UCLA Exploring Volcanoes Worksheet

Part 1: Exploring VolcanoesSetup Instructions:
We will once again use Google Earth, with the plate boundaries overlay that we used in the
Week 3 lab.
1. If necessary, re-download “plate-boundaries.kmz” from the course site, or from
https://www.usgs.gov/media/files/plate-boundaries-kmz-file
2. Go to https://www.google.com/earth/ and click “Launch Earth”. (Chrome or Firefox
recommended)
3. Click the “Projects” icon on the left-hand side (3rd icon from bottom: a waypoint symbol
on top of a square).
4. In the Projects menu that appears, click “Open”, then click “Import KML file from
computer,” and select “plate-boundaries.kmz”
5. Click the “Projects” icon again to minimize the Projects menu. You should now see
Google Earth overlayed with the locations of the world’s plate boundaries. They are labeled
by color, and have arrows indicating the direction of motion of one tectonic plate relative to
another. In the upper-left corner is a legend, indicating that divergent boundaries are
shown in green, transform in red, and convergent in blue.
Navigate to Hawaii (you can type “Hawaii” into the search bar, which is accessed by
clicking the magnifying glass icon on the left-hand side of the screen). Zoom in on the big
island of Hawaii (the largest island, and the island farthest southeast). Zoom in on Mauna
Loa, a tall mountain and the world’s largest and most famous shield volcano. Note the
depression in the center (the “summit caldera”), filled with fresh, black volcanic rock.
Q1. What kind of volcanic rock is this black rock at the summit?
a. basalt
b. granite
C. rhyolite
D. Andesite
Relatively recent/fresh volcanic flows can be seen radiating outward from the summit and
flowing downhill. The fresh, black volcanic rock of these flows stand out against a
background of older, discolored rock and lush green vegetation.
Q2. Most of these flows initially flowed what directions away from the summit?
a. southwest and northeast
b. north and south
c. west and east
d. northwest and southeast
Q3. As you wave your cursor over an area in Google Earth, the elevation (above sea level)
of that point is displayed at the bottom-right of the screen. What is the approximate
elevation of the summit of Mauna Loa?
a. 2000 m
b. 3000 m
c. 4000 m
d. 5000 m
Q4. The deep ocean floor surrounding the big island of Hawaii is at a depth of about 5000
m below sea level. This means that the total height of Mauna Loa, from ocean floor to
summit, is:
a. 10,000 m
b. 6000 m
c. 8000 m
d. 9000 m
e. 7000 m
For comparison, the height of Mount Everest, the highest point on Earth, is 8848 m above
sea level.
Q5. Hawaii is far from any tectonic plate boundary. Why is there volcanic activity here?
a. Not enough data to know
b. a new plate boundary is forming here
c. Hawaii sits atop a “hotspot”
d. there used to be a plate boundary here
Each of the Hawaiian Islands formed where the big island of Hawaii is now, and was then
carried northwestward with the rest of the Pacific plate. This carried them off of their
source of magma (the term for lava underground), and so volcanic activity stopped (the big
island of Hawaii is the only volcanically active island in the chain).
Q6. Given this, which of the following islands is oldest:
a. Hawai’i
b. O’ahu
c. Kaua’i
d. Maui
Zooming back into the big island, we can see that Mauna Loa isn’t the only volcano there.
In fact, there are five. From north to south, these are: Kohala, Mauna Kea, Hualālai, Mauna
Loa, and Kīlauea. Take a moment to type each of these into the search bar and examine
them.
Q7. Which of these should be the oldest, based on Q6 and the text just before it?
a. Kohala
b. Hualālai
c. Mauna Kea
d. Mauna Loa
e. Kīlauea
Mauna Loa is not the only one of these that is active. The most active of the five is Kīlauea.
Zoom in on it, and notice the recent volcanic flows covering the hillsides downhill from it.
Now search Kalapana. This is a community downslope from Kīlauea, which was overrun
with lava flows in 1990. The neighborhood was destroyed and buried. Notice that some
residents have rebuilt atop the new flows!
Q8. Given the type of magma erupting at Hawaii, do you expect many people to have died
during these eruptions?
a. yes
b. no
Q9. Move your cursor along the volcanic rock right along the coast, just northeast of
Hakuma point. About how low do the elevations get according to Google Earth, taking your
cursor near the shore, but keeping it on the dry land side of the beach?
a. -5 m
b. -15 m
c. 0 m
d. -10 m
e. -50 m
This is obviously an error, and the source of this error is that the elevation data here have
not been updated since these flows in 1990: just a few decades ago, this part of the island
didn’t exist yet!
