EC Quiz #3_ Chapters 4-5

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Geology

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Dec 6, 2023

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1. Which statement about the May, 1980, eruption of Mount St. Helens is FALSE? ○ During the eruptive period, the mountain peak was substantially built up by new lava flows and pyroclastic debris. 2. Which one of the following shows the correct order (left to right) of decreasing magma viscosity? ○ Rhyolite, andesite, basalt 3. Kilauea and Mauna Loa are ________. ○ Basaltic shield volcanoes 4. Cinder cones are built from ________. ○ Ejected lava fragments from fine ash to bombs 5. Which of the following statements about pyroclastic flows is TRUE? ○ They consist of hot gasses infused with ash and lava fragments and move at extremely high speed. 6. Which kind of volcanism is typical of mid-oceanic ridge systems? ○ submarine; basaltic lava flows 7. What are the three components of magma? ○ the liquid portion (mobile ions of the eight most common elements found in the Earth's crust) called melt, the solid portion which consists of silicate mineral crystals, and the gaseous portion called volatiles 8. How does the crystallization of igneous material occur? ○ The liquid igneous material cools, the ions within slow in their movement, and they pack more closely together. When sufficiently cooled, ions become confined to a crystalline arrangement. 9. What is the difference between extrusive igneous rocks and intrusive igneous rocks? ○ Extrusive igneous rocks cool and solidify on the Earth's surface, whereas intrusive igneous rocks cool and solidify beneath the Earth's surface. 10. Fill in the blanks using the choices below: ____ are minerals typically found in igneous rocks that have a high silica content, whereas ____ are minerals that are typically found in igneous rocks with a low silica content. ○ Plagioclase, feldspar, and quartz; pyroxene and olivine 11. What type of texture occurs in igneous rocks that form deep underground?

○ phaneritic (coarse-grained) 12. Which of the following is an extrusive igneous rock? ○ Pumice 13. What does the term "texture" refer to when describing an igneous rock? ○ the appearance of a rock based on the size(s), shape(s), and arrangement of the mineral grains it contains 14. What factors influence the texture of an igneous rock? ○ the rate at which the rock cools, the amount of silica that is present in the magma from which it forms, and the amount of dissolved gases present in the magma 15. Which of the following is a probable history of an igneous rock with porphyritic texture? ○ The rock began cooling under the Earth's surface, but then was moved to above the Earth's surface where it finished cooling. 16. Fill in the blanks in this sentence using the terms below: Granite and rhyolite are both ____, but they differ in ____. ○ Felsic; crystal size 17. Which of the following choices correctly classifies the four listed igneous rocks by composition? ○ Gabbro is mafic; obsidian is felsic; granite is felsic; andesite is intermediate. 18. Which of the following choices classifies the three listed rocks by composition and texture? ○ Diorite is intermediate with a phaneritic texture; rhyolite is felsic with an aphanitic texture; basalt porphyry is mafic with a porphyritic texture. 19. In what way do tuff and volcanic breccia differ from other igneous rocks such as granite and basalt? ○ Tuff and volcanic breccia do not consistently belong to a single compositional category, unlike granite, which is always felsic, and basalt, which is always mafic. 20. How do batholiths, stocks, and laccoliths differ? ○ Batholiths are the largest type of igneous bodies and occur in a linear fashion with a distance of 100km or more; stocks are smaller than batholiths; laccoliths bend the sedimentary layers above them, whereas the sedimentary layers below remain relatively undeformed.

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