Download LAB 4 - W.W. Norton

Environmental Geology 103L
Name _____________________________
_____________________________
_____________________________
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Volcanoes and Volcanic Hazards
NOTE: The Contents page of your lab manual has a separate section called “Earth.” This section contains
additional chapters that come after the lab manual chapters, and are excerpts of chapters from the
accompanying textbook, “Earth.” The authors put chapters pertaining to lab in the back of the manual, knowing
that not all students are asked to buy the textbook. Chapter 9, on Volcanism, starts on page 272 IN THE
BACK of the manual. Please ask your TA or instructor for assistance if you are confused; you will need this
section many times over the course of 103 and 105.
PART 1: Intro to Volcanoes and volcano types
Use the first three slides on the following website to learn about volcanoes and answer the following questions:
http://nationalgeographic.org/encyclopedia/magma/
1. What is magma? ___________________________________________________
2. What is the difference between magma and lava?
____________________________________________________________________________
3. Where is magma formed? ________________________________________________________
4. Look at the third slide: in which three locations does magma “well up” (rise to the surface)?
____________________________________________________________________________
We are going to explore two main volcano types in lab today: shield and composite (also called
stratovolcanoes). Use page 284 in the back of your manual to answer the following:
5. What is the main shape of a shield volcano? __________________________________________
6. What is its general eruption style? __________________________________________________
7. What is the main shape of a composite or stratovolcano? _______________________________
8. What is its general eruption style? __________________________________________________
9. Make a general sketch of each one below:
Shield:
Composite:
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PART 2: Where are volcanoes located?
Pages 36-49 and your copy of Lab 1 will help answer the following questions.
A. Plate Tectonics and Volcanism
1. Using your knowledge from the Plate Tectonics lab, answer whether or not the following plate boundary
types have volcanoes:
a. Divergent plate boundaries: _______
b. Continental-Continental Convergent plate boundaries: _______
c. Continental-Oceanic Convergent plate boundaries: _______
d. Oceanic-Oceanic Convergent plate boundaries: _______
e. Transform plate boundaries: _______
2. Turn to Figure 9.17 in the back section of your lab manual on page 294. Are most of the volcanoes
located along a plate boundary? __________
3. Recall that subduction leads to volcano formation, but subduction is not necessary to create a volcano.
Which plate boundary (ies) above has (have) volcanoes but not subduction?
_____________________________________________________________________________
4. Shield and composite volcanoes are going to be the focus for this lab. However, there is an eruption of
lava at divergent plate boundaries as well. Explore the following link and answer the questions below:
http://www.geology.sdsu.edu/how_volcanoes_work/seafloorvol_page.html
a. What feature is created at divergent plate boundaries, ridges or trenches? (circle one)
b. How does that feature form?
____________________________________________________________________________
____________________________________________________________________________
c. What type of eruption is usually seen at divergent boundaries? __________________________
d. Are these violent or gentle eruptions? (circle one)
B. Intraplate Volcanoes
5. There are clusters of volcanoes on the map not located near a plate boundary, such as Hawaii. What
are they called?
_________________________________________________________________________________
6. How does a hotspot form (see pages 295-6 in the back of your manual and check out this video):
https://www.youtube.com/watch?v=jG-Sy0y08GM?
(Here is another great hotspot video: http://www.pbslearningmedia.org/resource/ess05.sci.ess.earthsys.hawaii/plate-tectonics-thehawaiian-archipelago/ )
_____________________________________________________________________________________
_____________________________________________________________________________________
7. There are five hotspots on the map on page 294 in the back of your manual. Find the Yellowstone and
Hawaii hotspots (indicated with an “H,” and note on which type of crust are they located (oceanic or
continental):
a. Hawaii Hotspot: Crust type? ________________________
b. Yellowstone hotspot: Crust type? ________________________
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PART 3: What determines a Volcano’s shape and eruption style?
