Sample Problems for Earth Materials & Volcanoes

1) A large number of people were killed by ash flows in the 1815 eruption of Tambora in Indonesia, but many people also died of starvation in Europe as crops failed due to the cooler summer produced by the eruption.  Based on this description, in which plate tectonic setting was the volcano most likely located?

• a convergent subduction zone
• a continental transform boundary  
• a convergent collision zone  
• an oceanic hotspot                                 
• a continental hot spot

2) Which of the following was the most likely process by which the magma that fueled the Tambora eruption formed?

• Water was introduced into hot mantle rock, causing some of the rock to melt.
• As rock masses rose towards the Earth’s surface, the pressure decreased causing some of the rock to melt.
• As rock masses ground past one another along faults, friction caused some of the rock to melt.
• As rock masses sank into the Earth, the pressure rose high enough to cause some of the rock to melt.
• As a subducting plate sank into the Earth, the temperature rose high enough to melt some of the roc

• It would be more violent because it would be more silica-rich and there would be more polymerization in the magma.
• It would be less violent because it would be more silica-rich and there would be less polymerization in the magma.
• There would be no difference, because basaltic ones do form from complete melting of the mantle.
• It would be more violent because it would be less silica-rich and there would be more polymerization in the magma.
• It would be less violent because it would be less silica-rich and there would be less polymerization in the magma.

4) If we were to change the laws of physics and chemistry, so that no covalent bonds existed and only ionic bonds formed, then all of the following would be true, EXCEPT:

• Most minerals would tend to be less resistant to weathering than they are at present.
• More basaltic magma would form, as water would be even more effective at generating magmas at spreading zones.
• In general most rocks would be more easily altered than they are at present.
• More andesitic and rhyolitic magma would form, as water would have an even greater affect on mineral melting points.
• Overall, there would be an increase in volcanic activity on Earth.

5) All of the following are TRUE statements concerning volcanic gifts (or volcanic resources) EXCEPT:

• Lava flows typically contain high amounts of valuable metals that are an important resource for human societies.
• Hot deep sea vents associated with past seafloor volcanism created rich mineral deposits for human societies.
• Volcanic deposits weather at the Earth’s surface to form rich soils that are important in agriculture.
• Volcanic processes are responsible for concentrating many of the light elements necessary for life at the Earth’s surface.
• Volcanic processes built the high moisture-producing mountains and natural harbors of many volcanic coastlines.

                                                                                                                                                                                                                                                                                                                                                                                        6) All of the following are TRUE statements concerning the role salt has played in human history, EXCEPT:

• Rock salt or evaporated salt were necessary resources for the development of agricultural based societies.
• Rock salt or evaporated salt were necessary resources for the initial rise of hunting and gathering societies.
• Rock salt or evaporated salt were necessary resources for the domestication of cattle, sheep and pigs.
• The salt trade was a driving force behind the development of Mediterranean trade routes and merchant societies.
• The salt trade was a driving force behind the development of the steamboat and the Erie Canal.

7) If the Earth’s continental crust was less silica rich than the underlying mantle rock, how would this affect the Earth’s volcanic activity?

• The total amount of volcanic ash produced would be much greater than it currently is.
• There would be much less volcanic activity than there currently is.
• Magma’s that underwent extensive mixing with continental crust would tend to have much less violent eruptions.
• Magma’s that underwent extensive mixing with continental crust would tend to have much more violent eruptions.
• There would be no significant difference in the Earth’s volcanic activity or behavior.

8) One of the earliest recorded attempts to control a volcanic eruption occurred when the men of one village, using hide shields as protection, successfully broke through the chilled margin of a lava flow to redirect the lava flow through a neighboring community rather than their own.  If all of this volcano’s magma was similar to this eruption, how did the magma most likely originate?

• Water was introduced into hot mantle rock, causing some of the rock to melt.
• As rock masses rose towards the Earth’s surface, the pressure decreased causing some of the rock to melt.
• As rock masses ground past one another along faults, friction caused some of the rock to melt.
• As rock masses sank into the Earth, the pressure rose high enough to cause some of the rock to melt.
• As a subducting plate sank into the Earth, the temperature rose high enough to melt some of the rock.

                                                                                                                                                                                                                                                                                                                                                                                        9) If all of the magma associated with the volcanic system above behaved in a similar manner to that of the described eruption, in which plate tectonic setting did this volcanic system most likely occur?

• a convergent subduction zone
  
• a continental transform boundary        
• a convergent collision zone
• an oceanic hotspot 
• a continental hot spot

10) Although small amounts of rhyolitic magma do occur in many volcanoes, we have never had a historic eruption of a rhyolitic-dominated volcano (Yellowstone being the most recent). Why is this so?

• Rhyolitic magmas are denser than andesitic or basaltic magmas, so they tend to sink into the Earth, rather than rise to its surface.
• Most rhyolitic magmas form deep within the Earth’s mantle, so large amounts rarely reach the Earth’s surface.
• Rhyolitic magmas only form at extremely high temperatures, so its is very rare for them to occur anywhere near to the Earth’s surface.
• Very little rhyolitic magma is generated in the Earth, so it is unlikely to dominate a volcanic system.
• As rhyolitic magmas rise towards the Earth’s surface they tend to lose their water content and crystallize below the surface.

Answers