Abstract
Many submarine slope failures in hydrate-bearing sedimentary deposits might be directly triggered, or at least primed, by gas hydrate dissociation. It has been reported that during the past 55 years (1955–2010) the 0–2000 m layer of oceans worldwide has been warmed by 0.09 °C because of global warming. This raises the following scientific concern: if warming of the bottom water of deep oceans continues, it would dissociate natural gas hydrates and could eventually trigger massive slope failures. The present study explored the submarine slope instability of oceanic gas hydrate-bearing deposits subjected to bottom water warming. One-dimensional coupled thermal-hydraulic-mechanical (T-H-M) finite difference analyses were performed to capture the underlying physical processes initiated by bottom water warming, which includes thermal conduction through sediments, thermal dissociation of gas hydrates, excess pore pressure generation, pressure diffusion, and hydrate dissociation against depressurization. The temperature rise at the seafloor due to bottom water warming is found to create an excess pore pressure that is sufficiently large to reduce the stability of a slope in some cases. Parametric study results suggest that a slope becomes more susceptible to failure with increases in thermal diffusivity and hydrate saturation and decreases in pressure diffusivity, gas saturation, and water depth. Bottom water warming can be further explored to gain a better understanding of the past methane hydrate destabilization events on Earth, assuming that more reliable geological data is available.
Highlights
Submarine slope failure is a fundamental shear failure process that occurs in submarine sediment formations [1,2,3]
If bottom water warming continues in the deep oceans, it would cause the dissociation of natural gas hydrates, which in turn could trigger a slope failure in hydrate-bearing deposits
In which the base of the hydrate occurrence zone (BHOZ) were located at shallower depths of 100–200 m, e.g., the Cascadia continental margin, Gulf of Mexico, and the Arctic regions in permafrost environments, the temperature increase at the BHOZ is expected to occur more rapidly
Summary
Submarine slope failure is a fundamental shear failure process that occurs in submarine sediment formations [1,2,3]. Increase in shear stress or decrease in shear strength can lead to shear failure in sediments, which in turn leads to slope failure. The mechanisms that potentially cause shear failure include (a) removal of lateral supports, (b) increase in weight of overlying sediment, (c) generation of excess pore pressure (overpressure), (d) upward fluid flow, and (e) earthquakes [3]. One mechanism, e.g., generation of overpressure, may prime a slope for failure before another one, e.g., earthquake, triggers slope failure [3]
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