What are the most common gases

Composition of volcanic gases

The most common volcanic gas is water vapor or H.2O. There is also carbon dioxide (CO2), Sulfur dioxide (SO2) and subordinate also carbon monoxide (CO), hydrochloric acid (HCl), hydrogen (H2) and hydrogen sulfide (H2S), whereby the proportionate composition of the gases can vary (see figure above). The effects that volcanic gases have on the environment are very diverse. Hydrogen sulfide, for example, is poisonous and can cause health damage to people in the immediate vicinity of the volcano.

The escape of volcanic gases also changes the composition of the atmosphere, especially when the gases reach higher layers. In the upper atmosphere, the stratosphere, for example, sulfur dioxide, which forms aerosols from sulfuric acid with water, causes the air layer to heat up. However, the solar radiation is also reflected, so that less radiation reaches the earth's surface, which means that the temperature cools down.

The composition of the volcanic gases depends on the chemical and mineralogical composition of the magma. A high silica content (SiO2) largely determines the explosiveness of a volcano, while lavas that are low in silica and thus at the same time rather hot and thin, are usually released in a less dangerous manner. A high silica content makes the magma viscous. As a result, the water vapor, the most important volcanic gas, cannot escape when the magma rises, so that the internal pressure of the gases in the molten rock increases. As a result, the rock material is literally pulverized during the eruption, and ash columns with high levels of particulate matter can arise well over 10 kilometers.

Volcanic eruptions are often highly explosive, particularly along the subduction zones, where oceanic crust is submerged under continental crust. Examples of this can be found in the Andes along the South American Pacific coast or in Indonesia and Japan. Further information can be found in the ESKP article "Dangerous water vapor: phreatic eruptions".

Text: Dr. Ute M√ľnch "Knowledge Platform" Earth and Environment "(ESKP), technical review of the German Research Center for Geosciences (GFZ), updated in March 2020 by the ESKP editorial team.