The Veiðivötn 1477CE (Iceland) Plinian basaltic eruption: A review of eruptive processes and plume dynamics

The Veiðivötn 1477CE (V1477) eruption in Iceland occurred along a ~70km long discontinuous fissure between the Torfajökull and Bárdarbunga volcanic systems in the Southern highlands of Iceland. The southwestern end of the fissure, where it intersected the silicic Torfajökull system, produced only minor silicic tephra, while small basaltic lava flows were emitted from the northeastern segment. Basaltic tephra (Sio₂: 49.99 ±1.35 wt.%) erupted from a 20 km long fissure segment and deposited over half of the country (> 50,000 km²), with a total volume of 10.8 ± 0.5 km³ (or 4.3 km³ DRE), corresponding to a Volcanic Explosivity Index of 5.

The eruptive sequence comprises 32 tephra fall units, with little to no variation in groundmass glass composition. We divide the eruptive sequence into three stages: (i) stage I exhibits the lowest vesicularity, a unimodal grain-size distribution (GSD), and shows no evidence of interaction with external water; (ii) stage II has the highest vesicularity, multimodal GSDs, and evidences of instability in conduit processes and interaction with external water limited to passive secondary fragmentation; and (iii) stage III shows rhythmic instabilities while returning to initial eruptive conditions.

Field data coupled to physical models of volcanic plumes show that the maximum column height reached 30.7 ± 3 km during the eruption peak. 1D plume modelling using the Paris Plume Model yields a mass eruption rate of 2.6 ± 1.3 × 10⁸ kg/s under windy conditions, placing the eruption within the Plinian to Ultra-Plinian range. Model results suggest that a volatile content of >2 wt.% would be required to sustain such a plume height, exceeding the typical volatile contents (< 1wt%) of Veiðivötn basaltic magmas. While magma-water interaction can be invoked to explain this discrepancy, vesicularity data (71–84%) indicate predominantly magmatic fragmentation, with magma reaching full vesiculation prior to fragmentation. Thus, external water likely played only a passive role, contributing to secondary fragmentation that increased the proportion of fine ash visible in GSDs. Furthermore, no evidence of microlite-rich pyroclasts was observed.

The V1477 eruption expands the record of basaltic Plinian eruptions and highlights the need to reassess conventional assumptions regarding the driver mechanisms of such eruptions.