Lab 11 Volcanic Hazards (1).docx

Geol 116 Fall 2023 Name Nicholas DeNobrega Lab 11 Volcanic Hazards Volcanoes present a wide range of different hazards as a result of the variation in magma composition and eruptive style (Table 1 is a nice review). While most areas of the United States are not locations of active volcanoes, the impacts of major eruptions can be widespread. In this lab we’ll look at hazards associated with three different styles of volcanoes in the U.S.—Yellowstone, Kilauea, and Mt. Rainier— to get a good sense of the types and distributions of hazards. Table 1. Relationships among magma composition, viscosity, volcano form, typical eruption products. Yellowstone National Park Most of Yellowstone National Park is a caldera, formed at the active end of the Snake River Hot Spot. A generalized geologic maps is shown in Figure 1. The caldera has produced major eruptions about 2.0 million, 1.2 million, and 0.62 million years ago, with estimated volumes of material of 2500, 275, and 1000 cubic km, respectively. The two biggest eruptions produced widespread ash falls (tephra), extending across much of the western half of the country, as shown in Figure 2. Since the 0.62 Ma eruption, smaller rhyolite eruptions have occurred within and outside of the caldera itself. Earthquakes have been occurring under and adjacent to the caldera, some shallow enough to suggest that magma may be moving toward the surface. And certainly there is considerable heat being generated, as evidenced by the famous geysers and hot springs of the park. Use the figures to answer the following questions. 1. Other than its world-famous geysers and hot springs (which are a local hazard due to the hot water), what volcanic hazard(s) are likely to exist in the Old Faithful area (west-central part of the park) due to renewed eruption? What is the basis for your hazard analysis?

Figure 1. Simplified geologic map of Yellowstone National Park. Thin lines represent contacts between different rock units; thick lines represent the locations of faults. Squiggles cover lakes (Yellowstone Lake in the large one in the center of the park). 2. Are there different hazards that might exist at the Mammoth Hot Springs area on the north edge of the map? Explain. 3. Which of the ash deposits (Figure 2) covers a larger area? Were the wind directions at the time of eruption the same or different?

Figure 2. Ash distribution from Yellowstone eruptions. Points show locations where the ash deposit has been identified.

4. The Huckleberry Ridge ash represents an eruption that was 2.5 times the volume of the Lava Creek event. But the area depicted for the Huckleberry Ridge ash is not 2.5 times the area depicted for the younger Lava Creek ash. What eruption characteristics and/or post-eruption processes could explain the difference in the areas covered by these ash deposits? 5. Scientists expect that the Yellowstone caldera will erupt again in the not-too-distant future (at least in geological time frame). What would be the principal impacts of a future mega-eruption? Hawaii—Kilauea Volcano The Kilauea volcano on the “big island” of Hawai’i has been extremely active historically, and indeed throughout the last thousand years (Figure 3). Ongoing eruptions have been occurring since 1983—the longest eruptive episode during recorded history. The spring and early summer of 2018 saw a significant increase in lava volume emitting from fissures in the East Rift Zone area (Figure 4). These eruptions destroyed more than 700 houses and other buildings. Use the maps of Figures 3-6 to answer the following questions. 1. Sketch on lined or graph paper a topographic profile from the city of Hilo through the summit of Mauna Loa from the topographic map, Figure 5. Based on the shape, is Mauna Loa a basaltic shield volcano, an andesitic composite volcano, or a dacitic-rhyolitic caldera? 2. What hazard would you expect at Hilo from an eruption of Mauna Loa? Kilauea? 3. How does the area affected by the 2018 lava flows (Figure 4) relate to the other historical flows at Kilauea (Figure 6)? How does it compare to the longer-term history of flows from Kilauea (Figure 4)?

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