GMPV9.1

GMPV9 EDI
The sustained low-intensity 2021 Fagradalsfjall eruption, Iceland: precursors, nature and impact 

The Fagradalsfjall eruption on the Reykjanes Peninsula of Iceland started on 19 March 2021. It provides a unique opportunity to study all aspects of a low-intensity effusive basaltic eruption in great detail using multidisciplinary approaches. The Fagradalsfjall eruption followed a several-week long period of intense seismicity and deformation associated with formation of the feeding dike. The eruption terminated on September 18, 2021, after producing a lava field covering about 4.5 km2. The eruption progressed through several phases, each characterized by different emission sources, eruptive style, intensities, and associated hazards. The eruption may be representative of the formation of a shield volcano, a process that the scientific community has had limited chances to observe in real time.

We welcome submissions on sustained low-intensity basaltic eruptions including (but not limited to) the 2021 Fagradalsfjall eruption; their plumbling systems, eruptive products, and impacts. We particularly encourage comparative studies across different regions that may help us to better understand the volcanic processes that are active in the Fagradalsfjall eruption.

Topics may include, for example: physical volcanology of eruptive products and eruptive behavior; lava flow modeling; acoustic studies; petrology; geochemistry and interaction with groundwater; studies of volcanic gases; crustal deformation; seismology; volcano monitoring; social effects; health effects; hazard mitigation; tectonic implications; volcano-tectonic interactions; atmosphere-climate interactions, etc.

Co-organized by AS4/NH2/SM6/TS11
Convener: Halldór Geirsson | Co-conveners: Eva EiblECSECS, Thorvaldur Thordarson, Sara Barsotti, Eniko Bali
Presentations
| Thu, 26 May, 08:30–11:50 (CEST)
 
Room -2.47/48

Presentations: Thu, 26 May | Room -2.47/48

Chairpersons: Eva Eibl, Thorvaldur Thordarson, Eniko Bali
08:30–08:33
08:33–08:43
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EGU22-9207
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solicited
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Highlight
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Virtual presentation
Gro Pedersen, Joaquin M. C. Belart, Birgir Vilhelm Óskarsson, Magnús Tumi Guðmundsson, Nils Gies, Thórdís Högnadóttir, Ásta Rut Hjartardóttir, Virginie Pinel, Etienne Berthier, Tobias Dürig, Hannah Iona Reynolds, Christpher W. Hamilton, Guðmundur Valsson, Páll Einarsson, Daniel Ben-Yehoshua, Andri Gunnarsson, and Björn Oddsson

The basaltic effusive eruption at Mt. Fagradalsfjall began on March 19, 2021, ending a 781-year hiatus on Reykjanes Peninsula, Iceland. At the time of writing (January 7, 2022), no eruptive activity has been observed since September 18, 2021. To monitor key eruption parameters (i.e., effusion rate and volume), near-real time photogrammetric monitoring was performed using a combination of satellite and airborne stereo images.

By late September 2021, 32 near real-time photogrammetric surveys were completed, usually processed within 3–6 hours. The results are a significant achievement in full-scale monitoring of a lava flow-field providing 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 pathways and lava advancement were very complex and changeable as the lava filled and spilled from one valley into another and short-term prediction of the timing of overflow from one valley to another proved challenging. Analysis of thickness maps and thickness change maps show that the lava transport into different valleys varied up to 10 m3/s between surveys as lava transport rapidly switched between one valley to another.

By late September 2021, the mean lava thickness exceeded 30 m, covered 4.8 km2 and has a bulk volume of 150 ± 3 × 106 m3. Around the vent the thickness is up to 122 m. The March–September mean effusion rate is 9.5 ± 0.2 m3/s, ranging between 1–8 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. This behavior may have been due to widening of the conduit by thermo-mechanical erosion with time, and not controlled by magma chamber pressure as is most common in the volcanic zones of Iceland.

