When it comes to searching for domestic methane hydrates, however, JNOC must move underwater. Japan has no permafrost of its own. The lair of most methane hydrates lies far from shore and deep below the waves. There, in water depths of at least 600 to 800 m, low temperatures and extreme pressures in the sediments combine to squeeze methane and water into a crystalline structure. Each molecule of methane gets trapped within a cagelike lattice of frozen water molecules, an arrangement that greatly concentrates a large amount of methane into a small space.
Hydrates also go by the name of clathrates, a term derived from the Latin word for lattice.
The methane in most hydrate deposits originally comes from bacteria living beneath the seafloor. As they consume bits of plant and animal remains in the sediment, the bacteria excrete methane, a process still going on today. When conditions are cold and the pressure is high, the bacterial gas gets locked up into hydrates. In some deposits, the source of the gas lies much deeper, in sediments warmed by Earth's internal heat. Several kilometers below the seafloor, the temperature in the sediment rises so high that it cooks the buried organic debris.