Icy Bay Mega Tsunami


[Boat captain giving safety talk] So this event,
this landslide and tsunami that occurred here in Taan Fjord, is a huge event. It’s one of the largest tsunamis we’ve
ever seen in modern history. [Sounds of rockslide growing into
massive rumble.] [Helicopter flight sound] [Background music plays] So we’re here in Icy Bay. In Alaska. In Taan Fjord. So, at the head of Taan Fjord, we had a very
large landslide; large enough to generate a wave that was probably about 300 feet high
when it was first generated. That wave produced run-up values
in excess of 600 feet right near the source and waves as large as 200 feet and 100 feet
throughout the fjord. So, we are here looking at the
tsunami. We’re recording tsunami evidence. We’re trying to understand how the tsunami
evolved throughout the fjord, how it evolved outside the fjord, how it was able to move
sediment, how it was able to damage trees, and how it was able to change the landscape. This is a very, very remote setting. We are a long way from any sort of support
and we have a pretty limited budget as well for such a large team. On this side of the [Wrangell-St.
Elias National] park, the Yakutat District, it’s part of the largest coastal mountain
range in the world. In front of me is Mount Saint Elias at a little
over 18,000 feet tall; the second highest peak in the U.S. and it comes straight up
from sea level in just eleven miles -eleven or twelve miles from sea level up to that
height. There’s a huge amount of tectonics
going on and the tectonics are responsible for some of the huge mountains like [Mount]
Saint Elias back here, which has just insane relief. We’re at sea level here and it’s 18,000
feet up and that’s only like 10 miles away. So the tectonics are responsible for
that but we’re also high latitude so you have a lot of glaciation on these high mountains
and these glaciers are also retreating and have been for quite some time. They are retreating faster because of more
modern things going on. That retreat is also causing uplift
to occur, too. So, it’s just an incredibly dynamic place. [Muffled voices talking over marine
radios.] “you’re over at the stream on Hoof Hill Fan?” “Yea, that’s right. We’re over here at the fan. We’re going to take a quick look and then
paddle back.” “Sure. I’ll endeavor to rendezvous.” It’s one of the largest tsunamis
we’ve ever seen in modern history. What it allows us to do; it allows us to study
tsunamis on a scale we’ve never done before. As soon as you bump up the scale, you start
to look at huge things; you get a lot more information. You can see effects that in other tsunamis
are small or not noticeable. Here they are huge because everything
is blown up. Everything is bigger. When you can do that, you get so
much more information. You understand details about the flow. With that information we go back
and we try to apply it to our models and to our physical understanding. We try to back out what the water probably
did. Once we can do that and we have some confidence
that these models are reproducing these really complex physics that we see in tsunamis and
we have some confidence moving forward that we can use these types of tsunami models to
predict events like this in the future. There haven’t been a whole lot
of studies using this kind of high resolution data to look at landslide deposits underwater. So that will be of interest in and of itself,
but also this entire event was discovered from a desk in New York by Colin Stark, one
of the collaborators on this project, by taking advantage of all the seismic network around
here. Once we have a better handle on
the topography of the landslide in the water, we can start to tease apart where the landslide
is and where it isn’t to try to come up with a total volume for the landslide, which
will help constrain his model of landslide detection, from seismic data. But then also, some of our other
colleagues will be running tsunami propagation models through the fjord here to try to get
a better handle on how the physics of these [tsunamis] operate. To do that, they need good topographic data. I was in Japan at the time, about
to have a baby. On almost exactly the due-date of the baby,
my colleague Eron Extrum, in New York, where I am usually based, where we have a system
running to detect earthquakes. He spotted a likely landslide earthquake. This is using a system called a global seismographic
network. Most of the seismic events in the
Saint Elias area are tectonic in origin because it’s an incredibly tectonically active area. But just occasionally, when you look at the
seismic signature, you say, ah ha! This is not a tectonic source but a landslide
source. The shapes of the waveform are different. Then, subsequently, we got a
Worldview GOI image, which is 50 centimeter resolution. A beautiful image. One of the best I’ve ever seen. The light quality was fantastic. You could see the spectacular,
and truly huge landslide. We realized that it was the west flank of
the head of the fjord. Sure enough, the landslide had
entered the water. Some of it had dumped directly onto the front
of the glacier, which is very unusual combination. Given the nature of the seismic
analysis we are able to glean some very important information from the seismic data. Including, most importantly, the force involved,
which in this case came out to be about 200 giganewtons. Which, to put that in real terms, turns out
to be about 100 to 200 million tons – metric tons – of mass, that must have entered the
water at an acceleration of one to two meters per second squared. So what I am really interested
in is…all the material that ends up in the fjord, where is it coming from? What processes are driving it? So, one individual event, does it equal one
hundred years of regular…the glacier is slowly moving back and it is adding more material
and as it is pulling back all these mountains that you see here and those gullies and rills
– those are slowly adding material into the fjord. So we’re not necessarily teasing the sediment
out, we’re looking at…OK, now we know between May and August how much landslide
material was added in. And, from what we looked at in May to back
in time, before the tsunami and landslide happened, how much material was added in there. You can use the sediments and the
size of the sediments and how they are arranged to start to estimate the speed of the water
and the depth of the water, which helps understand the dynamics of how the flow evolved as the
tsunami came ashore. Something that’s interesting for this setting
is there are so many sediments. Normally you have a vegetated surface and
the tsunami might erode some of it but it doesn’t erode everywhere that is goes in. Usually a tsunami will pick up sand from the
beach and maybe just next to the beach and then it’ll spend the rest of the time on
land slowing down and depositing that sediment. But here, this is fascinating. The tsunami seems to have just scoured down
through the soil – the soil here is just decades old, so it’s not very strong. The roots of the vegetation wasn’t very
good at holding the sediment in place. The tsunami picked up and moved the sediment
and kept picking it up the ground surface the entire way, almost, that it went in. It’s a new way of thinking about how tsunamis
are moving sediment. [Quiet background voices] “There are also several points that would
significantly expand what we have, including the highest run-up. Access at best, is sketchy.” [Radio voice] “No problem. Thank you” “I’m going to slide down here for a second,
Bjorn.” We are extremely fortunate to
have been supported by NSF to come so quickly after the event. If would have waited until next year or a
couple years from now, much of the evidence from the tsunami would be gone and we wouldn’t
be able to understand some…we wouldn’t be able to do some of the science that we
can do because we were here so soon. That’s of tremendous value. Of societal importance…absolutely. We are in a spectacular fjord in southeast
Alaska and while there aren’t typically people right where we are, in any large numbers,
there are many, many fjords like this in southeast Alaska where there are large numbers of people. There are some communities around, but also,
in the summertime, like now, there are cruise ships. In Glacier Bay, for example, where cruise
ships that hold thousands of people go up and down the bay everyday. Should one of these large landslides come
down into the water and trigger a tsunami, the devastation could be quite horrific. So absolutely, the combination of being able
to get here so quickly with a whole suite of sophisticated instruments, we’re hoping
really provides with the means to make some big advances in tsunami science. I’ve been on surveys, I’ve
looked at a number of tsunamis over the last 15 years. Since those first ones, you realize first
how important it is to be in the field. When you’re in the field, you see things
that are so complex. They require you to think about the processes
that happened around you and it requires you to dig into the physics that probably happened
and you learn so much. It is so important to come out and see these
things. There is no replacement for seeing one of
these events. In some sense, it’s almost like
the perfect experiment. Find the remotest area in North America where
you can generate a landslide tsunami, run the experiment and make a host of observations
from that. Then learn from that and apply it to building
some sense of what will happen when a similar event occurs, which will inevitably happen
in a much more populated area. It’s sort of an ideal, natural, field-scale,
gigantic experiment. So that engineering connection
becomes really important. You have to be able to convert this basic
scientific understanding, which is really important; it’s the most important piece
of this puzzle, understanding these things that we’ve never really seen before. Taking that scientific information, putting
it through the engineering interpretation and then being able to provide a product to
policy-makers, to local emergency managers that allows them to make decisions when events
do occur…this is the end goal. There’s maybe one or two other
events that we can point at that are maybe bigger but this one was pretty dramatic. It’s happening in an environment, which is very
similar to other areas the National Park manages – where there are lot’s of people who
are going in those areas. Like In Glacier Bay National Park or Kenai
Fjords. Those are very similar environments. They are coastal, the glaciers are retreating
and you have de-buttressing of hill-slopes, potentially there is some mountain permafrost
thawing going on and if you have very large landslides hitting bodies of water you could
have tsunamis that could affect people. Nobody died in this one, nobody got hurt,
and no one even knew about it until they saw the satellite photos, but we should take the
opportunity to learn from the experience where nobody got hurt so we can maybe be proactive
about the areas where people could get hurt. [Credits music plays]

