Dual magma chambers discovered beneath Great Sitkin volcano, Alaska

A study conducted by scientists at Purdue University reveals that the Great Sitkin volcano, one of the most active in Alaska, has two magma chambers. This discovery explains the changing locations of seismic activity that has perplexed scientists since the volcano began erupting in May 2021.

A volcano’s aboveground manifestations are often just the tip of the iceberg, with the real action taking place far below the surface. There, magma accumulates and seismic activity builds, monitored by scientists using seismic data to study the inner workings of volcanoes and try to predict their behavior. Volcanic eruptions can cause regional disruption and even influence global weather patterns, making their study crucial to mitigating their impacts.

“The unpredictability of volcanic activity can be societally disastrous,” warns Dr. Xiaotao Yang, an assistant professor at Purdue University’s Department of Earth, Atmospheric, and Planetary Sciences, who led the study into the Great Sitkin volcano.

Yang’s team has examined seismic data from the volcano, located in Alaska’s Aleutian Arc, since it started erupting in May 2021. The eruption has been characterized by ongoing lava effusion since late July 2021. Their findings, published in the American Geophysical Union’s Geophysical Research Letters, offer an unprecedented glimpse into the workings of this active volcano.

Using data collected by the Alaska Volcano Observatory from 2019 to 2020, Yang and his team constructed a seismic velocity structure for the uppermost 6 km (3.7 miles) of the volcano. The team found two magma chambers, providing an explanation for the alternating seismic activity observed in regions northwest and southeast of the volcano summit.

According to Yang, this alternating seismic activity or “spatiotemporal migration” has been observed at other volcanoes, but Great Sitkin offers a unique case study due to the clear lateral migration of seismicity. “The new seismic velocity model reveals two crustal magma reservoirs, with distinctly low seismic velocities,” he explains.

Yang’s team proposes that the Great Sitkin Volcano operates on a six-stage eruption cycle, diverging from the typical five-stage cycle. The additional stage involves the activation of a second, shallower magma chamber following the initial eruption, most likely triggered by the deeper chamber. This interaction between the two chambers results in alternating eruptions.

Seismic activity at the volcano alternated between the two chambers, with peak seismicity at the southeastern reservoir recorded a year before the eruption on May 26, 2021. The initial eruption was explosive but resulted in negligible magma eruption, followed by a two-month gap before lava effusion began. A second phase of lava effusion took place a year after the initial eruption.

Yang emphasizes that the findings from Great Sitkin have even broader implications. “It can be generalized to help us understand how multiple reservoirs, which may be in different sizes, could interact and influence the initialization and development of the eruption as well as magma flux.”

To better predict future volcanic behavior, scientists will need to integrate a range of data, including gas emissions, surface deformation, and temperature changes. “Our work at Great Sitkin Volcano demonstrates the complexity of active magmatic systems and the importance of real-time monitoring of active volcanoes,” says Yang.

References:

¹ New study explains what drives Great Sitkin Volcano’s long-lived eruption – Purdue University – June 12, 2023

² Double Reservoirs Imaged Below Great Sitkin Volcano, Alaska, Explain the Migration of Volcanic Seismicity – Xiaotao Yang – Geophysical Research Letters – June 8, 2023 – https://doi.org/10.1029/2022GL102438 – OPEN ACCESS

Featured image: Great Sitkin volcano. Credit: Dave Clum