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RRS Discovery DY190
Cruise summary report
| Cruise Info. | |
| Ship name (ship code) | RRS Discovery (74EQ) |
| Cruise identifier | DY190 |
| Cruise period | 2025-03-03 — 2025-03-28 |
| Status | Completed |
| Port of departure | Heraklion, Greece |
| Port of return | Heraklion, Greece |
| Purpose | Research |
| Objectives | Caldera volcanoes generate the most powerful explosive eruptions on Earth, yet the processes controlling why some eruptions are catastrophic while others are comparatively mild remain poorly understood. A critical uncertainty is the role of fluids—particularly hydrothermal, meteoric, and seawater—in regulating volcanic explosivity. Interactions between these fluids and magma can either enhance explosivity by sealing permeability pathways, trapping magmatic gases, and promoting over-pressurisation, or reduce explosivity by maintaining permeable pathways that allow efficient outgassing. Because direct evidence of these processes is commonly destroyed during eruptions, this represents a major blind spot in volcanic hazard forecasting, especially for calderas that are submerged or host crater lakes, such as Campi Flegrei, Taupo, Yellowstone, and Santorini. Understanding how hydrothermal circulation modulates eruption dynamics is therefore essential for improving global assessments of volcanic risk.
The scientific justification for this expedition is to directly characterise a caldera hydrothermal system and its connection to the underlying magma reservoir in unprecedented detail, before it is disrupted by eruption. By mapping permeability pathways, measuring how hydrothermal alteration modifies rock strength and porosity, and quantifying how magmatic volatiles are transferred into hydrothermal fluids, the project aims to resolve the paradox of fluids both increasing and decreasing eruption explosivity. Central scientific questions include where hydrothermal pathways are located and how they evolve, how effectively hydrothermal systems outgas magmatic intrusions, and how these systems respond to renewed magma input during periods of unrest, potentially triggering phreatic or phreatomagmatic explosions. The expedition focuses on the Christiana–Santorini–Kolumbo volcanic field, using Santorini and Kolumbo as complementary case studies of low-temperature and high-temperature caldera-hosted hydrothermal systems. By integrating high-resolution geophysical imaging of subsurface fluid pathways with detailed geochemical analyses of vent fluids and altered rocks, the project will determine how geological structure controls fluid flow, how hydrothermal systems regulate magmatic outgassing, and how they evolve during intrusion. The ultimate aim is to produce globally applicable models that link hydrothermal circulation to eruption style, providing a step change in forecasting volcanic behaviour and mitigating the hazards posed by caldera volcanoes worldwide. The expedition combined a wide range of marine geophysical, geochemical, and sampling equipment to characterise hydrothermal activity within and around the calderas of Santorini and Kolumbo. Key tools included broadband ocean bottom seismometers (OBS) and ocean bottom electromagnetometers (OBEM) to image subsurface structure and fluid pathways, controlled-source electromagnetic (CSEM) systems to map electrical conductivity related to hydrothermal circulation, and multibeam and sub-bottom profilers for high-resolution seafloor and shallow subsurface mapping. Remotely operated vehicle (ROV) dives were central to the programme, enabling direct visual observations, precise temperature measurements, fluid and gas sampling, rock sampling, and the collection of push cores. These datasets were complemented by gravity coring to recover longer sediment records, McLane pumps and radium samplers to quantify fluid fluxes and residence times, and heat-flow probes to characterise |
| Chief scientist | Isobel A Yeo (National Oceanography Centre, Southampton) |
| Project | HYDROMOX |
| Coordinating body | Natural Environment Research Council (NERC) |
| Ocean/sea areas | |
| General | Aegean Sea (The Archipelago) (Mediterranean Sea) |
