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Norco College *

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Geology

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May 9, 2024

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docx

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P. 1 Homework Ch. 14: Volcanoes Use the book and my PPT for the homework! Watch the attached videos : 1. Volcanoes 101 | National Geographic and 2. 5 Most Deadly Volcanic Eruptions In Human History - Great Animation 1. Explain in a paragraph the nature of the volcanos: origin, where on planet are the eruptions more frequent and why? The origin of volcanoes is related to the movement of tectonic plates that make up the Earth's lithosphere. Volcanic activity is more frequent in three types of plate boundaries: convergent (where plates collide), divergent (where plates separate), and at hotspots (fixed locations over the Earth's mantle). Eruptions are more frequent along convergent and divergent boundaries due to the thinning of the Earth's crust, which allows magma to rise to the surface. Hotspots, like the one under the Hawaiian Islands, are not related to plate boundaries but are instead areas of intense heat within the Earth's mantle that cause magma to melt and rise. 2. Define and contrast:  Magma: A mixture of molten rock, volcanic gases, and crystals that forms in the Earth's mantle.  Lava: Magma that has reached the Earth's surface and is in the process of cooling and solidifying.  Pyroclastics: Fragments of solidified lava and volcanic glass ejected during an eruption. These fragments can vary in size from tiny ash particles to large volcanic bombs. 3. The general formation and shape of the volcanic peaks , as well as the style of the volcanic eruption are determined by the chemistry of the magma. Provide a short comparison of: - Granitic (Felsic) magma: This magma has a high silica content, which makes it thick and sticky. It tends to produce explosive eruptions, forming steep-sided stratovolcanoes (composite volcanoes) with thick layers of ash and lava flows. - Basaltic (Mafic) magma: This magma has a low silica content, making it runny and less prone to explosive eruptions. It forms broad, gently sloping shield volcanoes, like those in Hawaii, with fluid lava flows. 4. The Hawaii volcanoes are the best examples of Shield volcanoes. Watch the video : 3. Hawaii Volcanoes National Park - See the Biggest Volcano in The World. Write a paragraph about the origin of the Hawaii islands and the lava behavior. Examples: The Hawaiian Islands were formed by the movement of the Pacific Plate over a hotspot in the Earth's mantle. As the plate moves, it allows magma to rise and create new volcanoes. Over time, the older volcanoes become extinct, and new ones form further upstream. The lava in Hawaii is primarily basaltic, which results in low-viscosity lava flows that can travel long distances. This behavior contributes to the formation of the broad, shield-like volcanic peaks observed in the region.

5. On the next page compare the two major volcanic Peaks: Shield volcanoes and Composite (Strato) volcanoes. Shield volcanoes (e.g., Hawaii) vs. Composite (Strato) volcanoes:  Height: Shield volcanoes are much larger in volume but have lower heights compared to composite volcanoes.  Lava: Shield volcanoes have more fluid, basaltic lava, while composite volcanoes have thicker, more viscous lava.  Slope: Shield volcanoes have gentle slopes (less than 10 degrees), while composite volcanoes have steeper slopes (up to 30 degrees).  Eruptions: Shield volcanoes typically have non-explosive eruptions, while composite volcanoes have explosive eruptions.  Material: Shield volcanoes are primarily built of fluid lava flows, while composite volcanoes are built of alternating layers of ash, lava, and volcanic bombs.

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