According to NASA's Earth Observatory, a satellite image of Pagan acquired on 7 May showed a gas-and-steam plume drifting W. The plume's blue tint suggested the presence of sulfur dioxide; elevated levels of sulfur dioxide to the W of the volcano were detected in satellite images later that day. The USGS reported that minor steam-and-gas plumes were observed in partly cloudy satellite images during 4-11 May. The Volcano Alert Level remained at Advisory and the Aviation Color Code remained at Yellow.

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: NASA Earth Observatory, Emergency Management Office of the Commonwealth of the Mariana Islands and United States Geological Survey Volcano Hazards Program