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File name:		 04-22
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Title: AA LAVA FLOW
Caption: This active aa lava flow is moving over an earlier flow of solidified pahoehoe lava. Both aa and pahoehoe are common types of basaltic lava. Aa has a blocky surface that develops from cooler, thicker, slower moving, and less fluid lava. (© J. D. Griggs/CORBIS. All rights reserved.)
Keywords: volcanoes, volcanism, volcanic eruptions, plate tectonics, tectonic plates, intraplate volcanism, mantle plumes, hot spots, shield volcanoes