Volume, Effusion Rate, and Lava Transport During the 2021 Fagradalsfjall Eruption: Results From Near Real‐Time Photogrammetric Monitoring

Abstract

The basaltic effusive eruption at Mt. Fagradalsfjall lasted from 19 March to 18 September 2021, ending a 781‐year repose period on Reykjanes Peninsula, Iceland. By late September 2021, 33 near real‐time photogrammetric surveys were completed using satellite and airborne images, usually processed within 3–6 hr. The results provide unprecedented temporal data sets of lava volume, thickness, and effusion rate. This enabled rapid assessment of eruption evolution and hazards to populated areas, important infrastructure, and tourist centers. The lava flow field has a mean lava thickness exceeding 30 m, covers 4.8 km2 and has a bulk volume of 150 ± 3 × 106 m3. The March–September mean bulk effusion rate is 9.5 ± 0.2 m3/s, ranging between 1 and 8 m3/s in March–April and increasing to 9–13 m3/s in May–September. This is uncommon for recent Icelandic eruptions, where the highest discharge usually occurs in the opening phase.

Rapid shifting of a deep magmatic source at Fagradalsfjall volcano, Iceland

“…Taking the latter as 10 m 3 s −1 (ref. 16 ), and for a timescale of 20 days, the initial melt lens volume was of the order of 2 × 10 7 m 3 . This is equivalent to an approximately 6-m-thick disc of radius 1 km, which is consistent with estimates considering changes in effusion rates during the eruption 16 and conceptual models of sill-like melt storage in the Icelandic lower crust 7 .…”

“…16 ), and for a timescale of 20 days, the initial melt lens volume was of the order of 2 × 10 7 m 3 . This is equivalent to an approximately 6-m-thick disc of radius 1 km, which is consistent with estimates considering changes in effusion rates during the eruption 16 and conceptual models of sill-like melt storage in the Icelandic lower crust 7 . This simple model captures the rapid change in melt compositions, and predicts that the geochemically depleted end-member melt (present at the start of the eruption) was largely drained from a melt lens, which was replenished with enriched melt within 20 days (Fig.…”

“…The first several weeks of the eruption were characterized by a low to modest magma effusion rate of 1-8 m 3 s −1 from multiple vents, associated with formation of spatter cones and low-viscosity lava flows. The eruption style changed after April 27th with an increased discharge rate (9-13 m 3 s −1 ) from a single vent and high (more than 450 m) lava fountaining 16 .…”

Supplemental Material: Deep magma mobilization years before the 2021 CE Fagradalsfjall eruption, Iceland

“…Between March and September, the lava flow field produced a mean lava thickness exceeding 30 m, covered 4.8 km 2 and reached a bulk volume of 150 ± 3 × 10 6 m 3 . The March-September mean bulk effusion rate was 9.5 ± 0.2 m 3 /s, ranging between 1 and 8 m 3 /s in March-April and increasing to 9-13 m 3 /s in May-September (Pedersen et al, 2022).…”

The complex construction of a glaciovolcanic ridge with insights from the 2021 Fagradalsfjall Eruption (Iceland)

“…On 19 March 2021, a fissure eruption began as an effusive outpouring of basaltic lava from closely-spaced vents (Bindeman et al, 2022;Halldórsson et al, 2022). After about a month of activity, five additional vents opened along a 1 km-long segment extending to the northeast (Bindeman et al, 2022;Pedersen et al, 2022). During this first eruptive phase, effusion rates were low to moderate (Pedersen et al, 2022) and periodic fire fountaining from multiple vents built spatter cones and fed lava flows (Bindeman et al, 2022;Halldórsson et al, 2022).…”