Hazard Notification System (HANS) for Volcanoes


U.S. Geological Survey
Friday, December 9, 2022, 10:27 AM ChST (Friday, December 9, 2022, 00:27 UTC)

Report prepared by the U.S. Geological Survey.

20°25'12" N 145°1'48" E, Summit Elevation -449 ft (-137 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Evidence for a possible submarine eruption of Ahyi Seamount continued over the last week. Underwater pressure sensors on Wake Island (1,410 miles east of Ahyi) detected possible explosion signals from the direction of Ahyi on December 2–7. High-resolution satellite images recorded plumes of discolored water on December 2, 4, and 6 all originating from the summit region of Ahyi. No observations indicate activity has breached the ocean surface.

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.

Ahyi seamount is a large conical submarine volcano that rises to within 79 m of the sea surface about 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 (+/- 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.


No eruptive activity or significant unrest was detected at other 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.

For definitions of Aviation Color Codes and Volcano Alert Levels, see: http://volcanoes.usgs.gov/activity/alertsystem/index.php

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


CNMI Homeland Security and Emergency Management

USGS Northern Mariana Duty Scientist (907) 786-7497

Satellite information, Washington VAAC