Geological Society - Volcanic Gases

The mixture of gases released by volcanoes varies but, consists mainly of:

water vapour (steam) - about 78%
carbon dioxide - about 12%
sulphur dioxide - about 7%
other gases - about 3%.

When large amounts of volcanic gases are released from magmas, then highly explosive eruptions take place, forming clouds of volcanic ash and lethal pyroclastic flows.

Steam Vents

Steam Vents occur on most active volcanoes and are a sign that magma lurks beneath the surface!

Gases, released from solution in the magma, along with ground-water heated by the molten rock, escape to the surface through cracks and fissures to form steam vents and geysers.

Video: Eruption of volcano in Kamchatka, Siberia.
Source: Stromboli Online.

Volcanic explosions

Volcanic explosions of steam and other gases released from magma may blast rock and lava fragments (pyroclastics) high into the air as seen in this video clip from Kamchatka, in Siberia.

Video: Eruption of volcano in Kamchatka, Siberia.
Source: Stromboli Online.