Gas hydrates are ice-like solids composed of natural gas, usually methane in marine environments, and water. Hydrates are known to exist in the Cascadia margin, west of Vancouver Island, beneath the seafloor. Sediment stiffness is increased by frozen hydrates, like ice in winter mud. The degree of stiffness is an indicator of the amount of hydrate present per unit volume. Gas hydrate outcrops, venting and topography in the Cascadia margin have been intensively studied and are observed to change over time. Does the volume of hydrates also change with time? University of Toronto researchers Lisa Roach and Nigel Edwards are trying to find out. An uncommon, specialized exploration technique, known as seafloor compliance is used to probe beneath the seafloor, by examining the deflection of the seafloor caused by waves on the ocean surface. Waves on the surface create pressure changes on the seafloor; as they “push” the seafloor down, it deflects them. The amount of seafloor deflection depends on the stiffness of the sediment, which, in turn, depends on hydrate content. In areas where there are fewer buried hydrates, the seafloor is more compliant (less stiff). The depth at which hydrates are buried beneath the seafloor can be inferred from gravity wave frequency at the seafloor. A compliance value in the higher frequency range describes shallower hydrates, while lower frequencies describe deeper deposits.