You may not have noticed it, but for the past month or so, a huge volcano has been erupting on US shores. – or we should say under US shores. The reason you’ve probably not been aware of it is that it’s been happening deep beneath the Pacific Ocean, in the US Commonwealth of the Northern Mariana Islands.
The Ahyi Seamount, an underwater volcano that sits on the ocean floor about 18 kilometers (11 miles) off the island of Farallon de Pajaros (Uracas) in the Northern Mariana Islands, has been acting up lately – at least, so volcano-watchers think.
“There are no local monitoring stations near Ahyi Seamount, which limits our ability to detect and characterize volcanic unrest there,” pointed out the US Geological Survey in a statement last week. “We will continue to monitor available remote hydrophonic, seismic, and satellite data closely.”
Hydroacoustic sensors on Wake Island, a coral atoll in the western Pacific Ocean, first started picking up signals suggesting volcanic activity back in mid-October. It wasn’t until that data was combined with information from as far afield as Tahiti, Guam, and Chichijima Island, Japan that Ahyi Seamount was pinpointed as the source of the rumblings.
At first, it wasn’t clear whether the source of the activity was a series of shallow earthquakes or an underwater volcanic explosion. But on November 6, researchers found a smoking gun – literally. Satellite imagery showed discoloration on the surface of the ocean, right where Ahyi Seamount is located. That’s a pretty good indication that there’s material being expelled from the volcano, scientists explained.
“Nothing is certain yet, but I have been included on some emails where scientists from NOAA were discussing going to Ahyi by ship to make observations, such as bathymetry [sea or lake depth] measurements,” USGS research geophysicist Matt Haney told Newsweek.
Nevertheless, the evidence so far seems pretty convincing. “Taken together, these data strongly suggest Ahyi is the source of the activity, in spite of there being several other seamounts in the area,” the USGS stated.
“Several” is perhaps underselling it: Ahyi Seamount is part of the Mariana Volcanic Arc, a chain of over 60 active volcanoes and one of the most active volcanic regions on Earth. Ahyi itself has a long history of seismic activity: in 2014, for example, it erupted so hard that its explosion was heard by divers at Farallon de Pajaros, and a new crater was formed near its summit. Before that, an eruption in 1979 gave a fishing crew a shock – a series of shocks, in fact, followed by an upwelling of sulfurous water in the area.
That’s why USGS scientists are recommending that mariners try to avoid the area for now – even though “there’s nothing right now that suggests that this eruption will intensify and become a large eruption,” Haney told AP News.
For now, though, activity seems to be slowing down. “The hydroacoustic signals are ongoing at this time,” notes the USGS statement, "Although the number of the events being detected has declined over the past three days.”