Stratovolcano PowerPoint Questions
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Chaffey College *
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101
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Geology
Date
Dec 6, 2023
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8
Uploaded by DeaconSwanMaster597
Stratovolcano PowerPoint Questions
Directions:
Be sure to place the answer for each question on the line below the
question. Then either highlight, use another color, or some other method to make your
answer easy to read.
1. What are the 2 layers that make up a stratovolcano?
Pyroclastic debris and thicker andesite lava flows
2. What is the geological cause for most stratovolcanoes?
Subduction zones
3. What are 2 reasons that andesite is so explosive?
Andesite lava is made of 60% silica at 1000°C so it is fairly viscous (thick) and with
moderately high gases it readily explodes.
4. What lava type makes up stratovolcanoes?
Pyroclastic
5. What is a pyroclastic flow?
A pyroclastic flow is the most dangerous eruption because it is a cloud of superheated
gases, ash, and rocks.
6. Montserrat’s volcano in the Caribbean erupts a thick andesite lava and when it
extrudes out of the crater, the lava collapses to form a pyroclastic flow that races down
the mountain. How fast can this pyroclastic flow go?
Over 100mph downslope
7. When they do autopsies on people who died in pyroclastic flows, what do you think
they find in their lungs?
Ash
8. What is the composition of the top part of a pyroclastic flow?
hot lava blocks, pumice, ash, and volcanic gas
9. What type of terrain should you avoid at the base of a stratovolcano when pyroclastic
flows are descending?
The surrounding area
10. Why would it be super dangerous for a hurricane to pass over a stratovolcano
during a large eruption of pyroclastic material?
The pyroclastic debris can also dam rivers to create unstable lakes
11. Where is Mt. St. Helens located?
Washington state
12. Looking at Mt. St. Helens in slide # 6, what would you estimate the angle of the
slope to be? Choose one: 10, 30, 60 degrees.
60 degrees
13. What covered the top of Mt. St. Helens before it erupted in 1980?
A large Glacier
14. In one word, what is the cause of MSH’s volcanism?
It is a cascade volcano along the ring of fire
15. According to the diagram in slide #7, what ocean plate is subducting underneath
MSH?
Juan de Fuca
16. What color is andesite rock?
Grey with white and black crystals inside
17. According to the diagram in slide #7, what is pushing the ocean plate under
Washington state?
The mid-ocean ridge or the Pacific plate
18. What are 3 methods that geologists can use to monitor a volcano?
seismometers, sulfur dioxide gas detectors, and tiltmeters to measure inflation
19. In slide #8’s diagram, what 2 things is MSH erupting?
plume and pyroclastic flow
20. How could MSH disrupt logging operations during rainstorms when it was erupting
heavy ash clouds?
It only affects eruptions through mid-may
21. In slide #9’s diagram, what have the explosions done to the crater?
The explosion widened the crater
22. In 1980, what did scientists think was causing the bulge on the north side of MSH?
They believed the bulge was a slow-motion landslide
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23. Scientists didn’t understand what was causing the blister to grow on the north side
of MSH. What was under the bulge?
It was an intrusions of magma
24. What event triggered the collapse of MSH?
An earthquake of 5.1
25. How did the north side of the volcano respond to the earthquake?
It causes a huge landslide on the north side
26. What cataclysm followed the landslide?
The lateral blast
27. Which was fastest – the landslide or the pyroclastic surge?
Pyroclastic surge
28. What is dissolved in magma to cause it to explode?
Andesite
29. What was the final step in the May 18, 1980 eruption?
The vertical blast that continued for 9 hour
30. What occasionally happened to the vertical explosion that created danger on the
ground around the volcano?
Well it affected the vertical part of where it erupted which was the bulge
31. How much of the top of MSH was lost?
1,300 ft was lost
32. How did Spirit Lake get raised by 200ft?
A tsunami had happened which then caused the water to come back 200 feet higher
33. What had to be vented before andesite lava could be extruded out of the crater?
that viscous andesite lava was able to extrude and come out of a tube
34. What is the name of the roundish lava formation inside the crater?
A lava dome
35. What now surrounds the dome?
A glacier
36. Which volcano is ranked as the most dangerous in the U.S. by the USGS?
Kilauea
37. What 2 factors contributed to the fast regrowth of vegetation around Mt. St. Helens?
Volcanic ash
38. How many active volcanoes does California have?
About 7
39. Which country is the Fuego volcano located in?
Central America specifically Guatemala
40. Which ocean plate is subducting underneath Fuego?
Juan de Fuca
41. What plate is southern Guatemala and Fuego located on?
Cocos plate and the ring of fire
42. What type of plate boundary is represented by the dashed red line running across
central Guatemala?
Motagua fault
43. What causes the mantle to melt during plate subduction?
The plates move against each other which then creates a line of stratovolcanoes
44. What is the name of the less active stratovolcano adjacent to Fuego?
Acatenango
45. Why do the tour guides avoid taking hikers to Fuego?
it has mini eruptions every 15-20 minutes
46. In slide #20, what are the 2 things coming out of Fuego that put the strato in
stratovolcanoes?
Spilling lava and the release of andesite
47. In slide #20, what is the name for the incredible band of stars seen only in areas
away from city lights? (If you don’t know the answer, try this one: what is causing the
diffuse lights in the lower distance beyond Fuego’s erupting volcano?
The ash or the fog from the explosions
48. What is the killer that the Fuego volcano unleashes during its largest eruptions?
Pyroclastic flows and falling ash
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49. Why was there no evacuation on June 4, 2018, before the large eruption at Fuego
volcano?
Because there were no signs that it was going to erupt
50. Kilauea’s east rift zone was erupting when Fuego took 159 lives. Why is Kilauea a
safer volcano?
Because flowing basalt is easier to move away from
51. What is a lahar?
Lahars are mudflows created when water and volcanic ash mix.
52. How do volcanoes cause earthquakes?
Pressure within the volcano moving magma
53. Which type of tremor happens when magma pulsates for long periods through the
volcano's conduits?
Harmonic
54. Which type of tremor is a dangerous warning sign that lava might explode through
the crater at any moment?
Tornillos
55. What 2 instruments are used to measure the inflation and deflation of the volcano?
Tiltmeters and GPS receivers
56. Why do geologists measure sulfur dioxide emissions from the volcano rather than
the 2 more common volcanic gases of water vapor and carbon dioxide?
monitors that can collect data from satellites or on the ground miles away from the
volcano and because rainwater and vegetation can interfere with the volcanic signature
57. What does the presence of SO
2
gas at a volcano indicate?
Magma is near the surface