Volcano Watch: Alaskan volcano elusive in signs of unrest

Volcano Watch is a weekly article and activity update written by USGS Hawaiian Volcano Observatory scientists and affiliates.

Volcanoes usually give us clues that they will erupt. Before an eruption, gas, magma, and other liquids move under the volcano’s surface and usually cause earthquakes. This movement can also create a signal called a volcanic tremor, which can often be observed on local seismometers. Seismometers, which measure the movement of the Earth, are important tools for monitoring volcanic activity.

An ash plume produced during the August 2007 Pavlov eruption in Alaska. The ash plume was about 5.2-5.5 km (about 17,000-18,000 feet) high. Photography by Chris Whithomas, 2007 (Alaska Volcano Observatory, USGS).

As magma migrates to shallow depths, it causes the volcano to grow and expand, resulting in an upward and outward terrestrial displacement that can be seen on local earth deformation tools. The increased pressure below the surface – due to moving magma – can cause surrounding rock to fracture, causing small earthquakes. But do volcanoes always show clear indications that they might erupt?

Alaska is home to 54 active volcanoes and accounts for 80% of the active volcanic activity in the United States. Prior to several recent eruptions in Alaska, increases in the number of earthquakes, volcanic tremor onset, and/or rapid ground displacement were observed. These changes are called precursors and automated monitoring of them can help predict volcanic eruptions. They are especially important in Alaska, where weather can prevent other visible precursors, such as steam, volcanic gas, and thermal anomalies, from being detected by satellites and cameras.

Various types of introductory behavior can occur on scales of months, weeks, days, or even hours before the explosion. However, such indications of an impending eruption are not always observable at all Alaskan volcanoes. Pavlof volcano, at about 2,440 meters (8,000 ft), located within the Aleutian volcanic arc, has remained elusive in providing evidence of an imminent eruption.

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Pavlof’s most recent eruptions in 2013, 2014 (volcanic eruptions) and 2016 did not show preparatory seismic activity, and the 2007 eruption showed only hours of preparatory seismic activity. Moreover, satellite observations of the volcano show that previous eruptions occurred here without causing preliminary deformation of the Earth.

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Lava studies from previous eruptions at Pavlof show that the magma that feeds these eruptions is stored at depths (greater than 20 km, or 12 miles, below its surface). When Pavlov does not erupt, the magma will likely remain deep as gases accumulate within this deep magma storage system.

It is believed that gas-filled magma quickly rose to the surface before the eruption of the volcano in Pavlof. Deep storage followed by rapid ascent of magma from depth immediately preceding volcanic eruption complicates our ability to observe long-term eruption precursors such as shallow earthquake activity and land deformation.

The gas-rich nature of Pavlof’s magma usually leads to explosive eruptions, resulting in the formation of ash plumes reaching high altitudes. For example, ash plumes between 10 and 17 km (about 33,000 and 56,000 feet) in height were created during eruptions at Pavlof in 1986, 2014, and 2016.

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These ash plume heights are in line with typical sailing heights for commercial flights. Because volcanic activity in Pavlof occurs frequently and can produce ash plumes of great height, the volcano poses a significant risk to the 60,000 people who fly over or downwind of the Aleutian Arc each day.

Scientists at the Alaska Volcano Observatory (AVO) are watching the Aleutian arc carefully because of the risks to flying by Pavlof and other active volcanoes there.

Currently, AVO is completing a project to modernize existing ground equipment used to monitor these volcanoes to improve their ability to predict volcanic eruptions. After recent upgrades, in July 2021, AVO scientists observed the onset of volcanic tremor on Pavlof’s network of seismic instruments indicating the movement of gas, magma, and other liquids in the Earth’s interior. Pavlof’s volcanic flight color code has been raised from green to yellow, indicating that the volcano was showing signs of volcanic unrest. A month later, Pavlov entered a period of continuous eruption and the color code was raised to ORANGE, indicating an eruption with slight ash emissions.

Success in predicting Pavlov’s current eruption suggests that improvements in ground-based observational equipment near the volcano may have allowed AVO scientists to identify tremor that may not have been detected in previous eruptions.

Time will tell if a pre-eruptive volcanic tremor is a telltale sign of an impending eruption in Pavlof. However, improvements to ground-based observation tools at this and other volcanoes give AVO scientists a stronger set of tools for predicting potential eruptions.

Volcano activity updates

Kīlauea volcano erupts. USGS Volcano Alert Level at WATCH (https://www.usgs.gov/natural-hazards/volcano-hazards/about-alert-levels). Kīlauea updates are released daily.

Lava continues to erupt from a single vent in the western wall of Halemaʻumaʻu crater. Lava activity is restricted within Halemaʻumaʻu crater in Hawai’i Volcanoes National Park. Emission rates of sulfur dioxide remain high and were estimated at 3,600 tons per day on October 28, 2021. Seismicity is high but stable, with few tremors and persistent volcanic tremors. Summit tilt gauges have been relatively flat over the past week. For more information on the current eruption of Kīlauea volcano, see the recent eruption (usgs.gov).

Mauna Loa is not erupting and is still at volcano alert level. This alert level does not mean that a volcano eruption is imminent or that progression to an eruption from the current level of disturbance is certain. Mauna Loa updates are released weekly.

In the past week, about 62 small earthquakes on the Richter scale have been recorded below the summit and upper elevation sides of Mauna Loa – and most of these have occurred at shallow depths of less than 10 kilometers (6 miles). GPS measurements show no significant distortion over the past week. Gas concentrations and fumarole temperatures at both the summit and in the sulfur cone of the Southwest Rift Zone remain stable. Webcams do not show any changes to the landscape. For more information on current monitoring of Mauna Loa, see: https://www.usgs.gov/volcanoes/mauna-loa/monitoring.

There have been 4 events with 3 or more poetic reports in the Hawaiian Islands during the past week: M3.4 earthquake 4 km (2 mi) southwest of Pahala at a depth of 35 km (21 mi) on November 2 at 5:07 PM HST, M3.2 3 km (1 mi) earthquake south of Pahala at a depth of 31 km (19 mi) on November 2 at 2:27 a.m. HST, M3.3 earthquake 8 km (4 mi) east of Pahala at 33 km (20 mi) ) depth on Oct. 31 at 8:59 p.m. HST, and the M3.4 earthquake 1 km (0 mi) SSE from Pahala at a depth of 35 km (21 mi) on Oct. 31 at 4:40 a.m. HST.

HVO continues to monitor the ongoing eruption of Kīlauea and Mauna Loa closely for any signs of increased activity.

Please visit the HVO website for past Volcano Watch articles, Kīlauea and Mauna Loa updates, volcano images, maps, recent earthquake information, and more. Email questions to [email protected].

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