| Specific | Santorini and Kolumbo |
| Measurements | |
| Chemical oceanography | |
| Other chemical oceanographic measurements | Quantity: number of samples = 5 Description: Radium pumped samples |
| Geology and geophysics | |
| Core - soft bottom | Quantity: number of cores = 50 Description: Sediment gravity cores |
| Core - soft bottom | Quantity: number of cores = 38 Description: ROV push cores |
| Bottom photography | Quantity: activity duration in hours = 160 Description: ROV video at seabed from ROV ISIS on three cameras |
| In-situ seafloor measurement/sampling | Quantity: number of samples = 55 Description: Niskin seawater samples |
| In-situ seafloor measurement/sampling | Quantity: number of samples = 27 Description: Fluid Samples |
| In-situ seafloor measurement/sampling | Quantity: number of measurements = 64 Description: Sediment Heat flow measurements |
| In-situ seafloor measurement/sampling | Quantity: number of measurements = 290 Description: Sediment temperature measurements |
| In-situ seafloor measurement/sampling | Quantity: number of samples = 24 Description: Rock samples |
| In-situ seafloor measurement/sampling | Quantity: number of samples = 4 Description: Radium fibre bag samples |
| Geophysical measurements made at depth | Quantity: track kilometres = 111 Description: Electromagnetics - 8 TX deployments, transmissions at ca. 5630 stations, combined profile length ca. 111km, ca. 30Gb of data |
| Geophysical measurements made at depth | Quantity: activity duration in hours = 100 Description: Seismicity - BBOBS and OBX |
| Multi-beam echosounding | Quantity: track kilometres = 25 Description: SBP - Kongsberg SB27, also run in background on some multibeam lines |
| Multi-beam echosounding | Quantity: track kilometres = 370 Description: Multibeam bathymetry - Hull Mounted EM122 (around 370 km of data collected, however also run in background during operations within the caldera. |
| Moorings, landers, buoys | |
| Geology and geophysics | |
| In-situ seafloor measurement/sampling | 36° 38' 58" N 26° 14' 48" E — OBX23 Site D |
| In-situ seafloor measurement/sampling | 36° 26' 13" N 25° 23' 12" E — OBEM 06 � Santorini deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 25' 55" N 25° 22' 5" E — OBEM 33 � Santorini deployment 3, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 36' 28" N 26° 13' 17" E — OBX18 Site B |
| In-situ seafloor measurement/sampling | 36° 25' 44" N 25° 22' 14" E — OBEM 30 � Santorini deployment 3, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 44' 7" N 26° 11' 0" E — OBX20 Site C |
| In-situ seafloor measurement/sampling | 36° 26' 24" N 25° 23' 3" E — OBEM 07 � Santorini deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 38' 35" N 25° 36' 57" E — OBS01 Caldera |
| In-situ seafloor measurement/sampling | 36° 52' 39" N 25° 48' 53" E — OBS04 Kolumbo |
| In-situ seafloor measurement/sampling | 36° 45' 58" N 25° 53' 31" E — OBS06 Anhydros |
| In-situ seafloor measurement/sampling | 36° 44' 9" N 25° 57' 11" E — OBS07 Anhydros |
| In-situ seafloor measurement/sampling | 36° 54' 59" N 25° 38' 44" E — OBS09 Anhydros |
| In-situ seafloor measurement/sampling | 36° 55' 0" N 25° 59' 51" E — OBS11 Anhydros |
| In-situ seafloor measurement/sampling | 36° 59' 54" N 25° 58' 23" E — OBS12 Anhydros |
| In-situ seafloor measurement/sampling | 36° 39' 47" N 26° 10' 0" E — OBX14 Site A |
| In-situ seafloor measurement/sampling | 36° 38' 26" N 26° 12' 10" E — OBX16 Site B |
| In-situ seafloor measurement/sampling | 36° 36' 43" N 26° 12' 59" E — OBX17 Site B |
| In-situ seafloor measurement/sampling | 36° 44' 7" N 26° 11' 0" E — OBX21 Site C |
| In-situ seafloor measurement/sampling | 36° 39' 6" N 26° 14' 50" E — OBX24 Site D |
| In-situ seafloor measurement/sampling | 36° 39' 9" N 26° 10' 46" E — OBX25 Site E |
| In-situ seafloor measurement/sampling | 36° 39' 11" N 26° 10' 49" E — OBX26 Site E |
| In-situ seafloor measurement/sampling | 36° 39' 10" N 26° 10' 47" E — OBX27 Site E |
| In-situ seafloor measurement/sampling | 36° 38' 52" N 26° 10' 5" E — OBX28 Site F |
