Seafloor breathing helping forecast hydrate-related geohazards

Abstract

Gas hydrate dissociation may pose serious geohazards. The response of the seafloor to hydrate dissociation is important for geohazards, marine environments and global climate. We studied how hydrate dissociation affects underground temperature and pressure and how dissociation may lead to seafloor deformation. Here, we designed a laboratory model experiment to visualize fluid migration and seafloor deformation during hydrate dissociation at atmospheric pressure. Our experiments show visible gas pipes, migratory gas and gas pockets due to hydrate dissociation and explain the newly discovered discordance between the slide plane and the base of the gas hydrate stability zone. We found that the underlying free gas and gas conduits not only are favorable factors for forming hydrates but also can be promoted by hydrate dissociation. The temperature, pressure, and seafloor deformation are collected during the experiments. Our results show that the hydrate dissociation process is an endothermic reaction. More importantly, hydrate dissociation-induced overpressure exhibits a sudden decrease after slow growth and this inflation–deflation cycle resembles breathing. In our experiments, seafloor deformation are dominated by underground overpressure and lags up to about ten minutes. This deformation pattern could help forecast seafloor subsidence based on deformation observations. Overpressure monitoring is effective and saves time to cope with imminent geohazards. This pattern is important for geologists and engineers to forecast hydrate-related geohazards.

Keywords

• Gas hydrate
• Geohazards
• Seafloor deformation
• Overpressure
• Inflation–deflation cycle