Volcanic Ash, Gases & Vog

Any or all of volcanic ash, gas and vog may blow downwind and over broad areas in volcanic eruptions. It can be difficult to unpick the impacts caused by each, and impacts reportedly caused by one may in fact be due to others or a combination. For example, crop leaf damage on Ambae, Vanuatu 2018 may have been from discrete periods of gas-derived acid rain but coincided with ongoing intermittent ashfall.

• Volcanic ash consists of tiny jagged pieces of rock and glass. It is hard, abrasive, mildly corrosive, conducts electricity when wet, and does not dissolve in water.
• Volcanic gases are emitted from a volcanic vent before, during or after a volcanic eruption. The most abundant volcanic gases include water vapor (H2O), carbon dioxide (CO₂) and sulfur as either sulfur dioxide (SO₂) or hydrogen sulfide (H₂S).
• The term 'vog' refers to a hazy mixture of mostly SO2 gas and very small acidic particles. More information can be found on the Hawaii Interagency Vog Information Dashboard.
• Acid rain is mostly derived from rain that has fallen through a cloud of volcanic gas or vog.

Subsections listed to the left of this page include more detail on volcanic ash, including how it is dispersed and deposited, and what ash deposits look like. Also listed are specific sections on volcanic gases and vog, and acid rain.