- Thanks to Surf Shark with
Incogni for supporting PBS. Unlike hurricanes, tornadoes or wildfire, large subduction
zone earthquakes are rare, but they have the potential
to cause catastrophic damage and produce massive tsunamis
that can travel the speed of a 737, that's over 500 miles per hour. And these tsunamis aren't
something you can just ride out. - Normal ocean waves are produced by wind. It's almost like you have
your coffee cup, it's too hot and you just blow on it and you
create waves on the surface. But now let's suppose that
you put down your coffee cup abruptly, then what you do
is you create a tsunami, tsunamis, they're
generated by a displacement of the ocean floor. They move the entire ocean column up. I mean the wavelength is of
the order of several miles. - And another thing that's particularly scary about tsunamis, - So you have this mountain
of water that's coming in, slows down, slows down, slows down. You sit there looking at it and suddenly it hits
the shoreline and woosh The tsunami accelerates when it hits, you know, the dry beach. - Every coastline around the
world is at risk of tsunamis, but some areas are particularly prone and they can be deadly. In 2004, a magnitude 9.1
earthquake off the coast of Sumatra spawned the deadliest
tsunami in modern history, reaching as high as 100 feet and killing more than 230,000
people in the west coast of North America is overdue for a subduction zone earthquake,
the Cascadia megaquake, which could produce a
series of deadly tsunamis. And here we didn't start
planning for tsunamis until well after we created our whole
modern built environment. So there are just a lot of places where there isn't anywhere to evacuate to. So we wanted to know how
can you survive a tsunami and what do you do if
there's no high ground? - There are several communities
where the time it takes to walk is far greater than
the estimated wave arrival - time. It's a known loss of life. - Unless we change our course. The death toll from the Cascadia
subduction zone earthquake and tsunami will almost certainly
surpass any other natural disaster in US history. So keep watching to find out
what the number one factor is that determines the difference
between life and death. Tsunamis can be caused by
landslides, volcanic eruptions, even meteor impacts, but their most commonly
caused by earthquakes. And the biggest are
caused by subduction zone or mega thrust earthquakes. These are earthquakes which
occur along fault lines between tectonic plates. - It took us a long time to understand why these
big earthquakes were happening, where they were happening. The knowledge of plate tectonics
is surprisingly recent. That really became a formally accepted theory in the sixties. The earth is made out of
these broken up plates, these shells of crust that are floating and then sometimes they
crash into each other. And when they crash into each other, that's a subduction zone. When Earth formed, it
was really, really hot. You know, four and a
half billion years later, it's still cooling the
tectonic plates at the top. They're the coldest part of the earth 'cause they're the outside rind of the planet, but the inside is still warm. So what ends up happening
is the plates, as they cool, they begin to sink back into the earth. And new warmer material sort
of bubbles up to the surface. It's like a spherical lava lamp where there's blobs coming up and then blobs going down just at really, really slow speeds. It's about an inch, two
inches per year, and that's - About the speed that
your fingernails grow. - So even though the plates
are moving where they touch, they tend to get stuck
just because of friction. It's like sandpaper. And so yes, there's an inch
of movement every year, but for 300 or 400 years, the plates remain stuck at their contact, which means there's 300
or 400 inches of movement that were accumulating over
the decades and centuries. And eventually the rocks
can't take it anymore. And when they give way,
those 300 inches move. And that's the earthquake itself. And that's what creates
the really strong shaking that damages buildings. That's what creates the tsunami. That's what wreaks havoc. And - These subduction zones are
found all over the world. More than 80% of all tsunamis happened in
the Pacific Ocean along what's known as the ring of fire and the Cascadia subduction
zone along the west coast of the US has gotten a lot
of attention in recent years because scientists only
recently figured out that it too is capable of producing massive
earthquakes and tsunamis. - In the eighties and nineties, scientists
started digging in and looking for past tsunami deposits and evidence of past earthquakes, and they found evidence of drowned forests or ghost forests that indicated that the land had suddenly changed. And then they discovered they could date some of the tree rings from these
drowned forests and trees. In - Cascadia, we know January
26th, 1700 there was at least a magnitude 8.7 most likely
something like a magnitude nine. And that produced a very big
tsunami that you can see today. If you go and scrape around in the rocks, you can actually put your
finger on sand deposits from the tsunami here at location on Red Coast. And it's in historical
records in in Japan. - That's right. The
tsunami that was triggered by the Cascadia mega
quake did massive damage all the way across the ocean. In Japan, - They called it the orphan tsunami 'cause they didn't feel the earthquake and so they weren't
sure where it came from. - And now city officials and disaster planning experts
all across the west coast are planning for the next one. Scientists predict that
there's a one in three chance of at least a partial rupture happening within the next 50 years. We actually have two
videos on this earthquake, which we'll link below. But here's a quick description of what it'll feel like when it happens - For Cascadia. We expect for one of
these full margin ruptures that the shaking could
last three to six minutes. If you feel earthquake
shaking for a very long period of time, that's one of your clues that a Cascadia earthquake has happened and that a tsunami is coming. - So when the tsunami starts, it propagates in both directions. The speed of a tsunami depends
