5_Volcanoes_StudyGuide_GEOL101

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May 6, 2024

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GEOL101 Study Questions for Lesson 6: Volcanoes Use these questions to evaluate your knowledge of the material to better target concepts you should study further. They can provide a personalized road map of what concepts you need to focus on. The following questions will help you review the MAJOR concepts and relationships you should understand and may not comprehensively cover every question on the exam for this unit. Many of the questions require synthesis and integrate several concepts; they will take you some time to complete. Therefore, you work through these questions as we cover them in class to allow enough time for you to identify areas you need to study in more detail. Trying to complete this study guide hours before the exam will be overwhelming and is not the best approach for concept mastery. You do not have to submit this for a grade. In addition to these questions, you should review all assigned readings and videos, assignments, quizzes, and handouts. Igneous Processes and Eruption Style 1. Know and be able to apply the vocabulary terms listed at the beginning of the lecture slides. 2. What two criteria that determine how igneous rocks are classified? Extrusive and Intrusive 3. Explain how and where volcanic glass forms and how its cooling rate compares with plutonic and volcanic rocks and their resulting textures. Incorporate the following in your answer: glassy, phaneritic, aphanitic. 4. Volcanic glass forms in oceans where lava does not have time to crystalize at all giving rocks like obsidian a glassy texture. It almost instantly cools while plutonic and volcanic rocks take a little longer to cool and have the opportunity to crystalize. In plutonic and volcanic rocks there are microscopic crystals making the rock have a phaneritic 5. Sketch a porphyritic texture and explain how it forms. What type of igneous rock is a porphyry classified as and why? Porphyritic texture = chocolate chip cookie – it is classified as a volcanic/extrusive rock because they are pyroclastic rocks 6. How are the two most common elements in Earth’s crust relevant to the formation of minerals and rocks? Explain how they’re related to the following terms: mafic, intermediate, and felsic. Include the weight % breakdown for those 3 terms in your answer. Silicon and oxygen are the most abundant and depending on the amount of these minerals that each rock contains depends on whether they are going to be felsic, mafic, or intermediate. Mafic rocks don’t have as much silicon as felsic and the amount of oxygen 7. Describe how color can be used to determine the silica content of igneous rocks. The darker color the rock the less silica the rock is going to have 8. Explosivity is determined by what 2 MAIN factors? Determined by gas or volatiles and the viscosity of the lava rock 9. Give some examples of viscous and non-viscous fluids. Viscous - Paste - Syrup - Molasses Non viscous Water

- Detergent 10. Describe how and why composition and temperature affect a volcano’s explosivity. Composition of volcanoes affects the explosiveity because those that can obtain a higher higher viscous magma will have greater amounts of volitales that will be more explosive. Hotter temperatures will volcanoes will form more mafic rocks which will erupt more effusively while explosive volcanoes will be cooler. 11. Fill in rows 1-7 of the Volcanic (and Igneous) Concepts Table. 12. Break down a volcanic eruption into steps. Explain what happens as magma rises through a volcanic conduit. Magma forms in the crust; it melts pre existing rock and gas is dissoleved in magma of high pressure. Magma then rises through the lithosphere due to density differences and coalesces, forming larger bodies of magma. Gas bubbles begin to form due to lower pressures. Think of it like a can of soda exploding for explosive volcanoes. 13. What constitutes pyroclastic debris? Ash, volcanic bombs and block, toxic gasses, pumice, volcanic gas shards and crystals 14. List the 3 most abundant volcanic gases. H20, C02, S03 Volcanic Landforms 15. Describe the physical differences between the 3 volcanic CONES as discussed in lecture. Summarize how each form and what they’re primarily made of. Include a scale drawing of each in your explanation (consult the figure on last slide titled “Volcanic Landforms…” of Part 2: Volcanic Landforms). A shield volcano is bigger than a stratovolcano to cinder cone. Because it sits on top of a magma chamber, the volcano can also be very long and erupt in different places. Cinder cones are the smallest out of the 3 and are composed only of cinders which are solid pieces of lava that cool in the air. They are steep sided and easily erode. Stratovolcanoes are composed of layers of intermediate and felsic lava. They are stronger than cinder cone volcanoes and are steeper. They usually have a crater where the volcano erupts. 16. Discuss the cascade of events that triggered the 1980 Mt. St. Helen’s eruption (see the textbook for additional details). 17. What is a lava dome? Which type of volcanic CONE are they usually associated with and why? volcanic products (ex. la A lava dome is when hot, viscous lava starts to build up in the crater of a volcano into a dome shape that allows for the reconstruction of the volcano. They tend to occur in stratovolcanoes with high explosivity. 18. How does a caldera differ from a crater? What types of volcanoes can calderas be associated with? Explain how temperature, silica content, viscosity, and gas content determine the type of volcanic products (ex. la A lava dome is when hot, viscous lava starts to build up in the crater of a volcano into a dome shape that allows for the reconstruction of the volcano. They tend to occur in stratovolcanoes with high explosivity. Unlike a crater, a caldera is when rock collapses inward in a magma chamber creating a lake over that magma chamber while a crater is where volcanic material erupts from and is just a dent 19. vas vs. pyroclastic material) produced during an eruption and, in turn, how they dictate the type of volcanic landforms created. 20. Fill in row 10 of the Volcanic (and Igneous) Concepts Table.

