An erupting volcano will release gases, tephra, and heat into the atmosphere. The largest portion of gases released into the atmosphere is water vapor. Other gases include carbon dioxide (CO2), sulfur dioxide (SO2), hydrochloric acid (HCl), hydrogen fluoride (HF), hydrogen sulfide (H2S), carbon monoxide (CO), hydrogen gas (H2), NH3, methane (CH4), and SiF4. Some of these gases are transported away from the eruption on ash particles while others form salts and aerosols.
Volcanic gases are also produced when water is heated by magma. Gases also escape from pyroclastic flows, lahars, and lava flows, and may also be produced from burning vegetation.
Acid rain can be produced when high concentrations of these gases are leached out of the atmosphere. When Katmai erupted in 1912, acid rain damaged clothes that were drying outside on a line 2000 km away from the erupting volcano in Vancouver, British Columbia (Bryant, 1991). High concentrations of CaF2 can burn vegetation and other material on contact. Fluoride and chloride can contaminate water. Livestock have died from
drinking such contaminated water. Fluoride and chloride can also be irritating to the skin and eyes of animals, and can damage clothes and machinery. Carbon monoxide and carbon dioxide are usually produced in small amounts. However, large amounts of these gases will sometimes build up in low lying areas and can asphyxiate livestock and harm vegetation (Bryant, 1991 and Scott, 1989).
Recently, a new volcanic hazard involving tropical lakes in volcanic regions was discovered. Carbon dioxide built up at the bottom of tropical Lake Nyos was released from the bottom of the lake when the lake overturned. Fifteen hundred people were killed and 10,000 people burned in this disaster (Bryant, 1991).
Harmful concentrations of volcanic gases usually do not extend further than 10 km from the volcano (Scott, 1989). Remote sensing instruments have been used to track volcanic gases such as SO2. To find out more information about remote sensing and volcanic clouds click here . Other instruments have also been used to monitor volcanoes. These instruments measure amounts and types of volcanic gases. Currently much research is being done on how volcanic gases may contribute to changes in climate.
Text by C.M. Riley, Photo courtesy of the U.S. Geological Survey at CVO