During 4-5 December, residents 3 km SW of Pagan reported ashfall that accumulated in their camp at a rate of about 6.4 mm per day. They also described a plume from the summit that rose to an altitude of 640 m (2,100 ft) a.s.l. and a sulfur smell that occasionally wafted through their camp. Based on satellite imagery, the Washington VAAC reported a gas-and-ash plume that drifted mainly W on 5, 6, and 8 December. Satellite imagery showed no further activity through 11 December.

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.

Sources: Emergency Management Office of the Commonwealth of the Mariana Islands and United States Geological Survey Volcano Hazards Program, US Geological Survey Volcano Hazards Program, Washington Volcanic Ash Advisory Center (VAAC)