In-situ horizontal pressure measurements at seepage sites west of Svalbard

Why gas emissions from the seafloor have stopped thousands of years ago in some areas, while it persists exclusively on the eastern part of the Vestnesa sedimentary ridge? This is the question that drives our scientific objectives in the last research campaign planed under the SEAMSTRESS project.

The answer to this question is likely related to the type of sediment and the disposition of the sediment to fracture. To investigate this further we need to measure sediment properties such as in-situ pore fluid pressures, horizontal stress, shear strength. Conducting these measurements is not so easy because it requires expensive and technically challenging instrumentation. The SEAMSTRESS project assumes the challenge of conducting the geotechnical experiments that are lacking to understand the pressure behavior at deep marine seafloor seepage systems in our favorite Arctic laboratory: The Vestnesa Ridge. These challenging experiments are the core of SEMSTRESS which main objective is to advance knowledge on the pressure (stress) field that controls seafloor methane emissions.

In a collaboration with MSH – Marine Sampling Holland and the Marchetti laboratory we are planning to deploy the Medusa dilatometer designed by the Marchetti Lab to measure in-situ the pressure of the Earth at ease and therefore the horizontal stress. To deploy this instrument offshore there is need for a seafloor (sort of) rig. Our colleagues from MSH joined us onboard with their Geomil’s Manta 200 rig, an instrument designed for conducting cone penetration tests in the soil. Geomil started developing this type of instrumentation in the 30s to help the Netherland overcome a struggle with railway failures due to soft sediment.

Manta is a big machine, heavier than anything that has been deployed so far from R/V Kronprins Haakon. The machine also has a power supply requirement that differs from what the ship can provide. Our mission therefor starts with a few days in the fjord working hard to overcome all the technical challenges to get the machine ready for deployment before sailing offshore.

Photo: The Geomil’s Manta-200 rig for Cone Penetration Test (CPT)  onboard R/V Kronprins Haakon. The MSH team together with the ship crew prepare the winches and solvent challenges with the power supply.

Text and photo: Andreia Plaza-Faverola