Huge quantities of CH4 are stored in marine sediment in the form of methane hydrate, bubbles, and dissolved CH4 in pore water. Here I discuss the various pathways for methane to enter the ocean and atmosphere, including: (i) Methane hydrate dissolution or dissociation as it rises through seawater. The dissociation rate can be 2 to 3 orders of magnitude greater than the dissolution rate. (ii) The dissolution and expansion of a bubble with or without a hydrate shell as it rises through seawater. There is a critical radius (which depends on depth), above which a bubble would reach the surface or even become larger as it rises. I also propose and model the dynamics of a new type of terrestrial gas-driven eruptions: methane-driven oceanic eruptions. Such eruptions not only represent a yet unrecognized geohazard, but also provide a pathway for CH4 to rapidly enter the atmosphere as a greenhouse gas.