The US Geological Survey reported that an eruption began at Ruby on 15 September. A submarine plume of discolored water was identified in satellite images at around 0650 but there was no activity above the water surface. Eruption signals began at 1427 on 15 September based on retrospective analysis of seismo-acoustic data from a geophysical monitoring station on Saipan, 50 km SE. The activity was also recorded on other regional geophysical monitoring networks in the Pacific. The submarine plume had detached from the source vent by the morning of 16 September and no additional activity was recorded by geophysical networks. The Volcano Alert Level was raised to Advisory (the second level on a four-level scale) and the Aviation Color Code was raised to Yellow (the second level on a four-color scale).

Geological Summary. Ruby is a basaltic submarine volcano that rises to within about 200 m of the ocean surface near the southern end of the Mariana arc NW of Saipan. An eruption was detected in 1966 by sonar signals (Norris and Johnson, 1969). Submarine explosions were heard in 1995, accompanied by a fish kill, sulfurous odors, bubbling water, and the detection of volcanic tremor.

Source: US Geological Survey