How to cite: Pedersen, G., Belart, J. M. C., Óskarsson, B. V., Guðmundsson, M. T., Gies, N., Högnadóttir, T., Hjartardóttir, Á. R., Pinel, V., Berthier, E., Dürig, T., Reynolds, H. I., Hamilton, C. W., Valsson, G., Einarsson, P., Ben-Yehoshua, D., Gunnarsson, A., and Oddsson, B.: Volume, effusion rate, and lava transport during the 2021 Fagradalsfjall eruption: Results from near real-time photogrammetric monitoring, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9207, https://doi.org/10.5194/egusphere-egu22-9207, 2022.

08:43–08:50
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EGU22-8304
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ECS
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Virtual presentation
Edward Marshall, Maja Rasmussen, Saemundur Halldorsson, Simon Matthews, Eemu Ranta, Olgeir Sigmarsson, Jóhann Robin, Jaime Barnes, Enikö Bali, Alberto Caracciolo, Guðmundur Guðfinnsson, and Geoffrey Mibei

The recent eruption of the Fagradalsfjall complex in the Reykjanes Peninsula of Iceland represents incompletely mixed basaltic magma directly erupted from a sub-crustal storage region. The eruption comprises olivine tholeiite lava with whole rock MgO between 8.7 and 10.1 wt%. The macrocryst cargo comprises olivine up to Fo90, plagioclase up to An89, and Cr-rich clinopyroxene up to Mg# 89. Gabbro and anorthosite xenoliths are rare. Olivine-plagioclase-augite-melt (OPAM) barometry of the groundmass glass from tephra collected from 28th April to 6th May yield high equilibration pressures and suggest that this eruption is originally sourced from a deep (0.48±0.06 GPa) storage zone at the crust-mantle boundary.

 

Over the course of the eruption, Fagradalsfjall lavas have changed significantly in source signature. The first erupted lavas (mid-March) were more depleted (K2O/TiO2 ­= 0.14, La/Sm = 2.1, 87Sr/86Sr = 0.703108, 143Nd/144Nd = 0.513017, 206Pb/204Pb = 18.730) and similar in composition to basalts previously erupted on the Reykjanes Peninsula. As the eruption continued, the lavas became increasingly enriched and were most enriched in early May (K2O/TiO2 = 0.27, La/Sm = 3.1, 87Sr/86Sr = 0.703183, 143Nd/144Nd = 0.512949, 206Pb/204Pb = 18.839), having unusual compositions for Reykjanes Peninsula lavas and similar only to enriched Reykjanes melt inclusions. From early May until the end of the eruption (18th September), the lava K2O/TiO2 and La/Sm compositions displayed a sinuous wobble through time at lower amplitude than observed in the early part of the eruption. The enriched lavas produced later in the eruption are more enriched than lavas from Stapafell, a Reykjanes eruption thought to represent the enriched endmember on the Reykjanes. The full range of compositional variation observed in the eruption is large – about 2.5 times the combined variation of all other historic Reykjanes lavas.

 

The major, trace, and radiogenic isotope compositions indicate that binary mixing controls the erupted basalt compositions. The mixing endmembers appear to be depleted Reykjanes melts, and enriched melts with compositions similar to enriched Reykjanes melt inclusions or Snaefellsnes alkali basalts. The physical mechanism of mixing and the structure of the crust-mantle boundary magmatic system is a task for future study.

 

In contrast to the geochemical variations described above, the oxygen isotope composition (δ18O) of the groundmass glass (5.1±0.1‰) has little variation and is lower than MORB (~5.5‰). Olivine phenocrysts δ18O  values range from typical mantle peridotite values (5.1‰) to lower values (4.6‰), with the lower values in close equilibrium with the host melt. Given the crust-mantle boundary source of the eruption, these low δ18O values are unlikely to represent crustal contamination, and are more likely to represent an intrinsically low δ18O mantle beneath the Reykjanes Peninsula.

