Barry Arm_Tsunami_Assignment
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Dec 6, 2023
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Lituya Bay and Barry Arm, Alaska: Megatsunamis!
In this week’s activity, you will learn about a phenomenon and a geologic setting that poses a
significant tsunami hazard. First, you are going to explore what happened at Lituya Bay, Alaska,
on July 9
th
in 1958. Then, you will learn about other tsunami hazards in Alaska, including a
potentially dangerous situation that is being actively monitored by scientists at Barry Arm,
Alaska.
Part 1. Lituya Bay
Figure 1. Lituya Bay, Alaska. Landsat 8 - OLI. Image credit NASA.
It’s time to learn about the biggest tsunami in history. You may be surprised to discover that this
event did not occur as a result of the March 2011 earthquake that dramatically impacted Japan
and damaged the Fukushima Daiichi nuclear power plant, but instead occurred in 1958 in a
remote part of Alaska. First, watch the following video, which discusses some of the weird
observations that geologists had made at this location prior to the July event. Then, read the
summary pages for the Lituya Bay tsunami and the Fairweather Fault and answer the following
questions.
Video link:
https://www.youtube.com/watch?v=2uCZjqoRLjc
Lituya Bay article link:
https://earthquake.alaska.edu/60-years-ago-1958-earthquake-and-lituya-
bay-megatsunami
1
Fairweather Fault:
https://www.usgs.gov/centers/pcmsc/science/earthquake-hazards-
southeastern-alaska?qt-science_center_objects=0#qt-science_center_objects
1. What were the geologists Don Miller and George Plafker initially looking for in Lituya Bay?
a.
Oil
b.
Evidence of a prior series of mega tsunami
c.
Evidence of prior large landslides
d.
They were sent by the government to assess earthquake risk
2. Which of the following pieces of evidence were used by Miller and Plafker to supported their
hypothesis that something unusual had happened in Lituya Bay prior to the 1958 event? Select
all that apply.
a.
They observed something unusual called a “trim line”: the oldest trees in Lituya Bay
were only above certain elevations, and below this, forests were much younger
b.
They found tree ring evidence of a physical impact that hit trees along the shoreline
c.
They had access to previous eyewitness accounts from residents of Lituya Bay
d.
They discovered tsunamite deposits in the geologic record
3. What kind of a fault is the Fairweather fault? You will want to google to find this answer.
a.
Strike slip
b.
Normal
c.
Reverse
d.
Oceanic
4. What caused the displacement of water that resulted in the 1958 megatsunami?
a. Normal faulting
b. Reverse faulting
c. A landslide that was triggered by an earthquake
d. A meteorite impact
e. The sudden melting of a glacier at the head of narrow Lituya Bay
2
Figure 2. This image shows a USGS scientist, Adrian Bender, examining the Fairweather
Fault scarp. Note the tilted trees and also the change in the ground surface across this fault.
Image Credit: Rob Witter, USGS, Alaska Science Center. Public domain.
5. How tall was the tsunami run up generated by the 1958 event?
a.
1,720 feet
b.
150 meters
c.
900 feet
d.
100 feet
e.
1,720 meters
6. How do scientists think that glacial retreat could impact the frequency of these types of
events?
a.
The loss of glaciers will reduce the likelihood of megatsunami, since the glaciers won’t
fall into bays and displace large amounts of water in glacial calving events
b.
The loss of glaciers will increase the likelihood of these events, since glaciers can help
support steep slopes
c.
Glaciers will increase the likelihood of landslides as they melt, since their melting may
oversaturate and destabilize valley slopes
d.
There is no connection between the presence of glaciers and the likelihood of tsunami
3
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7. These hazards are somewhat common along the coast of Alaska, where large earthquakes,
tides, and underwater landslides could all trigger tsunami. How do the authors of the article on
Lituya Bay think that these hazards should be addressed?
a.
By putting in extensive warning systems in populated areas
b.
By regularly surveying slopes to determine which might be in the process of failing
c.
By people who live in these areas learning tsunami warning signs and running uphill
when they observe large landslides or feel earthquakes
d.
By moving everyone out of Alaska
8. What evidence did this event leave behind? You should write a short paragraph (3-5 sentences)
detailing the specific ways that this mega tsunami impacted the landscape.
The mega tsunami impacted a lot of things. While sitting along two faults. Alaska had a 7.8
magnitude earthquake which triggered a landslide in the Lituya Bay which ended up to being a
tsunami and the largest ever to hit that area. After many people love to go and see it attracting
more than a million tourist each year to go and see.
Part 2. Hazards along the Alaskan Coastline
Figure 3. Fjords in Alaska at Kenaj Fjords National Park. Image USGS, public domain.
Much of Alaska’s coastline is characterized by the presence of fjords: steep sided coastal inlets
that form when previously (or currently) glaciated valleys are filled by the sea, either as a result
4
of sea level rise or submergence of the coastline. Practically, this means that there are lots of
narrow, water-filled valleys, some with cities and towns lining their edges.
This site (
https://earthquake.alaska.edu/tsunamis
), maintained by the Alaska Earthquake Center
at the University of Alaska at Fairbanks, allows you to investigate risks to different cities by
using a tsunami hazard mapping tool.
