A cone of
lava fragments built on the surface of a
lava flow pouring into a body of water, usually the sea, is called a
littoral cone ("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.