Gas Hydrates Off the Oregon Coast

Gas hydrates are created when water and gas combine to form a crystalline substance that looks like ice. This occurs when excess methane is present, and when temperature and pressure conditions are suitable. Gas hydrates are common in marine sediments along the margins of continents, where the methane originates from the decomposition of living things. Off the Oregon coast, the Juan de Fuca plate slides beneath the North American plate in a process called subduction. As subduction occurs, sediments are scraped off the Juan de Fuca plate and form ridges on the edge of the North American plate. This process leads to formation of gas hydrates.

Since the 1980's, Hydrate Ridge, an accretionary ridge of the Cascadia subduction zone located 80 km west of Newport Oregon has been the focus of much biogeochemical research by investigators at OSU and elsewhere. The College of Oceanic and Atmospheric Sciences has played an integral role in the multidisciplinary research conducted on Hydrate Ridge. Since 1996 our faculty have been involved in the geochemical characterization of the local sediments and interstitial fluids, and extensive structural and tectonic mapping of this active accretionary structure. The geophysics group has studied the complicated subsurface plumbing associated with the presence of hydrate and free gas through several regional reflection and refraction surveys including a 3D survey conducted in preparation for Leg 204 of the Ocean Drilling Program (ODP) in 2002. This work is complemented by velocity modeling of the hydrate and free gas zone, especially around the occurrence of the BSR (bottom simulating reflector).

Our work continues to take on the challenges of these little understood structures. We are engaged in quantifying and calibrating hydrate and free gas volumes using remotely sensed geophysical data, to understand how this relates to the velocity and structure of the sediments. Ultimately this will help us with a better understanding of hydrate formation and destablization, as well as the past and future roles of hydrates in the environment. We have also documented the first gas hydrates on a transform margin (link to Gorda).

We are collaborating with OSU colleagues Marta Torres and Jim McManus (sediment geochemistry), Bob Collier and Gary Klinkhammer (water column geochemistry), and Chris Goldfinger (seafloor mapping) on this multidisciplinary project. The seismic work has been done in collaboration with Nathan Bangs at UTIG. Ongoing analysis of data from Leg 204 is underway in collaboration with other members of the Leg 204 Shipboard Science Party.

Download:

Brochure summarrizing gas hydrate research at OSU (PDF) ODP Leg 204 Press Release (PDF)

Related Links:

General Background on Gas Hydrates (http://ocean.tamu.edu/Quarterdeck/QD5.3/sassen.html)

TECFLUX Project (http://www.geomar.de/projekte/tecflux_e/)

PUBLICATIONS:

Trehu, A.M., G. Lin, E. Maxwell, C. Goldfinger, A seismic reflection profile across the Cascadia subduction zone offshore central Oregon: new constraints on the deep crustal structure and on the distribution of methane in the accretionary prism, Jour. Geophys. Res, v. 100, pp. 15,101-15,116, 1995. (PDF)

Suess, E., M.E. Torres, G. Bohrmann, R.W. Collier, J. Greinert, P. Linke, G. Rehder, A. Trehu, K. Wallmann, G. Winckler, E. Zuleger, Gas hydrate destabilization: enhanced dewatering, benthic material turnover, and large methane plumes at the Cascadia convergent margin, Earth and Plan. Sci. Let., v. 170, 1-15, 1999.

Trehu, A., M. Torres, G. Moore, E. Suess, G. Bohrmann, Dissociation of gas hydrates in response to slumping and folding on the Oregon continental margin, Geology, 27, 939-942, 1999. (PDF)

Tryon, M., K. M. Brown, M.E. Torres, A.M. Trehu, J. McManus, R.W. Collier, Measurements of transience and flow cylcing near episodic methane gas vents, Hydrate Ridge, Cascadia, Geology,v. 27, p. 1075-1078, 1999.

Trehu, A.M., and E. Flueh, Estimating the thickness of the free gas zone beneath Hydrate Ridge, Oregon continental margin, from seismic velocities and attenuation, Jour. Geophys. Res., v. 106, p. 2035-2045, 2001. (PDF)

Suess, E., G. Bohrmann, D. Rickert, W. Kuhs, M.E. Torres, A.M. Trehu, P. Linke, Properties and fabric of near-surface methane hydrates at Hydrate Ridge, Cascadia margin, Proceedings of the Fourth International Conference on Gas Hydrate, Yokohama, Japan, May 19-23, 2002.

Torres, M.E., J. McManus, D.E. Hammond, M.A. de Angelis, K.U. Heeschen, S.L. Colbert, M.D. Tryon, K.M. Brown, E. Suess, Fluid and chemical fluxes in and out of sediments hosting methane hydrate deposits on Hydrate Ridge, OR, I: Hydrological provinces, Earth and Planetary Science Letters, 201, 525-540, 2002. (PDF)

Trehu, A.M., N.L. Bangs, M.A. Aresnault, G. Bohrmann, C. Goldfinger, J. Johnson, Y. Nakamura, M.E. Torres, Complex subsurface plumbing beneath southern Hydrate Ridge, Oregon continental margin, from high-resolution 3D seismic reflection data, Proceedings of the Fourth International Conference on Gas Hydrate, Yokohama, Japan, May 19-23, 2002.(PDF)

Heeschen, K.U., A.M. Tréhu, R.W. Collier, E. Suess, and G. Rehder, Distribution and height of methane bubble plumes on the Cascadia margin offshore Oregon from acoustic imaging, Geophys. Res. Let., v. 30, No. 12, doi:10.1029/2003GL016974, 2003. (PDF)

Last updated 20-JUL-2003 - Under Construction!