Copy of Lab 05 Volcanoes
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106
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Geology
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Dec 6, 2023
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GEOSCI/ENVIR ST-106: Environmental Geology
Lab 5: Measuring Volcanoes and Eruption Hazards
Volcano: A vent in the crust of the Earth from which eruptions of molten rock, hot rock
fragments, and hot gases can occur
Assignment Overview:
The effects of
plate tectonics can have major impacts on
human life, in the form of volcanic activity
and earthquakes. Geologists collect a
variety of data about historical
earthquakes and volcanoes in order to
understand future risks. In this lab, you
will use data from maps and seismic
stations, along with simple computations,
to explore these hazards.
IMPORTANT NOTES:
1.
Download the .KML dataset
associated with this lab, which is linked
on the course Canvas page. All instructions below reference commands used in Google Earth
Pro, which is
highly suggested
for this lab.
Submission:
To submit the assignment on Canvas, use the following steps:
1.
In Google Docs, generate a PDF: File → Download as → PDF Document
2.
In Google Docs, use Share → Get Shareable Link, and copy the link address
3.
In Canvas, upload your PDF to the assignment, and paste the link address to your
Google Doc in the assignment comments.
1
Assignment Questions and Responses
Instructions:
Fill out each red highlighted field (_________), according to the question
instructions.
Volcanic Eruptions: Mt. St. Helens (1980)
In the KML file associated with this lab, you have been given a set of digital maps including a
1980 USGS topo (topographic) map, which mapped the land surface
before
the 1980 Mt. St.
Helens eruption. Try turning these topographic maps on and off. By exploring in Google Earth,
you should see that the Mt. St. Helens volcano juts up sharply against surrounding topography,
which doesn’t go much above 4,400 feet. (Note: The elevations displayed on this contour map
are different from the elevations that Google Earth would display natively if you removed the
topographic map. Google Earth’s elevation map is based on the
current
elevation of Mt. St.
Helens
Tips:
If you have not looked at a topo map before, these tips may help you interpret what you
see:
●
The red lines circling the volcano are “contour lines” showing locations with the same
elevation.
●
Lighter contour lines are not labeled, but are equally spaced in terms of elevation difference
between the thicker (labelled) contour lines
1.
Estimating Volcano Slope:
Using the line tool in Google Earth, draw a line from the
original,
1980
(topographically mapped) peak of Mt. St. Helens to the north, until you reach the 4,400
foot contour line on the map. What is the average slope of the volcano along this line? (Hint:
Slope = elevation change in miles / lateral distance in miles. Remember that there are 5,280
feet per mile). Describe briefly how you arrived at this result (2 points).
(9677-4400)/12371.17 ft= 5277/12371.17= 0.99/2.34=
0.427
The highest elevation is 9677 feet. The base elevation is 4400, so the elevation of the volcano is
9677-4400 which is 5277 ft or 0.99mi. The lateral distance was 12371.17 or 2.34 mi, which we
found by drawing a line on the map. You divide the elevation by the lateral distance to get 0.427
as the slope.
2.
Estimating Above-ground Volcano Volume:
Using the polygon tool in Google Earth, trace a
rough outline of the 4,400 elevation contour on the topographic map, which represents an
approximate “background” elevation for the region. This represents the area of the “base” of the
volcano. Then, calculate the total above-ground volume of the volcano (in cubic miles) using the
following formula (4 points):
𝑉
????
= (𝐴
????
× ℎ)/3
2
Paste a picture of your polygon representing the area of the base here (you may want to use
“Absolute elevations” and transparency to help with visualization of this polygon):
_PASTE PICTURE HERE_
=
__21 mi^2_______
𝐴
????
(?𝑖
2
)
(peak elevation above background, converted to miles)
=
_____0.999 mi____
ℎ (?𝑖)
=
____6.996 mi^3_____
𝑉
????
(?𝑖
3
)
3.
Estimating Erupted Volcano Volume:
If you remove the old topo map from Google Earth
(un-check the box associated with the topographic maps from the menu on the left), you will see
how drastically the shape of Mt. St. Helens has changed. Fill in the following values in order to
estimate the volume of the “cone” of material that was actually erupted (3 points).
(use the provided “Crater Outline”): ____1.57 mi^2____
𝐴
??????
(?𝑖
2
)
3
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(elevation of
original 1980
peak above
current
crater rim, converted to miles):
ℎ
???𝑘
(?𝑖)
___1980 peak: 0.507 mi______
(Note: for this value, you should choose a rough average of the crater rim elevation, ignoring the
complication of the “blow out” to the north.
=
__0.265 mi^3_______
𝑉
???????
(?𝑖
3
)
4. Impact of the Eruption
: The Seattle metropolitan area is roughly 84 mi
2
(square miles). If all of
the rock erupted from Mt. St. Helens (as calculated in the previous question) had landed on
Seattle, how deep would that rock layer be, in feet? Give a brief description of computations for
how you got this answer (2 points).
(Hint: Dividing the volume of rock (cubic miles) by the area over which it fell (in square miles) will
give you a depth in miles. Remember to convert this back to feet!)
16.678 ft.
The volume calculated of rock from the eruption is 0.265mi^3 and the area of the city is 84
mi^2. So you divide 0.265 by 84 to find the depth everything would be covered in miles, then
multiply by 5280 to find how deep it would be covered in rock in feet. Which is 16.68 ft.
Highway 504, North of Mt. St. Helens, post-eruption. (USGS)
Comparing Volcano Size
5.
Shield volcano vs. stratovolcano topography
: Hawaii’s Big Island has the largest volcanoes in
the United States. Unlike Mt. St. Helens and the other stratovolcanoes in the Cascades, these
are shield volcanoes. The largest volcano on the Big Island is Mauna Loa. Note that this
volcano is so big that much of its slope is under water!
4
In the Google Earth file, open the “Mauna Loa” folder and investigate the two transects using
the “Show Elevation Profile” option for lines. Even though Mauna Loa is far from a perfect
cylinder, we can still apply formulas above to approximate the volume of the Mauna Loa
volcano.
a.
Using the transects, estimate the following values. Paste a picture of the transect you
used, highlighting the points you used to determine these values (4 points):
h1: Peak elevation (to the nearest 1,000ft):
____13000 ft_____
h2: Base elevation (to the nearest 1,000ft):
____-12000 ft_____
h = h1 - h2:
____25000 ft_____
r: Radius of volcano (to nearest mile):
____32 mi_____
_PASTE PICTURE HERE_
b.
Next, calculate an approximate volume of the Mauna Loa volcano using the same
formula as before (2 points):
𝑉
????
= (𝐴
????
× ℎ)/3
5
And, approximate the area of the base of the volcano as
𝐴
????
= π?
2
Remember to ensure you are using consistent units!!
Approximate volume of Mauna Loa (in cubic miles):
_5183.54 mi^3__
c.
How many times bigger is Mauna Loa’s above-sea-level volume than Mt. St. Helens’
volume? (1 points)
____Mt. St. Helens is 740.5 times bigger. _____
6
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