Hydrate Ridge—A Gas Hydrate System in a Subduction Zone Setting


Hydrate Ridge is a 6–10 km wide, 22 km long N–S striking thrust ridge within the Cascadia accretionary prism offshore of Oregon in the NE Pacific Ocean. Over the past four decades it has been a primary focus site for studies of gas hydrate/free gas systems within a convergent margin setting. A local peak called the North Hydrate Ridge (NHR), located at a depth of 590 m, hosts the first documented cold seep system driven by convergent margin processes and supports chemosynthetic communities sustained by the anaerobic oxidation of methane. A southern peak at 780 m depth, known as the South Hydrate Ridge (SHR), is actively venting gas around an area of seafloor bacterial mats and a 40 m high carbonate chimney within a long-lived vent system separate from NHR. Bottom simulating reflections (BSRs) observed in seismic profiles indicate these vents are part of a broad gas hydrate province that extends across all of Hydrate Ridge. Hydrate Ridge has been the focus of extensive geophysical surveys, water column acoustic and sampling surveys, high-resolution seafloor mapping using remotely operated, autonomous and deep-towed vehicles, seafloor fluid flow monitoring, and a site for the Ocean Observatories Initiative (OOI). All of these are in support or complementing Ocean Drilling Program (ODP) drilling efforts during Legs 146 and 204 to quantify and characterize the gas hydrate/free gas system. Hydrate concentrations are up to 45% of pore space (30% of total volume), but typically 2–20%, and are strongly coupled with the structure and stratigraphy within the thrust ridge.


Earth Sciences

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World Atlas of Submarine Gas Hydrates in Continental Margins



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