What is it about?

How do we know in advance where in the oceans there is a risk of volcanic eruptions? If we are honest, oceanic eruptions are not so dangerous as it is relatively easy to spot signs of them from the bridge of a ship. However, will there be issues in doing so in the transition to autonomous shipping? On RV Urania in 1999, we observed close-hand the Serreta Ridge submarine eruption (Terceira), which was more subdued than shown by De La Beche. There was floating pumice around the ship and it was easy to imagine that the eruption might have been problematic if excessive bubbles led to loss of vessel buoyancy (the crew were not so keen on our geotourism). There are also risks of eruptions causing tsunamis, either directly or via landslides triggered by them.

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Why is it important?

In this study led by Yingchen Liu, we analysed 3 months of recordings from five ocean-bottom seismometers placed around a 2019-2020 seismic swarm west of Faial Island in the Azores. The swarm potentially indicated a submarine eruption was occurring so the UK Ocean‐Bottom Instrumentation Consortium was tasked with deploying a set of instruments around the site. The P-wave polarities of some events were found to be reversed, indicating changed stress within rock above an intrusion. Separately, analysis has found no evidence of a change at the seabed (Mitchell et al. 2025), so there was no eruption as such, rather an incremental inflation of an intrusion that may lead to an eruption in the future.

Perspectives

After some delays due to the UK now being out of the EU, which made transporting the instruments into Portugal complicated, the deployment went very well. We thank the UK Ocean‐Bottom Instrumentation Consortium and the Durham OBS group in particular - Christine Peirce, Ben Pitcairn, Anna Bird, and Andrew Clegg (the last two for reclaiming the instruments under COVID-19 restrictions). Thanks also to the crew of RV Arquipelago and staff of the IMAR/OKEANOS (University of Azores), particularly Octávio Melo, for their help with logistics and assistance in deploying the OBSs. Further thanks to Fernando Tempera, Telmo Morato and Rui Marques for help with planning the deployments. Funding was from the NERC (instruments) and China Scholarship Council (Yingchen's stipend). I acknowledge also the crucial roles of my co-authors Dietrick Lange and Ingo Grevemeyer in this study, both for supporting Yingchen's work and preliminary analysis (such as estimating clock drifts, as the instruments had lost battery power by recovery).

Dr Neil C. Mitchell
University of Manchester

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This page is a summary of: An Inflating Upper Mantle Magma Reservoir Beneath the Tip of the Condor Seamount, Azores Revealed by Rapid‐Response Ocean‐Bottom‐Seismometer Data, Geophysical Research Letters, August 2026, American Geophysical Union (AGU),
DOI: 10.1029/2025gl119884.
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