Methane hydrate. Basically an ice-like substance of methane trapped in water crystals. It can stay in that form when trapped under ocean sediments (there are va

Methane hydrate. Basically an ice-like substance of methane trapped in water crystals. It can stay in that form when trapped under ocean sediments (there are vast amounts in the ocean), but when pressure is released and it's exposed to warmth, the methane can escape the water structure.