Nemesio M. Pérez^1,2, Gladys V. Melián^1,2, Eduardo Lodoso^1,2, Beverley C. Coldwell^1,2, 

Óscar Perdomo-Sosa^1,2, Pedro A. Hernández^1,2, María Asensio-Ramos¹,

Eleazar Padrón^1,2 and Germán D. Padilla^1,2

¹Instituto Volcanológico de Canarias (INVOLCAN), 38400 Puerto de la Cruz, Tenerife,

Canary Islands, Spain

²Instituto Tecnológico y de Energías Renovables (ITER), 38600 Granadilla de Abona, Tenerife, Canary Islands, Spain

Abstract: 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 ashsamples. 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. A single geochemical population is identified for Hg concentrations in the Tajogaite ash, with a geometric mean of 1.00 μg·kg^-1, with a one-sigma interval (±1σ) ranging from 0.46 to 2.18 μg·kg^-1. Estimated daily Hg/SO₂ molar ratios were calculated from Hg concentrations in the ash and SO₄^2- concentrations in ash leachates. This ratio may represent a useful proxy for estimating the Hg/SO₂ ratio in volcanic plumes. Daily Hg emission rates were estimated by combining SO₂ emission rates with the Hg/S mass ratio obtained from Tajogaite ash-fall samples. Statistical-graphical analysis of daily Hg emission rates revealed a geometric mean of 50 kg·d^-1, with a one-sigma interval (±1 σ) ranging from 10 to 258 kg·d^-1. Relatively high daily Hg emission rates and concentrations, along with elevated molar ratios (Hg/Cl, Hg/F, and Hg/S), appear to correlate with episodes of deep recharge, as indicated by increased deep seismicity and supported by fluid inclusion data. The estimated total Hg emission from Tajogaite eruption (85 days) was about 14.0 ± 1.4 t. If we assume that the minimum and maximum estimated global annual atmospheric Hg emissions from volcanic activity are of the order of 50 and 700 tonnes, respectively, the contribution from the Tajogaite volcanic eruption would represent approximately 28% and 2%, respectively.

Keywords: Mercury emission; Tajogaite eruption; La Palma; Canary Islands; Spain

Author Profile (first or corresponding author):

Nemesio M. Pérez, INVOLCAN’s Scientist-in-charge, mainly engaged in geochemical research applied to volcano monitoring, surface geothermal exploration, groundwater studies and environmental issues, etc.

E-mail: nperez@iter.es