How to cite: Marshall, E., Rasmussen, M., Halldorsson, S., Matthews, S., Ranta, E., Sigmarsson, O., Robin, J., Barnes, J., Bali, E., Caracciolo, A., Guðfinnsson, G., and Mibei, G.: An overview of the geochemistry and petrology of the mantle-sourced Fagradalsfjall eruption, Iceland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8304, https://doi.org/10.5194/egusphere-egu22-8304, 2022.

08:50–08:57
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EGU22-13461
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Virtual presentation
Michelle Parks, Kristín S. Vogfjörd, Freysteinn Sigmundsson, Andrew Hooper, Halldór Geirsson, Vincent Drouin, Benedikt G. Ófeigsson, Sigrún Hreinsdóttir, Sigurlaug Hjaltadóttir, Kristín Jónsdóttir, Páll Einarsson, Sara Barsotti, Josef Horálek, and Thorbjörg Ágústsdóttir

The 2021 effusive eruption at Mt. Fagradalsfjall, on the Reykjanes Peninsula oblique rift in Iceland, was preceded by a 14-month long period of volcano-tectonic unrest (comprising both significant ground deformation and intense seismicity). A seismic swarm was initially detected in the Fagradalsfjall region between the 15th to 20th December 2019. Following a short quiescence, activity re-commenced on the 21st January 2020, with a small cluster of earthquakes near Grindavík (~ 10 km west of Fagradalsfjall). Concurrent deformation was detected on two GNSS stations in this area and on Sentinel-1 interferograms. Geodetic modelling of these observations indicated the deformation most likely resulted from the intrusion of a magmatic sill, directly west of Mt. Thorbjörn, at a depth of about 4 km. This was followed by two additional sill-type intrusions in a similar location, between 6th March - 17th April and 15th May - 22nd July 2020 respectively. The three intrusions comprised a total volume change of about 9 million cubic meters. In mid-July 2020, inflation was again detected on the Reykjanes Peninsula, this time in the Kýsuvík volcanic system to the east of Fagradalsfjall. This episode of inflation lasted several weeks and geodetic inversions indicated the observed signal was produced by the combination of a deflating sill-like source at a depth of ~16 km and inflation of a body at a depth of ~6 km. The latter, corresponding to a volume change of about 5 million cubic meters. During this period of intrusive activity, seismicity shifted along various regions across the Peninsula, in relation to a combination of processes – magma migration, triggered seismicity and tectonic earthquakes.

 

Intense seismic swarms commenced on the 24th February 2021, concentrated at both Fagradalsfjall and also extending across a 20 km segment along the plate boundary – including triggered strike-slip earthquakes up to Mw5.64. At the same time, deformation was detected on local GNSS stations, and subsequent Interferometric Sythethic Aperture Radar Analysis (InSAR) of Sentinel-1 data confirmed the observed deformation was primarily the result of a dike intrusion and slip along the plate boundary. Geodetic inversions indicated a ~9 km long dike with a total intruded volume of around 34 million cubic meters (Sigmundsson et al., in review). During this period, stored tectonic stress was systematically released, resulting in a decline in deformation and seismicity over several days preceding the eruption onset, on 19th March 2021 in Geldingadalir at Mt. Fagradalsfjall. The eruption continued until the 18th September 2021 and produced a lava field covering an area of 4.8 km2 with an extruded bulk volume of 150 ± 3 × 106 m3 (Pedersen et al., in review).

 

References

Sigmundsson et al. (in review). Deformation and seismicity decline preceding a rift zone eruption at Fagradalsfjall, Iceland.

 

Pedersen et al. (in review). Volume, effusion rate, and lava transport during the 2021 Fagradalsfjall eruption: Results from near real-time photogrammetric monitoring. DOI:10.1002/essoar.10509177.1.

How to cite: Parks, M., Vogfjörd, K. S., Sigmundsson, F., Hooper, A., Geirsson, H., Drouin, V., Ófeigsson, B. G., Hreinsdóttir, S., Hjaltadóttir, S., Jónsdóttir, K., Einarsson, P., Barsotti, S., Horálek, J., and Ágústsdóttir, T.: Evolution of deformation and seismicity on the Reykjanes Peninsula, preceding the 2021 Fagradalsfjall eruption, Iceland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13461, https://doi.org/10.5194/egusphere-egu22-13461, 2022.

