NORTHERN MARIANA ISLANDS VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, July 21, 2023, 9:45 AM ChST (Thursday, July 20, 2023, 23:45 UTC)
Report prepared by the U.S. Geological Survey.
AHYI SEAMOUNT (VNUM #284141)
20°25'12" N 145°1'48" E, Summit Elevation -259 ft (-79 m)
Current Volcano Alert Level: UNASSIGNED
Current Aviation Color Code: UNASSIGNED
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. As a result, the Aviation Color Code was lowered from YELLOW to UNASSIGNED and the Volcano Alert Level was lowered from ADVISORY to UNASSIGNED earlier this week. Future weekly updates for Ahyi Seamount will be included in reports with other volcanoes of the Northern Marianas Islands unless new volcanic activity or unrest is detected.
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 260 feet (79 m) of the sea surface about 11 miles (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 (+/- 9 miles or 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.
NORTHERN MARIANAS VOLCANOES
No eruptive activity or significant unrest was detected at the 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/
CONTACT INFORMATION:
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
NMI/USGS Volcanic Activity Notice
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: Tuesday, July 18, 2023, 11:02 AM ChST
Source: U.S. Geological Survey
Notice Number: 2023/N168
Location: N 20 deg 25 min E 145 deg 1 min
Elevation: -259 ft (-79 m)
Area: Northern Mariana Islands
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.
Recent Observations:
[Volcanic cloud height] No volcanic cloud produced
[Other volcanic cloud information] Water discoloration no longer observed above seamount in satellite images
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 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.
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.