on the depth of the ocean. The deeper the ocean, the faster the, that the tsunami travels, the
the shallower, the the ocean, the the tsunami slows down. But - After combing through amateur video of the 2004 tsunami in the Indian Ocean, scientists notice something unusual while the tsunami slows down. As it climbs the sloping beach,
it actually accelerates just after hitting the shoreline. This can give onlookers an
artificial sense of security before inundating the area. - The tsunami, most of
the time looks like a fast receding tide. People are not prepared, - And it's not just one wave. - Tsunami waves don't just
come once they come in a series of waves and they are kind
of like sloshes in a bathtub. They can get bigger
with each incoming wave. - If you've seen footage of
storm surge in hurricanes, it's a, looks a little bit more like that where the water just starts
rising and keeps rising and keeps rising and keeps rising - And with nothing in its way. It can travel many, many miles
inland in Washington state. It's modeled to travel through the Strait of Juan de Fuca down into the Puget Sound. - That means in the event
of a Cascadia Megaquake, even cities like Seattle and Portland will likely
be impacted by the tsunami. So what's the one factor
that determines if you live or die? REACTION TIME - The first variable that
determines survival rates is how quickly you move out of harm's way. - Early warning systems
can be helpful, especially for tsunamis that are generated
from a distant earthquake where you won't feel the shaking. But for a local subduction zone event, even the best early warning systems may not give you enough time. - Using a combination of GPS and seismic stations, we
measure the earthquake, then we can say, okay, the
earthquake is about this long, it has about this magnitude. And so we can make a crude guess that that's gonna make a
tsunami of about that size. And we can typically do that in the first five
minutes after an earthquake. - But in the Pacific
Northwest, there are places where the tsunami may
hit in as little as 10 to 15 minutes after the quake. So you can't afford to wait
around for those five minutes when every moment counts. What do you do? - In all reality, if
you feel an earthquake and you're near the
coast or a body of water, that is your warning
that a tsunami may come and you should evacuate to
high ground immediately. - But that's easier said than done. - You need to know where safety is, and that's not immediately obvious. - You need to be able to react fast, and that means already
having a plan in place before the earthquake hits. You should know where high
ground is, what's high enough, and how you're gonna get there. And perhaps most importantly,
you should practice. And there are helpful tools with this tsunami evacuation zone map, which we'll link in the description. You can input the address of your home or where you're vacationing, and it'll tell you where
you need to go to get to high ground and how long it'll take for you to walk there. But there are some places
where there is no high ground for miles. Long Beach Washington is particularly vulnerable. Its entire population and all of its businesses are
within the inundation zone and there are communities in Oregon and California in the same situation. - Those are really precarious locations. You'd have to run at Usain Bolt speeds for 40 minutes sustained to
be able to get outta the way. That's just not going to happen. - That's where vertical
evacuation structures come in. But we've built shockingly few of them, just three in the US in fact. And one of them is the Hatfield
Marine Science Center in South Beach, Oregon. - It actually sits on a
hundred foot foundation. It is tied to that foundation
with 50 foot leg bolts to make sure that the building and the foundation stay
together during the shaking. And then when the tsunami wave
hits the building, the walls of the building are designed to fall off and that will allow the water to move through the building while we are safe. On top of the roof, we
have a cache of supplies that will take care of
the nearly 1000 people that are expected to take
refuge on top of the roof, - And they're expecting to
stay on top of the roof for up to two days until the water leaves and it's safe to come down. - I make models of
tsunamis. This is my job. I will go and enjoy the beach and I will just, you know, point the car in the right direction and make sure I'm aware of
where a hundred feet is. And I'll look at Google
Maps at the topography and make a little plan in
my head of what I would do, you know, collect the dog and go that way. - Those people that recognized the signs and moved immediately
away, they were saved. - There's still a lot
that needs to be done to prepare communities for
this inevitable tsunami. We need more vertical
evacuation structures, more signage and more outreach. - Let's not be scared. Let's
take charge of the situation. Science and technology are awesome. If we get together and do the work, the consequences
might be a lot less than if we just stick our head in the sand and pretend like la, la, la, la, la. I can't hear anything. That's a lot worse. Inaction is the worst decision. - That's pretty profound, isn't it? Not only might humans benefit
from embracing the sentiment in regards to the inevitable
Cascadia Subduction zone, megaquake and tsunami. Perhaps this is a sentiment that humans would benefit
from in general as we continue to experience natural disasters
in ways like never before. Ignorance is bliss. But is it best? As I digress,
if you're in an area at risk of a tsunami and you'd like to do what Dr. Melgar said and take
charge of your situation, here are some things that you can do. First, be sure to know ahead of time where high ground or safety is. Map out and practice your evacuation. Prepare a go bag with essentials. Know the signs of a
tsunami, be sure to prepare. Stay safe and see you next time. Thank you to Surf Shark with
Incogni for supporting PBS. Incogni is a data broker removal
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