Following reports of tremors and smoke emissions from the public, the USGS has increased the volcanic warning level. Mount Pagan, which is located on Pagan Island in the Commonwealth of the Northern Mariana Islands, is the focus of the reports.
The Northern Mariana Islands (NMI) USGS office monitors the volcano, located just north of Saipan and Guam.
"At around 4:30 UTC on July 29, ground-based reports from local people suggest that there were felt tremors and light emission from Mount Pagan (2:30pm local time July 28). Therefore, the Aviation Color Code/Volcano Alert Status for Mount Pagan has been modified to YELLOW/ADVISORY due to this departure from background activity, according to the USGS NMI office.
Aviation Codes and Volcanic Activity Alert Levels are issued by the USGS NMI. Green, yellow, orange, or red is the many types of aviation codes. When ground-based equipment fails to prove that a volcano is operating at a normal background level of activity, it is simply designated as "unassigned."
Yellow indicates that a volcano displays symptoms of increased unrest above known background levels, whereas green indicates usual activity associated with a non-eruptive condition.
The color of a volcano changes from red to orange when it experiences increasing or rising instability with an increased risk of eruption. Finally, the code becomes red when an eruption is imminent, with substantial volcanic ash emissions predicted in the atmosphere or when an eruption is underway. Major volcanic ash emissions are expected in the atmosphere.
The activity of Volcanoes Normal, advise, watch, and warning are the four degrees of alert. If data is inadequate, it is simply classified as "unassigned," as with aviation codes. It is deemed normal when the volcano is operating at normal background levels in a non-eruptive condition.
An advisory is issued if the volcano shows symptoms of increased disturbance above the background level. A watch is issued when a volcano shows signs of increased or rising disturbance, whereas a warning is issued when a dangerous eruption is imminent.
Mount Pagan is one of the numerous volcanoes monitored by the NMI office; nevertheless, extreme weather and a lack of maintenance have rendered scientists there almost blind to what's going on below the surface
"Ground-based geophysical monitoring data from stations on Anatahan and Sarigan islands have been inaccessible since storm damage in August 2017," according to the latest NMI update for July. Due to current logistical constraints in the CNMI, visits to these sites to perform repairs are not possible. As a result, it's unclear when these stations will be operational again."
Mount Pagan, unlike other volcanic locations such as Hawaii's Kilauea and Mauna Loa, is not monitored using ground-based geophysical instruments.
"We will continue to analyze satellite images, distal geophysical data, on-island, and mariner reports as available," the USGS NMI wrote in an update, "but we cannot give prior warning of activity. Because the volcano is not monitored with ground-based instruments."
Being one of the island's two volcanoes, Mount Pagan is located on the island's northern end and is one of the most historically active volcanoes in the Northern Mariana Islands. The volcano's most recent major eruption occurred in 1981, followed by three and a half decades of sporadic activity. Before 2016, strong steam plumes and degassing from a shallow magma source characterized recent activity.
UN Trust Territory
After World War II, the volcano became part of the UN Trust Territory of the Pacific Islands World War II, when it was occupied by the US. Pagan was finally given Commonwealth status in the United States. The United States Navy maintained a minor facility on Pagan after WWII. Several public facilities were constructed in the 1950s, including a church, a storehouse, a hospital, and a schoolhouse.
The population had decreased by the 1970s, with many people working and residing on the adjacent bigger island of Saipan. Then, Mount Pagan erupted on May 15, 1981, resulting in lava flows engulfing much of the island's agricultural area and a portion of the airfield runway.
The island's residents were evacuated to Saipan during the eruption. The eruption lasted until 1985, followed by smaller eruptions in 1987, 1988, 1992, 1993, 1996, 2006, 2009, 2010, and 2012.
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