Geology 101 Study Guide: Unit 1 The purpose of this study guide is to help you prepare for the first unit exam by focusing your studying and providing example essay questions. You will not be asked to submit this study guide for a grade. In the Focus On section you will find the primary ideas that you should understand as you prepare for the first unit exam. Some sample essay questions are given in the second section of this Study Guide. Please bring this Study Guide with you to class each day because we will use some of these questions as in-class problems for group work. Recommendations: 1) Take careful notes in class during the lectures as well as the information given in the slides presented during class 2) In class we will have several group discussion problems. Write these questions in your notes. Take time after class to write the answers provided during class. If you do not understand the answers to the questions, please see me for help. 3) A good method of studying is to teach someone else what you are trying to learn. Do not assume that you know a topic by just recognizing a term. You should be able to explain the idea to someone else. 4) Anything covered during our classes and in the readings specified in the Reading Guides is fair game for the exams, but almost all of the questions will be over information covered during lectures or labs. The list of topics below is a good starting point as you study for the exam. PART I: Focus on: Ch. 1: What is the difference in a hypothesis and a theory? You should be prepared to site an example from the text. Ch. 2: What are the three major types of plate boundaries? Chs. 4 and 5: Volcanoes and Igneous Processes: characteristics of basaltic, andesitic, and rhyolitic lavas and their viscosities the factors which control the viscosity of lavas/magmas. You should be able to apply those factors to help explain the characteristics of volcanic eruptions. interaction between the viscosity of a magma and the release of volcanic gases. relationship between the amount of silica in a magma and the tendency to form lava and/or pyroclastics types of volcanoes (shield, composite, scoria cones, volcanic domes, and fissure eruptions). You should be able to identify the types of volcanoes from images and from topographic maps. What are the typical styles of eruptions for these different types of volcanoes? connections between the types of volcanic rocks and the types of volcanoes similarities/differences between magma and lava the rock types in the volcanic (extrusive) group and the rock types of the plutonic (intrusive) group. For example, you should be able to recognize that basalt and gabbro originate from the same magma, but differ in the way they crystallize. characteristics of pyroclastic flows and the hazards they pose to people and property near a volcano cooling structures within lava flows, for example, columnar structures, pillows, and lava tubes. Should be able to explain how they form. fractional crystallization-- how does one magma generate volcanic eruptions with different silica contents?
what happened at Mt. St. Helens in 1980? (The events that preceded the major eruption and what triggered the eruption.) you should be able to use the tephra and other volcanic deposits around a volcano to answer questions about the volcano, such as its type, character of eruptions, and the changes in the history of the volcano similar to the Volcano X group problem in class. when a mountain such as Rainier is dormant, is there a way to predict when it will erupt next? What was the main point of the movie and videotape footage shown in class? Use the in-class problems as a means to prepare for the questions on the exam. Make sure you understand the main point of the questions. Ch 6: Weathering: what controls the amount of chemical and mechanical weathering the effects of different temperatures on hydrolysis the basic hydrolysis reaction presented in class differences and similarities between chemical and mechanical weathering rates of chemical weathering in various climates in the common igneous rocks types (such as granite, gabbro, rhyolite, basalt) which will weather fastest/slowest? hydrothermal alteration (such as the mudpots in Yellowstone and the alteration of andesite at Mt. Rainier) PART II: Sample questions to prepare for the essay part of the first unit exam These questions will help you prepare for the first exam. They are listed roughly in the order we will cover them in-class. 1. How does viscosity affect the nature of a volcanic eruption? 2. What is the role of the gases in magma as that magma approaches the earth s surface? 3. In class we observed a movie about the Heimaey eruption in Iceland and a typical Hawaiian eruption. The Icelandic eruption had much more tephra and was more explosive than the Hawaiian eruption. Both of these eruptions were basaltic. Explain how two basaltic eruptions could be so different. 4a. The volcano illustrated in the photo to the right is several thousand feet in elevation from its base to its summit. What type of volcano is illustrated in the photograph to the right? 4b. How would you characterize a typical eruption from this volcano? 4c. What is the most likely silica content of this volcano? (USGS photograph) 5. In class, we made the generalization that basaltic magmas normally form low viscosity lava flows and only minor amounts of tephra. However, most cinder cones are built of basaltic tephra. Explain the conditions under which basalt can erupt enough tephra to form cinder cones. (There should be two answers to this question.) 2
6. Complete the following chart: Name Silica content Color Viscosity rhyolite high basalt darkest lowest 7. Explain how you can determine whether an igneous rock cooled deep within the Earth or whether the rock cooled at or near the Earth s surface. 8. Why is it somewhat uncommon to find the plutonic equivalent of a mafic magma? 9. The diagram below is an igneous rock. What is the texture of this rock? If the groundmass of the rocks is gray and fine-grained, what type of rocks is this? What does this texture tell you about the cooling history of this rock? 10. What type of volcano is illustrate in the photograph to the right? b. Describe a typical eruption from this type of volcano c. What would be the most common silica content erupted from this type of volcano? 11. Explain how an intermediate lava flow could be erupted from a magma that was initially mafic in composition. 12. Volcano X started erupting 100,000 years ago. Its early eruptions were basaltic. About 50,000 years ago, the composition of the lavas and tephra erupted was andesite. A recent eruption (10 years ago) was a dacitic plug dome. Other than the introduction of different magmas, what reasons can you suggest to explain the change in composition of the volcanic materials erupted from Volcano X through time? 13. How might a person determine if an exposed layer of igneous rock is a sill or a lava flow covered by a later of rock? 14. Basalt may be found in dikes and sills. Is this statement true or false? Explain your choice. 3
