speed of a tsunami is basically set by
the depth of the ocean so if we use an average depth of the ocean about five kilometres it’s
basically the speed of a jet. So that’s 700-800 kilometres per hour. You’re on an aircraft coming from Japan for
example towards Canada during the 2011 Japanese tsunami your jet plane would just be able
to keep up with that wave as it crossed the ocean. It took it nine hours and fifty-seven
minutes to get to Bamfield on the west coast of Vancouver Island. So this massive wave can move at the speed
of a jet! What are the odds of a tsunami landing here?
And if one does, what should we do? The likelihood of a tsunami coming to Vancouver
Island is actually very good. We live in a very seismically active region
and so we are at a high risk of tsunamis. So any Pacific based earthquake, and large
Pacific based earthquake could cause a tsunami which could
impact British Columbia’s Pacific coast. We have developed with Rick Thomson very very
precise sensors on the bottom of the ocean that actually measure the actual pressure
of the water which is really equivalent to the height and we can precisely measure to
sub-millimeter detail in 3 kilometers of water how high that wave is. And so with those sensors we can then begin
to use models to predict the speed and direction and the height of the wave that will impact
our coast. If there is a mega thrust earthquake off our
coast we will have a major tsunami and we want to be able to provide much more direct
warning. Now we wouldn’t be doing this directly, we
have to work with our emergency management teams here in British Columbia but that’s
the direction we want to go in. The information and data that’s collected
from Ocean Networks Canada helps emergency managers to understand what kind of tsunami
might be coming in at any given time. We have the ability with the technology we
have, to do an early detection of an earthquake when it first hits. We may be able to give
places in Vancouver and Victoria a thirty to forty second warning of major ground shaking
hitting. That’s a lot. People say well that’s not very much but it
can turn off a valve, it can stop trains, it can set off an alarm in schools. So there’s
many things we can do with that. So we’re working with a team of people in
British Columbia over a five year time period to see if we can implement something like
that. I think the most important thing about tsunamis
is understanding your risks, where you live, where you work and where you play. So if you’re
travelling to an area that has tsunami risks to understand that there is a tsunami risk
and then to understand what you would take, what actions you would take to keep yourself
safe in the event of a tsunami. You’re walking the beaches in Tofino and there
is a big earthquake, don’t even wait for any warning just go to higher ground because you’re
going to have about half an hour, at most three quarters of an hour before that tsunami
hits and it’s going to be big on the outer coast. Today we had a chance to learn more about
tsunamis. Thanks to the team at Ocean Networks Canada and thanks to you for being part of
our ongoing explorations here at Ocean Alive!

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