Mercury emission from the Tajogaite eruption La Palma, Canary Islands

Mercury (Hg) is a volatile and highly toxic metal released into the environment from both natural and anthropogenic sources. Volcanic activity represents one of the major primary natural contributors to atmospheric Hg, with previous estimates of global annual volcanic emissions ranging from approximately 50 to 700 t·a^-1 (e.g., Nriagu and Becker, 2003; Pyle and Mather, 2003). The main sources of uncertainty of the total emission of volcanic Hg are rooted in a lack of measurements from volcanic eruptions, due to the logistical challenges of collecting gaseous Hg samples from actively erupting plumes. One potential method to quantify volcanic Hg emission from eruptions is through the analysis of Hg adsorbed to the surface of volcanic ash particles, which can readily be sampled on the ground downwind of eruptions.

The purpose of this study is to estimate mercury emissions from the 2021 Tajogaite eruption at Cumbre Vieja volcano (La Palma, Canary Islands), a record-breaking event characterized by exceptionally high volatile output, with CO₂ and SO₂ emissions of 28 ± 14 Mt (Burton et al., 2023) and 1.6 ± 0.1 Mt (Esse et al., 2025), respectively.

Mercury degassing during the Tajogaite eruption was estimated using Hg/SO₂ molar ratios derived from sulphate (SO₄^2-) concentrations in ash leachates and mercury content in dried volcanic ash samples. Volcanic ash from the eruption was collected almost daily at five monitoring stations located at varying distances from the vents. Sulphate and Hg analyses were performed via ion chromatography and mercury-specific atomic absorption spectrometry (AAS-Hg) using a RA-915 Mercury Analyzer. In terms of analytical performance, an adequate linear factor adjustment (R²= 0.99) and linear range (0.3-30 ng Hg) were achieved for the quantification of Hg in ash samples.

The average sulphate concentration in the ash leachates was 3.49 × 10⁴ µg·kg⁻¹, ranging from 1.21 × 10⁴ to 8.48 × 10⁴ µg·kg⁻¹, while the average Hg content in the dried ash was 1.69 × 10³ µg·kg⁻¹, ranging from 0.28 × 10³ to 9.40 × 10³ µg·kg⁻¹. These measurements yield an estimated average Hg/SO₂ molar ratio of 1.55 × 10^-5, with a range from 0.76 × 10^-5 to 3.54 × 10^-5. Considering an SO₂ emission of 1.6 Mt from the Tajogaite eruption, the corresponding estimated mercury emission is 77.6 t on average, with a range of 3.8 to 177 t.

References
Burton, M., Aiuppa, A., Allard, P. et al. (2023). Exceptional eruptive CO₂ emissions from intra-plate alkaline magmatism in the Canary volcanic archipelago. Commun. Earth Environ. 4, 467. https://doi.org/10.1038/s43247-023-01103-x

Esse, B., Burton, M., Hayer, C. et al. (2025). Forecasting the evolution of the 2021 Tajogaite eruption, La Palma, with TROPOMI/PlumeTraj-derived SO₂ emission rates. Bull. Volcanol. 87, 20,  https://doi.org/10.1007/s00445-025-01803-6

Nriagu, J. and Becker, C. (2003). Volcanic emissions of mercury to the atmosphere: global and regional inventories. Sci. Total Environ. 304, 3–12.
Pyle, D.M. and Mather, T.A. (2003). The importance of volcanic emissions for the global atmospheric mercury cycle. Atmos. Environ. 37, 5115–5124.