UISH

Correlation with volcanic activity

Etna's activity over the last biennium (2024–2026) has been particularly intense, alternating violent explosive paroxysms with towering ash columns and predominantly effusive eruptions (lava flows).

To correlate volcanic events with air quality in the surrounding area, the key technical parameters to consider are:

• Height and direction of the eruptive column (plume): directly correlated with PM₁₀ peaks and fine particulate matter at ground level in downwind sectors (e.g. volcanic ash and glassy fragments).
• Eruptive style (explosive vs. effusive): explosive activity fragments magma generating PM₁₀. Stable effusive phases or continuous open-air degassing release enormous masses of gas, strongly impacting SO₂ (sulphur dioxide) concentrations, which can also oxidise in the atmosphere forming sulphate aerosols (additional secondary particulate matter).

Mount Etna volcano lava flow - February 17th, 2025. Modified Copernicus Sentinel data, processed by Pierre Markuse. Ref: https://commons.wikimedia.org/wiki/File:Mount_Etna_volcano_lava_flow_(3D),_Sicily,_Italy_-_February_17th,_2025_(54369315461).jpg

Eruption chronology (2024–2026) and technical parameters

1. The great sequence of Voragine paroxysms (July–August 2024)

After months of quiet, the Voragine crater returned to centre stage with a series of extremely violent, closely spaced paroxysmal episodes (in particular on 4–5 July, 7 July, 15 July and 3–4 August 2024).

• Eruptive style: explosive at very high energy (lava fountains and paroxysmal Strombolian activity).
• Column height: reached heights between 6,000 and 10,000 m a.s.l.
• Plume direction: predominantly towards the southern, eastern and south-eastern sectors (affecting Catania, Acireale and the Etnean towns).
• Impact on pollutants:
  • PM₁₀: exceptional ground-level peaks due to intense rainfall of fine volcanic ash and lapilli.
  • SO₂: very strong release of sulphur dioxide into the atmosphere, massively detected by both satellite sensors (TROPOMI) and ground stations during fountaining hours.

2. The subterminal effusive eruption of February 2025

In early February 2025, Etna initiated a predominantly effusive phase originating near the South-East Crater and Bocca Nuova, with lava flows that also spread over snow-covered slopes (e.g. Monte Pecoraro / Galvarina area).

• Eruptive style: predominantly effusive (stable lava flows) accompanied by moderate Strombolian activity at the "saddle vent".
• Column height: limited, with mild ash emissions that rarely exceeded 4,000 m a.s.l.
• Impact on pollutants:
  • PM₁₀: direct impact from ash fallout very limited and confined to summit areas or their immediate vicinity.
  • SO₂: continuous and prolonged SO₂ flux linked to the steady effusion rate of the erupting magma. The gas remained closer to the lower atmospheric layers compared to the summer 2024 paroxysms, potentially causing local exceedances in mountain-belt municipalities.

3. The explosive paroxysm of the South-East Crater (June 2025)

A violent and sudden reawakening of the South-East Crater in early June caused a partial collapse of the crater rim and a rapid explosive phase.

• Eruptive style: mixed (rapid explosive/effusive) with structural collapse.
• Column height: imposing eruptive column estimated at approximately 8,000 m a.s.l.
• Plume direction: driven by winds towards the north-east flank (direction Linguaglossa / Piano Provenzana).
• Impact on pollutants: sharp increase in PM₁₀ in the north-eastern sector of the island due to material fragmentation caused by the collapse and subsequent explosion. Impulsive (brief but intense) release of SO₂.

4. The effusive and Strombolian activity of August 2025

A new summer eruptive cycle concentrated on the summit craters with lava flows directed mainly towards the barren Valle del Bove.

• Eruptive style: effusive with weak intracrateric Strombolian activity.
• Column height: low or absent (plume of gas and vapour only).
• Impact on pollutants: PM₁₀ levels within normal ranges in urban areas. Monitoring focused on the dispersion of volcanic gases (SO₂ and acid gases such as HCl and HF) which, in the absence of strong wind, tend to stagnate in the valleys adjacent to the volcano.

5. The return of the North-East Crater and the fissure in Valle del Bove (December 2025–January 2026)

Between late December 2025 and early January 2026, Etna showed a change of scenario: first a spectacular explosive reactivation of the North-East Crater, followed by the opening (1 January 2026) of an eruptive fissure at 2,100 m a.s.l. at the base of the northern wall of Valle del Bove (Monte Simone area).

• Eruptive style: effusive from a lateral/subterminal fissure (average effusion rate of approximately 5 m³/s), associated with weak Strombolian activity and mild ash emissions at Voragine and the North-East Crater.
• Lava field length: approximately 2.8 km of flow confined within Valle del Bove.
• Column height: very limited.
• Impact on pollutants:
  • PM₁₀: negligible impact at urban level, given the low production of fine ash.
  • SO₂ and other gases: the opening of a fissure at a relatively low elevation (2,100 m) shifts the gas emission source closer to populated centres compared to summit eruptions (3,300 m). Degassing from the flow and fissure generated a steady SO₂ flux carefully monitored for possible gaseous fallout phenomena (vog, volcanic smog) in municipalities on the eastern flank during winter thermal inversions.

Summary table for environmental correlation

Note on data correlation: to cross-reference these events with the ARPA monitoring stations in the Province of Catania, PM₁₀ peaks occur in the hours immediately following the onset of the paroxysm (following the wind vector), whereas SO₂ undergoes sudden variations even in the absence of ash if there is strong open-air degassing from active effusive vents.

Keywords: Correlation, Volcanic activity