A stratovolcano just outside Sitka, Alaska is showing some signs of life just as the 2022 Alaska Cruise Season begins. Mount Edgecumbe is a 3,202 feet high volcano on Kruzof Island which is located just 15 miles west of Sitka. Sitka is a popular cruise destination for cruise lines traveling up the coast of America’s 49th state; this weekend marks the kick-off of the 2022 cruise season in Alaska. Royal Caribbean, Carnival Cruise Line, Celebrity Cruises, and Norwegian Cruise Lines all have scheduled visits around Sitka, despite concern to the Edgecumbe Volcano, no cruise lines or tour companies have announced any changes to itineraries yet.
Mount Edgecumbe is located within a broader volcanic of lava domes and craters on southern Kruzof Island and surrounding submarine vicinity. According to USGS, there are no written observations of eruptions from the volcanic field; indigenous Tlingit oral history describes small eruptions from about 800 years ago. Geologic investigations show that eruptions 13,000 to 14,500 years ago produced at least one widespread regional tephra layer around 3 feet thick near Sitka and over 100 feet thick on parts of Kruzof Island. Scientists believe smaller eruptions occurred between 6,000 and 4,000 years ago. In general, the volcanic field has erupted a wide range of basalt to rhyolite compositions from numerous vents over the past 600,000 years.
The volcano has been considered dormant until now. In recent weeks, analysis by the Alaska Volcano Observatory (AVO) have observed hundreds of small earthquakes.The swarm of earthquakes was detected in the vicinity of Mount Edgecumbe beginning on Monday, April 11, 2022. There were hundreds of small quakes in the swarm, though the large majority were too small to locate. Over the past few days, earthquake activity has declined and is currently at background levels. However, this recent swarm inspired an in-depth analysis of the last 7 and a half years of ground deformation detectable with radar satellite data. According to AVO, analysis of this data from recent years reveals a broad area of about 10.5 miles in diameter of surface uplift centered about 1.5 miles to the east of Mount Edgecumbe. The analysis suggests that this uplift began in August 2018 and has been continuing to the present at a rate of up to 3.4″/year in the center of the deforming area. AVO adds that deformation has been constant since 2018, and there has not been an increase with the recent earthquake activity. The total deformation since 2018 is about 10.6″.
AVO’s retrospective analysis of earthquake data in the area of Mount Edgecumbe shows that a small number of earthquakes started occurring under the volcano in 2020. However, the recent earthquake activity that started on April 11 was unusual in having a greater number of events. The earthquakes detected under the volcano since 2020 are all magnitude 3.0 or smaller.
Based on their comprehensive analysis of the stratovolcano, AVO/USGS says that the coincidence of earthquakes and ground deformation in time and location suggests that these signals are likely due to the movement of magma beneath Mount Edgecumbe, as opposed to tectonic activity. Initial modeling of the deformation signal shows that it is consistent with an intrusion of new magma material at about 3.1 miles below sea level. The earthquakes likely are caused by stresses in the crust due to this intrusion and the substantial uplift that it is causing.
The big question now is where does that magma go. “Intrusions of new magma under volcanoes do not always result in volcanic eruptions,” AVO said in a bulletin just released. “The deformation and earthquake activity at Edgecumbe may cease with no eruption occurring. If the magma rises closer to the surface, this would lead to changes in the deformation pattern and an increase in earthquake activity. Therefore, it is very likely that if an eruption were to occur it would be preceded by additional signals that would allow advance warning.”
The primary hazards of past eruptions, and thus likely in future eruptions, have been volcanic ash emissions producing local and region ashfall and drifting ash clouds. Volcanic lahars, which are sediment-rich debris flows, pyroclastic flows, which are hot rock avalanches, and lava flows have also occurred on the flanks of Mount Edgecumbe in the past. Any strong earthquake or volcanic eruption here also has the potential to produce a tsunami.
For now, there is no local volcano monitoring network at Edgecumbe. According to USGS, the closest seismic station is in Sitka and is operated by the National Tsunami Warning Center. Updated satellite radar observations become available on weekly timescales. To improve the frequency of data captured, AVO has begun plans to add to current monitoring capabilities, possibly by adding instruments closer to the volcano. AVO will continue to monitor Edgecumbe using existing regional seismic stations and satellite data.
Tour companies, the fishing industry, and nearby residents around Sitka will also be closely monitoring trends.
As of today, USGS has yet to issue any Aviation Code nor any Volcanic Activity Alert Level for Edgecumbe. 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.
Cruise lines will continue to monitor developments at the volcano and possible impacts to Sitka port calls. In December 2019, a Royal Caribbean excursion from the Ovation of the Seas cruise ship made an excursion to White Island off the coast of New Zealand; that visit to the volcano turned deadly, with a sudden eruption killing 22 and injuring 25. While tourists on the excursion were killed by the volcano, the ship was far enough away from it not to have any impacts to it or other guests on-board.
Within the United States, the USGS tracks 161 potentially active volcanoes, most of which are in Alaska. 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.