Fill in the Blanks 172-testOnline version 172-test by Farhad Key 1 out killing cloud harmless concentrated this off were underground Volcanoes blast more than 100 million tons of carbon dioxide into the atmosphere every year but the gas is usually . When a volcano erupts , carbon dioxide spreads into the atmosphere and isn't in one spot . But sometimes the gas gets trapped under enormous pressure . If it escapes to the surface in a dense , it can push out oxygen - rich air and become deadly . Huge clouds of carbon dioxide released from California's volcanic Mammoth Mountain in 1984 , thousands of trees . The U . S . Forest Service declared the area - limits to campers and keeps a close eye on gas levels there to day .
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