USGS Volcano Notice - DOI-USGS-NMI-2024-11-21T22:23:09+00:00

NORTHERN MARIANA ISLANDS VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, November 22, 2024, 8:45 AM ChST (Thursday, November 21, 2024, 22:45 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: ADVISORY
Current Aviation Color Code: YELLOW

Plumes of discolored water drifting up to several hundred yards (meters) away from Ahyi seamount have been observed sporadically in satellite data over the past few weeks. A retrospective analysis of older satellite data shows weak activity extending back to August 5, 2024. Some of these satellite images, including the most recent one, show what might be pumice floating on the ocean surface. Nothing significant has been detected from the direction of Ahyi seamount in hydroacoustic array data at Wake Island, although submarine plumes have been observed at the volcano in the past without clear hydroacoustic signals.

The possible presence of pumice, in addition to the plume of discolored water, suggests an ongoing submarine eruption at Ahyi seamount. In response, the Aviation Color Code and Volcano Alert Level were raised to YELLOW and ADVISORY on November 21 (Chamorro Standard Time).

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 satellite and distal hydroacoustic data closely for additional evidence for, or escalation of, volcanic activity.

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. More recently, the volcano erupted from October 2022 to May 2023 and again from December 2023 to April 2024, characterized by submarine plumes and geophysical detections of activity on the hydrophone arrays at Wake Island. The current episode of unrest began in August 2024.

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