Exploring Igneous Rocks
Using pages 86-88 of your lab manual, answer the following:
1. Name the three classes of rocks and briefly explain how they are each formed:
a. ________________________________________________________________________
b. ________________________________________________________________________
c. ________________________________________________________________________
2. Which class which would you expect to find at volcanoes? _______________________________
3. Figure 4.1 shows the rock cycle. Which rock class(es) can become igneous rocks?
_____________________________________________________________________________
Remove Specimens # 2, 3, 4, 5, 8, 9, 11, 12 from the ROCK drawer.
Use pages 116-118, especially Figure 5.7 (p.118), to answer the following questions. Note that Figure
5.7a lists mineral composition and 5.7b lists texture.
A. COMPOSITION of igneous rocks:
1. Composition tells us which minerals are present in which igneous rocks, and it is one of the two ways in
which igneous rocks are classified. Igneous rocks have four major compositional groups. Name them in
order from most Silica content to least:
a. ________________________ MOST SILICA / LEAST IRON and MAGNESIUM
b. ________________________
c. ________________________
d. ________________________ LEAST SILICA / MOST IRON and MAGNESIUM
2. We are going to focus on three compositions: felsic, intermediate, and mafic. So why do we care?
a. Rocks with more silica are more viscous. Define viscosity (p 275 in the BACK of your manual):
________________________________________________________________________
b. What is more viscous: water or maple syrup? ___________________________________
3. Do you think rocks with a high silica content, which are more viscous, produce more explosive or less
explosive eruptions? WHY?
__________________________________________________________________________________
__________________________________________________________________________________
4. Do you hypothesize that a violent eruption would cause a tall and steep volcano (composite) or one
with gentle slopes (shield)? ____________________________________________________
5. In general, continental crust is made up of more silica-rich rocks, and oceanic crust is made up of more
mafic-rich rocks. Name if each of the following settings would be explosive, or not very explosive:
a. Continental-Oceanic convergence: ________________________________________________
b. A hot spot underneath continental crust: ____________________________________________
c. A hot spot underneath oceanic crust: __________________________________________
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d. Two oceanic plates diverging: _______________________________________________
e.
NOTE: oceanic-oceanic convergence probably seems to you as if it would produce non-violent eruptions. But
because the sediment that collects over time on the subducting plate has a high content of dissolved water and CO2,
they can actually be quite violent.
6. Complete the table below:
Composition Name
Silica Content:
High, Intermediate,
or Low?
Viscosity:
High, Intermediate,
or Low?
Eruption:
Violent or Gentle?
Crust Type:
Oceanic or
Continental?
Felsic
Intermediate
Mafic
7. You can USUALLY see the composition of a rock by looking at the color of the minerals present (you
will see an exception to this today!).
Separate the rocks you have into the three piles listed below, a-c, and list the specimen #s that
correspond to each pile (PUT 4 & 9 ASIDE; WE WILL USE THEM LATER):
a. Felsic rocks: MAINLY pink and white minerals: __________________________________
b. Intermediate rocks: MAINLY gray minerals: _____________________________________
c. Mafic rocks: MAINLY black, gray and green minerals: _____________________________
d. Keep these piles separated as you answer the following questions.
B. TEXTURE of igneous rocks: (Pages 116-118)
8. Igneous rocks are classified by composition (or mineral content), which you explored above, and what
other characteristic? _____________________________________________________________
9. We will be focusing on two different main textures, coarse-grained and fine-grained:
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Coarse-grained means you can visibly see crystals
Fine-grained means you can’t, and that the rock has a generally homogenous (same)
appearance.
