EARTH: AN INTRODUCTION TO PHYSICAL GEOLOGY

Chapter 5: Volcanoes and Other Igneous Activity

Chapter Test

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Choose the best possible answer to the following questions for all of "Chapter 5."

1. A magma's viscosity is affected by its composition, temperature, and amount of dissolved gases.  
 
2. The most abundant gas expelled during a volcanic eruption is __________.  

3. In general, the less silica in a magma, the greater its viscosity.  
 
4. A magma's viscosity is directly related to its __________ content.  

5. Rhyolitic (felsic) magma is typically less fluid than basaltic (mafic) magma.  
 
6. What is the major dissolved volatile constituent in both magmas and volcanic gases?  

7. The viscosity of the magma, plus the quantity of dissolved gases and the ease with which they can escape, determines how violent a volcanic eruption will be.  
 
8. Why do magmas rise toward the Earth’s surface?  

9. Magmas that produce felsic rocks (granite and its extrusive equivalent, rhyolite) typically contain less than 50 percent silica.  
 
10. Pahoehoe, ash, and lapilli are all forms of pyroclastic materials.  
 
11. The smallest of the three volcano types are the cinder cones.  
 
12. The structures that result from the emplacement of igneous material at depth are called lahars.  
 
13. Most volcanoes are fed magma through short conduits or pipes.  
 
14. Shield volcanoes are the most common product of __________ volcanism. [Hint]

15. Shield cones are typically large, built primarily of basaltic lava flows, and contain a small percentage of pyroclastic material.  
 
16. Which volcano type is a very large, gently sloping mound composed mainly of basaltic lava flows?  

17. The largest intrusive igneous bodies are batholiths.  
 
18. Dikes are tabular discordant bodies that are produced when magma is injected into fractures.  
 
19. A large depression at the summit of a volcano is called a __________.  

20. The largest intrusive igneous bodies are __________.  

21. Many subduction-zone volcanoes are located in a region on Earth called the "Ring of Fire."  
 
22. Most mare volcanism on the Moon has occurred in the bottoms of very large, very old __________. [Hint]

23. The greatest volume of volcanic rock is produced along the oceanic ridge system.  
 
24. Mantle plumes and hot spots are often associated with intraplate volcanism.  
 
25. The Columbia Plateau in the northwestern United States was produced by numerous fissure eruptions of very fluid basaltic lava.  
 
26. Most active composite cones are located in the region of the central Pacific Ocean.  
 
27. Most intraplate volcanism occurs where a mass of hotter than normal mantle material ascends toward the surface.  
 
28. Andesitic or rhyolitic magma is characteristically extruded from volcanoes within a continental margin volcanic arc.  
 
29. The relation between volcanic eruptions and climate cannot be established.  
 
 




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