For the first time, the Kolumbo submarine volcano located just 7km off Santorini, the most active volcano in the Eastern Mediterranean, has been closely monitored as part of the research project SANTORY: SANTORini’s seafloor volcanic observatorY” (www.santory.gr). SANTORY is funded by the Hellenic Foundation for Research and Innovation and by the financial support of the Municipality of Thira. Within the framework of the SANTORY project, a total of three oceanographic cruises were performed. The first two cruises were carried out in December 2022 and June 2023, to deploy and maintain the seafloor observatory, which is a new generation automated geochemical recording system that collects data of acoustics, dissolved CO₂  and CH₄, O₂, T °C, hydrostatic pressure, EC, pH, and turbidity. Additionally, various measurements on Kolumbo’s crater with multiple innovative sensors were conducted (T-sensors, Inclinometers, Pressure gauges), and the active hydro-thermal vent field is continuously recorded with stand-alone optical cameras, multispectra and the “THEIA” stereo camera. For the first time, real-time measurements for radioactivity were achieved by using the prototype radioactivity sensor γSniffer and the γ-radiation imager SUGI in collaboration with the EU-funded project RAMONES (www.ramones-project.eu).

The third oceanographic mission took place on October 20-25, 2023, with the research vessel FILIA of HCMR and the remotely operated vehicle maxRover in collaboration with the National Kapodistrian University of Athens (NKUA). In this mission, a large data set was collected from the already deployed monitoring instruments, while new sensors were also installed. The mission included scientists from the National Technical University of Athens (NTUA), the National Institute of Geophysics and Volcanology in Italy (INGV), the University of Milan Bicocca in Italy, the Mediterranean Institute of Oceanography of the University of Aix-Marseille in France and PLOATECH company in Spain. Gas and hydrothermal fluid samples were collected with special gas-tight samplers specifically projected and developed during the project; after analysis in specialized laboratories, the results will be compared with corresponding measurements made in 2013 and 2014. Samples were also collected from the water column and special analysis will also be made for mercury (Hg).

What do the first data tell us so far?

“Until now, a significant amount of data has been collected from the specialized and innovative instruments and sensors that had been deployed,” according to the coordinator of the SANTORY project, Associate Professor at NKUA, Dr. Paraskevi Nomikou. “Inside the crater of Kolumbo at a depth of 500 meters below the sea surface, the sea floor is covered by numerous polymetallic “chimneys” which are very active and emit hydrothermal fluids. We now have evidence on how they differentiate across time, how they spread along the water column, if their activity increases or decreases, how their temperature changes and if any changes at the slope of the seafloor occurred during the last year. At the same time, a significant number of samples have been collected to investigate the chemical composition of the gasses and waters in the active area of ​​the crater as well as the microorganisms that live there” added Dr. Nomikou. Additionally, sensors detected significant changes in the temperature with warming events reaching up to 230^oC. This is extremely consistent and suggests an overall warming of the water mass within the crater due to both adjective and conductive heating linked to hydrothermal activity.

Acoustic data show several local VT events, testifying that Kolumbo’s vent field is very active. Current meter measurements show current speeds increasing during five distinct cooling periods (over the ~190 days of recording) that last a few days that are modulated by tides. “In situ adioactivity measurements indicate that near the hydrothermal vents, radioactivity levels  increase impressively to approximately three orders of magnitudes higher values (1000 Hz) than the typical background counting rates recorded by our prototype γSniffer detectors (1-2 Hz) away from the seabed and the known hydrothermal vent sources. The large difference stresses the presence of radioactive substances outflow from the Hellenic Volcanic Arc, most likely associated to the outgassing of the radioactive radon gas”, stated Associate Professor of NKUA, Theo Mertzimekis.

“The submarine Kolumbo volcano is a biotechnological oasis, in which a large number of different microbial species lives there, adapted to the extremes of temperature, pH, and high concentration of heavy metals in the active area. The samples are currently being analyzed for their metagenomic content, i.e., by using state of the art next generation sequencing technologies which are currently available at the labs of the Institute of Marine Biology, Biotechnology and Aquaculture of HCMR in Heraklion of Crete”, said Dr. Paraskevi Polymenakou, who is responsible of the microbiological analysis of the program and a Principal Researcher of HCMR. “We will analyze all the genes of all the microorganisms present and we will uncover the vast taxonomic and metabolic diversity of the extreme environments of Kolumbo volcano. During all three oceanographic expeditions, the hydrothermal fluids emitted by the active chimneys were collected by the ROV and pH was immediately measured onboard.  Although no significant changes were observed in past expeditions in 2013 and 2014, this time we saw a drop in pH values ​​from December 2022 to present. More specifically, pH value in the active area of Kolumbo volcano decreased from 6.8 in December 2022 to 6.4 in June 2023 and to 5.3 during the last expedition in October. That means a value drop by 1.5, a reduction that we consider significant. We also observed changes on microbial mats covering the seafloor of the Kolumbo volcano compared to previous expeditions. Our up to now analysis has revealed that the Kolumbo volcano, due to its extreme conditions, hosts a large number of multidrug resistant microbes that must be monitored in order to get a better understanding of their potential impact on the environment and human health” added Dr. Polymenakou.

 

SANTORY observatory: the multiparametric monitoring of Columbus that must continue.