To access the hazard mapping tool, click here:
https://earthquake.alaska.edu/sites/all/tsuMap/html/tsunami.html
. You will notice that city names
are shown on the right-you can click on any of these to view a map of tsunami risk for that
particular location (Figure 4). You can also zoom in and out to get a bigger picture, or a closer
look at a particular city.
Figure 4. Tsunami hazard map for Nanwalek, Alaska. ~40-50% of the buildings in
Nanwalek appear to be within the inundation zone. The red line shows how high water
might run inland during a tsunami. For some cities, there will be a box below this with the
words “water depth” to the right-when you click on this, it will show how deeply parts of a
particular area will be inundated.
Use this hazard mapping tool to provide the information below for Whittier and two more cities
of your choice. You will want to Google some of the information (specifically, population size).
You can click on “Publication” to see a larger hazard map and also, in some cases, to access the
scientific report for different locations where scientists modeled different tsunami scenarios.
City Name-
Cold Bay
Population-
50 (2020)
% City inundated in tsunami scenario-
78%
Part 3. Barry Arm
Whittier (learn more about the city here, where everyone lives in one building!
https://www.youtube.com/watch?v=Pxha9T-eScc
) is currently an area that scientists are
5
particularly interested in. Whittier sits within a few dozen miles of Barry Arm, Alaska, another
narrow fjord (Figure 5). One can hypothesize that a tsunami at Barry Arm could propagate to
Whittier. And indeed, there is some evidence that Barry Arm may be susceptible to a landslide in
the near future.
Figure 5. Location of Whittier, Alaska relative to Barry Arm. Image Google Maps.
Barry Arm has also experienced the recent retreat of the glacier that used to fill this fjord (Figure
6). Some scientists hypothesize that this may reduce slope stability by removing support at the
base of the valley walls, increasing the likelihood of a landslide into the bay.
Figure 6. Retreat of glaciers at Barry Arm. September 15, 2013 is shown on the left and
August 24
th
, 2019 is shown on the right.
Let’s start by applying what we learned at Lituya Bay.
9. What kind of evidence might you look for, to indicate that a tsunami had happened before in
this area
?
If you see the water levels rising or decreasing. If you also see if the sea levels have
risen on the city .
6
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Interest in Barry Arm has risen dramatically since 2019. Read the article below to understand
why, and then answer the following questions.
Barry Arm article:
https://earthobservatory.nasa.gov/images/147345/the-specter-of-a-mega-
tsunami-in-alaska
Figure 6. Potential slide areas in Barry Arm, Alaska. Image from USGS Facebook page.
10. How does Chunli Dai study landslides?
a.
She uses high resolution imagery and machine learning to detect slope movement
b.
She maps landslides in the field
c.
She kayaks the fjords of Alaska, looking for slope scarps
11. Which of the following statements about slope movement in Barry Arm are accurate? Select
all that apply.
7
a.
If this slope failed, it would produce eleven times more energy than the slope failure at
Lituya Bay
b.
If this slope failed, it would involve more debris than Lituya Bay
c.
If this slope failed, it would produce a run up of 1,720 feet in Lituya Bay, since Lituya
Bay is the next fjord over
d.
Slope failure could produce waves hundreds of feet high in Barry Arm fjord
12. What were some of the challenges that Chunli Dai faced when she tried to convince other
scientists that her original analysis was correct, and how did she make a case for her hypothesis?
Answer in 3-5 sentences.
At first she was realizing this was going on and started to calculate all the numbers and she
thought to herself saying these numbers just don’t add up.
the volume of land that was slipping,
and the angle of the slope, we calculated that a collapse would release sixteen times more debris
and eleven times more energy than
Alaska’s 1958 Lituya Bay landslide and mega-tsunami
. She
kept using satellite date she found from years apart that they looked different and showed her
other colleagues and proved that he theories were correct.
13. You have now worked through an exercise and hopefully learned something about
megatsunami in Alaska. What is one thing that surprised you, one thing that you are still working
on understanding about this system, and one thing that you’ll take away and remember for a long
time? Answer in three sentences.
a.
One thing that surprised me was that a 7.8 magnitude earthquake set off one of the
biggest tsunamis. One thing Im still looking to understand is how does Chunli Dai get the
satellite info and how does she know its right. Last, one thing Ill take away is that
Glaciers will increase the likelihood of landslides as they melt, since their melting may
oversaturate and destabilize valley slopes.
Learn more!
Lituya bay websites:
http://www.sitnews.us/Kiffer/LituyaBay/070808_lituya_bay.html
8
https://geology.com/records/biggest-tsunami.shtml
https://earthobservatory.nasa.gov/images/147557/lituya-bays-apocalyptic-wave
https://earthquake.alaska.edu/60-years-ago-1958-earthquake-and-lituya-bay-megatsunami
Barry Arm websites:
https://dggs.alaska.gov/hazards/barry-arm-landslide.html
https://earthobservatory.nasa.gov/images/147345/the-specter-of-a-mega-tsunami-in-alaska
https://www.eurekalert.org/pub_releases/2020-11/nsfc-rgp111320.php
9
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