Download Lab 3: Volcanic Hazards

Environmental Geology 103L
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Lab 3: Volcanic Hazards
Suppose you have been assigned a job with the Volcanic Hazards Program of the United States Geological Survey
(USGS) and were asked to provide a hazard analysis of several active volcanic locations. What would you need to
know in order to complete your analysis? How would you approach this study? What would you do first?
In order to understand, predict, and plan for hazards associated with a particular volcano, it is necessary to know
the type of volcano and the composition of the magma. Magma composition plays are primary role in determining
whether the eruption style will be effusive (fluid) or explosive. The eruption type is primarily dictated by the viscosity
(stickiness) of the magma: the greater the viscosity, the more explosive (and more dangerous!) the eruption.
Typically, shield volcanoes are formed by effusive (fluid, flowing) lava eruptions, while composite volcanoes (also
called stratovolcanoes) are formed by explosive pyroclastic eruptions alternating with viscous (sticky) lava flows. By
examining the surrounding volcanic rock, geologists can gain understanding of magma composition and potential
hazards associated with a particular volcano.
PART I: HOW VOLCANOES FORM
Watch the Discover channel video about how volcanoes form and the hazards associated with each type, and
review the types of volcano shapes in the second website.
http://videos.howstuffworks.com/discovery/29182-assignment-discovery-volcano-basics-video.htm
http://science.howstuffworks.com/nature/natural-disasters/volcano6.htm
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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
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Go to this website and explore the site: http://news.discovery.com/games/volcano-explorer.htm
Open the ‘Virtual Volcano’ link to build your own volcano.
Summarize what happens when you vary the silica and gas concentrations in the magma.
Describe the type of volcano that forms, the type of eruption created – violent, gentle, etc., the types of
hazards generated, etc.
 Record your observations in the chart below.
Silica Content
Gas Content
Type of Eruption
Hazards
Type of Volcano
(Explosive,
(list all shown
(High OR Low)
effusive, etc)
with each
eruption)
High
High
High
Low
Low
Low
Low
High
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4. Which factor had more of an effect on the type of volcano formed: silica content or gas content?
5. Increasing the silica content of a magma increases its viscosity (its resistance to flow, or “stickiness”).
Based on your results in the chart above, does low viscosity magma lead to more explosive or more
effusive eruptions?
6. What conditions are required for the most explosive types of eruptions?
PART II: EXPLORING VOLCANOES
A. Hawaii Volcanoes
http://kilauealavaflowmount.files.wordpress.com/2008/03/eruption1.jpg
First, 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
7. Would you describe the lava as being high viscosity (think toothpaste) or low viscosity (think maple syrup)?
8. What does this tell you about the silica content of this lava?
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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.
 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.
9. Describe the basic shape of Mauna Loa/Kilauea volcano (flat and wide or tall and skinny):
10. How does the silica content and viscosity from questions 1 & 2 above affect the shape of the volcano?
Now examine the 3D HAWAII topographic map. Please DO NOT WRITE on these maps. They are VERY
expensive and hard to replace.
Refer to Chapter 8: Scales on pages 205-208, and Chapter 9: Topographic Maps, pages 212-222, in your lab
manual for help with the following questions. You can also go to http://serc.carleton.edu/mathyouneed/units/ and
http://serc.carleton.edu/mathyouneed/units/UnitExample.html for help with converting units.
Now look at the contour lines. Notice that where the topography is steep, the lines are close together, whereas the
lines are far apart where the topography is flat.
11. What is the CONTOUR INTERVAL (the change in elevation between adjacent contour lines) of the Hawaii 3-D
map? ________________feet
12. What is the change in elevation between INDEX CONTOURS (the darker contour lines) for the Hawaii 3-D
map? ____________feet
13. Determine the height of the volcano by using the formula: (Elevation of summit) – (Elevation of base) = Height of
volcano (in feet). For Mauna Loa, the elevation of the base = 0’ (sea level).
Height of Mauna Loa = __________ ft
14.Determine the width Mauna Loa by measuring the distance from Palemano Pt across the summit to Kapoho Pt.
