USGS Volcano Notice - DOI-USGS-NMI-2026-07-30T20:18:54+00:00

NORTHERN MARIANA ISLANDS WEEKLY UPDATE
U.S. Geological Survey
Friday, July 31, 2026, 7:02 AM ChST (Thursday, July 30, 2026, 21:02 UTC)

Report prepared by the U.S. Geological Survey.

AHYI SEAMOUNT (VNUM #284141)
20°26'13" N 145°1'48" E, Summit Elevation -180 ft (-55 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Summary: No underwater plumes observed in satellite images or in distal geophysical data this past week.

There were several clear satellite images of the ocean over Ahyi Seamount this past week, but there were no observations of underwater plumes. Distal geophysical monitoring showed no evidence of activity. 

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 previous eruptions to 180 feet (55 m) below sea level, but the lack of local real-time data means we are unable to forecast or warn of impending eruptions. We will continue to monitor satellite and distal hydroacoustic data for additional evidence for, or escalation of, volcanic activity.

Ahyi seamount is a large conical submarine volcano that rises to within 180 feet (55 m) of the sea surface about 11 miles (18 km) southeast of the island of Farallon de Pajaros (Uracas) in the Northern Mariana Islands. Water discoloration has been observed over the submarine volcano during previous periods of activity, and in 1979 the crew of a fishing boat felt shocks over the summit area followed by upwelling of sulfur-bearing water. From April 24 to 25, 2001, an explosive submarine eruption was detected seismically from a seismic station on Rangiroa Atoll, Tuamotu Archipelago. The event was well constrained (+/- 9 miles or 15 km) at a location near the southern base of Ahyi; the summit of the seamount lies within the location uncertainty. Another eruption was detected from April 24 to May 17, 2014, using data from seismometers located on subaerial volcanoes in the Northern Mariana Islands and hydrophone arrays at Wake Island. NOAA divers also reported hearing explosions while conducting coral reef research on nearby Farallon de Pajaros. The 2014 eruption of Ahyi formed a new crater near the summit of the volcano and a large landslide chute developed on its southeast flank. The most recent eruptive activity began in 2022. 

Northern Mariana Islands Volcano Observatory

Summary: No signs of significant volcanic unrest.

NORTHERN MARIANAS VOLCANOES
No signs of significant unrest were detected at any Northern Mariana Island volcanoes during the past week.  Geophysical data streams were temporarily interrupted due to Typhoon Bavi, but have since been restored.

Monitoring of Northern Mariana Islands Volcanoes

Northern Mariana Island volcanoes are monitored using seismo-acoustic sensors on Saipan, and by examining satellite imagery. We also use distant seismic stations in Guam and Chichijima, Japan, and hydroacoustic data from Wake Island, when available.

This level of monitoring can detect significant volcanic activity in the CNMI but cannot provide advanced warning of eruptions.

Due to a lack of geophysical monitoring on any of the volcanic islands, the following volcanoes have alert levels of UNASSIGNED: Anatahan, Sarigan, Farallon de Pajaros, Supply Reef, Maug, Asuncion, Agrigan, Pagan, Almagan, and Guguan.

For definitions of Aviation Color Codes and Volcano Alert Levels: https://www.usgs.gov/programs/VHP/volcanic-alert-levels-characterize-conditions-us-volcanoes

SUBSCRIBE TO VOLCANO ALERT MESSAGES by email: http://volcanoes.usgs.gov/vns/
 

CONTACT INFORMATION:

USGS Northern Mariana Duty Scientist (907) 786-7497
http://volcano.wr.usgs.gov/cnmistatus.php

CNMI Homeland Security and Emergency Management
https://opd.gov.mp/library/agency/homeland-security-and-emergency-management.html

Satellite information, Washington VAAC
http://www.ssd.noaa.gov/VAAC/washington.html