The big island of Hawaii is still growing, and a more dramatic growth is underway off the
southeast coast of the island. Search for Lōʻihi Seamount in the search bar. This will take
you to a volcano that is still below sea level, but is gradually growing upwards, and will
eventually breach the surface and become the youngest part of the Hawaiian Islands.
To see the oldest parts of the Hawaiian Islands, we would need to look northwest instead.
Follow the island chain northwest past Kauai and Ni’ihau, the the last of the major islands,
and notice that there is a long chain of small islands and atolls, extending all the way to
Midway Atoll (site of a famous battle in World War 2), and Kure Atoll just past it.
Q10. Zoom out so that Midway Atoll and the big island of Hawaii are both visible, then use
the ruler tool (the ruler icon on the left-hand side) to measure the distance between the
two. What is this distance?
a. 2500 km
b. 1500 km
c. 1000 km
d. 500 km
Q11. Close the pop-up window that opened with the ruler too, then use the ruler tool once
more to measure the distance between Kauai and the big Island of Hawaii. What is this
distance?
a. 500 km
b. 1000 km
c. 700 km
d. 200 km
Q12. Given that the big island of Hawaii is still forming today, and Kauai formed about 4
million years ago, about how long ago did Midway Atoll form (assuming the speed of the
Pacific Plate has not changed)?
a. 20 million years ago
b. 8 million years ago
c. 28 million years ago
d. 4 million years ago
Farther northwest, the chain continues, but these islands have sunk down beneath the
surface, and are now seamounts hidden below the waves. You can follow this chain all the
way north to the western end of the Aleutian Islands off the coast of Alaska. The chain
would continue even farther, except these older seamounts have been subducted beneath
the North America plate.
On the opposite (north) side of the convergent plate boundary from the seamount chain
are the Aleutian Islands. These islands are volcanoes related to the convergent plate
boundary, which is why they run parallel to the boundary.
Q13. Zoom in on some of these islands, and note that many have a crater at the top, and
the sort of “classic” or stereotypical shape most people think of when they think of
volcanoes. What kind of volcanoes are these?
a. lava domes
b. shield volcanoes
c. cinder cones
d. composite volcanoes (stratovolcanoes)
e. calderas
Follow the plate boundary eastward, then southward, until you are looking at the
convergent plate boundary off the coast of Oregon and Washington. Because this is an
ocean-continent convergent boundary, instead of an ocean-ocean convergent boundary
like the Aleutian Islands, this plate boundary forms a volcanic mountain range, rather than
a chain of volcanic islands. This mountain range is the Cascades, and it is inland of and
parallel to the convergent boundary. Even when zoomed far out, you should see little
circular bits of white in the satellite image, in a mountain range dominated by green. The
green is forest, and the white is snow and ice: these white circles are snow-capped
volcanoes.
Search for “Mount St. Helens”, and examine this volcano.
Q14. What kind of volcano is this?
a. shield volcano
b. cinder cone
c. composite volcano (stratovolcano)
d. caldera
e. lava dome
Q15. Notice that, where the rock shows through the snow, it is more of a gray color, as
opposed to the black color of the volcanic rocks in Hawaii. What kind of rock is this?
a. diorite
b. granite
c. basalt
d. rhyolite
e. andesite
Q16. How does the hazard posed by volcanoes such as this compare to those posed by
the volcanoes we looked at in Hawaii?
a. the Cascades volcanoes are more hazardous than the Hawaiian volcanoes
b. the Cascades volcanoes are less hazardous than the Hawaiian volcanoes
c. the hazards are comparable
Q17. Mount St. Helens had a famous eruption in 1980, which blew out the side of the
mountain and inundated the surrounding countryside with pyroclastic material. Examining
the volcano in Google Earth (be sure to tilt your view so that you can see it in 3-D), which
side of the volcano blew out?
a. the west side
b. the south side
c. the north side
d. the east side
Q18. Note the wide area that was devastated by this eruption and has yet to recover: the
ground is dramatically barer than the rest of the landscape nearby, which is heavily
forested (there are also some patches in the area that have been cleared by logging
operations, which is unrelated). This region of greatest devastation extends from Mount
St. Helens all the way to the slopes north of Coldwater Lake. Zoom way in on these slopes.
