GEL111Homework4

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School

Stanly Community College *

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111

Subject

Geology

Date

Apr 3, 2024

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docx

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3

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Christian Nelson GEL-111 29, January 2024 Chapter 4 Homework 1. Distinguish among magma, lava, and pyroclastic debris. - Lava refers to magma that emerges onto the Earth's surface. Lava is molten magma that streams from a volcanic vent onto the terrain. In contrast, pyroclastic material consists mainly of ash and solid rock propelled into the air during a volcanic eruption marked by explosions. 3. Does Photo B illustrate a lava flow or an ash accumulation? The eruption responsible began about36 hours before the photo was taken; what is the maximum age of the black rock visible in the photo? - Photo B is likely portraying the aftermath of a volcanic eruption, with the black rock observed having a maximum age of approximately 36 hours. This rock accumulated during the eruption within that specific time period. Therefore, Photo B likely illustrates a volcanic eruption and the subsequent buildup of black rock or volcanic material. 4. What type of melting does the subduction of an oceanic plate, as shown in Diagram A, trigger? Show where the volatiles involved in this process enter the mantle, and where melting takes place. Do volcanoes form on the subducting or overriding plate? - The initiation of flux melting is prompted by the subduction of an oceanic plate. Volcanoes are formed on the subducting plate as the less dense continental plate is pushed beneath the more
dense oceanic plate. The subducted plate undergoes liquefaction due to the combination of intensity and contact. 7. On what basis do geologists distinguish among magma compositions? What is the difference between mafic and felsic magma? What is the relationship between the minerals in an igneous rock and the chemical composition of the rock? - In the field of geology, the term "felsic" is used as an adjective to characterize igneous rocks that have a relatively high content of elements forming feldspar and quartz. On the other hand, "mafic" is associated with rocks that are comparatively richer in magnesium and iron. One significant distinction lies in the viscosity, where felsic magma or lava tends to be more viscous than mafic magma/lava. 9. Why does magma rise? How does its viscosity during flow depend on its composition? - Increased silica content in magma correlates with higher viscosity, where viscosity is a measure of a liquid's resistance to flow. The viscosity of magma plays a crucial role in determining its behavior. Mafic magma, characterized by lower silica content, exhibits lower viscosity, allowing it to flow easily to the surface.
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