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USGS Volcano Notice - DOI-USGS-NMI-2025-07-23T23:35:09+00:00
Volcano: Ahyi Seamount (VNUM #284141)
Current Volcano Alert Level: UNASSIGNED
Previous Volcano Alert Level: ADVISORY
Current Aviation Color Code: UNASSIGNED
Previous Aviation Color Code: YELLOW
Issued: Thursday, July 24, 2025, 10:47 AM ChST
Source: U.S. Geological Survey
Notice Number: 2025/N47
Location: N 20 deg 25 min E 145 deg 1 min
Elevation: -259 ft (-79 m)
Area: Northern Mariana Islands
Volcanic Activity Summary:
Ahyi Seamount has been erupting intermittently since October 2022 with a declining intensity with time. The latest phase of activity has produced visible plumes of discolored seawater observed sporadically in satellite images since August 2024. No significant seismic or explosive activity has been observed on regional hydroacoustic sensors during this time. The last observed plume was about 98 ft (30 m) across directly above the seamount on May 28, 2025. Currently, there is no sign of continued submarine eruptive activity. Due to this cessation of activity, the Aviation Color Code and Volcano Alert Level are both lowered to UNASSIGNED. More details will be provided as an Information Statement issued by the Alaska Volcano Observatory.
We will continue to monitor satellite and distal hydroacoustic data for evidence for renewed volcanic activity.
Recent Observations:
[Volcanic cloud height] Unknown
[Other volcanic cloud information] Unknown
Hazard Analysis:
[Other hazards] Shallow submarine eruptions may present hazards to mariners in the water above the vent.
Remarks:
Ahyi seamount is a large conical submarine volcano that rises to within 164 ft (50 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.
Contacts:
CNMI Homeland Security and Emergency Management
https://opd.gov.mp/library/agency/homeland-security-and-emergency-management.html
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: | (20250724/0047Z) |
| (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: | 2025/N47 |
| (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: |
Ahyi Seamount has been erupting intermittently since October 2022 with a declining intensity with time. The latest phase of activity has produced visible plumes of discolored seawater observed sporadically in satellite images since August 2024. No significant seismic or explosive activity has been observed on regional hydroacoustic sensors during this time. The last observed plume was about 98 ft (30 m) across directly above the seamount on May 28, 2025. Currently, there is no sign of continued submarine eruptive activity. Due to this cessation of activity, the Aviation Color Code and Volcano Alert Level are both lowered to UNASSIGNED. More details will be provided as an Information Statement issued by the Alaska Volcano Observatory. We will continue to monitor satellite and distal hydroacoustic data for evidence for renewed volcanic activity.
|
| (12) Volcanic cloud height: | Unknown |
| (13) Other volcanic cloud information: | Unknown |
| (14) Remarks: | Ahyi seamount is a large conical submarine volcano that rises to within 164 ft (50 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
|
| (16) Next Notice: | A new VAN will be issued if conditions change significantly or alert levels are modified. |