Submarine eruptions of basaltic magma range from highly explosive events to quiet lava effusions. Explosivity, driven by rapid exsolution of magmatic volatiles and/or steam explosions during interaction with external water, is increasingly suppressed by hydrostatic pressure. In this project a shallow marine Surtseyan deposit and a deep marine volcaniclastic rock sequence from a seamount at 2000 m bsl are studied to assess the limits of phreatomagmatic processes, esp. the role of steam at different depth levels. Moreover, hyaloclastite depositional mechanisms are analysed as well as the formation of limu o''Pele. In a nutshell, small volume fluxes, a forced, confined style of magma-water interaction combined with minimal exsolution of magmatic volatiles seem to be the controlling factors to generate limu o''Pele-bearing deep sea hyaloclastites, whereas open-vent eruptions and abundant degassing favour Surtseyan style eruptions. This book is aimed at all those volcanophils interested in the physical processes and dynamics of magma fragmentation during submarine eruptions.