After several days of preparation aboard the CNR research vessel Gaia Blu, we have reached an important milestone in our HYDROSENSE expedition: the deployment of our fiber-optic sensing system inside the crater of Kolumbo submarine volcano, approximately 500 meters (1,640 feet) beneath the sea surface.

The instrument we deployed, called Geo-Sense, is a seafloor system designed to investigate how distributed acoustic sensing (DAS) can be used to monitor submarine geological processes. The system uses an optical interrogator connected to a fiber-optic cable, allowing us to measure tiny changes in strain associated with vibrations and acoustic disturbances along the cable. 

Our goal is to investigate whether we can detect the signatures of volcanic earthquakes, seismic tremors, and hydrothermal activity. At Kolumbo, hot fluids and gases escape through hydrothermal vents within the crater, generating a complex acoustic environment. We are particularly interested in whether DAS can record signals associated with fluid circulation and gas bubbling, and whether these signals can help us understand how hydrothermal and volcanic processes are related. A hydrophone will provide complementary acoustic measurements of higher frequency signals.

The operation began with the deployment of Geo-Sense from the aft deck of Gaia Blu, using the vessel’s lifting equipment. This required close coordination between the scientific team, engineers, and vessel crew to safely lower the system into the water. Once the instrument reached the seafloor, we used MBARI’s MiniROV, a portable remotely operated vehicle, to position the fiber-optic cable across the crater floor, including areas of active hydrothermal venting.

The MiniROV provided the underwater visibility and precise maneuverability needed to guide the cable across the irregular seabed. Positioning the fiber-optic cable near active hydrothermal features is particularly important because we want to investigate how the recorded signals change with distance from potential acoustic and seismic sources. Surveying the cable with mapping sensors developed by MBARI’s CoMPAS Lab enabled the team to get an accurate final position after deployment, providing important context for the DAS data.

The deployment was the result of considerable teamwork, from preparing and checking the equipment aboard the vessel to coordinating the lifting operations and underwater positioning. Working at these depths leaves little room for error, and the success of the operation depended on the combined expertise of scientists, engineers, ROV pilots, and the Gaia Blu crew.