USGS Volcano Notice for Aviation - DOI-USGS-NMI-2023-07-17T17:50:40-07:00

(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20230718/0102Z)
(3) Volcano:	Ahyi Seamount (VNUM #284141)
(4) Current Color Code:	UNASSIGNED
(5) Previous Color Code:	YELLOW
(6) Source:	U.S. Geological Survey
(7) Notice Number:	2023/N168
(8) Volcano Location:	N 20 deg 25 min E 145 deg 1 min
(9) Area:	Northern Mariana Islands
(10) Summit Elevation:	-259 ft (-79 m)
(11) Volcanic Activity Summary:	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.
(12) Volcanic cloud height:	No volcanic cloud produced
(13) Other volcanic cloud information:	Water discoloration no longer observed above seamount in satellite images
(14) Remarks:	Ahyi seamount is a large conical submarine volcano that rises to within 450 ft (137 m) of the sea surface about 11 miles (18 km) southeast of Farallon de Pajaros (Uracas) Island in the northern Marianas, about 370 miles (600 km) north of the island of Saipan. In the past, discolored water has been observed over the submarine volcano. In 1979, the crew of a fishing boat felt shocks over the summit area and then observed upwelling of sulfur-bearing water. On April 24-25, 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.
(15) Contacts:	CNMI Homeland Security and Emergency Management http://www.cnmihsem.gov.mp/ USGS Northern Mariana Duty Scientist (907) 786-7497 http://volcano.wr.usgs.gov/cnmistatus.php Satellite information, Washington VAAC http://www.ssd.noaa.gov/VAAC/washington.html
(16) Next Notice:	A new VAN will be issued if conditions change significantly or alert levels are modified.