Possible undersea eruption provokes alert level change

Although signals seem to indicate that the possible underwater eruption near Uracas in the Northern Islands may be diminished now, some signs are still being seen, prompting the CNMI Homeland Security and Emergency Management yesterday to raise the Aviation Color Code in the area from “Unassigned” to “Yellow” and the alert level from “Unassigned” to “Advisory.”

An HSEM news release yesterday said that geophysical data from satellites and remote locations have shown indications of instability at Ahyi Seamount last Nov. 18, 2022, at 9am and, although hydrophone signals have diminished over the past few weeks, they are still being seen.

“Yellow” and “Advisory” essentially have the same meaning and reflect an activity level that is elevated above background.

According to the U.S. Geological Survey website, both the Volcano Alert Level and Aviation Color Code reflect the danger a volcano poses to people on the ground and infrastructure. The Aviation Color Code is designed specifically for the aviation sector and was originally developed to rapidly communicate to pilots, dispatchers, and air traffic controllers the threats posed to aviation by restless or erupting volcanoes.

The Ahyi seamount is a sizable conical submarine volcano that rises to within 450 ft of the sea surface and is located about 18 kilometers (11 miles) southeast of Farallon de Pajaros (Uracas) Island in the Northern Marianas and is about 370 miles north of the island of Saipan.

Over the underwater volcano, cloudy water has been seen in the past. A fishing boat’s crew experienced shocks over the summit region, and they later noticed sulfur-containing water upwelling. An explosive undersea eruption was discovered, by a seismic station on Rangiroa Atoll in the Tuamotu Archipelago at a site not far from the southern base of Ahyi. The event was well contained within nine miles. There may be marine risks above or nearby a restless seamount volcano. Only in the event of increasing activity are aviation hazards potential.

The HSEM news release said that satellite imagery has consistently shown a plume of discolored water above Ahyi Seamount.

“Due to a lack of nearby monitoring stations, we are unable to definitively establish whether this discoloration is triggered by degassing or eruption at the volcano,” it stated.

Hydroacoustic sensors at Wake Island, 1,410 miles east of Ahyi, started capturing sounds corresponding to activity from an undersea volcanic source in the middle of October. Recent combined study of the hydroacoustic signals and data from seismic stations in Guam and Chichijima Island, Japan, in cooperation with the Laboratoire de Geophysique in Tahiti, confirm that the source of this activity is at or near Ahyi seamount. (Saipan Tribune)