USGS Volcano Notice - DOI-USGS-NMI-2022-11-28T11:02:08-09:00

NMI/USGS Volcanic Activity Notice

Volcano: Ahyi Seamount (VNUM #284141)

Current Volcano Alert Level: ADVISORY
Previous Volcano Alert Level: UNASSIGNED

Current Aviation Color Code: YELLOW
Previous Aviation Color Code: UNASSIGNED

Issued: Tuesday, November 29, 2022, 8:54 AM ChST
Source: U.S. Geological Survey
Notice Number: 2022/N50
Location: N 20 deg 25 min E 145 deg 1 min
Elevation: -449 ft (-137 m)
Area: Northern Mariana Islands

Volcanic Activity Summary:

Signs of unrest at Ahyi Seamount have been observed in satellite and remote geophysical data. A plume of discolored water above Ahyi Seamount has been visible persistently in satellite data since November 18, 2022. This discoloration could be due to degassing or eruption at the volcano, but we cannot say for certain due to a lack of local monitoring stations.

Starting in mid-October, hydroacoustic sensors at Wake Island, 2,270 km (1,410 miles) east of Ahyi, 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, confirm that the source of this activity is at or near Ahyi seamount. Hydrophone signals continue to be observed but have decreased in the past few weeks.

Due to the current activity, the aviation color code is being raised from UNASSIGNED to YELLOW and the alert level is being raised from UNASSIGNED to ADVISORY.

Recent Observations:
[Volcanic cloud height] No volcanic cloud produced
[Other volcanic cloud information] Water discoloration observed above seamount in satellite images

Hazard Analysis:
[General hazards] Marine hazards possible above or near restless seamount volcano. Aviation hazards possible only in event of increased activity.

Remarks:

Ahyi seamount is a large conical submarine volcano that rises to within 137 m (450 ft) of the sea surface about 18 km (11 mi) southeast of Farallon de Pajaros (Uracas) Island in the northern Marianas, about 600 km (370 mi) 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 (+/- 15 km or 9 miles) at a location near the southern base of Ahyi.

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

Next Notice:

A new VAN will be issued if conditions change significantly or alert levels are modified.

(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20221128/2254Z)
(3) Volcano:	Ahyi Seamount (VNUM #284141)
(4) Current Color Code:	YELLOW
(5) Previous Color Code:	UNASSIGNED
(6) Source:	U.S. Geological Survey
(7) Notice Number:	2022/N50
(8) Volcano Location:	N 20 deg 25 min E 145 deg 1 min
(9) Area:	Northern Mariana Islands
(10) Summit Elevation:	-449 ft (-137 m)
(11) Volcanic Activity Summary:	Signs of unrest at Ahyi Seamount have been observed in satellite and remote geophysical data. A plume of discolored water above Ahyi Seamount has been visible persistently in satellite data since November 18, 2022. This discoloration could be due to degassing or eruption at the volcano, but we cannot say for certain due to a lack of local monitoring stations. Starting in mid-October, hydroacoustic sensors at Wake Island, 2,270 km (1,410 miles) east of Ahyi, 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, confirm that the source of this activity is at or near Ahyi seamount. Hydrophone signals continue to be observed but have decreased in the past few weeks. Due to the current activity, the aviation color code is being raised from UNASSIGNED to YELLOW and the alert level is being raised from UNASSIGNED to ADVISORY.
(12) Volcanic cloud height:	No volcanic cloud produced
(13) Other volcanic cloud information:	Water discoloration observed above seamount in satellite images
(14) Remarks:	Ahyi seamount is a large conical submarine volcano that rises to within 137 m (450 ft) of the sea surface about 18 km (11 mi) southeast of Farallon de Pajaros (Uracas) Island in the northern Marianas, about 600 km (370 mi) 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 (+/- 15 km or 9 miles) 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.