In addition to naturally occurring oil and gas seeps in the Santa Barbara Channel, north of Los Angeles, methane and hydrogen sulfide gases are actively discharging at the crest of a mud volcano only 24 kilometers west-southwest of Redondo Beach, California. The mud volcano is 30m high and its top is about the size of a football field. It formed as gas-charged sediment from depth squeezed up to the sea floor, probably along an active fault at the edge of the offshore Santa Monica Basin. The top of the mud volcano is about 800m below the sea surface, and at this depth the water pressure is 80 times the atmospheric pressure at sea level. As a result, water and methane gas at this pressure "freezes" to form what is termed a methane hydrate. The hydrate ice becomes incorporated in the surrounding ocean-floor sediment. The photo of a cross-section of a sediment core (see below) reveals the rapidly disassociating chunk of hydrate (methane ice).
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When the core was opened on the deck of the research ship, the intense "rotten egg" smell of the hydrogen sulfide, which is incorporated in the hydrate ice along with the methane, together with the hissing and sizzling sounds of the vaporizing gas, made everyone scramble to make sure there were no sources that might ignite the gases, all the while gasping for fresh air. The map below shows where the mud volcano lies in relation to the Southern California coast, and the seismic-reflection profile gives an idea of its size and shape.
The core sample is the only proven occurrence of methane gas hydrate between the continental shelf off Northern California and the Gulf of California, Mexico.
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