Tephra generated by steam explosions built this small littoral cone along the southern shoreline of Kilauea Volcano, Hawaii. Note pahoehoe flow nearing the ocean below the cone. Credit: L. Keszthelyi / US Geological Survey.
A littoral cone is a cone of lava fragments built on the surface of a lava flow pouring into a body of water, usually the sea ('littoral' refers to a shoreline). Lava entering the ocean heats and boils seawater, often generating steam explosions that hurl tephra onto the shore, including spatter, bombs, blocks, ash, lapilli, and, rarely, limu. As the various tephra accumulates on the shoreline, a well-developed cone may be created.