Volcanic eruptions are accompanied by numerous geophysical effects most pronounced at the explosive stage of volcanic activity. Magnetic and atmospheric–electrical effects are observed [2–6] along with major local atmosphere disturbances resulting from severe ejections of a mixture of gas and pyroclastic material, yielding, in particular, atmospheric waves [1]. Atmospheric waves and electrification of an eruptive cloud affect the complicated impact of volcanic eruptions on the environment. The study of physical field variations caused by volcanoes is of particular interest both from the point of view of expanding the understanding of phenomena mechanisms and processes that accompany volcanic eruptions and from the standpoint of assessing and predicting their environmental consequences.

This paper considers the geophysical effects caused by the activity of Stromboli Volcano on October 9, 2022. The volcano with a height of ~900 m above sea level is located in the Tyrrhenian Sea (GEO: 38.79° N; 15.21° E) about 75 km north of the Island of Sicily (Fig. 1). The volcano is periodically active. The last strong eruption as an alternation of two explosions and powerful blowing between them occurred in July–August 2019 [2, 3].

Fig. 1.
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Map of the observatories in the European part of the INTERMAGNET network; (A) Stromboli Volcano.

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On October 9, 2022, the maximum explosive acti-vity of Stromboli Volcano was observed at ~06:15 UTC. At ~07:22 UTC, a formed pyroclastic flow reached the coastline and spread over the sea for a few hundreds of meters. The pyroclastic flow was followed by a massive lava flow that had subsided by ~18:00 UTC.

The initial data included instrumental observations of microbaric variations and the geomagnetic field obtained at the Mikhnevo Observatory of Sadovsky Institute of Geosphere Dynamics of Russian Academy of Sciences (MHV; GEO: 54.94° N; 37.73° E) [7], as well as of the microbaric and electric field variations at the Center for Geophysical Monitoring in Moscow (CGM; GEO: 55.71° N; 37.57° E) [8].

Microbaric variations at MHV were measured using a MB-03 microbarometer providing a stable recording of acoustic signals with an amplitude of 0.01 to 200 Pa in the range of 0.0003–10 Hz. Acoustic signals caused by the volcanic eruption were sought by analysis of an original recording in the range of 0.005–1 Hz, taking into account the distance to the signal source (~2460 km) and the likely propagation velocity in the stratospheric waveguide (280–310 m/s) [9].

The magnetic field induction components Bx, By, and BzFootnote 1 were recorded with a LEMI-018 digital magnetometer providing a reliable recording in the range of ±68000 nT with a resolution of 10 pT (sampling frequency 1 s–1). When analyzing the magnetic effect caused by the volcanic eruption, we also used the data of magnetic measurements performed at the INTERMAGNET network observatories (Table 1) located at different distances from the volcano (R).

Table 1. Geomagnetic observation points
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When describing the electrical effect of the volcanic eruption, the records of the vertical component of the atmospheric electric field E obtained in the CGM were used. The electric field strength was measured using an INEP electrostatic fluxmeter [10] in the range of 0–20 Hz with a sampling frequency of 1 s–1. E  was analyzed using the digital recording ranges obtained with a discreteness of 5 s.

At MHV and CGM, the meteorological parameters were monitored using Davis Vantage Pro 2 automated digital weather stations.

It should be noted that the instrumental observation period was characterized by a relatively quiet magnetic environment (Table 2) and the absence of significant local perturbations of the atmosphere and the atmospheric electric field. These facts greatly simplified the study of geophysical effects caused by a volcanic eruption.

Table 2. Station K (according to the MHV data) and planetary Kp indices of magnetic activity during the eruption of Stromboli Volcano on October 9, 2022
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Assessing the volcanic eruption impact on the ionosphere involved the data on a critical frequency of the F2-layer in the f0F2 ionosphere obtained at the ground-based vertical ionosphere sounding station of Rome located at a distance of ~440 km from the volcano (GEO: 41.8° N; 12.5° E) [11].

According to the observation results, the active (explosion) stage of the volcanic eruption was accompanied by generation of an acoustic signal the form of which is shown in Fig. 2 based on the data of the MHV observatory located at a distance of ~2460 km from the  volcano. The signal was recorded by MHV at ~08:45 UTC (propagation velocity ~290 m/s). The general shape of the evoked signal is a well-defined train of individual signals corresponding to the data reported in Bulletin no. 41/2022 dated October 11, 2022, of the Italian National Institute of Geophysics and Volcanology (INGV), indicating repeated volcanic explosions over a short period of time [12]. The maximum acoustic signal amplitude in MHV was ~6 Pa.

