Santorini volcanic system: New measurements for improved early warning systems

Research expedition M215 expands observation systems as part of the third DAM research mission mareXtreme

17. December 2025 | Kiel / Heraklion

An international research team led by the GEOMAR Helmholtz Centre for Ocean Research Kiel set sail today on the research vessel METEOR for the M215 expedition (MULTI-MAREX Cruise 3) to the Greek island group of Santorini. The aim of the expedition is to conduct a detailed investigation of the Santorini-Kolumbo submarine volcanic system and to test innovative observation and monitoring systems that will contribute to improved risk assessment and early warning of extreme marine events in the future.

The expedition is part of the MULTI-MAREX research project, which is being carried out as part of the third research mission of the German Marine Research Alliance (DAM) ‘mareXtreme – Ways to improve risk management in the field of marine extreme events and natural hazards’. As part of this mission, a living lab is being set up in the central Mediterranean region to systematically record and model processes such as earthquakes, volcanism and tsunamis and to better assess their social impact.

The RV METEOR in Heraklion harbour. Foto: Roberto Benavides, GEOMAR

Unique data basis after seismic crisis

Immediately after the first MULTI-MAREX expedition in winter 2024, an exceptionally intense earthquake swarm occurred around Santorini in spring 2025, with more than 28,000 individual earthquakes recorded. As measuring instruments had already been installed before the seismic crisis began and additional data could be collected during the events, the research team now has a rare, almost complete data basis.

‘From a scientific point of view, we are in an exceptional situation,’ explains Jens Karstens, marine geophysicist at GEOMAR and co-expedition leader. ‘We can compare measurements taken immediately before, during and after a seismic crisis. This comparative data provides insights that would otherwise often require decades of observation.

Santorini as a geological and social risk area

Santorini is located in one of the most tectonically active regions of the eastern Mediterranean. The archipelago forms the edge of a volcanic caldera that was created around 3,600 years ago by one of the largest known eruptions in human history. About seven kilometres to the northeast is the active undersea volcano Kolumbo, part of a system consisting of more than 20 submarine volcanoes. At the same time, Santorini is one of Greece's most important tourist destinations, attracting up to 3.5 million visitors per year, which further underscores the relevance of robust risk and early warning concepts.

In order to test a long-term observation network, the researchers will conduct tests and communication experiments using so-called MOLA systems (Modular Ocean Landers), among others. Foto: Jens Karstens, GEOMAR

Early warning one step earlier

Analyses by GEOMAR and GFZ researchers indicate that the earthquake swarm in early 2025 was triggered by magma movements at depth. The M215 expedition now aims to better understand the response of the volcanic system and assess possible future scenarios.

‘Previous early warning systems have been based primarily on land-based seismometers and GPS measurements,’ explains expedition leader Prof. Dr. Heidrun Kopp, Professor of Marine Geodesy at GEOMAR and project manager of MULTI-MAREX. "As part of mareXtreme, we want to start a step earlier and record processes on the seabed before they become noticeable on land. To this end, we are also in close contact with the relevant authorities in Greece’.

Another focus is on the stability of the volcanic slopes in the Santorini-Kolumbo volcanic field and their behaviour during tectonic activity – a key aspect for assessing potential landslides and tsunami-generating processes.

Innovative measurement and communication systems

During the expedition, existing measuring stations will be recovered and new instruments installed. These include MOLA (Modular Ocean Lander) systems, which can register acoustic signals, temperature and chemical changes on the seabed and communicate with each other. The aim is to test a network that will eventually transmit data to land in near real time.

There will also be a special focus on the use of the MOMO video sled developed at GEOMAR, which allows millimetre-precise mapping of the seabed. By comparing measurements from December 2024, changes in hydrothermal systems in the crater of the Kolumbo volcano and within the Santorini caldera can be analysed in detail.

The work is supplemented by ocean floor seismometers, magnetotelluric measuring stations, autonomous underwater vehicles, drone flights and high-resolution echo sounder measurements.

Contribution to the third DAM research mission mareXtreme

The data obtained during the expedition will be directly incorporated into the objectives of the third DAM research mission mareXtreme. The overarching goal of this mission is to establish a scientifically sound basis for improved risk management of marine extreme events, thereby providing long-term support for decision-making processes in politics, administration and society.