After this lava delta collapsed, new lava spewed from the tube like a fire hose into the ocean 60 feet below. This story appears ... Back home, Peter marked the puka, or cave entrance, on a ...

The Canary Islands not only boast the third largest volcano in the world, but also the largest natural underwater lava tunnel ... and a blend of dry and submerged cave sections.

Researchers want to know if volcanic lava tubes could support a moon base and they are looking for answers deep below ...