Fig. 2.
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Acoustic signal caused by the Stromboli Volcano eruption on October 9, 2022, according to the MHV data.

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The analyzed magnetic measurements are indicative of the fact that the active volcanic eruption stage was accompanied by variations in the Earth’s magnetic field, moreover, at considerable distances from the volcano. Figure 3 shows as an example the \(B_{x}^{*}\) variations relative to the horizontal component trend of the magnetic field Вх, most sensitive to external disturbances, according to some magnetic observatories.Footnote 2 It follows from Fig. 3 that well-defined geomagnetic field variations were observed as a negative bay complicated by sign-alternating \(B_{x}^{*}\) variations during the explosive stage of the Stromboli eruption on October 9, 2022, at approximately 06:40–07:40 UTC. It is characteristic that the maximum amplitude of the induced B* variations occurs in the relatively narrow range of 3.1–4.8 nT, regardless of the distance R (Table 1).

Fig. 3.
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Variations in the horizontal geomagnetic field component according to the data of MHV and some INTERMAGNET observatories during the maximum activity period of the Stromboli Volcano eruption on October 9, 2022 (the vertical dashed line is the time of maximum explosive activity of the volcano).

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Based on the data of this work, it can be suggested that anomalous geomagnetic variations are observed not only during the maximum volcanic activity, but also with the arrival of the volcano-induced acoustic signal at the recording point. Figure 4 shows as an example the geomagnetic variations with the arrival of the acoustic signal at MHV. It follows from Fig. 4 that the acoustic signal caused sign-alternating variations of the vertical \(B_{z}^{*}\) and horizontal \(B_{x}^{*}\) magnetic field components relative to the trend with an amplitude of ~2.5 nT and ~4.5 nT, respectively.

Fig. 4.
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Variations in the horizontal and vertical geomagnetic field components at MHV during the arrival of an acoustic signal caused by the Stromboli Volcano eruption on October 9, 2022 (a vertical dashed line is the time when this acoustic signal arrived at MHV).

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The volcanic activity of October 9, 2022, caused changes in the electric field strength–time t relation. Figure 5 shows the measured vertical component of the electric field E at the MHV observatory located at a considerable distance from Stromboli (Table 1). According to Fig. 5, the period of about 06:43–07:15 UTС was marked by well-defined anomalous variations in E(t) as alternating pulsations with a period of ~20 min and a maximum amplitude of ~30 V/m.

Fig. 5.
figure 5

Variations in the vertical component of the electric field strength at MHV during the maximum activity period of the Stromboli Volcano on October 9, 2022.

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The ionospheric effect of the eruption as variations in critical frequency f0F2 recorded at the ground-based Rome sounding station using the DPS-4 ionosonde is shown in Fig. 6. The same figure shows the Δf0F2 differences between f0F2 values on October 9, 2022 and median values for October 2022. It follows from Fig. 6 that the activity of the volcano caused well-defined alternating variations in the critical frequency f0F2 in the period from ~06:15 UTC to ~09:00 UTC (period ~45 min, maximum amplitude ~1 MHz). In addition, a noticeable increase in the critical frequency of the ionosphere F2-layer compared to the background one was observed from 09:10 UTC to ~17:00 UTC as a positive bay.

Fig. 6.
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Variations in the critical frequency of the ionospheric F2-layer  f0F2 on October 9, 2022; Δf0F2 difference between f0F2 values on October 9, 2022, and median values for October 2022.

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According to the data obtained, it can be assumed that the active stage of the Stromboli Volcano eruptions on October 9, 2022, was accompanied by the generation of an acoustic signal the parameters of which made it possible to record it at a considerable distance from the source, as well as by pronounced geomagnetic and electric field variations. In addition, it should be especially noted that the induced variations in the magnetic field were recorded at all magnetic observatories in approximately the same time period. This fact can be indicative of the global nature of these disturbances. It is characteristic that the maximum amplitudes of the induced magnetic field variations did not change much over a fairly wide distance range from ~300 to ~6600 km.

The ionospheric effect of the volcanic eruption is of particular interest. This issue requires additional, more detailed studies not only in terms of interpreting the effect discovered, but also in terms of searching for the most likely disturbing effect of the explosion and intensive lava flow on the physical characteristics of the ionosphere.

In our opinion, the data obtained will be useful as a basis for verification by researchers in theoretical and computational modeling of the impact of a volcano on the geophysical environment.