08:57–09:04
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EGU22-10219
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On-site presentation
Ólafur Flóvenz, Rongjiang Wang, Gylfi Páll Hersir, Torsten Dahm, Sebastian Hainzl, Magdalena Vassileva, Vincent Drouin, Sebastian Heimann, Marius Paul Isken, Egill Árni Gudnason, Kristján Ágústsson, Thorbjörg Ágústsdóttir, Josef Horálek, Mahdi Motagh, Thomas R Walter, Eleonora Rivalta, Philippe Jousset, Charlotte M Krawczyk, and Claus Milkereit

A period of intense seismicity started more than a year prior to the 2021 Fagradalsfjall eruption in Iceland. During the same period, repeated cycles of surface uplift and subsidence were observed in the Svartsengi and Krýsuvík high-temperature (HT) fields, about 8-10 km west and east of the eruption site in Fagradalsfjall, respectively. Such an uplift has never been observed during 40 years of surface deformation monitoring of the exploited Svartsengi HT field. However, cycles of uplift followed by subsidence have been observed earlier at the unexploited Krýsuvík HT field.

Shortly after the start of the unrest, a group of scientists from GFZ-Potsdam and ÍSOR installed additional seismometers, used an optical telecommunication cable to monitor the seismicity and performed gravity measurements in the unrest area.

The data was used for multidisciplinary modelling of the pre-eruption processes (see Flóvenz et al, 2022. Cyclical geothermal unrest as a precursor to Iceland's 2021 Fagradalsfjall eruption. Nature Geoscience (in revision)). It included a poroelastic model that explains the repeated uplift and subsidence cycles at the Svartsengi HT field, by cyclic fluid intrusions into a permeable aquifer at 4 km depth at the observed brittle-ductile transition (BDT). The model gives a total injected volume of 0.11±0.05 km3. Constraining the intruded material jointly by the deformation and gravity data results in a density of 850±350 kg/m3. A high-resolution seismic catalogue of 39,500 events using the optical cable recordings was created, and the poroelastic model explains very well the observed spatiotemporal seismicity.

The geodetic, gravity, and seismic data are explained by ingression of magmatic CO2 into the aquifer. To explain the behaviour of cyclic fluid injections, a physical feeder-channel model is proposed.

The poroelastic model and the feeder-channel model are combined into a conceptual model that is consistent with the geochemical signature of the erupted magma. It explains the pre-eruption processes and gives estimates of the amount of magma involved.

The conceptual model incorporates a magmatic reservoir at 15-20 km depth, fed by slowly upwelling currents of mantle derived magma. Volatiles released from inflowing enriched magma into the sub-Moho reservoir migrated upwards. The volatiles were possibly trapped for weeks or months at the BDT at ~7 km depth beneath Fagradalsfjall, generating overpressure, but not high enough to lift the overburden (~220 MPa) and cause surface deformation. After reaching a certain limiting overpressure, or when a certain volume had accumulated, the magmatic volatiles were diverted upwards, just below the BDT towards the hydrostatic pressurized aquifer (~ 40 MPa) at 4 km depth at the bottom of the convective HT fields. They passed through the BDT and increased the pressure sufficiently (>110 MPa) to cause the uplift.

The lessons learned enlighten the most important factors to help detect precursory volcanic processes on the Reykjanes Peninsula; including detailed monitoring of seismicity, surface deformation, gravity changes and gas content in geothermal fluids. Furthermore, geophysical exploration of the deeper crust by seismic and resistivity measurements are crucial to map possible melt and possible pathways towards the surface.

