Pillow lava, formed at a deep ocean hydrothermal vent. Pillow lava forms when molten rock (magma) oozes out from underwater vents. When the molten rock makes contact with the cold water it rapidly solidifies, forming a hard crust. The inside of the rock remains molten for longer than the outside, and the flow of molten rock into the hard crust insinflatesins the crust, forming these rounded pillows. Here, a thin layer of sediment has formed over the pillow lava, allowing the age of the lava to be estimated. Parts of the submersible used to explore this region are seen around the image. Photographed on the East Pacific Rise.