Answer the following using your three composition piles. Continue to exclude #s 4 and 9.
a. You are going to separate each of the three composition piles into two piles. From each
composition pile you will have one rock that you think is coarse-grained and one that you think
is fine-grained.
b. Which rocks #s do you think are coarse-grained, or phaneritic? _____________________
c. Which rock #s do you think are fine-grained, or aphanitic? _________________________
10. Crystals can take a while to form, or nucleate. Would you hypothesize that fine-grained textures cooled
quickly or slowly? ________________________________________________________________
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11. If an eruption happens suddenly, the magma can be ejected quickly above ground and the lava then
cools and forms a rock. Conversely, if a magma chamber slowly rises beneath the ground the magma
can cool below ground. Would you hypothesize that coarse-grained textured igneous rocks usually form
above or below ground? ____________________________________________________________
12. Therefore, answer the following (circle one of each):
Aphanitic, fine-grained rocks:
a. Cool SLOWLY or QUICKLY
b. Cool ABOVE or BELOW ground
Phaneritic, coarse-grained rocks:
c. Cool SLOWLY or QUICKLY
d. Cool ABOVE or BELOW ground
13. Rock #s 4 and 9 have different textures. Feel them both and determine which specimen # goes with the
following textures:
a. Vesicular: ________
b. Glassy: ________
14. The glassy rock has a high silica content, despite its dark color. A high silica content makes the
composition of rock #9 Felsic or Mafic? (circle one)
15. Look at the table below and see if you can place a rock in each box using your composition and texture
piles. Using Figure 5.7 in your manual, determine the names of the rocks you have using the word bank
below, and write the rock name and specimen # in the appropriate box. (Don’t worry about volcano
type right now)
16. VERY IMPORTANT: **The library has the same samples as the lab. You check them out from the circulation desk. In order to
study, you need to know which rock corresponds to which specimen #. You are responsible for being able to visually identify
each rock, and for knowing its corresponding characteristics and name.
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COMPOSITION
Fast cooling rate
Slow cooling rate
Fast cooling rate
Fast cooling rate
Vesicular
Glassy
COARSE-GRAINED
(Phaneritic)
FINE-GRAINED
(Aphanitic)
TEXTURE
FELSIC
(high silica content)
Rock name:
Rock name:
MAFIC
(low silica content)
Rock name:
Specimen #:
Specimen #:
Specimen #:
Volcano type:
Volcano type:
Volcano type:
Rock name:
Rock name:
Rock name:
Specimen #:
Specimen #:
Specimen #:
Volcano type:
Volcano type:
Volcano type:
INTERMEDIATE
Rock name:
Specimen #:
Volcano type:
Rock name:
Specimen #:
Volcano type:
WORD BANK FOR IGNEOUS ROCK ID CHART:
* Basalt *Granite *Andesite *Gabbro *Rhyolite *Diorite * Pumice * Obsidian
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C. EXPLORING volcano shape and viscosity in Google Earth
Hawaii Volcanoes
Watch this video of an eruption of Kilauea, the most currently active volcano in the Hawaiian island chain.
https://www.youtube.com/watch?v=90XFpu-65JY
17. Would you describe the lava as having high or low viscosity? ___________________________
18. What does this tell you about the silica content of this lava?
_________________________________________________________________________
Next, we will be using the Google Earth file, Dynamic Earth. It will need to be downloaded to your computer from OAKS.
DO NOT OPEN THE FILE.
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Open Google Earth.
Go to File: Open and navigate to where you downloaded the Dynamic Earth file and open it.
Under Places, click on the down arrow next to the name of the file to open the subfolders.
Scroll down until you locate the Plate Boundary Model folder and click the down arrow to view the subfolders.
Click the box next to the Plate Boundaries folder to open it. The plate boundaries should appear on the map of
Earth.
Scroll down again until you locate the Volcanoes of the World file. Click the down arrow next to the name of the
file to open the subfolders
Scroll down the file until you locate the file named: Hawaii and Pacific Ocean. Click on the down arrow to open
the subfolders.
Scroll down until you locate Hawaiian Islands and click on the box to open the files.
