Question

the eruption of mount st. helens on may 18, 1980
volcanoes cycle carbon from below the earths surface back into the atmosphere. volcanoes emit co₂, ash, and other gases. over billions of years, volcanoes have added a significant amount of co₂ to the atmosphere.
however, the amount of co₂ that volcanoes contribute each year is small compared to other carbon sources. for example, the eruption of mount st. helens in washington emitted 10 million tons of co₂ into the atmosphere over 9 hours. by comparison, human activities release the same amount of co₂ in about 2.5 hours.
how do volcanoes affect the carbon cycle? select the true statements.

• volcanoes emit more co₂ per year than human activities.
• volcanic eruptions move carbon from below earths surface to the atmosphere.
• volcanoes have added co₂ to the atmosphere over billions of years.
• volcanic activity is a carbon sink.

Explanation:

1. Analyze "Volcanoes emit more CO₂ per year than human activities": The text says human activities release the same CO₂ as Mount St. Helens' eruption (10 million tons) in ~2.5 hours, while the eruption took 9 hours. So human activities emit more per year. This statement is false.
2. Analyze "Volcanic eruptions move carbon from below Earth's surface to the atmosphere": The text states "Volcanoes cycle carbon from below the Earth's surface back into the atmosphere". This matches, so it's true.
3. Analyze "Volcanoes have added CO₂ to the atmosphere over billions of years": The text says "Over billions of years, volcanoes have added a significant amount of CO₂ to the atmosphere". This is true.
4. Analyze "Volcanic activity is a carbon sink": A carbon sink absorbs carbon, but volcanoes emit CO₂ (release carbon), so this is false.

Answer:

• Volcanic eruptions move carbon from below Earth's surface to the atmosphere.
• Volcanoes have added CO₂ to the atmosphere over billions of years.