Consistent signs of unrest at Ahyi Seamount have not occurred for over four weeks. Underwater pressure sensors near Wake Island have not detected clear signs of underwater volcanic activity since early June and the last satellite observations of discolored water near the seamount was seen on May 22, 2023. As a result, the Aviation Color Code was lowered from YELLOW to UNASSIGNED and the Volcano Alert Level was lowered from ADVISORY to UNASSIGNED earlier this week. Future weekly updates for Ahyi Seamount will be included in reports with other volcanoes of the Northern Marianas Islands unless new volcanic activity or unrest is detected.

There are no local monitoring stations near Ahyi Seamount, which limits our ability to detect and characterize volcanic unrest there. We will continue to monitor available remote underwater pressure sensors, seismic, and satellite data closely.

NORTHERN MARIANAS VOLCANOES
No eruptive activity or significant unrest was detected at the Northern Mariana Island volcanoes during the past week.

Monitoring of Northern Mariana Islands Volcanoes

Northern Mariana Island volcanoes are monitored remotely with satellite data, distant seismic stations in Guam and Chichijima, Japan, and hydroacoustic data from Wake Island. These observations might detect significant explosive activity in the CNMI, but because of the absence of functional local ground-based monitoring stations at the volcanoes, we cannot provide advanced warning of activity.

Ground-based geophysical monitoring data from stations on Anatahan and Sarigan islands have been unavailable since storm damage in August, 2017. In addition, data flow from an intermittently operational seismo-accoustic network on Saipan stopped completely on June 7, 2022. Current logistical challenges in the CNMI prevent visiting these sites to make repairs. A timeline for returning these stations to operation is uncertain. Due to a lack of direct geophysical monitoring on the islands, Anatahan and Sarigan volcano alert levels are designated UNASSIGNED.

Other volcanoes in the CNMI including Farallon de Pajaros, Supply Reef, Maug, Asuncion, Agrigan, Pagan, Almagan, and Guguan are not seismically monitored and are normally designated UNASSIGNED, absent other observations of activity.

Consistent signs of unrest at Ahyi Seamount have not occurred for over four weeks. Underwater pressure sensors near Wake Island have not detected clear signs of underwater volcanic activity since early June and the last satellite observations of discolored water near the seamount was seen on May 22, 2023. 

Starting mid-October 2022, hydroacoustic sensors at Wake Island, 1,410 miles (2,270 km) east of Ahyi, began recording signals consistent with activity from an undersea volcanic source. In collaboration with the Laboratoire de Geophysique in Tahiti, a combined analysis of the hydroacoustic signals and data from seismic stations located at Guam and Chichijima Island, Japan, confirmed that the source of this activity was at or near Ahyi seamount.  Observations of discolored water above the seamount in satellite data confirmed activity at Ahyi. The activity appears to have paused beginning in early April but briefly resumed in late May.  

Due to the apparent absence of activity over the last month, the aviation color code is being lowered from YELLOW to UNASSIGNED and the alert level is being lowered from ADVISORY to UNASSIGNED.