Scroll down until you locate Mauna Loa. Double click on Mauna Loa to zoom to that location. This will also open
a text file containing information about Mauna Loa. Spend some time zooming in and out and exploring the
Mauna Loa volcano.
Scroll down until you locate Kilauea. Double click on Kilauea to zoom to that location. Repeat the procedure
above, zooming in and out to learn more about this volcano.
Leave this file open on Google Earth; you will be using it again on the next section.
19. Describe the basic shape of Mauna Loa/Kilauea volcano:
_____________________________________________________________________________
20. How does the silica content and viscosity affect the shape of the volcano?
__________________________________________________________________________________
Cascade Volcanoes (Mt. St. Helens and Mt. Rainier)
Click on the link below to watch a video of the 1980 eruption of Mt. St. Helens, a volcano in the Cascade chain
of volcanoes in western Washington and Oregon, along with Mt. Rainier.
https://www.youtube.com/watch?v=-H_HZVY1tT4
22. How would you describe the 1980 eruption of Mt. St Helens in terms of viscosity?
____________________________________________________________________________
23. What does mean about the silica content and gas content of the magma? _________________
Go Back to the Learn about Plate Tectonics file in Google Earth.
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In the Volcanoes file, scroll down the file until you locate the file named: Canada and Western USA. Click on
the down arrow to view the subfolders.
Scroll down until you locate USA (Washington) and open that file by checking the box.
Scroll down until you locate Rainier. Double click on Rainier to zoom to that location. This will also open a text file
containing information about Mt. Rainier. Spend some time zooming in and out and exploring the Rainier
volcano. After you have had time to explore Rainier, go back to the Places file located on the left side of the
monitor screen.
Scroll down until you locate St Helen’s. Double click on St Helen’s to zoom to that location. Repeat the
procedure above, zooming in and out to learn more about this volcano.
20.Describe the basic shape of Mt. Rainier and Mt. St. Helens (flat and wide or tall and skinny):
_______________________________________________________________________________
21.How does the silica content and viscosity affect the shape of these volcanoes?
_______________________________________________________________________________
D. Volcano type and igneous rocks
So can we tell whether a volcano is a shield or composite based on the volcano’s rocks? Let’s review what you
have learned (circle one of each option below):
22. A SHIELD volcano is:
a. TALL/SKINNY or
FLAT/WIDE
b. This shape is created by a GENTLE/EFFUSIVE or EXPLOSIVE eruption
c. This is because the explosion is produced by HIGH or LOW viscosity lava
d. So therefore composition of the rocks found at this volcano type would be
FELSIC/INTERMEDIATE or MAFIC
e. Found in which of the following settings:
i. Divergent Plate Boundaries
ii. Hotspot underneath oceanic crust
iii. Hotspot underneath continental crust
iv. Convergent plate boundaries (where subduction is present)
23. A COMPOSITE volcano is:
a. TALL/SKINNY or FLAT/WIDE
b. This shape is created by a GENTLE/EFFUSIVE or EXPLOSIVE eruption
c. This is because the explosion is produced by HIGH or LOW viscosity lava
d. So therefore composition of the rocks found at this volcano type would be
FELSIC/INTERMEDIATE or MAFIC
e. Found in which of the following settings:
i.
Divergent Plate Boundaries
ii.
Hotspot underneath oceanic crust
iii.
Hotspot underneath continental crust
iv.
Convergent plate boundaries (where subduction is present)
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24. Now in the table where you matched rock names to specimen numbers on page 6, determine whether
each igneous rock is associated with a shield or composite volcano. Page 129 of your manual will help.
PART 4: Why do we care? Exploring volcanic hazards
Note: This is not an exhaustive list of hazards from volcanoes. Your manual goes into more detail on page 299 (in the
back), such as gases and landslides.
Watch this video about pyroclastic flows and answer the following questions: http://www.discovery.com/tvshows/discovery-presents/videos/ultimate-guide-to-volcanoes-pyroclastic-flow/
1.
