Increased seismicity at Pagan volcano, Aviation Color Code raised to Yellow, Mariana Islands

Local residents are reporting increased seismicity and light emissions from Pagan volcano, Northern Mariana Islands, prompting NMI/USGS to raise the Aviation Color Code to Yellow. The last eruption of this volcano took place in 2012 (VEI 2).

Ground-based observations from local residents indicate that there were felt earthquakes and light emissions from the volcano at approximately 04:30 UTC on July 29, 2021.

This represents a departure from background activity and therefore the Aviation Color Code was raised to Yellow and the Volcano Alert Status to Advisory.

Mount Pagan is not monitored with ground-based geophysical instrumentation. Furthermore, no indications of the current unrest have been detected in satellite or distal seismic data.

"We will continue to evaluate satellite imagery, distal geophysical data, on-island, and mariner reports when available, but because the volcano is not monitored with ground-based instruments, we cannot provide advanced warning of activity," NMI/USGS said.

Mount Pagan, one of two volcanoes that make up Pagan Island, is located on the northern end of the Island and is one of the most historically active volcanoes in the Northern Mariana Islands.

The last large eruption (VEI 4) of the volcano was in 1981, followed by three and a half decades of intermittent activity. Recent activity prior to 2016 was characterized by vigorous steam plumes and degassing from a shallow magma source.

Pagan Island on June 2, 2021. Credit: USGS/Landsat-8

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 (4.3 and 2.5 miles) 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 17^th 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. (GVP)

Featured image: Pagan Island on June 2, 2021. Credit: USGS/Landsat-8