Hazard Notification System (HANS) for Volcanoes

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NORTHERN MARIANA ISLANDS VOLCANO OBSERVATORY INFORMATION STATEMENT
U.S. Geological Survey
Tuesday, November 15, 2022, 7:14 AM ChST (Monday, November 14, 2022, 21:14 UTC)


Report prepared by the U.S. Geological Survey.

AHYI SEAMOUNT VOLCANO (VNUM #284141)
20°25'12" N 145°1'48" E, Summit Elevation -449 ft (-137 m)
Current Volcano Alert Level: UNASSIGNED
Current Aviation Color Code: UNASSIGNED

Starting in mid-October, hydroacoustic sensors at Wake Island began recording signals consistent with activity from an undersea volcanic source. In collaboration with the Laboratoire de Geophysique in Tahiti, recent combined analysis of the hydroacoustic signals together with data from seismic stations located at Guam and Chichijima Island, Japan, suggest that the source of this activity is at or near Ahyi seamount. Furthermore, satellite imagery from November 6 shows discoloration on the surface of the ocean at Ahyi's location. Taken together, these data strongly suggest Ahyi is the source of the activity, in spite of there being several other seamounts in the area.

The hydroacoustic signals are ongoing at this time, although the number of the events being detected has declined over the past three days.

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 hydrophonic, 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 Farollon 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.



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/


CONTACT INFORMATION:

CNMI Homeland Security and Emergency Management
http://www.cnmihsem.gov.mp/

USGS Northern Mariana Duty Scientist (808) 967-8815
http://volcano.wr.usgs.gov/cnmistatus.php

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