USGS Raises Alert Level ORANGE / Watch Due to Volcanic Explosion in Alaska

A volcano explodes in Alaska, which prompted experts at USGS to raise the color code in the area from yellow to ORANGE while raising the alert level from advisory to WATCH. 

Ash-Producing Events

A brief explosion at Alaska's Semiscopchnoi Volcano at 1:47 pm local time resulted in ash emissions that could be seen in nearby camcorders. Ash emissions stopped at 2:16 p.m. in the same time zone, according to the Alaska Volcano Observatory (AVO) of the USGS.

AVO wrote in their update for today that in satellite images, the ash plume could not be seen above the meteorological clouds, indicating that it was less than 20,000 feet above sea level.

Similar eruptions to this one have been seen at Semisopochnoi over the past year, with the last known on June 12.

USGS/AVO warns that the recent activity has been characterized by minor eruptions that have left behind minor ash deposits close to Mount Cerberus' active north crater and ash clouds that are typically less than 10,000 feet above sea level. Extended ash-producing events could happen again without prior notice.

Semisopochnoi

Semisopochnoi, located 9.7 miles to the west of the 180th Meridian in Alaska, is located in the easternmost land in the United States and North America based on its position on the globe at 179°46′ East. The Aleutian Islands are a group of 14 sizable volcanic islands and 55 other smaller islands, including Semisopochnoi. These islands make up the northernmost portion of the Pacific Ring of Fire with their 57 volcanoes.

Semisopochnoi is monitored by various equipment, which includes local seismic and infrasound sensors, regional infrasound, satellite data, and lightning detection instruments.

Read also: Volcanic Eruptions can Worsen as Heavy Rainfall Persists Near Volcanoes Like Mt. St. Helens, Study Suggests 

Interpreting Color Codes, Alert Levels

The USGS keeps tabs on 161 foreseeably active volcanoes in the country. Though there are over 130 volcanoes and volcanic fields in Alaska, only a handful of them has been active for more than a million years. AVO also studies the 50 volcanoes that have been active ever since the middle of the eighteenth century.

Volcanic Activity Alert Levels and Aviation Codes are issued in the US by the USGS and regional volcano observatory units. Aviation Codes include green, yellow, orange, and red.

It is simply "unassigned" if ground-based instrumentation is inadequate to prove that a volcano is operating at a standard background level of activity. Yellow indicates that a volcano is showing signs of increased unrest above established background levels, whereas green denotes typical activity attributed to a non-eruptive state. The color of a volcano changes to orange when it is increased or escalating unrest with a greater likelihood of eruption. The code turns red when an eruption is about to occur with significant volcanic ash emission anticipated in the atmosphere or if an eruption is already underway with significant volcanic ash emission into the atmosphere.

Alert levels for volcanic activity include normal, advisory, watch, and warning. Similar to aviation codes, if there is not enough information, it is simply marked as "unassigned."

It is regarded as normal when the volcano exhibits typical background activity in a non-eruptive state. An advisory is issued if the volcano shows indications of elevated unrest exceeding background levels. A watch alert level is issued if a volcano shows increased or escalating unrest, and a warning is issued whenever a dangerous eruption is about to occur, Weatherboy reports.

Related article: Four U.S. Volcanoes on Elevated Risk Orange Status, USGS Warns