USGS and their Alaska Volcano Observatory (AVO) is maintaining their WATCH level advisory level and ORANGE level aviation color code with the Shishaldin volcano currently experiencing an active eruption. According to AVO, at least two explosions have occurred at the volcano since midnight local time. A little after 7 am local time today, a small steam and ash eruption was observed. AVO warns, “If you’re in the area, please note that these explosions can occur with little to no warning.”
Strongly elevated surface temperatures began to be observed at the summit of Shishaldin Volcano in satellite data beginning on July 11 and seismic tremor was identified on local geophysical stations. In response, the Alaska Volcano Observatory raised the Aviation Color Code to Yellow and the Alert Level to Watch. In the following 24 hours, strongly elevated surface temperatures continued to be observed in satellite data and seismic tremor amplitudes increased. In addition, incandescence at the summit was observed in web camera images from Tuesday night and sulfur dioxide was detected in satellite data. Together, these observations suggest that lava is likely present within the summit crater of Shishaldin. In response, the Alaska Volcano Observatory raised the Aviation Color Code to ORANGE and the Alert Level to WATCH on Wednesday.
All of the volcanoes in the United States are in western states, Alaska, and Hawaii. 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, only HVO and AVO are tracking unrest; none of those other observatories are reporting unusual activity or signs of anything more than background noise for now.
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.
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 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.
Shishaldin Volcano is located on Unimak Island in the Aleutian Islands chain of Alaska; it is the highest mountain peak of the Aleutians, rising to 6,500 feet. It is a large stratovolcano; in 1967, it was designated as a National Natural Landmark by the National Park Service.