Based on reports from the Washington VAAC, the USGS stated that on 15 April intermittent plumes of steam from Pagan rose to an altitude of 1.8 km (6,000 ft) a.s.l. and drifted 37 km W. Observers on a ship reported that a white plume "with some black" rose 1.8 km (5,700 ft) from the volcano. On 16 April a diffuse plume drifted 85 km W. USGS raised the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory. The next day fishermen again reported a plume.

Geological Summary. Pagan Island, the largest and one of the most active of the Mariana Islands volcanoes, consists of two stratovolcanoes connected by a narrow isthmus. Both North and South Pagan stratovolcanoes were constructed within calderas, 7 and 4 km in diameter, respectively. North Pagan at the NE end of the island rises above the flat floor of the northern caldera, which may have formed less than 1,000 years ago. South Pagan is a stratovolcano with an elongated summit containing four distinct craters. Almost all of the recorded eruptions, which date back to the 17th century, have originated from North Pagan. The largest eruption during historical time took place in 1981 and prompted the evacuation of the sparsely populated island.

Source: Emergency Management Office of the Commonwealth of the Mariana Islands and United States Geological Survey Volcano Hazards Program