Introductory Geology Volcanoes 9.12 Student Responses

1. Type 19 53 48.36 N 155 34 58.11 W in the search bar on Google Earth, and zoom

out to an eye altitude of ~615 miles. The magma that resulted in the formation

of these islands was generated by what process?

a. decreased pressure (arrow “b”)

b. the addition of water (arrow “d”, which shifts the solidus to the left)

c. increased temperature (arrow “a”)

2. Type 50 16 27.25 N 29 22 05.11 W in the search bar on Google Earth, and zoom

out to an eye altitude of ~2663 miles. The magma generated at this location is

due to:

a. decreased pressure (arrow “b”)

b. the addition of water (arrow “d”, which shifts the solidus to the left)

c. increased temperature (arrow “a”)

3. Type 36 11 46.85 S 71 09 48.03 W in the search bar on Google Earth, and zoom

out to an eye altitude of ~ 2865 miles. The magma responsible for this volcano

was generated by what process?

a. decreased pressure (arrow “b”)

b. the addition of water (arrow “d”, which shifts the solidus to the left)

c. increased temperature (arrow “a”)

4. Type “San Andreas Fault” in the search bar on Google Earth; no magma is

generated here, because this plate boundary is _____________________.

a. a divergent plate boundary, with decompression melting occurs

b. a convergent plate boundary, where water lowers the melting temperature of rock

c. a transform plate boundary, where no magma is produced

5. A(n) ________________________ at the Mid-Ocean Ridge, where oceanic

plates are diverging and magma is generated by partial melting of the mantle.

a. ultramafic magma is produced b. mafic magma is produced c. intermediate magma is produced d. felsic magma is produced Page | 222 Introductory Geology Volcanoes 6. Type 19 28 19.70 N 155 35 31.94 W in the search bar on Google Earth, and zoom

out to an eye altitude of ~119 miles. This volcano is composed of:

a. mafic rocks, because a hotspot partially melted the mantle below the oceanic crust

b. mafic rocks, because a hotspot partially melted the oceanic crust

c. ultramafic rocks, because a hotspot partially melted the mantle below the oceanic crust

d. ultramafic rocks, because a hotspot partially melted the oceanic crust

7. Type 35 35 08.45 S 70 45 08.22 W in the search bar in Google Earth. This

volcano formed from an intermediate magma type, because:

a. subduction of oceanic crust beneath the continental crust occurs here

b. continental crust is subducting, causing magma to form

c. a hot spot is partial melting the continental crust

d. this is the result of a divergent plate boundary

8. Type 36 40 41.62 N 108 50 17.22 W in the search bar in Google Earth. The dark

colored rock that forms a straight line on the surface is most likely:

a. a pluton of ultramafic rock b. a dike of ultramafic rock

c. a sill of mafic rock d. a dike of mafic rock

9. Intermediate lavas can flow _____ than mafic lavas, due to the _______

viscosity.

a. slower, higher b. slower, lower c. faster, higher d. faster, lower 10.Let’s relate food items to magmas of different viscosity; if we compare how

honey and water flow when poured from a container:

a. then the honey represents felsic magma, and the water represents mafic magma

b. then the honey represents mafic magma, and the water represents mafic magma. Page | 223 Introductory Geology Volcanoes 11. Imagine putting the honey in the refrigerator overnight; will its viscosity be

affected?

a. yes; the viscosity will increase

b. yes, the viscosity will decrease

c. no. there will be no change as the composition stays the same

12. Keep the honey in mind while you answer this question: when it is first erupted,

basalt lava typically erupts at 1200°C; after flowing away from the vent, the

temperature falls, therefore the viscosity of the basaltic lava will:

a. increase b. decrease c. stay the same 13. Type 43 25 04.18N 113 31 37.38 W in the search bar of Google Earth. Zoom out

to an eye elevation of ~90 miles. Based on the size of the area which is dark

colored and sparsely vegetated, this region is:

a. a basaltic dike b. a shield volcano c. a lava dome d. a flood basalt 14. Click on the nearby photo icon (SW of your latitude/longitude coordinate in

Question 13) to view a picture of the area as seen from the ground. This is a

picture of:

a. a basalt flow b. a felsic dome c. a plutonic rock d. an ultramafic rock 15. How many miles in length is this dark colored feature? (measure the greatest

length)

a. ~8 miles b. ~20 miles c. ~40 miles d. ~50 miles 16. Type 46 12 07.84N 121 31 02.85W in the search bar of Google Earth. This

volcano (Mt. Adams) has a lot of snow cover and small glaciers on it, but you

can still see the volcanic rock, especially on the eastern flank (side) of the

volcano. Zoom in to an eye altitude of ~9000ft to closely examine the rocks

on this eastern side of the volcano; do you see any evidence of layering? This

volcano is:

a. a shield volcano b. a lava dome c. a composite volcano d. a large volcanic dike Page | 224 Introductory Geology Volcanoes 17. How tall is Mt. Adams, and what is the length of its base (in the widest, N-S

dimension)? You will need to zoom out to an eye altitude of ~17 miles to

measure the base.

a. ~12,290 ft above sea level, and over 7 miles long

b. ~11, 890 ft above sea level, and over 4 miles long

c. at least 12, 703 ft above sea level, and over 6 miles long

d. unable to determine because of the ice 18.Compared to the Big Island of Hawaii (19 53 48.36 N 155 34 58.11 W, or refer to

Figure 9.6), which is actually the volcano Mauna Loa, Mt. Adams is:

a. the same height, but the base is a lot smaller

b. the same height, but the base is a lot wider

c. smaller in height, and smaller at the base

d. smaller in height, but larger at the base

19. Type in 58 15 58.56 N 155 09 35.98 W in the search bar of Google Earth.

Examine the shape of this feature by zooming in to an eye altitude of ~3330 ft;

use the eye icon in the upper right corner to rotate the view. Now zoom out to

an eye altitude of ~7306 ft to see the entire structure and the surrounding area.

Based on the size and appearance of this volcanic feature, this is a:

a. dike b. shield volcano c. lava dome d. flood basalt 20.Type Mount St. Helens, WA in the search bar in Google Earth and examine the

crater at an eye altitude of ~26,000 ft. Based on the appearance of the crater:

a. a lahar removed the north side of the volcano

b. a pyroclastic eruption removed the north side of the volcano

c. a lava dome grew so large that it is higher than the north side of the crater

d. a glacier has eroded the north side of the crater Page | 225 Introductory Geology Volcanoes 21. Type Mount Rainier, WA in the search bar in Google Earth. The Carbon River

flows from the north part of Mount Rainier (fed by meltwater from the Carbon

Glacier on the flank of the volcano). At an eye altitude of ~20,000ft, follow the

course of the Carbon River, past the town of Carbonado and stop at the town

of Orting. Based on the locations of these two towns, which do you think is in

danger from a lahar?

a. Both are in danger of lahars

a. Carbonado, because it is closer to Mount Rainier

b. Orting, because it is in a low lying area along Carbon River

c. Neither one is in danger because Mount Rainier is dormant Page | 226