Wikipedia:Monthfeature/2004September
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Volcanism of the Mount Edziza volcanic complex in British Columbia, Canada, spans more than 7 million years. The first magmatic cycle took place between 7.5 and 6 million years ago and is represented by the Raspberry, Little Iskut and Armadillo geological formations. Volcanism has taken place during five cycles of magmatic activity, each producing less volcanic material than the previous one. During these cycles volcanism has created several types of volcanoes, including cinder cones, stratovolcanoes, subglacial volcanoes, shield volcanoes and lava domes. The roughly 1,000-square-kilometre (400-square-mile) volcanic plateau of the MEVC originated from the successive eruptions of highly mobile lava flows. Several types of volcanic rocks were deposited by multiple eruptions of the MEVC. At least 10 distinct flows of obsidian were produced by volcanism of the MEVC, some of which were exploited by indigenous peoples in prehistoric times to make tools and weapons. (Full article...)