What do you see?
a. patchy vegetation and dead trees on the ground
b. dense forest
c.a complete lack of vegetation
Q19. Use the ruler tool to measure the distance from the center of Mount St. Helens to this
ridge. In the little pop-up window, use the little arrow next to the reported measurement to
change the units to “miles”.
a. 9 miles
b. 3 miles
c. 12 miles
d. 6 miles
This is the “direct blast zone” discussed in this section of the Wikipedia article on the 1980
eruption of Mount St. Helens. Have a quick read through this section now:
https://en.wikipedia.org/wiki/1980_eruption_of_Mount_St._Helens#Pyroclastic_flows
Q20. The article goes on to consider the “channelized blast zone.” This a larger zone, in
which the devastation was still great, but confined to the bottoms of valleys and channels,
which the pyroclastic material was flowing down and contained within due to gravity.
According to this article, the channelized blast zone extended out to distances as far as:
a. 19 miles
b. 15 miles
c. 12 miles
d. 8 miles
Q21. Speaking of lakes, look at Spirit Lake, also near Mount St. Helens, and notice that the
northeastern end of the lake has a strange texture in the satellite image. Zoom way in on
this area, and examine it (the image is somewhat clearer towards the northeast end of this
textured part of the lake than at the southwest end). What is the cause of this texture?
a. waves/choppy water from winds blowing through the bare valleys
b. pyroclastic debris that washes down off the hillsides and clouds the water
c. lava flows poking through the lake level
d. trees killed in the eruption and floating on the lake
Now zoom out and look a little ways northeast, where you should see Mount Rainier (you
could also search for it in the search bar). This is another volcano like Mount St. Helens,
and is considered the single greatest volcanic hazard in the United States, because it is
close to the Seattle-Tacoma metropolitan area.
Q22. Using the ruler tool, about how far is it from the summit of Mount Rainier to the
closest edge of the suburbs to the northwest?
a. 15 miles
b. 45 miles
c. 5 miles
d. 25 miles
Q23. How does this distance compare to farthest extent of the channelized blast zone of
the Mount St. Helens eruption (Q21)?
a. It is a few miles greater
b. It is more than twice as far
c. It is less than half as far
d. It is a few miles less
Greater than the risk of pyroclastic flows is the risk posed by lahars. Lahars are deadly
mudflows that occur when snow and ice is suddenly melted during a volcanic eruption,
and flows downhill violently, mixed with dirt and debris. The white on Mount Rainier is not
just snow, but also substantial glaciers, which generate lahars during eruptions. The likely
extent of lahars during an eruption of Mount Rainier are shown here:
https://www.usgs.gov/volcanoes/mount-rainier/volcanic-hazards-mount-rainier
Q24. These lahars flow downhill down canyons and channels: what is the dominant
direction that lahars from Mount Rainier flow?
a. southwest
b. northwest
c. northeast
d. southeast
Proceeding south along the Cascades, we eventually come to Crater Lake. Like Mount St.
Helens and Mount Rainier, this is protected as part of the National Park system, and you
can go visit and explore these places if you like. Unlike the previous two locations,
however, Crater Lake is a massive depression in the ground (which has filled with water),
rather than a towering mountain.
Q25. What kind of volcano or volcanic feature is Crater Lake today?
a. shield volcano
b. cinder cone
c. caldera
d. composite volcano (stratovolcano)
e. lava dome
Q26. What kind of volcano was here before crater lake formed?
a. composite volcano (stratovolcano)
b. shield volcano
c. cinder cone
d. lava dome
e. caldera
Look at Wizard Island, a volcano which has grown within the lake after the crater formed.
Note the black color of the volcano where it is bare of vegetation, and the black color of the
lava flows along the shore on the northwest side of the island.
Q27. What kind of rock is this?
a. andesite
b. rhyolite
c. pumice
d. basalt
e. granite
This volcano is not nearly as large as Mount St. Helens or Mount Rainier, but it has a
comparable distinct shape: a conical volcano with a crater at the top. Note also that the
slopes look like they are made of loose material, rather than solid rock.
Q28. What kind of volcano is Wizard Island?
a. cinder cone
b. lava dome
c. caldera
d. composite volcano (stratovolcano)
e. shield volcano
California has some active volcanism, largely in the eastern part of the state, where the
North America plate is thinning, much like at a divergent plate boundary. Mammoth
Mountain poses a particularly large hazard, since a community sits right on its slopes.
Search for Panum Crater, which will take you to a volcano on the southern shore of Mono
Lake.