Volcanic Hazards and Volcanic Arcs 21. Why are lavas the greatest volcanic hazard in Hawaii? Describe the impact of disruptive lava flows on a community. They are the greatest hazard because it has a low viscosity with allows them to flow easily onto roads and where population is high. This kind of lava also takes time to cool down and solidify making it dangerous to walk on or do anything about it. 22. How does volcanic ash form? What hazards does it pose when it’s ejected into the atmosphere? Volcanic ash forms when and explosive volcano erupts, and the rocks cool faster in the air and break down into dust particles. When ejected into the atmosphere, it has the potential to pollute the air and make it hard for people to breathe. 23. Compare and contrast bombs and blocks. Where in the proximity of a volcano would they pose the greatest risk? volcanic bomb is molten volcanic material that cools in the air or on the ground. It around 2.5 inches while a block is part of the pre-existing volcano and is not molten. A block is solid when it is ejected. These objects would pose more risk to cities or towns that are in the vicinity of any stratovolcano. If they are in the path of a pyroclastic flow then they are also at risk of being hit by one of these bombs or blocks. 24. What is a pyroclastic flow? Why do they pose a risk to populations along the flanks of a volcano? Which volcanic CONE would they be associated with? Why? A pyroclastic flow is a very hot ash and debris cloud that has no predictable path and is usually caused by stratovolcanoes. They pose risk to populations along the flanks of a volcano because if part of a hot lava dome breaks off, it creates one and the paths of them are unpredictable. 25. What is a lahar? Why are they difficult to predict? What areas around a volcano must susceptible to lahar hazards? A lahar is basically mud from the ash and water of the volcano. Lahars are difficult to predict because it they're usually triggered by either tectonic activity or magmatic activity which are hard to predict as well. Areas with a lot of heavy rainfall like Seattle, Washington or Oregon are more succeptable to experiencing damage from lahars. 26. Why is Mt. Rainier such a dangerous volcano? What contributing factors are responsible for this? Mt. Rainier is one of the most dangerous volcanoes in the U.S. because of the deposits of it and how close it is to very populated cities. 27. Fill in row 11 of the Volcanic (and Igneous) Concepts Table. 28. From the Volcanic Arcs video lecture: How do volcanic island arcs form, and what kind of plate tectonic environment are they affiliated with? How is a continental volcanic arc different from a volcanic island arc? Draw a generalized cross-section of each type of volcanic arc, labeling the types of lithosphere, the mantle, the trench, and the location of volcanic arc. List a geographic example of each type of volcanic arc. A volcanic arc is formed at a subduction zone where the plates don't subduct at a 90 degree angle of Earth's surface. A continental arc forms when the overlying plate is continental lithosphere while an island arc is when 2 oceanic lithosphere converging together. Island arcs will always form volcanoes on the overlying plate.An example of where a volcanic arc is formed would be the ring of fire. An example of an island arc would be Mt. St.

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