Emergency managers in the Commonwealth of the Northern Mariana Islands are keeping an eye on the Ahyi Seamount, which has been showing signs of unrest in recent weeks.
The U.S. Geological Survey has issued an advisory about the seamount, a large conical submarine volcano that rises to within 164 feet of the sea surface about 11 miles southeast of Farallon de Pajaros and 370 miles north of Saipan.
“Eruptive activity at Ahyi Seamount may present a hazard to mariners in the water above and near the volcano,” the agency warned. ”The summit has shallowed over the course of previous eruptions to 164 feet below sea level, but the lack of local real-time data means we are unable to forecast or warn of impending eruptions. We also cannot be certain if plumes of discolored water represent vigorous hydrothermal activity or active eruptions, and it is possible that a large explosion from the seamount could breach the surface due to the decreased water depth above the vent.”
While the seamount in the Northern Islands is not producing a volcanic cloud, discolored water has been observed above the seamount in satellite images.
USGS reported plumes of discolored water were observed drifting up to 1 mile away from the volcano in satellite images on Oct. 20, 21, 26, 28 and Nov. 5.
An analysis of older satellite data shows weak plume activity becoming more consistent beginning Sept. 21, following sporadic plume observations from August to early September, according to USGS.
In 1979, the crew of a fishing boat felt shocks over the summit area and then observed an upwelling of sulfur-bearing water. On April 24-25, 2001, an explosive submarine eruption was detected at the seamount.
