USGS Volcano Notice - DOI-USGS-NMI-2025-07-24T01:10:16+00:00

Summary 

• The 2022-2025 eruption at Ahyi Seamount appears paused, with no signs of volcanic activity since May 28, 2025 
• Intermittent eruptions over the past 2.5 years have grown the volcano summit to 164 ft (50 m) below sea level, from its previous depth of 246 ft (75 m) 
• Though paused, the recurrent nature of unrest at Ahyi and the shallow summit present a potential marine hazard near the volcano 

 Recent observations 

Ahyi Seamount has been erupting intermittently since October 2022 with a declining intensity with time. The latest phase of activity has produced visible plumes of discolored seawater observed sporadically in satellite images since August 2024. No significant seismic or explosive activity has been observed on regional hydroacoustic sensors during this time. The last observed plume was about 98 ft (30 m) in diameter directly above the seamount on May 28, 2025. 

In May 2025, the Ocean Exploration Trust’s E/V Nautilus remapped Ahyi Seamount with multibeam sonar bathymetry as part of the Mattingan: Mariana Arc Volcanic Exploration Expedition (NA171) supported by the NOAA Ocean Exploration Program via the Ocean Exploration Cooperative Institute, Bureau of Ocean Energy Management, and the USGS. The new map reveals 82 ft (25 m) of new summit growth since 2022, and the top of the volcano is now 164 ft (50 m) below sea level. 

 A Remotely Operated Vehicle (ROV) dive at the same time observed blocky lava flows and a lack of fine ash deposits, suggesting edifice growth has occurred primarily through lava effusion. The ROV also observed widespread bubble emissions from the summit, which are interpreted as volcanic CO₂, along with widespread cloudy particle plumes, interpreted as due to volcanic SO₂ emission. 

 The observed plumes of discolored seawater in satellite images are likely primarily made up of these sulfur-rich particle plumes from discrete degassing events during eruption, or impulsive periods of vigorous hydrothermal activity. Due to the great distance away from any monitoring stations, these events have not been recorded in geophysical data, and it is difficult to determine how explosive they may be.  

Interpretations and Hazards 

Eruptive activity at Ahyi Seamount may present a hazard to mariners in the water above and near the volcano. The summit has shallowed over the course of this eruption to 164 ft (50 m) below sea level, and long pauses between events are not uncommon. We have not observed any activity in satellite imagery since May 28, 2025, but the lack of local real-time data means we are unable to forecast or warn of impending eruptions. We also cannot be certain if plumes of discolored water represent vigorous hydrothermal activity or active eruptions, and it is possible that a large explosion from the seamount could breach the surface due to the decreased water depth above the vent.