Stability of Fine-Grained Sediments Subject to Gas Hydrate Dissociation in the Arctic Continental Margin

Abstract

Significant venting of methane gas has been observed on the upper continental slopes of the Arctic Ocean, coinciding with the landward limit of the gas hydrate stability zone. It has been inferred that the methane gas venting is related to the dissociation of methane gas hydrate induced by the unprecedented Arctic warming that has occurred over the last 30 years. Historically, the influence of hydrate dissociation on sediment stability was considered in terms of hydrate dissociation increasing pore pressures, reducing effective stress and therefore sediment strength, leading to slope failures along these over pressurized layers. Recent evidence has shown that gas hydrate readily forms in clay-rich sediments as fracture-filled near-vertical veins, which upon dissociation gives rise to sediments exhibiting high water content, high sediment compressibility and very low shear strength. Thus gas hydrate dissociation in fine-grained sediments may lead to significant slope instabilities, which at present is poorly understood. Slope stability analyses carried out considering the potential influence of hydrate dissociation induced by warming of the Arctic slope suggest that instabilities are likely, with failures ranging from surficial sloughing to deep-seated failures. This paper highlights the importance of understanding the sediment processes in clay soils, and how dissociation of gas hydrate can induce instabilities through sediment softening and generation of excess pore pressure.