IDS 102 Study Guide: Unit 3 The purpose of this study guide is to help you prepare for the third exam by focusing your studying and providing example essay questions. In the Focus On section you will find the primary ideas that you should understand as you prepare for the exam. The second section of this Study Guide is a set of example questions for the exam. We will use some of these questions as in-class problems for group work. PART I: Focus on: Density and Pressure: You should be able to answer the types of questions given in the end of module questions. Volcanism 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 connections between the types of volcanic rocks and the types of volcanoes 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. what happened at Mt. St. Helens in 1980? (The events that preceded the major eruption and what triggered the eruption.) when a mountain such as Rainier is dormant, is there a way to predict when it will erupt next? hydrothermal alteration (such as the mudpots in Yellowstone and the alteration of andesite at Mt. Rainier) Inner Earth: You should know the basic subdivisions of the inner earth (crust, mantle, outer core, and inner core), what type of material is in each zone, and how we know about its existence. How does the density of the Earth change with depth inside the Earth? Which of the zones of the Earth has the greatest volume? What is the relative thickness of the continental crust versus the oceanic crust? What role do the seismic wave velocities play in our interpretation of the Earth s interior? How do we know the earth s magnetic field is not formed by a big magnet inside the earth? What forms the Earth s magnetic field? What is the effect of high temperature (like those inside the Earth) on magnets? What determines the velocity of seismic waves? How are p and s waves different? What creates the p-wave and the s-wave shadow zones? What do these zones tell us about the structure of the Earth s interior? You should be able to describe the principle of isostasy and how it helps shape the Earth s surface. Why are there ocean basins? What is the density of the oceanic crust compared to the continental crust? What causes the difference in density?
Plate tectonics: What were the types of evidence that Wegner used to support his hypothesis of continental drift? You should be able to describe these techniques and identify how they help support his idea. What are magnetic reversals and how do they help support seafloor spreading? What is the pattern of ages in the ocean basins? What are the three major types of plate boundaries? How do we recognize them? Is Hawai i and the other islands of that chain, a product of a divergent plate boundary? Why/ Why not? You should be able to draw a cross-section (not just a profile) starting from the Juan de Fuca ridge through Washington. In this cross section you should show the location of the Olympic Mountains, the Puget lowlands, and the Cascade Mountains. Why are there volcanoes in the Cascade Mountains (such as Mt. St. Helens)? How would you recognize the location of a divergent plate margin? A convergent plate margin? A transform plate margin? Why are there deep sea trenches at subduction zones? How does magma form in divergent plate boundaries? In convergent plate boundaries? PART II: Sample questions to prepare for the essay part of the third unit exam 1. How does viscosity of the magma affect the nature of a volcanic eruption? 2. What is the role of the gases in magma in determining the character of an eruption? 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. 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. Complete the following chart: Name Silica content Color Viscosity rhyolite high basalt darkest lowest 6. 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. 2
7. The illustration 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? 8. 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? 9. Basalt may be found in dikes and sills. Is this statement true or false? Explain your choice. 10. 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!) 11. How are pyroclastic flows and lahars similar? different? 12. 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? 3
13. 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? 14. Label the regions of the interior of the earth in the cross-sectional diagram of the earth below: For each of the regions noted: a) describe whether the material is a solid or liquid. b) discuss the composition of the material in the region and the lines of logic which indicate this composition. 4
15. Imagine that you have observed the following geographic map and you suspect that there may be a divergent plate boundary between Land A and Land B. What techniques could you use to determine if a divergent plate boundary is present? (The more techniques you suggest the better- as long as they will work!) Assume that you have sufficient time and money to do this. 15b. Are the earthquakes that happen at divergent plate margins shallow or deep hypocenters? Explain your answer. 16. Describe two methods one could use to determine the relative velocity of the earth's lithospheric plates. (Do not use the satellite (GPS) method). 17. At the mid-oceanic ridges, geologists believe that the Earth s crust is pulling apart along what we call a divergent plate boundary. If the Earth is under tension in this area (which appears to be true from earthquake studies), why is there a mountain range along this zone? 18. The extinction of the dinosaurs has puzzled earth scientists for a long time. About 30 years ago a hypothesis was proposed that mass extinctions, such as the one in which the dinosaurs became extinct, were created by the collision of meteorites and/or comets and the Earth. In the past 30 years a significant amount of data suggests that meteorite and/or comet impacts have had a major effect on life on Earth. There are about 150 known impact craters on the Earth. Most of these are "terrestrial," (on land). Since a majority of the Earth's surface is covered by water, it is likely that a significant number of meteorites and/or comets have landed in the oceans. (A crater has been found off of the coast of Mexico which dates to about 65 million years and is now assumed to be the impact site for the event at the end of the Cretaceous which ended the reign of the dinosaurs.) It is possible (likely) that there have been more impacts of meteors/comets in the ocean basins than the number of craters under the oceans. Explain two reasons that meteorites may have hit in the oceans, but today we cannot find a sufficient number of craters in the ocean basins (the water does not significantly "cushion" the impact of the object!). 5
19. If the distance from the oceanic trench to the line of andesitic volcanoes is 200 miles in one location and 300 miles in another location, what reasons can you suggest for this difference in distance? Explain your ideas as "far" as you can. 20. Describe the relative motion of the lithospheric plates of the western United States. Discuss the types of plate boundaries found between the various plates. Using arrows illustrate the relative motion of the various plates of the Pacific Northwest and California. 6
21. In the map below, a "new" hot spot has just formed under the Pacific plate. The Pacific plate is now moving in a northwesterly direction. Let's say for this problem that in 10 million years the Pacific plate changes its direction to a straight northerly direction. Draw what you think the series of seamounts would look like from this hot spot at 20 million years in the future. 22. Use the information on page 310 to explain the cross section of the Pacific Northwest below: W E Mtn Range A ocean Mtn Range B What range of mountains is Mtn Range A? Mtn Range B? Can you find the Juan de Fuca Ridge? The Juan de Fuca plate? The Pacific plate? Where would you find oceanic crust? Continental crust? Benioff zone? 7