2.
3.
4.
Is this hazard associated with more VIOLENT or GENTLE (relatively) eruptions? (circle one)
Does this type of hazard seem to have HIGH or LOW viscosity?
Would you except to see FELSIC TO INTERMEDIATE rocks, or MAFIC rocks?
At which type of volcano would you except to see a pyroclastic flow, SHIELD or COMPOSITE?
Watch this video about lava flows and answer the following questions: http://www.discovery.com/tvshows/discovery-presents/videos/understanding-volcanoes-lava-flow/
5.
6.
7.
8.
Is this hazard associated with more VIOLENT or GENTLE (relatively) eruptions?
Does this type of hazard seem to have HIGH or LOW viscosity?
Would you except to see FELSIC TO INTERMEDIATE rocks, or MAFIC rocks?
At which type of volcano would you except to see lava flows, SHIELD or COMPOSITE?
*NOTE: Lava flows are associated with both shield and composite volcanoes, however Lava flows are the MAIN hazard at
shield volcanoes, whereas the more explosive hazards are the main threats at composite volcanoes.
Watch this video about ash and the Mt. Pinatubo eruption, and answer the following questions:
http://www.pbslearningmedia.org/resource/ess05.sci.ess.earthsys.lahar/mount-pinatubo-the-aftermath-of-a-volcaniceruption/
9. Is this hazard associated with VIOLENT or GENTLE (relatively) eruptions?
10. Does this type of hazard seem to have HIGH or LOW viscosity?
11. Would you except to see FELSIC TO INTERMEDIATE rocks, or MAFIC rocks?
12. Which rock do they mention in the video as “raining down?” __________________________
13. At which type of volcano would you except to see pyroclastic flows and huge volumes of ash fall,
SHIELD or COMPOSITE?
Explore this page and watch the video about lahars and and answer the following questions:
http://blogs.agu.org/landslideblog/the-raw-power-of-the-lahar-a-volcanic-landslide-a-new-video-of-three-lahars-from-japan/
Page 299 in the BACK of your lab manual will also help!
14. What is a lahar made of? _____________________________________________________
15. How fast can they travel? __________________
16. Is this hazard associated with more violent or gentle (relatively) eruptions?
17. Would you except to felsic to intermediate rocks, or mafic rocks?
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Now, YOU will determine how violent or effusive the volcanic eruption by changing the amounts of gas
and silica composition in the magmas to create different types of volcanoes and eruptions.
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Go to this website: http://www.seeker.com/volcano-explorer-1817958198.html
o If the link is not working google “seeker volcano explorer.” Also, try a different browser, like
Firefox.
Open the ‘Virtual Volcano’ link to build your own volcano.
In the table below, summarize what happens when you vary the viscosity and gas concentrations in the
magma (by moving the arrows for each at the bottom and then clicking “Set Conditions”).
In the table below, describe the type of volcano that forms, the type of eruption created the types of
hazards generated, etc.
18. Record your observations in the chart below.
Viscosity
Gas Content
(High OR Low)
High
High
High
Low
Low
Low
Low
High
Type of Eruption
(Explosive/violent,
effusive/gentle,
etc.)
Hazards
(list all shown
with each
eruption)
Type of Volcano
19. Which factor had more of an effect on the type of volcano formed: viscosity or gas content? (circle
one)
20. Increasing the silica content of a magma increases its viscosity. Based on your results in the chart
above:
a. Low silica magma leads to MORE EXPLOSIVE or MORE EFFUSIVE eruptions (circle one)
b. High silica magma leads to MORE EXPLOSIVE or MORE EFFUSIVE eruptions (circle one)
21. What conditions are required for the most explosive types of eruptions?
__________________________________________________________________________
22. Which hazards would you expect to see at Kilauea?
__________________________________________________________________________
23. Which hazards would you expect to see at Mt. Rainier?
__________________________________________________________________________
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Case studies and Historic Eruptions:
24. On the west coast of South America, the oceanic Nazca plate is colliding with the continental edge
of the South American plate. Answer the following questions based on this information and what you
have learned so far in lab:
b. What type of plate boundary is this? _________________________________________
c. Would you expect to see subduction at this boundary? _______
d. Would you expect to see volcanoes at this boundary? _________
e. If so, what type? ________________________________
f.
