Cross-section of the pillow lava in Boatmans Harbour near Oamaru.br/br/Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava under water and are characterized by thick sequences of discontinuous pillow-shaped masses, commonly up to one metre in diameter. They occur wherever mafic to intermediate lavas are extruded under water, such as along marine hotspot volcano chains and the constructive plate boundaries of mid-ocean ridges. As new oceanic crust is formed, thick sequences of pillow lavas are erupted at the spreading center fed by dykes from the underlying magma chamber. br/br/The presence of pillow lavas in the oldest preserved volcanic sequences confirms the presence of large bodies of water on the Earth's surface early in the Archean eon, over 2,500 million years ago.