An explosion detected at the Atka volcano in Alaska led USGS to evolve different advisories for the area as they learned what exactly happened to trigger the blast at the volcanic complex there.
A small and brief explosion occurred at the Atka volcanic complex at 7:26 pm local time on February 20 and in response the Aviation Color Code and Volcano Alert Level were increased to ORANGE/WATCH. However, seismicity remained very low after this event and no further explosions were detected. As a result, the Aviation Color Code and Volcano Alert Level was decreased by USGS to YELLOW/ADVISORY this morning.
USGS says that further analysis of geophysical data confirms the source of the explosion as the summit lake region of Korovin Volcano, one of the volcanoes in the Atka volcanic complex, and satellite data from last evening show no evidence of hot material at the surface.
In a statement, Alaska Volcano Observatory scientists wrote, “Our interpretation is that this was a steam-driven explosion, caused by overpressure of the subsurface cap beneath the lake. This type of singular explosion is common at Korovin Volcano. Minor amounts of ash were likely erupted in the immediate vicinity of the vent but have not been confirmed. Additional explosions are possible in the near future, but unlikely. ”
Local seismic and infrasound sensors, and web cameras are used to monitor the Atka volcanic complex. The local sensor network is supplemented with regional infrasound and lightning networks, and satellite data.
USGS is responsible for monitoring volcanoes and earthquakes around the United States and its territories. Today, of the volcanoes it is monitoring, it has two at an alert level of WATCH and a color code of ORANGE while it has two others at an alert level of ADVISORY and a color code of YELLOW. The 4 volcanoes around the U.S. with the heightened alert level are Great Sitkin in Alaska (WATCH/ORANGE), Spurr in Alaska (ADVISORY/YELLOW), Kilauea in Hawaii (WATCH/ORANGE), and the Ahyi Seamount near the Northern Marianas (ADVISORY/YELLOW). All of the other volcanoes USGS is monitoring today are either at GREEN or unrated conditions.
Within the United States, the USGS tracks dozens of potentially active volcanoes, most of which are in Alaska. In Alaska alone, 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 the Alaska Volcano Observatory (AVO) studies those too.
The U.S. is only home to a fraction of the world’s volcanoes: according to USGS, there are normally around 2 dozen erupting volcanoes around the world at any given time. The USGS says there are about 1,500 potentially active volcanoes worldwide, with about 500 of the 1,500 erupting in modern historical times.
The Hawaii volcanoes are monitored by the Hawaii Volcano Observatory (HVO) while the Alaska volcanoes are monitored by the Alaska Volcano Observatory (AVO.) In addition to the AVO and HVO, there are also the California Volcano Observatory , Cascades Volcano Observatory, the Yellowstone Volcano Observatory, and the Northern Mariana Islands Volcano Observatory. Each of those additional volcano observatories within the USGS are monitoring volcanoes in their respective regions. At this time, none of those other observatories on the U.S. mainland are reporting unusual activity or signs of anything more than background noise for now.
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.