Which igneous rocks would be present, felsic/intermediate or mafic? (circle one)
g. Would you expect a volcano in this location to have high or low viscosity? (circle one)
h. What hazards would you expect to see at this volcano?
_____________________________________________________________________
i.
Which of the two volcanoes below do you think you would find there, LEFT or RIGHT?
27. Yellowstone National Park is located in WY, ID, and MT. Answer the following:
http://www.yellowstonepark.com/how-the-yellowstone-caldera-formed/
a. Is Yellowstone located near a plate boundary? _________
b. What is the term for the location of a volcano that is not on a plate boundary? (Think Hawaii!)
__________________________________
c. The Yellowstone hotspot is located under: Oceanic or Continental crust? (circle one)
d. Therefore, the crust will be more: Mafic or Intermediate/felsic in composition?
e. What hazards would you expect to see there?
______________________________________________________________________
f.
Yellowstone has had three major eruptions in the last 2 million years. The last eruption was
640,00 years ago and was 2500 times larger than the one at Mt. St. Helens in 1980. What do
you think would happen if another large eruption occurred again soon?
______________________________________________________________________
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g. At the very bottom of this site you will see a map showing the path of the Yellowstone hotspot.
Click on the image to enlarge it and answer h-j below:
https://volcanoes.usgs.gov/volcanoes/yellowstone/yellowstone_geo_hist_52.html
h. If the top of the map is north, where are the oldest volcanic eruptions from the Yellowstone
hotspot? (name the cardinal direction)? _________
i.
Where are the youngest eruptions? _______
j.
What does this tell you about the direction of plate motion of the North American plate?
______________________________________________________________________
Use the packet titled “Caribbean Volcanoes” to answer the following questions
28. Locate the map that shows the volcanoes in the Lesser Antilles and West Indies. You will see the
Atlantic Plate on the east meeting the Caribbean plate to the west of it. Answer the following:
a. What type of plate boundary is this? (Be specific! What crust types?)
______________________________________________________________________
b. Would you expect to see subduction here? (Refer to Lab 1) ______________________
c. If so, which plate is subducting, and HOW do you know?
29. Mt.Pelee is located on the island of Martinique in the Caribbean. Look through the photos of the 1902
explosion of Mt.Pelee, as well as the photos of the city of St. Pierre before and after the eruption and
the article about the eruption.
a. Read through the article on the eruption. How many people died in the town of St.Pierre?
b. Why didn’t people evacuate?
c. What type of volcano is this, and how can you tell?
d. What major hazards do you observe, that likely killed so many people and buried a town?
30. Based on what you have learned about these two volcanoes (Q’s 28 & 29), what do you think the
viscosity of this magma camber is, High or Low? (circle one)
31. What do you think the composition of the magma chamber is, Felsic or Mafic? (circle one)
Use the packet titled “Mexico Volcanoes” to answer the following:
32. The volcano El Chichon erupted in 1982, killing 2,000 people. This volcano is located around 17o45’N
and 94o6’W. Locate this volcano on the plate tectonics map of Mexico and answer the following:
a. What type of plate boundary caused this volcano (be specific, which crust types?)?
b. Which two plates are colliding?
c. Look at the before and after pictures of the 1982 eruption. What hazard(s) do you think killed
200 people?
PART 5: Summary Table Handout
INSTRUCTIONS: Complete the tables on the Volcano Summary chart Handout, making sure all team members
thoroughly understand all relationships and concepts.
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