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Volcanoes Guided Reading Key
Read 88-102. Then define the terms.
Lava- liquid magma that reaches the surface- makes rock when cooled
Magma-molten mixture of rock, gases, and water in the mantle.
Hot Spot-area where magma deep in the mantle melts through the crust
Pahoehoe-fast, moving hot lava- smooth, ripples when cools
aa- cooler, slow moving lava that cools in rough, chunks.
Answer the following questions.
1. In what ways are volcanoes a constructive force? they can add to land by adding new rock and creating
islands
2. Why do so many of Earth’s volcanoes occur along plate boundaries? Huge pieces of crust diverge or
converge and allows magma to reach surface.
3. Explain how hot spots create islands. Magma deep in the mantle melts through the crust. Over time the
addition of more and more rock creates and islands. The plate continue to move though the hot spot
doesn’t and makes a chain of islands.
4. What is the difference between magma and lava? Magma is under the crust and lava is the name of the
mixture when it is on the surface.
5. Why does magma in the mantle rise through the crust above it? Gases dissolved in the magma cause it to
rise when under intense pressure.
6. As magma rises toward the surface, what happens to the gases in it? Why ? The bubbles in the gas dissolve
and pressure is released.
7. What three things determine how thick or thin magma is? Temperature, amount of silica, and amount of
gas
8. What are the differences between pahoehoe and aa? What kind of eruption produces these types of lava?
Smooth and fast flowing vs. cooler, slower flowing that hardens in chunks.--Quiet
9. Identify three hazards of volcanic eruptions.
Burying entire towns, damage to crops, and clogging car engines
10. Where do most volcanoes occur on Earth’s surface? Divergent plate boundaries or at subduction zones.
11. How can oceanic crust eventually become magma? It subducts and melts to create magma, which will
eventually rise to the surface
12. What process forms island arcs? A moving plate and a hot spot- plate continues to move as magma is
released forming multiple islands
13. Name the continents where volcanoes are found. Asia, North and South America, Africa, Europe
14. What are the 3 location types where volcanoes can be found? Divergent boundary-mid-ocean ridges,
continental and oceanic crust collisions, oceanic crust and oceanic crust collisions.
15. What causes hot spot volcanoes to form? Magma deep in the mantle and busts through crust like a blow
torch
16. Name two rocks created from volcanic lava. Pumice, Obsidian, Pele’s hair, granite
17. What types of lava are produced from quiet eruptions? Pahoehoe, aa
18. What causes an explosive eruption? Thick sticky magma; much dissolved gases under intense pressure
19. How are volcanoes related to igneous rocks? Igneous rocks are made from volcanic activity
Draw a picture of a volcano on the back of this page. Be sure to include labels of the different parts!!!