Evidence from sampling and seismic-reflection records suggests that gas hydrates exist in great quantities beneath many continental margins and represent a huge potential energy source. The hydrates formed when hydrocarbon gases (primarily methane) percolated upward through the sediment and encountered the appropriate temperature and pressure conditions. It is believed that the hydrate in a zone, commonly hundreds of meters thick just below the seafloor, exists either as layers and veins interspersed with sediment, as discrete nodules, as a somewhat homogeneous matrix incorporating both sediment and hydrate, or as a combination of those types.' It is also believed that because permeability of the sediment-hydrate layer is low, gas is often trapped beneath it.2 If equilibrium conditions change and part of the hydrate dissociates, gas release may contribute to slope instability, and, since methane may be released as a result of mass movement and methane is a greenhouse gas, potential climatic effects could result.A test system that can simulate pressure and temperature conditions, and changes in those conditions, on the continental slope has been constructed to study the formation and properties of gas hydrate-sediment mixtures. We will measure sound velocity in various hydrate-sediment mixtures and apply the results to seismic modeling and interpretation of seismic-reflection profiles. We also intend to measure geotechnical properties of host media before, during, and after the presence of hydrates and use these experimental data, along with associated methane release data, to determine the effects of hydrates on slope stability and global warming.The computer-controlled test system consists of a mineral-oil-filled chamber that can apply a maximum pressure of 25 MPa (3600 psi) to the outside of a cylindrical sediment specimen (FIGURE 1). This pressure is representative of a 2400-m water depth. Consolidation of the sample will allow simulation of overburden, although there is evidence that hydrate cementation may reduce or eliminate the sediment density increase with depth that is typically caused by normal consolidation. The temperature on the upper surface of the specimen can be adjusted so as to impart a unidirectional cooling front through the sample controllable to kO.2"C. Tests will be 490

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Engineering) James G. W i 1 son NOTICE tprmmred by the Unitcd States Conrnmnt. Neither the United Stater nor the United Stater apPvrrnt of hw, nor my of their omployea, nor my of U~eu m y vrmnty, aprcu or Implied. OT uaumn MY kgl lhbility or mponability for the IseUnCy, cmnpleteness a usefulness of MY infomtion, ~pparatw. pmdwt OI pman dirlacd, or uprcrnb th.1 iu use would not DonV.StOIl, N k O n V I C l O I I. OI lhck atlpioyctr. maker