An open lava tube. This collapsed feature often occurs when the outer edges of
a flow are quickly cooled by contact with seawater. The insulated lava inside
remains viscous and eventually recedes, creating a void.
Image ID: expl6520, Voyage To Inner Space - Exploring the Seas With NOAA Collect Photo Date: 2011 July 20 Credit: NOAA Okeanos Explorer Program, Galapagos Rift Expedition 2011