Chapter 5: Volcanoes and Other Igneous Activity

1.	A magma's viscosity is affected by its composition, temperature, and amount of dissolved gases.     True False
2.	The most abundant gas expelled during a volcanic eruption is __________.   water vapor sulfur dioxide carbon dioxide nitrogen silicon dioxide
3.	In general, the less silica in a magma, the greater its viscosity.     True False
4.	A magma's viscosity is directly related to its __________ content.   iron oxygen aluminum potassium silica
5.	Rhyolitic (felsic) magma is typically less fluid than basaltic (mafic) magma.     True False
6.	What is the major dissolved volatile constituent in both magmas and volcanic gases?   water carbon dioxide hydrogen chloride methane sulfur
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.     True False
8.	Why do magmas rise toward the Earth’s surface?   Magmas are mainly liquid and contain dissolved fluids such as water, most are less dense than the adjacent solid rock and so move upward. Most magmas are richer in silica than most crustal and upper mantle rocks, and are less dense than the other rocks in the melting area, and so move upward. Magmas are more viscous than solid rocks in the crust and upper mantle, and are more dense than the adjacent rocks, and so move upward.
9.	Magmas that produce felsic rocks (granite and its extrusive equivalent, rhyolite) typically contain less than 50 percent silica.     True False
10.	Pahoehoe, ash, and lapilli are all forms of pyroclastic materials.     True False
11.	The smallest of the three volcano types are the cinder cones.     True False
12.	The structures that result from the emplacement of igneous material at depth are called lahars.     True False
13.	Most volcanoes are fed magma through short conduits or pipes.     True False
14.	Shield volcanoes are the most common product of __________ volcanism. [Hint] lahar explosive hotspot rift random
15.	Shield cones are typically large, built primarily of basaltic lava flows, and contain a small percentage of pyroclastic material.     True False
16.	Which volcano type is a very large, gently sloping mound composed mainly of basaltic lava flows?   caldera cinder cone stratovolcano composite shield
17.	The largest intrusive igneous bodies are batholiths.     True False
18.	Dikes are tabular discordant bodies that are produced when magma is injected into fractures.     True False
19.	A large depression at the summit of a volcano is called a __________.   lahar caldera neck fissure batholith
20.	The largest intrusive igneous bodies are __________.   sills batholiths laccoliths dikes none of the above
21.	Many subduction-zone volcanoes are located in a region on Earth called the "Ring of Fire."     True False
22.	Most mare volcanism on the Moon has occurred in the bottoms of very large, very old __________. [Hint] impact craters rifts calderas island arcs subduction zones
23.	The greatest volume of volcanic rock is produced along the oceanic ridge system.     True False
24.	Mantle plumes and hot spots are often associated with intraplate volcanism.     True False
25.	The Columbia Plateau in the northwestern United States was produced by numerous fissure eruptions of very fluid basaltic lava.     True False
26.	Most active composite cones are located in the region of the central Pacific Ocean.     True False
27.	Most intraplate volcanism occurs where a mass of hotter than normal mantle material ascends toward the surface.     True False
28.	Andesitic or rhyolitic magma is characteristically extruded from volcanoes within a continental margin volcanic arc.     True False
29.	The relation between volcanic eruptions and climate cannot be established.     True False