USGS Volcano Notice - DOI-USGS-NMI-2023-09-21T16:05:59-07:00

A submarine eruption at Ruby seamount on September 14–16 was detected in satellite imagery and seismoacoustic signals. The first indication of activity was volcanic tremor observed on a seismometer in Saipan (50 km from Ruby) beginning around 09:00 UTC on September 14 (19:00 ChST local time). This was punctuated by a signal that likely represents the start of the eruption at 14:16 UTC (September 15 00:16 ChST). A submarine plume of warm, discolored water is apparent in geostationary satellite imagery beginning around 18:00 UTC (September 15 04:16 ChST). Seismicity peaked with an event on September 15 at 04:26 UTC (14:26 ChST), that the U.S. Geological Survey measured as a magnitude 4.7 near Ruby volcano. The seismic waves from the event were strong enough to be observed on the infrasound sensor at the seismoacoustic monitoring station in Saipan. Later on September 15, the submarine plume noticeably weakened, becoming greener and narrower over time before eventually detaching from the vent on September 16 around 03:30 UTC (13:30 ChST). This plume of discolored water has since drifted in the ocean and is still visible as a zone of greenish water between Saipan and Anatahan. No evidence of further activity has been detected in regional seismic and infrasound data or satellite imagery since September 16.  

In response to this activity at Ruby, the Aviation Color Code and Volcano Alert Level were raised from UNASSIGNED to YELLOW/ADVISORY on September 19. Local observers reported seeing the plume of discolored ocean water in the area. Although no volcanic gas emissions have been detected in satellite data associated with the eruption or in the days after, haze was also reported in the region. Analysis suggests that, if volcanic, this was most likely sourced from the recent eruption of Kīlauea volcano in Hawaiʻi and not the submarine activity at Ruby. The U.S. Geological Survey is coordinating with CNMI Homeland Security and Emergency Management on this volcanic activity. We have received no further reports of impacts at this time. 
 
It is possible that further eruptive activity could occur at Ruby. There are no local monitoring stations at Ruby, which limits our ability to detect and characterize volcanic unrest there. The volcano is monitored by a regional geophysical monitoring network, including a station at Saipan (50 km away) as well as others in Guam, Japan, and  two arrays of underwater pressure sensors at Wake Island. Analysis of the geophysical data of the September 14-16 eruption was done in collaboration with the Laboratoire de Geophysique in Tahiti. 
 
Ruby is a submarine volcano that rises to within 230 m of the sea surface near the southern end of the Mariana arc northwest of the island of Saipan. The volcano was first detected in eruption in 1966 by sonar signals. In 1995, submarine explosions were heard, accompanied by a fish kill, sulfurous odors, bubbling water, and the detection of volcanic tremor.