15. You are on a vacation trip. In the distance you see a steep-sided conical hill which is about 600-800 feet higher than the land around it. You suspect this to be a volcano. What type of volcano do you think it is? Since you cannot go up to it and take a sample of the rock, what features could you look at through your binoculars to confirm that the hill is a volcano? (You should also be able to answer the same type of question using a topographic map!) 16. How are pyroclastic flows and lahars similar? different? 17. Volcano X started erupting 100,000 years ago. Its early eruptions were basaltic. About 50,000 years ago, the composition of the lavas and tephra erupted was andesite. A recent eruption (10 years ago) was a dacitic plug dome. Other than the introduction of different magmas, what reasons can you suggest to explain the change in composition of the volcanic materials erupted from Volcano X through time? 18. Magma Properties has a deal for you! A beautiful vacation property on the big island of Hawaii. We can promise you a "hot time." This property is located on the flanks of beautiful Mauna Loa volcano on the big island of Hawaii. Magma Properties will send you and a friend to Hawaii free of charge to investigate this great deal. This deal is offered for a limited time and is too good to turn down. Be the first on your block to buy a lot from Magma Properties. Magma Properties will not be responsible for personal injury or property damage due to volcanic eruptions during the visit or after the purchase of the properties. Imagine for the purposes of this problem that you are potentially interested in purchasing vacation property in Hawaii and you have decided to investigate the property offered by Magma Properties. Before going on your trip to Mauna Loa you need to construct a list of items to check related to the volcanic hazard of the area. You need to explain what you plan to check while on your trip and why these items need to be investigated. You should write your explanations so that another person in this class would be able to understand the logic behind your thoughts. Your ideas should be in order of importance, that is, list first those items for investigation that you believe is most important and so on. Assume that your only sources of information are the lectures and your textbook. You may assume that a typical Mauna Loa eruption is like the Hawaiian eruptions discussed in class. 19. Layers of tephra help us read the history of a volcano that is now dormant or extinct. Explain what information we can obtain from the layers of ash below: (My artistic ability is minimal!-- This is a side view of the ground--each of the layers is thicker on the left and the tephra particle sizes are larger on the left). 20. List and explain the series of events from March, 1980, to the catastrophic eruption of Mt. St. Helens on May 18, 1980. Which of the events would have been the best predictor of the major eruption on May 18 th? 4
21. A friend of yours is moving here from Kansas and wants to live in the vicinity of Mt. Rainier (outside of the National Park, of course). What kind of information can you provide your friend about the volcanic hazards of Mt. Rainier? 22. In Yellowstone National Park there are numerous "mudpots" in the thermal (geyser) basins, but none in the non-thermal areas. The mud is actually clay in which gases bubble through creating the illusion that the mud is boiling. a) The clay in the mudpots apparently has formed from the rhyolitic rock in the Yellowstone caldera. Explain the process that creates this clay. b) The mudpots are found in "hydrothermal" regions, but none in the non-thermal areas. (Rhyolite occurs throughout the park.) Explain why we find these mudpots in the thermal areas and not in other parts of the park. c) If the predominate rock type in Yellowstone was basalt rather than rhyolite, would the mudpots be smaller or larger, assuming all other conditions to be the same? 23. In the table below indicate the relative rate (slow, moderate, high) of the types of weathering in each climate. Consider only the natural climate and not other factors, such as pollution. Rate of hydrolysis Rate of mechanical weathering (slow, weathering (slow, moderate, or high) moderate, or high) _windward side of Hawaii (50 to 85 degrees F, 150-200 inches precip.) _Antarctica (-70 to 35 degrees F, dry) _Columbia Basin (10-110 degrees F and dry) _Cascade Mountains, WA (0 to 80 degrees F, 60 to 100 inches precip.) 5
24. Gold may be found in many different associations. One way that it occurs is in quartz "veins". Many veins are formed in the late phases of the crystallization of an intrusion. In our last unit we studied the fractional crystallization of magma. Remember that the minerals with the highest crystallization temperatures were formed first in the cooling of a pluton. One of the last parts of a pluton to crystallize is the quartz and other heavy metals such as gold, copper, zinc, etc. It appears that the quartz and gold are transported in hot water solutions from the crystallizing pluton into the surrounding rocks where they cool and form the vein. If one studies a quartz vein closely, one sees that the rock adjacent to the quartz vein has a lot of clay in it, while the same rock away from the quartz vein contains no clay. Why is the rock close to the quartz vein have significant quantities of clay? 25. Mt. Rainier may be one of the most rapidly weathering places in the United States because the weathering is occurring faster on the inside than the outside of the mountain. Explain how the steam from hot rocks inside the volcano and volcanic gases are causing this very rapid weathering. Be as specific as possible. 6
26. A map of volcano X is below. The lines are rivers running from the mountain. Cross sections were taken at stations A through J. Answer the following questions from the cross-sections and the map: (the numbers in the parentheses on the cross sections are the ages of the layers) a) Using the information from the cross-sections, what type of volcano is illustrated? What makes you think this? b) What types of evidence do we need to claim that a volcano erupted in the past? (For example, is the evidence of a lava flow from the mountain sufficient evidence that the volcano erupted at a particular time?) c) From the various cross sections, construct a single list of the dates (in years before present the same as the dates given) that this volcano has erupted. d) Imagine that a news reporter asks you which eruption from the volcano was the biggest, what criteria would you use to answer this question? Apply this criteria to the sediment cores and determine the date of the eruption you think was the biggest. e) For the 6600 year eruption, determine the direction the wind was blowing at the time of the eruption. f) When will the volcano erupt next? 7
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