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)
U.S. Geological Survey, U.S. Department of the Interior, Volcano Hazards Program, Glossary, Washington, DC, USA 2011. http://volcanoes.usgs.gov/vsc/glossary/alluvium.ht ml, (ND/ Volc Emr - Amer) {795}