The U.S. Geological Survey reported that a possible sulfur dioxide emission from Pagan was detected on 31 May. The Aviation Color Code and the Volcano Alert Level remained at Unassigned. There are no ground-based instruments, so Pagan is monitored with satellite imagery, distal geophysical data, and mariner reports.

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: US Geological Survey