Q29. Note that the volcanic rock here is lighter in color than any we’ve seen so far. What
kind of rock is this?
a. basalt
b. granite
c. rhyolite
d. andesite
Q30. This volcano is also a different shape than any we’ve seen so far. There is no crater in
the center: rather, it is a large mound or blob of cooled lava. What kind of volcano is this?
a. cinder cone
b. composite volcano (stratovolcano)
c. caldera
d. shield volcano
e. lava dome
Q31. Closer to UCLA is the Lavic Lake volcanic field. Search for this, and note the volcanic
flows here, which stand out in stark contrast to the desert sand around it. What kind of
rock makes up these lava flows?
a. andesite
b. basalt
c. granite
d. rhyolite
Return to the plate boundary in southern California, then follow this plate boundary south
into the Gulf of California (Sea of Cortez), where there are segments of divergent plate
boundaries (which are what have formed the gulf). Most of the volcanism at divergent
plate boundaries is usually underwater, but some volcanoes here can be seen at the
surface. Search for “Isla Tortuga, Mexico” (not to be confused with Tortuga Island of pirate
fame, which is in Haiti). This is a shield volcano. Note the gentle slopes and the depression
in the center.
To see more divergent plate boundary volcanoes on land, we can go to Iceland, where the
Mid-Atlantic Ridge (the divergent plate boundary in the Atlantic) rises above sea level
where it sits atop a hotspot. Search for Trölladyngja, a volcano in Iceland sitting right
along the plate boundary.
Q32. What kind of volcano is this?
a. composite volcano (stratovolcano)
b. caldera
c. lava dome
d. shield volcano
e. cinder cone
Part 3: Chemistry of Volcanic Rocks
For this last part of the lab, let’s consider why different volcanic rocks might have different
chemistry. We talked early in the class about efforts to make science more accessible and
reproducible, and how part of this effort involves databases accessible by all, so that
anyone can analyze data themselves and draw their own conclusions. A great example of
this in Earth sciences is the GEOROC database, which compiles information on the
chemistry of igneous rocks from all over the world. The database is here, and can be
queried by geologic setting, geographic location, details of chemistry, etc.:
http://georoc.mpch-mainz.gwdg.de/georoc/
Using this site, I downloaded data on the chemistry of volcanic rocks in the Rio Grande rift,
and the Aegean Sea.
The Rio Grande rift is an area centered in New Mexico that began to rift apart about 35
million years ago (it has not developed enough to be shown as a divergent plate boundary
on the Google Earth plate boundaries map, but is tectonically similar to the East African rift
or other young, developing divergent plate boundaries).
The Aegean Sea is on the over-riding plate of a convergent plate boundary in the
Mediterranean region between Africa, Eurasia, and Arabia (this convergent plate boundary
does show up on the Google Earth map).
Below are plots showing two of the more common components in rocks, calcium (CaO)
and potassium (K2O), plotted against silica (SiO2), the most abundant component of most
rocks. Notice that the chemistry of the volcanic rocks of the Rio Grande rift and of the
Aegean Sea are rather different. (note also that the scales of the plots are not the same).
Q34. What are the conceivable reasons why the chemistry of the volcanic rocks in these
two regions is different?
Once again, we find ourselves following the scientific method! We have made an
observation (the chemistry of the volcanic rocks in these two areas is different), posed a
question (why is the chemistry different?), and, in Q34, you have proposed some
hypotheses that could explain this.
Q35. The next step is to make testable predictions from your hypotheses. For the
hypotheses you chose, how would you predict the chemistry of volcanic rocks from
elsewhere in the world would compare to those of the Rio Grande rift and the Aegean?
Specifically, how would you predict the chemistry of volcanic rocks from the Cascade
range and from the Red Sea would compare?
Q36. The next step is to test your predictions. Use the provided spreadsheets (which were
downloaded from the GEOROC database) of chemistry data for the Cascade range and the
Red Sea to make the same types of plots (CaO vs. SiO2 and K2O vs. SiO2). Your TA will
demonstrate how to do this, and you can ask if you have any questions or encounter any
difficulties. You can make these plots in Google Sheets
Q37. How do your plots compare with those above? Which regions are most similar to one
another in their chemistry? (From question 34)
You’ve just used thousands of actual scientific measurements, compiled from hundreds of
different scientific studies over the past 80 years! (scroll down through the spreadsheets
to appreciate just how much information there is there). Professional scientists will
frequently draw from this database just as we’ve done to investigate various questions
relating to igneous rocks.
Q38. If you were going to investigate this question further, what might your next step be?

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