Integrated and multiparametric ocean observation is key to understanding unknown, potentially dangerous, deep-sea environments and to proposing and taking measures to mitigate potential associated risks. In recent years, a new generation of stand-alone systems has been implemented that aim to consistently and long-term count data series capable of describing the variability of observed phenomena which are difficult to detect by traditional, sporadic measurements. For the first time, as part of the SANTORY project, this advanced multiparameter monitoring system was placed on the most active submarine volcano of the Eastern Mediterranean and allowed the recording of a time series of valuable data that captures the state of the volcano. Through three oceanographic missions we managed to collect data that reveal changes in the crater of the volcano. Researchers from NTUA (Prof. Konstantinos Karantzalos and Dr. Valsamis Douskos) and PLOATECH have set up and deployed in Kolumbo a variety of instruments for monitoring a wide range of physical and chemical properties, including current speed and direction, temperature, oxygen levels, conductivity and turbidity. “In this expedition, most of the deployed instruments have been recovered, providing valuable data regarding the activity of the volcano in the previous 10 months” said researcher Dr. Angelos Mallios of PLOATECH. “Moreover, data from the novel, task-specific visual observation systems based on stand-alone cameras that have been deployed in June have been recovered, offering unique views from inside the volcano’s crater for the last four months in unperturbed conditions”.

 

“Hydrothermal systems hosted in submarine volcanoes, emit huge amounts of elements and acid fluids in the surrounding ocean. Such emissions may have a strong impact on the marine environment in terms of pollutants’ spreading and acidification. Submarine volcanoes and their hydrothermal vent systems, though being favorable sites for developing ecosystems independent from sunlight, could represent a potential hazard for human health and the environment and therefore, must be understood and continuously monitored”, said Dr. Manfredi Longo of INGV that participated in the third oceanographic mission. “For the first time, an autonomous module to measure consistently long-term data-series was properly configured to be deployed in a hydrothermally active area of the Kolumbo volcano. During the 10 months operative period, a variety of chemical-physical data have been collected, together with passive acoustic data. The latter represent a potential tool to investigate the ascending fluid dynamics and estimate the energy budget of the reservoir. Moreover, deeper mechanisms related to the volcanic activity can be detected as well, posing the basis to characterize the behavior of the Kolumbo volcano over a long period of time” Dr Longo added.

“The magmatic fluids degassed from melts produced in the mantle and rising within the crust often interact with shallow aquifers to form hydrothermal systems. These systems are responsible for the emission of CO₂-dominated fluids from the vents located in the sea-bottom as well as of the local micro-seismicity. The study of the composition of these fluids is of basic importance for the comprehension of their origin, their potential impact on local and regional environments and ecosystems, and, not least, the evaluation of the volcano state of activity” said Professor Andrea Luca Rizzo from the University of Milan Bicocca (Italy), who collected gas samples to determine their chemical and isotopic (CO₂, CH₄, N₂, He) composition.

In addition, samples were collected for mercury (Hg) measurements to understand and quantify the role of shallow hydrothermal Hg emissions from the volcano in both local marine ecosystems and the global mercury cycle. “Hg emissions at Kolumbo might locally enrich fish to levels that could present a risk for human consumers. The bioaccumulation of Hg might be exacerbated here because of the abundant bacterial mats that may effectively convert the Hg into its most toxic form, methylmercury” said Dr. Lars Eric Heinbürger-Boavida, CNRS researcher at the Mediterranean Institute of Oceanography from the University of Aix-Marseille in France who also participated in the mission.

 

Finally, in collaboration with the sister project RAMONES, an array of gamma radioactivity detectors has been deployed in Kolumbo in different configurations, to study both the distribution of radioactivity along the water column inside the volcano in a static setting, and in the proximity of active and inactive hydrothermal chimneys. “The collected measurements from active vents and the surrounding areas of Kolumbo offer preliminary findings that have already raised intriguing questions about the presence and distribution of radioactivity in this unique underwater environment,” said Dr. Mallios.

The financial support of the Municipality of Thira played a decisive role in realizing the goals of the oceanographic missions. “When we see changes either in the chemical composition of gasses/liquids or in the morphology of the bottom, the systematic monitoring of such an active volcano is mandatory. However, to draw correct conclusions and make correct estimates, we need more data over time, and for this the operation of the SANTORY observatory must continue”, added Dr. Nomikou. “Ensuring continued financial support for oceanographic missions, maintaining monitoring instruments at the submarine volcano observatory, and continuing measurements at Kolumbo are of utmost importance. The Municipality of Thira is steadfast in its commitment to promoting collaborations in pioneering scientific endeavors, alongside the University of Athens and other research bodies, and we hope that the new Municipal Authority will once again be a beacon for Kolumbo’s research”.

Continuous monitoring of Kolumbo’s activity offers scientists invaluable insights that could, in turn, assist government agencies and local communities in their preparedness and crisis management efforts. The unprecedented time series data collected by the SANTORY instruments will complement the extensive database gathered during numerous oceanographic missions, providing essential insight into the behavior and dynamics of Kolumbo. “This knowledge acquisition is critical to conducting hazard assessments, volcanic hazard assessment, and protecting vulnerable communities in the Kolumbo area,” concluded Dr. Nomikou. “By studying volcanic systems over extended periods of time, we can identify recurring patterns and unusual events, ultimately enhancing our ability to predict eruptions and mitigate their consequences.”