page_title: Methane clathrate
section_title: Natural deposits
hierarchical_section_title: Methane clathrate / Natural deposits
caption_attribution_description: English: Structure of a gas hydrate (methane clathrate) block embedded in the sediment of hydrate ridge, off Oregon, USA. The gas hydrates have been found during a research cruise with the German research ship FS SONNE in the subduction zone off Oregon in a depth of about 1200 meter in the upper meter of the sediment. The shown gas hydrate (white) has been deposited in thin layers into the sediment Français&#160;: Filons d'hydrate de gaz (clathrate, en blanc sur la photo) trouvé lors d'une expédition scientifique avec le navire de recherche allemand FS SONNE dans la zone de subduction située au large de l'Oregon, à une profondeur d'environ 1200 mètres. Cet hydrate de méthane était enfoui dans le premier mètre du sédiment (en gris sur la photo), dans la zone dite "hydrate ridge", au large de l'Oregon (États-Unis) Deutsch: Sediment mit Gashydrat (weiß) vom „Hydrate Ridge“, einer untermeerischen Erhebung vor der Küste von Oregon, USA. Das Gashydrat wurde auf einer Forschungsreise mit dem deutschen Forschungsschungsschiff FS SONNE aus etwa 1200 Metern Wassertiefe mit einem Schaufelgreifer aus dem obersten Meter des Sediments geborgen. Das hier abgebildete Gashydrat wurde in dünnen Schichten in das Sediment eingelagert
context_page_description: Methane clathrate or, also called methane hydrate, hydromethane, methane ice, fire ice, natural gas hydrate, or gas hydrate, is a solid clathrate compound in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice. Originally thought to occur only in the outer regions of the Solar System, where temperatures are low and water ice is common, significant deposits of methane clathrate have been found under sediments on the ocean floors of the Earth.
  Methane clathrates are common constituents of the shallow marine geosphere and they occur in deep sedimentary structures and form outcrops on the ocean floor. Methane hydrates are believed to form by the precipitation or crystallisation of methane migrating from deep along geological faults. Precipitation occurs when the methane comes in contact with water within the sea bed subject to temperature and pressure. In 2008, research on Antarctic Vostok and EPICA Dome C ice cores revealed that methane clathrates were also present in deep Antarctic ice cores and record a history of atmospheric methane concentrations, dating to 800,000 years ago.
context_section_description: Methane clathrates are restricted to the shallow lithosphere (i.e. < 2,000 m depth). Furthermore, necessary conditions are found only in either continental sedimentary rocks in polar regions where average surface temperatures are less than 0 °C; or in oceanic sediment at water depths greater than 300 m where the bottom water temperature is around 2 °C. In addition, deep fresh water lakes may host gas hydrates as well, e.g. the fresh water Lake Baikal, Siberia. Continental deposits have been located in Siberia and Alaska in sandstone and siltstone beds at less than 800 m depth. Oceanic deposits seem to be widespread in the continental shelf (see Fig.) and can occur within the sediments at depth or close to the sediment-water interface. They may cap even larger deposits of gaseous methane.
caption: Gas hydrate-bearing sediment, from the subduction zone off Oregon
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