Like the image in the previous post (Deep Pacific 1), this photo was taken from one of the small portholes of the research submersible Alvin at a depth of around two and a half kilometers in the eastern Pacific Ocean. The rounded forms you see are referred to as pillows, for obvious reasons. When basalt lava erupts slowly on the seafloor, it cools and becomes very viscous. Its surface freezes quickly into solid rock, but that creates an insulating barrier against the cold seawater, and the molten lava within the pillows continues to flow, slowly, like thick molasses, creating a series of interconnected pillows. If you look carefully at this picture you can see the connections and visualize the process.