USGS Volcano Notice - DOI-USGS-NMI-2026-07-16T22:31:59+00:00

NORTHERN MARIANA ISLANDS WEEKLY UPDATE
U.S. Geological Survey
Friday, July 17, 2026, 8:40 AM ChST (Thursday, July 16, 2026, 22:40 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: Plume of discolored water observed in satellite image this week, Color Code and Alert Level raised to YELLOW and ADVISORY.

A 1000 ft-long (200 m) plume of discolored water was observed in the water above Ahyi Seamount in a satellite image on July 11. This and other plume images in the last few weeks are likely the result of gas release into the water column. This activity could reflect vigorous hydrothermal degassing or be associated with an ongoing effusive eruption. In either case, the observations indicate increased volcanic unrest and potential for activity to breach the ocean surface. In response, the Aviation Color Code and Volcano Alert Level were raised to YELLOW and ADVISORY on July 16.

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.

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