You will need to use the horizontal scale on the map to help you determine the actual distance (not just the distance
on the map, which is a miniaturized version of real life).
Width of Mauna Loa
= ____________ft
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B. 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
15. How would you describe the 1980 eruption of Mt. St Helens?
16. What does mean about the silica content and gas content of the magma?
Now watch this video from later activity on Mt St Helens in 2004.
https://www.youtube.com/watch?v=5t_B3H3Bx_Q
https://www.youtube.com/watch?v=h6B1myUKAS4
17. How does this type of eruption differ from the 1980 eruption?
18. Would you describe the magma as high or low viscosity?
19. What does this tell you about the silica content and gas content of the magma?
Go Back to the Learn about Plate Tectonics file in Google Earth.
 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):
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21. How does the silica content and viscosity affect the shape of these volcanoes?
Refer to the 3-D MAP OF MOUNT RAINIER to answer the following questions.
22. What is the CONTOUR INTERVAL of the MOUNT RAINIER map?
___________feet
23. What is the change in elevation between INDEX CONTOURS for the MOUNT RAINIER map?
___________feet
24. Determine the height of the volcano by using the formula: (Elevation of summit) – (Elevation of base) =
Height of volcano (in feet). For Mount Rainier base elevation – use the 2000 ft contour, located on the
NW corner of the volcano, near the intersection of the Mowich River and Rushingwater Creek.
Height of Mt. Rainier = __________ ft
25. Determine the width Mt. Rainier by measuring the distance from the 2000 ft contour located on the NW
corner of the volcano, near the intersection of the Mowich River and Rushingwater Creek, and cross
over the summit to the intersection of the Chinook River and Ohanapecosh Rivers, also at 2000 ft.
(NOTE: the base of the volcano is measured from the point where it begins to noticeably change in
elevation from the surrounding areas). You will need to use the horizontal scale on the map to help you
determine the actual distance (not just the distance on the map, which is a miniaturized version of real life).
Width of Mount Rainier = ____________ft
C. DETERMINING VOLCANO TYPES BASED ON SHAPE
Shield and composite volcanoes have different shapes and slopes due to their different magma compositions.
Shield volcanoes have hot fluid magma. Composite volcanoes have relatively cool, viscous (thick) magma.
Because of the very different types of magmas, the resulting shapes and slopes of the volcanoes are very different.
The ratio of the height of the volcano ÷ the half-width of the base is one way to differentiate between a shield and
composite volcano.
Elevation of summit
Height of volcano = (Elevation of summit) – (elevation of base)
Elevation of base
Half-width of base

A shield volcano has a ratio value less than 0.18, typically about 0.10. This ratio gives the shield volcano a
gentle slope, less than 10° and usually about 5°.

A composite has a higher ratio, greater than 0.18, even as much as 0.25. This gives the composite a steeper
slope, greater than 10° and usually about 15°.
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HAWAII
Using the data you collected from the Hawaii contour map above, calculate the following (show your work for full
credit!
26. Half-width (the width of the base of Mauna Loa divided by 2) = __________________ ft.
27. Mauna Loa height/width ratio (the height of Mauna Loa from question 13 ÷ half-width of the base) =
________
28. Mauna Loa is a ___________________________ volcano.
MOUNT RAINIER
29. Half-width (the width of the base of Mt. Rainier divided by 2) = __________________ ft.
30. Mt. Rainier height/width ratio (the height of Mt. Rainier from question 24 ÷ half-width of the base) =
________
31. Mt. Rainier is a ___________________________ volcano.
PART III: HOW CAN YOU TELL A VOLCANO BY THE TYPE OF ROCK?
In order to understand, predict, and plan for hazards associated with a particular volcano, it is necessary to know
the type of volcano (in our case either shield or composite) and the composition of the magma. Magma
composition plays a primary role in determining whether the eruption will be effusive or explosive. Typically shield
volcanoes are formed by effusive mafic lava eruptions while composite volcanoes are formed by explosive
pyroclastic eruptions alternating with sticky felsic lava flows. By examining the surrounding volcanic rock,
geologists can gain understanding of the magma composition and potential hazards. In the following activity your
team will learn how to recognize igneous rocks.
