Drilling to assess Ulleung Basin gas hydrates and submarine landslides

Abstract

Submarine slope failure and derived sediment gravity flows are recognized as a major sedimentary process in basins worldwide. Their large failure volumes and long-runout distances pose significant tsunami hazard for offshore and coastal facilities, and thus it is important to understand the mechanisms and processes involved in the initiation of slope failure. One hypothesis currently being debated is that sea level fluctuations and ocean bottom temperature changes can cause gas hydrate dissociation and/or dissolution and/or gas exsolution and expansion leading to submarine slope failure. However, evidence that propagation in seafloor sediments of pressure and thermal perturbations associated with climate change induce slope instability is lacking, and more importantly there has not been a dedicated study to investigate these feedbacks. To move forward in our understanding of the roles of climate, sedimentation patterns, geomechanical properties of gas-hydrate bearing sediments and slope stability, we propose to acquire an expanded Quaternary record of mass-wasting activity, gas emissions, climatic/paeloceanographic proxies and physical properties to better constrain the gas hydrate-slope failure system. The Ulleung Basin, situated between the Korean peninsula and the Japanese archipelago, is an optimal study region because: (1) the high abundance of gas hydrates, particularly at the southern end of the basin (2) more than 50% of the >1000 m thick Plio-Quaternary succession is comprised of Mass Transport Deposits (MTDs), (3) high susceptibility of background sedimentary cycles to climate changes, and (4) extensive SiteSurvey Data has already been collected in this region which ensures proper site selection. The fundamental science objective of the IODP proposal ULYSSES (ULleung basin gas hYdrates and Submarine landSlides: climatE-driven hazardS?) will not only improve our understanding of the hydrate-slope failure link in relation to climate induced perturbations, but will enhance ourunderstanding of dynamic behavior of the MTDs and further help to address societally relevant problems related to assessing geohazards to adjacent land-masses