Pyroclastic deposits, produced during subaqueous volcanic eruptions, point to the existence of explosive processes. Magma/water interaction is a possible source of these explosions. Under atmospheric pressure a thermohydraulic explosion mechanism was identified that can explain the high kinetic energy release of phreatomagmatic explosion and the formation of typical subaerial phreatomagmatic pyroclastic deposits. The applicability of this mechanism under subaqueous physical conditions is discussed. Whereas the efficacy of heat energy transfer from magma to water in general increases with rising hydrostatic pressure, the conditions for the formation of a critical magma-water premix volume increasingly decline. Our analysis indicates that subaqueous volcanic thermohydraulic explosions should become increasingly improbable at water depths exceeding 100 m and practically impossible at water depths in excess of 1 km. Pyroclastic deposits found at greater depths, bearing signatures of phreatomagmatic origin therefore should be the result of comparably low energy magma-water interaction.