Remove Specimens # 2, 3, 4, 5, 8, 9, 11, 12 from the ROCK drawer.
a. Spend some time examining the rocks. Discuss your observations with your team.
b. Set aside specimens 4 and 9. We’ll explore them a bit later.
c. Group the remaining six rocks based on texture. The fine-grained rocks are volcanic (cooled extrusively at
the surface); the coarse-grained rocks are plutonic (cooled intrusively deep underground). We are most
interested in the volcanic rocks for this exercise, however all igneous rocks are related and it is important to
be familiar with the most common ones.
d. Now rank the rocks in each group from light (felsic) to dark (mafic). You have just sorted the specimens
based on composition!
e. Place the rocks in the proper squares on the chart below. This is a visual tool to help you remember the
relationships of the igneous rocks. Include specimens 4 and 9.
f. Using Figure 5.7 (page 118) and the instructions given in Exercise 5.7 (page 117) in your lab manual,
determine the names of the rocks. Complete the chart with rock names and specimen numbers.
g. For the volcanic rocks, include the type of volcano (shield or composite).
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PART IV: IGNEOUS ROCK IDENTIFICATION AND CLASSIFICATION CHART
Rock specimens: 2, 3, 4, 5, 8, 9, 11, 12
COMPOSITION
FINE-GRAINED
(Aphanitic)
INTERMEDIATE
MAFIC
(low silica content)
Volcano Type:
Volcano Type:
Volcano Type:
Volcano Type:
Volcano Type:
Volcano Type:
Fast cooling rate
Slow cooling rate
COARSE-GRAINED
(Phaneritic)
Glassy
FELSIC
(high silica content)
Fast cooling rate
TEXTURE
Fast cooling rate
Vesicular
Volcano Type:
Volcano Type:
32. Which of the above rocks would you expect to find at a volcano like those on Hawaii?
ROCK NAME
a. _________________
b. _________________
SPECIMEN #
________
________
33. Which of the above rocks would you expect to find at a volcano like those in the Cascade Range (Mt. Rainier
and Mt. St. Helens?
a.
b.
c.
d.
e.
ROCK NAME
_________________
_________________
_________________
_________________
_________________
SPECIMEN #
________
________
________
________
________
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PART IV: TYPES OF COMPOSITE VOLCANIC HAZARDS
To learn about the types of hazards that are associated with composite volcanoes, review the following
video clips. After viewing the video clips, answer the questions below.
Pyroclastic Flow: http://www.discovery.com/tv-shows/discovery-presents/videos/ultimate-guide-to-volcanoespyroclastic-flow/
Lava Flow ; http://www.discovery.com/tv-shows/discovery-presents/videos/understanding-volcanoes-lava-flow/
Mount St Helens: http://www.discovery.com/tv-shows/discovery-presents/videos/understanding-volcanoes-mtsaint-helens/
34. Describe the hazards associated with composite volcanoes:
35. How are these hazards different from shield volcanoes?
36. Which type of volcano is more dangerous? Why?
PART V: SUMMARY OF VOLCANOES, HAZARDS, AND PLATE TECTONICS
Rock Specimen #: 2, 3. 4, 5, 8, 9, 11, 12
TEAM INSTRUCTIONS: complete the table below, making sure all team members thoroughly understand all
relationships and concepts.
***CAREFULLY review Figure 5.9 and Table 5.3 about plate boundaries and igneous and volcanic processes, on
page 124 of your lab manual. A review of the animations may be of help.
TYPE OF
VOLCANO
PLATE
SETTING
(Hot Spot/
Mantle or
Convergent)
CRUST TYPE
(Continental or
Oceanic)
MAGMA (ROCK)
COMPOSITION
Felsic-Intermediate
OR Mafic
IGNEOUS
ROCKS
ASSOCIATED
WITH
EACH CRUST
TYPE
TYPES OF VOCANIC
HAZARDS
Basaltic Lava flows,
pyroclastic flows,
lahars, ash fall, etc.
Shield
Composite
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