An explosion today at a volcano prompted scientists with USGS to raise the color code there from yellow to orange while raising the alert level from advisory to watch. At 1:47 pm local time, a short-lived explosion at the Semiscopchnoi Volcano in Alaska occurred, producing ash emissions observed in local webcams. According to USGS’s Alaska Volcano Observatory (AVO), ash emissions ceased by 2:16 pm local time. “The ash plume was not visible above the meteorological clouds in satellite images, thus was below 20,000 feet above sea level,” AVO wrote in an update today. This event is similar to eruptive activity observed over the last year at Semisopochnoi, but not since June 12.
USGS/AVO warns that small eruptions producing minor ash deposits within the vicinity of the active north crater of Mount Cerberus and ash clouds usually under 10,000 feet above sea level have characterized the recent activity and more ash-producing events could occur again with little warning.
Based on its location on the globe at 179°46′ East, Semisopochnoi is the easternmost land location in the United States and North America, located just 9.7 miles west of the 180th Meridian in Alaska. Semisopochnoi is part of the Aleutian Islands, a chain of 14 large volcanic islands and 55 smaller other islands. These islands, with their 57 volcanoes, make the northernmost part of the Pacific Ring of Fire. Semisopochnoi is monitored by local seismic and infrasound sensors, satellite data, regional infrasound, and lightning detection instruments.
Within the United States, the USGS tracks 161 potentially active volcanoes. Alaska is home to many volcanoes, though; there are more than 130 volcanoes and volcanic fields which have been active within the geologically young last 2 million years. 50 have been active since the mid 1700s and AVO studies those too.
In the U.S., the USGS and volcano observatory units are responsible for issuing Aviation Codes and Volcanic Activity Alert Levels. Aviation Codes are green, yellow, orange, or red. When ground-based instrumentation is insufficient to establish that a volcano is at a typical background level of activity, it is simply “unassigned.” While green means typical activity associated with a non-eruptive state, yellow means a volcano is exhibiting signs of elevated unrest above known background levels. When a volcano exhibits heightened or escalating unrest with the increased potential of eruption, it jumps to orange. Finally, when an eruption is imminent with significant emission of volcanic ash expected in the atmosphere or an eruption is underway with significant emission of volcanic ash into the atmosphere, the code becomes red. Volcanic Activity Alert levels are normal, advisory, watch, or warning. As with aviation codes, if data is insufficient, it is simply labeled as “unassigned.” When the volcano is at typical background activity in a non-eruptive state, it is considered normal. If the volcano exhibits signs of elevated unrest above background level, an advisory is issued. If a volcano exhibits heightened or escalating unrest, a watch is issued while a warning is issued when a hazardous eruption is imminent.