How to cite: Flóvenz, Ó., Wang, R., Hersir, G. P., Dahm, T., Hainzl, S., Vassileva, M., Drouin, V., Heimann, S., Isken, M. P., Gudnason, E. Á., Ágústsson, K., Ágústsdóttir, T., Horálek, J., Motagh, M., Walter, T. R., Rivalta, E., Jousset, P., Krawczyk, C. M., and Milkereit, C.: A comprehensive model of the precursors leading to the 2021 Fagradalsfjall eruption , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10219, https://doi.org/10.5194/egusphere-egu22-10219, 2022.

09:04–09:11
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EGU22-2674
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Presentation form not yet defined
Tomas Fischer, Pavla Hrubcová, Ali Salama, Jana Doubravová, Josef Horálek, Thorbjorg Agustsdottir, Egill Gudnason, and Hersir Gylfi

 

The 6 months long effusive volcanic eruption of 19 March 2021 at Fagradalsfjall, Reykjanes Peninsula, Iceland was preceded by an intensive earthquake swarm lasting one month, with several earthquakes exceeding ML 5. We analyse seismic data recorded by the Reykjanet local seismic network to trace the processes leading up to the eruption in order to understand the relation between seismic activity and magma accumulation.

 

The precise relocations show that the seismicity is located in two clusters in the depth range of 1-6 km. A NE-SW trending cluster maps the dyke propagation; a WSW-ENE trending cluster follows the plate boundary. In comparison, we relocated the preceding earthquake swarms of 2017, 2019 and 2020 and found that they form two branches along the plate boundary, coinciding with the 2021 WSW-ENE trending cluster. These branches form a stepover of about 1 km offset, forming a pull-apart basin structure at the intersection with the dyke. This is the exact location of the eruption site, which shows that magma erupted at the place of crustal weakening.

 

The 2021 earthquake swarm initiated by a ML 5.3 earthquake on 24 February, which triggered the aftershocks along the plate boundary and in the dyke segment, both occurring in an area of elevated Coulomb stress. The swarm seismicity shows complex propagation of the dyke, which started at its northern end, migrated south-westward and then jumped back to the central part where the effusive eruption eventually took place. The strike-slip focal mechanisms of the larger magnitude events, with N-S striking fault planes, are interpreted as right-lateral antithetic Riedel shears that accommodate the left lateral slip along the plate boundary. The fact that both seismic and magmatic activities occur at the same location shows that the past seismic activity weakened the crust in the area of the eruption site. We show that the ML 5.3 earthquake on 24 February 2021 triggered the whole seismic swarm and perturbed the magma pocket which eventually led to the 19 March Fagradalsfjall eruption.

 

How to cite: Fischer, T., Hrubcová, P., Salama, A., Doubravová, J., Horálek, J., Agustsdottir, T., Gudnason, E., and Gylfi, H.: Swarm seismicity illuminates stress transfer prior to the 2021 Fagradalsfjall eruption, Iceland , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2674, https://doi.org/10.5194/egusphere-egu22-2674, 2022.

09:11–09:18
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EGU22-12435
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Presentation form not yet defined
Halldór Geirsson, Michelle Parks, Freysteinn Sigmundsson, Benedikt G. Ófeigsson, Vincent Drouin, Cécile Ducrocq, Hildur M. Friðriksdóttir, Sigrún Hreinsdóttir, and Andrew Hooper

Geodetic observations during volcanic eruptions are important to constrain from where the eruptive products originate in the sub-surface. Some eruptions are sourced from magma reservoirs shallow in the crust, whereas others may tap magma directly from the mantle. The 2021 Fagradalsfjall eruption took place on the Reykjanes Peninsula, Iceland, during March 19 to September 18, resulting in approximately 0.15 km3 of erupted basaltic lava. A wide-spread crustal subsidence and inward horizontal motion, centered on the eruptive site, was observed during the eruption. Nearest to the emplaced lava flows, additional localized subsidence is observed due to the loading of the lavas. The regional subsidence rate varied during the eruption: it was low in the beginning and then increased, in broad agreement with changes in the bulk effusive rate. In this study we use GNSS and InSAR data to model the deformation source(s) during different periods of the eruption, primarily aiming to resolve the depth and volume change of the magma source. We furthermore calculate crustal stress changes during the eruption and compare to the regional seismicity.

