Volcanoes are the sources of valuable gases in the Underwater world. The blue volcanoes provide oxygen, it can be consumed by your base and converted into money. Also the squirrel wheels consume oxygen to rotate.
Red volcanoes produce neon (red triangular particles). It is used by the Base boosters and Gas mixers.
Volcano reacts to taps: in the beginning every 3.9 taps produces one bubble. The more bubbles are produced, the more taps are needed for the next one (+0.001 tap per bubble created)
Volcano has 4 slots for a Hammer (Underwater).
New volcano can be discovered while exploring the sea with Clockwork crab or Scout submarine. Discovery probability is 9.5%.