The USGS has raised an alert level and aviation color code for the Iliamna Volcano from NORMAL to ADVISORY and from GREEN to YELLOW due to an increase in seismicity. Located on the western side of the lower Cook Inlet in the Lake Clark National Park, Iliamna is a snow-covered stratovolcano which stands at 10,020 feet above seal level. The volcano is located about 140 miles southwest of Anchorage, Alaska and about 70 miles southwest of Homer, Alaska.
Iliamna was ranked as a high-threat volcano by USGS in 2005 and 2018. The 2018 assessment ranked Iliamna as the 20th most hazardous volcano in the United States, with an aviation threat score of 34 and an overall score of 115, the second highest of the “high threat” category
The volcano is monitored by the Alaska Volcano Observatory (AVO) of USGS. In an update just released, AVO writes, “An increase in seismicity has been observed at Iliamna volcano beginning at about 12:00 pm AKDT June 5, 2023. The rate of earthquakes initially occurred in 1 minute intervals and have been becoming more closely spaced. There is a possibility that the earthquakes may be related to magmatic movement or hydrothermal fluids beneath the volcano. However, similar activity has been observed before large mass movements or avalanches at Iliamna volcano, and AVO cannot rule out either possibility at this time.”
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.
While the Alaska volcanoes are monitored by the Alaska Volcano Observatory (AVO), there are other units that monitor volcanoes in other regions of the country. The Hawaii volcanoes are monitored by the Hawaii Volcano Observatory (HVO) ; the California Volcano Observatory , Cascades Volcano Observatory, the Yellowstone Volcano Observatory, and the Northern Mariana Islands Volcano Observatory also monitor activity in their respective regions. . Each of those additional volcano observatories within the USGS are monitoring volcanoes in their respective regions.
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.
According to AVO, although steam plumes occur on its eastern flanks, there has been no volcanic activity at Iliamna in modern times. A volcanic eruption is believed to have occurred in 1867 and 1876; there were also unconfirmed eruptions in 1933, 1947, 1952, and 1953. Numerous fumaroles exist just below the summit; because they’re vigorous and emit an abundance of steam and sulfurous gases, their activity was often confused for eruptions in the past.
Iliamna joins other active volcanoes that have AVO-issued alerts on them; they include Great Sitkin, which is at ORANGE/WATCH, and Aniakchak, Semisopochnoi, Takawangha, Tanaga, and Trident which are all at YELLOW / ADVISORY.