Alaska Volcano Observatory

This Information Statement provides an update on ongoing volcanic unrest at Mount Edgecumbe volcanic field.  

Summary 

• Over the past several months, low-level unrest at Mount Edgecumbe continues and is consistent with magma intrusion at deep levels in the Earth’s crust (greater than six miles below sea level).  

• Ground deformation continues to be characterized by a steady rate of surface uplift. Low numbers of small earthquakes continue.  

• Additional signs of volcanic unrest would likely occur prior to an eruption as magma rises to the surface. Some magma intrusions do not erupt. 

• Future Alaska Volcano Observatory (AVO) plans include installation of additional sites on Kruzof Island to improve monitoring of the volcano. 

Current observations  

Earthquake activity beneath Kruzof Island continues at a low rate. Since the beginning of June 2022, there have only been 11 earthquakes large enough for AVO to locate. They range from M0.6 to M1.3 and in depth from about sea level to about 8 km (5 mi) below sea level. Other earthquakes, too small to locate, have also been observed over the past several months. A figure showing recent located earthquakes can be seen here: 
http://www.avo.alaska.edu/images/image.php?id=194130 

Ongoing analysis of radar satellite data shows that deformation of the ground surface at Edgecumbe continues. Inflation continues at steady rates through the most recent data acquisition on February 14, 2023. A figure showing the deformation can be seen here: 
http://www.avo.alaska.edu/images/image.php?id=194129 

Some Sitka residents observed bubbling water near the eastern shoreline of Kruzof Island near Mount Edgecumbe in fall 2022; This may or may not be related to the ongoing magmatic intrusion. AVO plans to further investigate these areas in summer 2023. 

Details of recent unrest 

A swarm of earthquakes was detected in the vicinity of Mount Edgecumbe volcano beginning on Monday, April 11, 2022. There were hundreds of small quakes in the swarm, though the large majority were too small to locate.  

The recent swarm inspired an in-depth analysis of the last 7.5 years of ground deformation detectable with radar satellite data. Analysis of these data from recent years revealed a broad area, about 17 km (10.5 miles) in diameter, of surface uplift centered about the summit region of Mt Edgecumbe. This uplift began in August 2018 and has been continuing to the present at a rate of up to 7.4 cm/yr (2.9 in/yr) in the center of the deforming area. Deformation has been constant since August 2018. The total deformation since 2018 is about 30 cm (11.8 inches).  
 
Retrospective analysis of earthquake data in the area of Mount Edgecumbe showed that a small number of earthquakes started occurring under the volcano in 2020. The increased earthquake activity that started on April 11, 2022, was unusual in having a greater number of events, however. The earthquakes detected under the volcano since 2020 are all M3.0 or smaller. Note that only the largest of the earthquakes can be located by regional seismic networks; hundreds of very small additional events have been detected, but not located. A map showing earthquake locations in the area, including those occurring on regional faults, can be found here: 
http://www.avo.alaska.edu/images/image.php?id=182214 
 
Prognosis 
 
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. Modeling of the deformation signal, published in a recent paper by Grapenthin and coauthors in 2022, shows that it is consistent with magma migration from a source region at about 20 km (12.4 mi) through a thin conduit to about 10 km (6.2 miles) below sea level. The earthquakes are likely caused by stresses in the crust due to this intrusion and the substantial uplift that it is causing. 
 
Intrusions of new magma under volcanoes do not always result in volcanic eruptions. 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. 
 
Current monitoring 
 
The Alaska Volcano Observatory installed a single temporary seismic station on Kruzof Island in May 2022, and revisited it in August 2022 to ensure it could operate over the winter. This station has improved our ability to observe activity and accurately locate earthquakes. The next closest seismic station is in Sitka, 24 km (15 miles) to the east of the volcano and is operated by the National Tsunami Warning Center. Updated satellite radar observations become available on weekly timescales. 

For current information about Edgecumbe, including our latest information releases and monitoring data, see AVO Edgecumbe - Activity Page (alaska.edu) 
 
AVO has plans to increase the number of monitoring stations on Kruzof Island as early as the summer of 2023. This will improve earthquake locations, allow for better detection of ground movement, and quickly detect any atmospheric disturbances were eruptive activity to occur. Planned volcanic gas measurements will help determine the magma depth and type of gases being released. 

Background
 
Mount Edgecumbe is a 976 m (3202 ft) high stratovolcano on Kruzof Island located 24 km (15 mi) west of Sitka, Alaska, and is part of a broader volcanic field of lava domes and craters on southern Kruzof Island and surrounding submarine vicinity. There are no written observations of eruptions from the volcanic field; Tlingit oral history describes small eruptions in the recent past. Geologic investigations show that eruptions 13,000 to 14,500 years ago produced at least one widespread regional tephra (ash) layer around 1 m thick near Sitka and over 30 m thick on parts of Kruzof Island. Smaller eruptions occurred between 6,000 and 4,000 years ago. The volcanic field has erupted a wide range of basalt to rhyolite compositions from numerous vents over the past 600,000 years. 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 (sediment-rich debris flows), pyroclastic flows (hot rock avalanches), and lava flows have also occurred on the flanks of Mount Edgecumbe. Mount Edgecumbe and the surrounding volcanic field lies within the Tongass National Forest.