NAME ______Date ______Class ______
Ch. 18 Study Guide (Earth Science)
18-1 Multiple Choice
Identify the choice that best completes the statement or answers the question.
____ 1. A bowl-shaped depression that forms around the vent of a volcano is a a. magma chamber. c. vent. b. crater. d. sill.
____ 2. Broad, gently sloping volcanoes with quiet eruptions are called a. cinder cones. c. shield volcanoes. b. hot spots. d. composite volcanoes.
____ 3. Lava erupts through an opening in Earth’s crust called a a. caldera. c. vent. b. volcano. d. crater.
____ 4. Which of the following forms when the top or side of a volcano collapses into the magma chamber? a. vent c. pyroclastic flow b. dike d. caldera
____ 5. Most volcanoes form a. at hot spots. c. in the center of ocean plates. b. in the middle of continents. d. at plate boundaries.
____ 6. The most explosive volcanoes are a. hot spots. c. cinder cones. b. composite volcanoes. d. shield volcanoes.
____ 7. When magma reaches Earth’s surface, it is called a. lava. c. calderas. b. a vent. d. a pyroclastic flow.
____ 8. ______form(s) where plates move apart. a. Hot spots. c. Subduction zones. b. Divergent volcanism. d. Convergent volcanism.
____ 9. Volcanoes that form far from plate boundaries are associated with a. subduction zones. c. ocean ridges. b. divergent boundaries. d. hot spots.
18-1 Continued
10. Label the diagrams as composite, cinder-cone, or shield volcano.
Identify the type or types of volcano being described as Shield, Cinder, or Composite Volcano.
11. ______Forms when small pieces of magma are ejected into the air then fall back to
Earth and pile up around a vent.
12. ______Has broad, gently sloping sides and a nearly circular base.
13. ______Mauna Kea in Hawaii is an example.
14. ______Forms when layers of basaltic lava accumulate during a nonexplosive
eruption.
15. ______Forms when layers of hardened lava chunks alternate with lava.
16. ______Small volcano with steep sides.
17. ______Forms from lava that contains relatively small amounts of gases and silica.
18. ______Forms from lava that is higher in water and silica content than lava that
forms shield volcanoes
19. ______Fueled by magma that contains large amounts of silica, water, and gases.
20. ______Potentially the most dangerous to humans and most destructive to the
environment.
21. ______Mount St. Helens and Mount Rainier are examples.
18-1 Continued
22. Use each of the terms below just once to complete the passage. Hawaiian Islands crust divergent hot spots Iceland mantle volcanoes ocean ridges Circum-Pacific Belt western convergent Most of the world’s volcanoes form along (a) ______plate boundaries. Slabs
of oceanic crust descend into the (b) ______and release water, causing portions
of the mantle to melt. The magma that forms is forced upward through the overlying plate and forms
(c) ______when it reaches Earth’s surface. The (d) ______
marks the locations of most convergent boundary volcanoes. It stretches along the
(e) ______coasts of North and South America and down the eastern coast of Asia.
At (f) ______plate boundaries, magma is forced upward into fractures
and faults that form as plates separate or spread apart. Most of the volcanoes that form along
divergent boundaries are located underwater along (g) ______. This type of
volcanic activity can be observed above sea level in (h) ______, which sits atop
the Mid-Atlantic Ridge.
Some volcanoes that form far from plate boundaries form over (i) ______,
which are unusually hot regions of Earth’s mantle. At hot spots, high-temperature plumes melt
rock. The magma that forms moves upward toward the (j) ______and melts
the crust to form a volcano. As a tectonic plate moves over a hot spot, a string of volcanoes forms.
The (k) ______are the result of a hot spot.
18-2 Continued Indicate whether the statement is true or false.
____ 23. Magma is a mixture of molten rock, suspended minerals, and gases.
____ 24. Pressure decreases with depth below Earth’s surface.
____ 25. Magma forms when rocks begin to melt.
____ 26. Wet minerals and rocks melt at lower temperatures than do dry minerals and rocks.
____ 27. As pressure increases, the temperature at which a dry substance melts increases.
18-2 Continued
Answer the following questions:
28. How does the viscosity of magma change as magma cools?
______
29. Does cooler magma flow more or less quickly than hotter magma?
______
30. Is the viscosity of magma that is high in silica higher or lower than magma that is low in silica?
______
31. Which type of lava—basaltic lava or rhyolitic lava—flows faster? Explain. ______
______
18-3 Matching
a. stock d. pluton b. sill e. batholith c. laccolith f. dike
____ 32. Largest pluton
____ 33. Mushroom-shaped pluton
____ 34. Instrusive rock body.
____ 35. Irregularly shaped pluton that is similar to a batholith, but smaller in size.
____ 36. Pluton that is parallel to the rocks it intrudes.
____ 37. Pluton that cuts across preexisting rocks.