The warmth for the incubation of the eggs of megapodes comes from the sun, decaying vegetation or volcanic sources.

Consequently at no stage of this civilization did volcanic sources do more than supplement the amazingly rich coal seams of Antarctica.

Lake Lanao waters come from a volcanic source, the lake being the crater of an extinct volcano.

Can't be from a volcanic source.

There aren't really any sources for sulfur except volcanic sources.

"I should have known that the building stones came from a volcanic source."

But getting close to volcanic sources is difficult and dangerous.

Behind me, higher up in the hills, solitary smudges of smoke drifted lazily above volcanic sources.

The city's ryokans and public onsen are amply supplied by the same volcanic source.

The contamination from local volcanic sources is sometimes detected at the observatory, and is then removed from the background data.