Modeling Gas, Hydrates, and Slope Stability on the U.S. Atlantic Margin during Pleistocene Glaciations

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Date

2023-09-28

Authors

Carty, Olin
Daigle, Hugh

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Abstract

Dissociation of methane hydrates in shallow marine sediments due to increasing global temperatures can lead to the venting of methane gas or seafloor destabilization. Along the U.S. Atlantic margin there is a well-documented history of slope failure and numerous gas seeps have been recorded. Several studies have linked slope failure to gas seepage and hydrate dissociation driven by glacial-interglacial transitions, but this linkage has not been quantitatively demonstrated. Along the shelf edge, in an area where shallow methane gas seeps have been identified, we modeled methane gas and hydrate formation over the last 120,000 to simulate a glacial-interglacial cycle. The development of hydrate and gas during this time was modeled using the PFLOTRAN software from Sandia National Laboratories, a parallel subsurface flow code. At 100-year intervals during this simulation, we calculated the factor of safety throughout the modeled sediment column. Factor of safety compares the shearing and resisting stresses of a slope and can be used to determine if sediment failure is likely to occur in an area. Modeling seafloor depths between 200-1000 m we predicted gas and hydrate development and calculated the associated factor of safety over time to determine if sediment failure was likely to be caused by hydrate dissociation. Parallelizing this code, we used Lonestar6 to run the one-dimensional fluid flow model and factor of safety model at 16044 individual locations in the region between 29°N – 45°N and 82°W – 66°W at a resolution of 1 x 1 arcminutes. We found that hydrate dissociation alone is unlikely to cause sediment failure in the region, implying that an additional driving force would be necessary for failure to occur. In addition, we see a shift down slope of when the minimum factor of safety is likely to occur and the depth below seafloor at which this minimum occurs.

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