| In-situ seafloor measurement/sampling | 36° 31' 19" N 25° 29' 5" E — OBEM 01 � Kolumbo deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 31' 19" N 25° 29' 18" E — OBEM 02 � Kolumbo deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 31' 29" N 25° 29' 5" E — OBEM 03 � Kolumbo deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 31' 29" N 25° 29' 18" E — OBEM 04 � Kolumbo deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 2" N 25° 23' 20" E — OBEM 01 � Santorini deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 25' 59" N 25° 22' 44" E — OBEM 04 � Santorini deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 6" N 25° 22' 58" E — OBEM 05 � Santorini deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 17" N 25° 22' 49" E — OBEM 08 � Santorini deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 10" N 25° 22' 35" E — OBEM 09 � Santorini deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 21" N 25° 22' 26" E — OBEM 10 � Santorini deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 29" N 25° 22' 41" E — OBEM 11 � Santorini deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 36" N 25° 22' 55" E — OBEM 12 � Santorini deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 25' 57" N 25° 23' 43" E — OBEM 14 � Santorini deployment 2, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 4" N 25° 23' 57" E — OBEM 15 � Santorini deployment 2, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 9" N 25° 23' 35" E — OBEM 17 � Santorini deployment 2, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 16" N 25° 23' 49" E — OBEM 18 � Santorini deployment 2, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 23" N 25° 24' 3" E — OBEM 19 � Santorini deployment 2, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 31" N 25° 23' 17" E — OBEM 21 � Santorini deployment 2, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 20" N 25° 23' 26" E — OBEM 22 � Santorini deployment 2, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 50" N 25° 23' 23" E — OBEM 23 � Santorini deployment 2, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 39" N 25° 23' 31" E — OBEM 24 � Santorini deployment 2, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 27" N 25° 23' 40" E — OBEM 25 � Santorini deployment 2, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 25' 39" N 25° 22' 36" E — OBEM 26 � Santorini deployment 3, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 25' 32" N 25° 22' 22" E — OBEM 27 � Santorini deployment 3, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 25' 25" N 25° 22' 8" E — OBEM 28 � Santorini deployment 3, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 25' 36" N 25° 22' 0" E — OBEM 29 � Santorini deployment 3, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 25' 51" N 25° 22' 28" E — OBEM 31 � Santorini deployment 3, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 2" N 25° 22' 19" E — OBEM 32 � Santorini deployment 3, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 25' 54" N 25° 23' 6" E — OBEM 02 � Santorini deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 41' 47" N 25° 36' 1" E — OBS02 Caldera |
| In-situ seafloor measurement/sampling | 36° 25' 47" N 25° 22' 52" E — OBEM 03 � Santorini deployment 1, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 26' 12" N 25° 24' 11" E — OBEM 16 � Santorini deployment 2, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 44' 57" N 25° 40' 14" E — OBS03 Caldera |
| In-situ seafloor measurement/sampling | 37° 0' 9" N 25° 55' 29" E — OBS05 Anhydros |
| In-situ seafloor measurement/sampling | 36° 53' 53" N 25° 27' 12" E — OBS08 Anhydros |
| In-situ seafloor measurement/sampling | 36° 42' 11" N 25° 45' 7" E — OBS10 Caldera |
| In-situ seafloor measurement/sampling | 36° 39' 48" N 26° 10' 0" E — OBX01 Site A |
| In-situ seafloor measurement/sampling | 36° 38' 7" N 26° 12' 0" E — OBX15 Site B |
| In-situ seafloor measurement/sampling | 36° 44' 11" N 26° 11' 3" E — OBX19 Site C |
| In-situ seafloor measurement/sampling | 36° 38' 48" N 26° 14' 37" E — OBX22 Site D |
| In-situ seafloor measurement/sampling | 36° 26' 43" N 25° 23' 9" E — OBEM 20 � Santorini deployment 2, bottom EM recorder |
| In-situ seafloor measurement/sampling | 36° 25' 47" N 25° 21' 51" E — OBEM 34 � Santorini deployment 3, bottom EM recorder |
