Ahyi Seamount

Multiple occurrences of volcanic activity have been detected at the Ahyi–Supply Reef region since the 1960s. Most observations of activity have come from hydrophone recordings or seismograph recordings with very large location uncertainty, which makes them unable to be assigned to a specific seamount. In other cases, observations came from direct observations at the location like discolored water on the sea surface,^[1][4] or new lava deposited since the last visual underwater inspection.^[2]

In 1969, seismic and hydrophone detections from far away of volcanic explosions from Ahyi were recorded, though the discolored water was seen a bit farther away from Ahyi, right in between Supply Reef and Ahyi. This activity in 1969 was described as similar to hydrophone recordings in the same region in 1967. In 1979, a fishing boat reported upwelling water and pumice with sulfur composition near Ahyi.^[4]

In late April 2014, Ahyi erupted, ending a 13-year dormancy period with an explosive eruption which lasted more than 2 weeks. At the time of the eruption, the remote location of the volcano and the presence of nearby volcanoes made it hard to understand the actual location of the eruption. The explosions were recorded by hydrophones in the region including in Wake Island and by seismographs including in Guam and Chichijima. Following May 8, acoustic waves from the events were observed until May 17. During the eruption, NOAA research divers and researchers on a ship near Farallon de Pajaros, around 20 km (12 mi) away from Ahyi, reported hearing explosions. In the same area, the NOAA crew observed orange-yellow bubbles covering parts of the sea surface. Despite these observations, satellite products did not show anything unusual throughout the whole eruption. During mid-May, an expedition on a NOAA ship which was planned to pass around the Ahyi eruption area was able to collect some samples and information about the eruption. Multibeam bathymetries were obtained at the same expedition. Comparison between 2003 and 2014 bathymetry proved that the summit depth of Ahyi had changed from 60 m (197 ft) in 2003 to 75 m (246 ft) in 2014. The bathymetry differences also revealed a new 95-meter-deep (312 ft) crater formed at the summit. South-southeast of the crater was a landslide trail towards the downslope with a deepest point of 2,300 m (7,546 ft). Plume particles were observed at three CTD casts of Ahyi.^[8]

The eruption had been occurring since November 18, 2022, until due to the lack of evidence of unrest, the Aviation Color Code for Ahyi was reduced to unassigned on April 26, 2023, and the eruption was declared over. On May 23, Ahyi was declared erupting again, having its aviation color code increased to Yellow and volcano alert level to Advisory.^[1] In 2025 the summit again was found to be within 50-60 m of the ocean surface.^[2]

• NW Rota-1

• Tepp, G.; Chadwick Jr., W. W.; Haney, M. M.; Lyons, J. J.; Dziak, R. P.; Merle, S. G.; Butterfield, D. A.; Young, C. W. (2019). "Hydroacoustic, Seismic, and Bathymetric Observations of the 2014 Submarine Eruption at Ahyi Seamount, Mariana Arc". Geochemistry, Geophysics, Geosystems. 20 (7): 3608–3627. Bibcode:2019GGG....20.3608T. doi:10.1029/2019GC008311. S2CID 198407967.
• Metz, D.; Grevemeyer, I. (2018). "Hydroacoustic Measurements of the 2014 Eruption at Ahyi Volcano, 20.4°N Mariana Arc". Geophysical Research Letters. 45 (20): 11, 050–11, 058. Bibcode:2018GeoRL..4511050M. doi:10.1029/2018GL079983. S2CID 134160489.
• Buck, N. J.; Resing, J. A.; Baker, E. T.; Lupton, J. E. (2018). "Chemical Fluxes From a Recently Erupted Shallow Submarine Volcano on the Mariana Arc". Geochemistry, Geophysics, Geosystems. 19 (5): 1660–1673. Bibcode:2018GGG....19.1660B. doi:10.1029/2018GC007470. S2CID 134737270.
• Neuholz, R.; Kleint, C.; Schnetger, B.; Koschinsky, A.; Laan, P.; Middag, R.; Sander, S.; Thal, J.; Turke, A.; Walter, M.; Zitoun, R.; Brumsack, H-J. (2020). "Submarine Hydrothermal Discharge and Fluxes of Dissolved Fe and Mn, and He Isotopes at Brothers Volcano Based on Radium Isotopes". Minerals. 10 (11): 0–31. Bibcode:2020Mine...10..969N. doi:10.3390/min10110969.
• Haney, M. M.; Chadwick Jr., W. W.; Merle, S. G; Buck, N. J.; Butterfield, D. A.; Coombs, M. L.; Evers, L. G.; Heaney, K. D.; Lyons, J. J.; Searcy, C. K.; Walker, S. L.; Young, C.; Embley, R. W. (2014). "The 2014 Submarine eruption of Ahyi volcano, northern Mariana Islands". AGU Fall Meeting 2014. 1 (1). Bibcode:2014AGUFM.V11B4727H.