What substance is primarily released during volcanic eruptions that form ash clouds?

The substance primarily released during volcanic eruptions that contributes to the formation of ash clouds is gases in magma. During an eruption, volcanic gases such as water vapor, carbon dioxide, sulfur dioxide, and others are expelled from the magma. As the pressure decreases when magma rises to the surface, these gases expand rapidly and escape, carrying solid fragments of volcanic rock and ash with them.

The interaction of these gases with the magma can lead to explosive eruptions, resulting in a significant amount of volcanic ash being ejected into the atmosphere. This ash consists of finely divided volcanic rock, and when it cools and solidifies, it solidifies into the ash cloud that can spread over large areas, impacting air travel and climate.

While water vapor is indeed a major component of volcanic gas emissions, it is not the primary substance solely responsible for forming ash clouds. Instead, it is the combination of gases along with the solid materials from the magma that primarily create the ash clouds observed during eruptions. Other gases, like carbon monoxide and hydrogen sulfide, may be released in smaller quantities but do not play a significant role in the formation of ash clouds.