Site Characterisation of a Submarine Volcanic Terrain: The Importance of Data Integration-Paper

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The study describes an integrated site-characterisation programme for a proposed export pipeline crossing a submarine volcanic terrain at approximately 100–120 m below the seafloor. Because the extensive, irregular igneous province could not be avoided, the project combined high-resolution bathymetry, sonar, magnetometer, underwater imagery and sub-bottom profiling with sediment sampling, rock coring, geological analysis and dating.<br /><br />The investigation proceeded in two phases. Initial geophysical and shallow-core data identified four volcanic-feature areas but could not establish the terrain’s subsurface extent or composition. These interpretations guided a second phase of targeted rock coring and laboratory testing. Integrating core logs and dating with geophysical evidence revealed basalt, layered volcaniclastic deposits and interbedded coastal, marine and estuarine sediments. The evidence indicates that changing sea levels during the Quaternary shaped the terrain and its depositional environments. Sedimentary dating suggests volcaniclastic deposits formed in the Late Pleistocene to early Holocene; basalt dating was less conclusive because of substantial uncertainty.<br /><br />The integrated model showed that volcanic material extended farther west than geophysical data alone had suggested. This improved understanding of potential installation challenges, including trenching refusal and the need for targeted rock placement. Although the study could not determine the terrain’s age or future eruptive potential with certainty, multiple lines of evidence support the conclusion that local basalt emplacement last occurred more than 15,000 years ago. The paper demonstrates how phased, multidisciplinary data integration can reduce uncertainty and support engineering decisions in unusual offshore environments.

Keywords

submarine volcanic terrain

export pipeline

integrated site characterization

geophysical survey

rock coring

basalt

volcaniclastic deposits

Quaternary sea-level change

Late Pleistocene

offshore engineering