Idealized phase diagrams illustrating where methane hydrate is stable in marine and permafrost settings. Hydrate can exist at depths where the temperature (blue curve) is less than the maximum stability temperature for gas hydrate (orange curve). Pressure and temperature both increase with depth in the Earth. Although hydrates can exist at warmer temperatures when the pressure is high (orange curve), the temperature at depth (blue curve) gets too hot for hydrate to be stable, limiting hydrate stability to the upper ~1km or less of sediment. The presence of salt, a gas hydrate inhibitor, shifts the gas hydrate stability curve (orange) to lower temperatures, decreasing the depth range of the gas hydrate stability zone. For seawater, this decrease is approximately 1.1°C (Dickens and Quinby-Hunt, 1994).
From collection: Frozen Heat - A Global Outlook on Methane Gas Hydrates