The USGS stated that a crew from a NOAA ship working at Pagan observed continuous steam emissions from the N crater during 21-22 April. Satellite imagery analyzed by the Washington VAAC showed a diffuse plume drifting 15 km W on 23 April. On 28 April, steam emissions had decreased so the Aviation Color Code and the Volcano Alert Level were lowered to "Unassigned." There are no monitoring instruments on Pagan, thus the levels "Green" or "Normal" do not apply because background activity is not defined. Monitoring is done by satellite and ground observers.

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