13 thoughts on “Icy Bay Mega Tsunami

  1. Great production and interesting scientific commentary. I like the simulation around minute 5 and a half.

  2. Like Iv said on other post . I have No, sympathy for anyone who lives on any coast , or near any river flood plain !! NONE !!! And Guess what ?? Mother Nature Don't Either !!! So When something happens to whom ever in These places . Tuff SHIT !!! Stupid People !! Don't deserve Any Help , except Mental health !!

  3. 600 foot high wave? Bullshit. That might be the distance up the sloped valley wall the wave traveled, but that wasn't the HEIGHT of the wave itself on the open water.

  4. Where can we look at results from this expedition? I think it's fascinating, and reminds me of the Lituya Bay tsunami.

  5. Thanks for the video AlaskaNPS. I live in Juneau and so this hits a bit close to home. There are landslides almost every year around Juneau but fortunately most of them are small and high up in the mountains. I own a sailboat and am out on it nearly every weekend during boating season and I rarely go a season where I don't see the evidence of a landslide somewhere. As for the Taan Fjord slide, I'm wondering if glacial rebound might have also been a cause.

  6. Lituyla bay1958 had a Mega Tsunami that stripped bare the land down to rock up to 1700 feet high on both sides of the bay. There were only 2 survivors. That tsunami is the largest in modern history. The damage can still be seen in photos taken from space. Google it and see for yourself and then imagine a 1700 foot wall of water coming right at you.

  7. science says, "Horrific devastation" Nature says, "A ship full of curious humans dies." Horrific (emotion) is due to point of view….. "Triggered" is a point of view thing and reality don't care.

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