Chapter 17 Section D: Volcanoes

- Immediately below the crust the earth is nearly molten
- Any slight increase in heat such as that generated by plate movements melts the rock
- The molten rock, known as magma, rises to the surface and generates volcanic eruptions
- An active volcano emits gases, liquids, and solids
- Gases: N2, CO2, HCl, HF, H2S, water vapor
- Volcanoes are the source of 2/3 of the sulfur in our air
- At high temperatures, the hydrogen sulfide gas given off is oxidized by air:
- 2H2S(g) + 3O2(g) 2SO2(g) + 2H2O(g)
- Some of the sulfur dioxide produced is reduced by hydrogen sulfide from the volcano:
- 2H2S(g) + SO2(g) 3S(s) + 2H2O(g)
- Some SO2 reacts with water to form acid rain
- The remaining SO2 is carried into the stratosphere by the eruption where it is oxidized to SO3
- SO3 is eventually converted to sulfuric acid aerosols
- These aerosols damage the ozone and absorb solar radiation, locally cooling the earth

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