New insights into submarine geohazard and sediment transport revealed by repeat seafloor surveys

Abstract

The prevalence of submarine geohazards poses significant threats to coastal communities and global economies. This thesis investigates three main types of submarine geohazards: submarine landslides, submarine channel evolution, and volcaniclastic density currents triggered by volcanic eruptions. Utilizing innovative repeat seafloor surveys, the research aims to elucidate the processes behind these hazards and their implications for hazard assessment, sediment transport pathways, and depositional fate. The survey compare seafloor changes as long as between 13 years (Knight inlet) as well as daily changes (Squamish prodelta). The study examines various settings prone to different submarine geohazards, including a submarine prodelta linked to a seasonally active meltwater-fed river (Squamish Prodelta), a confined fjord’s submarine channel system (Knight Inlet), and a remote volcanic island affected by a massive eruption (Hunga Tonga Volcano). The research seeks to enhance understanding of seafloor evolution, its effects on coastal infrastructure, and the interpretation of past sediment transport events from seafloor and depositional archives. Each chapter addresses a specific aspect of submarine geohazards, highlighting the central role of sediment dynamics. For instance, in the submarine channels of Knight Inlet, it is demonstrated for the first time that channel curvature significantly influences dominant processes and the rate of channel migration, with a threshold normalized radius of curvature of 1.54. The investigation of delta slope failures in Squamish Prodelta reveals that sediment loading and slope geometry are critical factors affecting the occurrence and magnitude of these failures. The study of seafloor changes following the Hunga Tonga volcanic eruption underscores the diverse scales of bedforms shaped on the seafloor and their impact on density flow pathways, ranging from zero to forty kilometres from the caldera. The identified hazards span a wide spatial and temporal spectrum, from events recurring over centuries (Hunga Tonga eruption) to daily occurrences (upstream-migrating bedforms in Squamish Prodelta). This thesis offers a nuanced understanding of the processes leading to submarine geohazards, emphasizing sediment dynamics' pivotal role. It advocates for continuous reassessment based on new empirical evidence. The implications extend beyond the specific geological phenomena studied, offering valuable insights for geological studies, environmental management, and risk assessment in submarine environments. The thesis concludes with a call for further exploration, emphasizing the need for ongoing monitoring, data acquisition, and interdisciplinary studies. This approach is essential to enhance understanding of submarine geohazards, contributing to the development of resilient infrastructure and improved hazard mitigation strategies.

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ORCID for Tim Minshull: orcid.org/0000-0002-8202-1379

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