Increased seismicity at Santa Barbara volcano, alert level raised to V3, Azores

On June 26, 2024, the Institute of Volcanology of the University of the Azores (IVAR) increased the volcanic alert level for the Santa Barbara volcano on Terceira Island to V3, and the Third Fissural Volcanic System to V1, on a scale ranging from V0 (green, normal) to V6 (red, erupting), due to seismic crisis that has been affecting the western part of the island since June 24, 2022, which continues to increase.

Alert level 3 means that certain geophysical parameters (such as seismicity) are strongly elevated. While it is not likely for an eruption to occur anytime soon, there is an increased risk of minor steam explosions caused by the shallow hydrothermal system. Of course, the situation can develop further and needs close monitoring.

The seismic activity has so far involved mostly micro-earthquakes (i.e. below magnitudes of 2) and been centered under the Santa Bárbara volcano, the youngest on the island, forming its western part. Overall, seismic activity in the central Azores has been elevated over the past few years, likely connected to the current crisis.

Since June 24, 2022, Terceira Island in the Azores has been experiencing a sustained seismic-volcanic crisis. The Volcanology Institute of the University of the Azores (IVAR), based on data from the monitoring network managed by the Azores Seismic and Volcanic Information and Surveillance Center (CIVISA), reports a noticeable increase in seismic activity.

The seismic events have mostly occurred within the Santa Bárbara Volcano’s perimeter, characterized mainly by microseisms. The most significant event happened on January 14, 2024, at 07:19 LT. This earthquake was recorded as M4.5, with an epicenter about 1 km (o.62 miles) east of Serreta. The quake was felt with a maximum intensity of VI on the Modified Mercalli Scale, particularly affecting the western part of the island. The tremor caused cracks in homes with low seismic resistance, the collapse of loose stone walls, damage to some roads, and landslides both inland and along cliffs.

“The volcanic alert scale follows a protocol we have been implementing and improving,” said João Luís Gaspar, academic, researcher, and leader of the Crisis Office at IVAR. “It currently includes 7 levels, ranging from V0 (resting state) to V7 (volcanic eruption of great magnitude).”

The V3 alert level for the Santa Bárbara Volcano confirms the reactivation of the deep volcanic system, whose instability was recognized around two years ago with the change to alert level V2, Gaspar said. “This change in level is the result of the increase in seismicity observed over the last two months and the detection of signs of deformation, albeit slight, in the same area.”

In addition to the Santa Bárbara, the Fissural Volcanic System has also recorded seismic activity, though less frequently. This activity has been noted especially in a section crossing the Serra de Santa Bárbara and extending to the vicinity of the Clube de Golfe to the east. Further seismic events have been generated to the south, east of the Santa Bárbara Volcano’s influence area, between Cinco Ribeiras and Angra do Heroísmo, and offshore to the west and south of the island.

Since March 2024, there has been a major increase in seismic activity in the western sector of Terceira Island, accompanied by signs of crust deformation. These observations suggest a magmatic intrusion at depth. Consequently, the Crisis Cabinet has raised the alert level of the Santa Bárbara Volcano to V3 and the Third Fissural Volcanic System to V1.

According to Gaspar, the change to alert level V1 for the Fissural Volcanic System is because seismicity sometimes extends further east than the Santa Bárbara Volcano and to our knowledge of the interaction between the two volcanic systems.

This phenomenon on Terceira Island is part of a broader increase in seismic-volcanic activity observed in the Azores region, particularly in the Central Group, since early 2022. The current pattern of activity indicates that further seismic events felt by the population may continue to occur, potentially reaching magnitudes and intensities greater than those recorded to date.

“In this context, it is essential to follow the recommendations of the civil protection authorities, which are typical for this type of situation and to which the population is accustomed, namely to avoid staying in buildings with low resistance to seismic action and not to drive near slopes that are susceptible to slope movements,” Gaspar said.

References:

¹ Última Hora- Ivar Azores – June 26, 2024

² Santa Bárbara volcano (Terceira Island, Azores): increased earthquake activity triggers volcanic alert – Volcano Discovery – June 27, 2024

³ Volcanic Crises and Earthquakes continue in Terceria Island-Azores. Researchers say that a large-scale eruption is unlikely, but there is still concern about the evolution of the seismic activity in the Santa Barbara region. – Novidades – June 28, 2024

Featured image credit: IVAR/Google