[geoffsanders]

Considering lava cools and darkens almost immediately under water, I'd imagine it would have to be an incredibly epic underwater eruption (and thus, detectible) for that much light to make its way through that much water and project itself onto the clouds above that location. Also, the light should diffuse as it makes its way through water, air, and onto the clouds above, so the seemingly neat circles of light don't seem to match up with a sea floor-based light source either.

[idlewords]

The light would also be much bluer if it had passed through any significant quanitity of seawater. Red light attenuates very fast.

[madaxe_again]

Not necessarily lava. Could be a pumice raft which had enough latent heat after floating up to re-ignite.

Clutching at straws.