Seafloor mapping for geohazard assessment: state of the art

Abstract

During the last two decades, increasing use of full-coverage sonic mapping of the seafloor has made us more aware of the large and different number of seafloor processes and events bearing significant geohazard potential. This awareness combines with the increasing use of the seafloor for infrastructure and with the high density of population and settlement on the coast. Seafloor mapping is the first step in making a census of the geohazard-bearing features present in a given offshore area. It often provides the only tool for a comprehensive, although non-specific, seafloor geohazard assessment over large areas that are scarcely groundtruthed by acoustic prospection and seafloor sampling. However, the characterization of geohazard features on a morphological basis alone is limited, and more detailed investigations are needed to define the character and state of activity of potentially hazardous features. Such investigations include the use of deep-tow or autonomous platforms designed to acquire high-resolution data at depth as well as in situ measurements, both being very expensive activities not applicable over large areas. Thus seafloor mapping is often not only the first and the main but also the only tool for a comprehensive seafloor geohazard assessment.This special issue represents an example of the diversity of approaches to seafloor geohazard assessment and summarizes the present state of this discipline. Both the diverse technologies applied and the specific aims of offshore geohazard assessment brought different communities to deal with the study of seafloor processes and events from remarkably distinct viewpoints. We identified three end members in offshore geohazard assessment: (1) geohazard assessment ''sensu stricto'', (2) ''engineering'' geohazard assessment, (3) ''non-specific'' geohazard assessment. These are being conducted by industry, academia and public agencies in charge of civil protection and land-use planning and management. Understanding the needs and geohazard perception of the different groups is a necessary step for a profitable collaboration in such an interesting and rapidly developing field of marine geology.

Seafloor geomorphic manifestations of gas venting and shallow subbottom gas hydrate occurrences

“…As a consequence, seafl oor seepage areas have become a focus of the research community. Seafl oor seepage sites also pose special geohazard issues, in part because of the potential for unstable seafl oor conditions and the possible existence of overpressured gas in the near subsurface (Chiocci et al, 2011). Thus, the hydrocarbon industry avoids installing seafl oor structures near seeps (Hough et al, 2011).…”

Seafloor Mapping – The Challenge of a Truly Global Ocean Bathymetry

“…Geohazard assessments in the marine realm are mainly based on bathymetric data. Although only a snapshot in time, bathymetric data deepens the understanding of the seafloor fabric and helps to identify potential risks linked to hazardous processes, such as slope failures or turbidity currents, and with repeat surveys, can be used to monitor seafloor changes over time (Chiocci et al, 2011). Clearly, bathymetric resolution appropriate to the target features is required.…”

Marine Geohazards: A Bibliometric-Based Review

“…Some manifest themselves on the surface of the seafloor, while others are concerned with processes that occur in the subsurface. This range of possibilities makes it uncommon for a single scientific peer-reviewed publication to investigate all categories of marine geohazards, except for a few conceptual or review articles [11,14,15].…”