Submarine lavas and hyaloclastite

Submarine lavas are important because they are the most widespread surficial igneous rocks on Earth. They are erupted at a variety of ocean water depths, display a wide spectrum of sizes, shapes, and compositions, and comprise up to 2 km of the uppermost ocean crust created at mid-ocean ridges or back-arc spreading centers (Chapter 3). Volcanoes at intra-oceanic convergent margins begin as small submarine volcanoes in deep water consisting of submarine lavas, hyaloclastite, intrusions, and in some cases submarine pyroclastic facies (Chapter 31). In submarine settings, rising magma commonly encounters thick successions of water-saturated, unconsolidated sediments and may fail to erupt, instead spreading laterally into the soft sediments to form shallow intrusions. Volcanoes also form on oceanic crust away from plate boundaries, and may grow large enough to form islands (e.g., Hawaii Emperor chain). This setting also includes huge submarine Java-dominated volcanic plateaus such as the Ontong-Java Plateau. Volcanic rocks from ancient submarine settings may be exposed on land, uplifted as a result of plate collisions. In this chapter, we summarize eruption styles and modem versus ancient products, present results from new studies of the modem seafloor, address the formation of hyaloclastite and peperite associated with seafloor lavas and intrusions, and review submarine felsic Java complexes.