150Lec17-1

150Lec17-1 - Lecture#17 Calderas(Abbott pp 206-214 240-242...

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Lecture #17: Calderas (Abbott, pp. 206-214, 240-242) Be able to locate these volcanoes on a map and know their major properties. Long Valley, California Location : Eastern California (Figure 8.37, p. 211; Figure 9.38, p. 241). Be able to locate the caldera on a map. http://vulcan.wr.usgs.gov/Imgs/Gif/Projects/Deformation/Cascades/map_volcanoes_defm.gif Type: Caldera Composition: Rhyolite, but flood basalts erupted in the area 2.5 to 3 million years ago followed by periodic intermediate lavas. Association: Basin and Range tensional zone (Figures 7.5-7.7, p. 168) in southeastern California and Nevada. Unlike the Red Sea, the tension in the Basin and Range will probably not be enough to split North America and form a spreading zone between two new plates. Important Major Eruptions: The caldera formed about 760,000 years ago. Periodic major eruptions occurred up to about 100,000 years ago. Status: Dormant; Dangerous magmatic carbon dioxide emissions in the area. Yellowstone National Park, Wyoming Location : Northwest corner of Wyoming (Figure 8.39, p. 213). Be able to locate Yellowstone on a map. Type: Three calderas in and around the park (Figure 8.39, p. 213). Composition: Rhyolite is associated with the formation of the calderas. Basalts and other volcanic rocks also occur in Yellowstone. Association: Hot spot. Because of movements of the North American plate, the hot spot was located in Idaho in the past and is now under Yellowstone (Figure 8.38, p. 212; Figure 8.37, p. 211). Important Major Eruptions: 2.0 million, 1.3 million and 620,000 years ago. Last significant eruption was about 70,000 years ago. Status: Dormant
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Crater Lake, Oregon (Mount Mazama) Location : Southern Oregon (Figure 9.7, p. 221). Be able to locate the volcano on a map. Type: Caldera Composition: Rhyolites and intermediate (andesite) Association: Ocean-continent zone (Juan de Fuca plate subducts under North American plate; Figure 9.5, p. 220; Figure 9.6, p. 221) Important Major Eruptions: The eruption that formed the caldera was about 7,700 years ago. Status: Dormant Santorini, Greece Location : Southeastern Greece (Figure 8.35, p. 209), Thera is the major island associated with the caldera. Be able to locate the volcano on a map. http://www.santorini-private-tours.com/Santorini-map.html Type: Two calderas Composition: Rhyolites and intermediate (andesite) Association: Oceanic parts of the African plate to the south are subducting under the Eurasian plate to the north. Important Major Eruptions: ~1620 BC that destroyed the Minoan civilization (Figure 8.36, p. 210) Status: Dormant ___________________________________ _
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Introduction The formation of calderas is a violent volcanic event, especially with felsic and intermediate volcanoes. As stated before, calderas are large circular depressions (over 2 km in diameter) that form from the collapse of volcanoes after magma chambers partially empty (p. 492). Figures 8.34 (p. 208) and 8.40 (p. 213) show how calderas may form.
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150Lec17-1 - Lecture#17 Calderas(Abbott pp 206-214 240-242...

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