What is the primary gas emitted during a volcanic eruption?

During a volcanic eruption, the primary gas emitted is water vapor. This occurs because when magma rises to the Earth's surface, the pressure decreases, causing dissolved gases within the magma to expand and escape. Water vapor is the most abundant gas released, often comprising the majority of the gas emissions during eruptions.

In addition to water vapor, other gases like carbon dioxide and sulfur dioxide are also emitted but in smaller quantities compared to water vapor. The presence of water vapor is significant in volcanic activity as it can influence the eruption style, contributing to explosive eruptions when combined with other gases and magma.

Understanding the role of water vapor in volcanic eruptions is essential as it affects not only the eruption dynamics but also the climate, as volcanic water vapor can enter the atmosphere and contribute to weather patterns.