How to cite: Geirsson, H., Parks, M., Sigmundsson, F., Ófeigsson, B. G., Drouin, V., Ducrocq, C., Friðriksdóttir, H. M., Hreinsdóttir, S., and Hooper, A.: Co-eruptive subsidence during the 2021 Fagradalsfjall eruption: geodetic constraints on magma source depths and stress changes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12435, https://doi.org/10.5194/egusphere-egu22-12435, 2022.

09:18–09:25
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EGU22-8804
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ECS
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On-site presentation
Esme Olivia Southern, Tim Greenfield, Tom Winder, Þorbjörg Ágústsdóttir, Bryndís Brandsdóttir, Tomas Fischer, Jana Doubravová, Nick Rawlinson, Robert White, Egill Árni Gudnason, Gylfi Páll Hersir, Pavla Hrubcova, and Conor Bacon

The 2021 Fagradalsfjall eruption on Iceland’s Reykjanes Peninsula was preceded by more than 12 months of elevated activity, beginning around November 2019. This dominantly consisted of episodes of intense seismic swarms, but also featured inflationary episodes in both the Svartsengi and Krísuvík volcanic systems. On 24th February 2021, an exceptionally intense episode of seismicity covering the length of the Peninsula marked the initiation of a dyke intrusion, which continued to develop until the 19th of March, when melt first erupted at the surface. The fissure eruption lasted 6 months, ending on 18th September 2021.

During the intrusion, melt first propagated northeast towards Mt Keilir, then to the southwest, eventually forming a 10 km-long dyke. This was marked by more than 80,000 microearthquakes, recorded by a dense local seismic network and detected and located using QuakeMigrate[1].

We present high precision relative relocations of the seismicity, and tightly constrained focal mechanisms of earthquakes which are dominantly located along the base of the dyke. We compare the Fagradalsfjall seismicity to the 2014-2015 Bárðarbunga-Holuhraun intrusion and eruption seismicity [2], in the context of the contrasting tectonic settings, and markedly different precursory activity.

1: Winder, T., Bacon, C., Smith, J., Hudson, T., Greenfield, T. and White, R., 2020. QuakeMigrate: a Modular, Open-Source Python Package for Automatic Earthquake Detection and Location. https://doi.org/10.1002/essoar.10505850.1

2: Woods, J., Winder, T., White, R. S., and Brandsdóttir, B., 2019. Evolution of a lateral dike intrusion revealed by relatively-relocated dike-induced earthquakes: The 2014–15 Bárðarbunga–Holuhraun rifting event, Iceland. https://doi.org/10.1016/j.epsl.2018.10.032

How to cite: Southern, E. O., Greenfield, T., Winder, T., Ágústsdóttir, Þ., Brandsdóttir, B., Fischer, T., Doubravová, J., Rawlinson, N., White, R., Gudnason, E. Á., Hersir, G. P., Hrubcova, P., and Bacon, C.: Relatively-relocated seismicity during the 2021 Fagradalsfjall dyke intrusion, Reykjanes Peninsula, Iceland: Detailed evolution of a lateral dyke, and comparison to Bárðarbunga-Holuhraun, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8804, https://doi.org/10.5194/egusphere-egu22-8804, 2022.

09:25–09:32
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EGU22-5649
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Highlight
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On-site presentation
Tim Greenfield, Thomas Winder, Nicholas Rawlinson, Esme Southern, Conor Bacon, Thorbjörg Ágústsdóttir, Robert S. White, Bryndis Brandsdottir, John Maclennan, Josef Horalek, Egill Árni Gudnason, and Gylfi Páll Hersir

Using a dense network of seismometers located on the Reykjanes Peninsula of Iceland we image a cluster of earthquakes located at a depth of 10-15 km, beneath the brittle-ductile transition and active before and during the Fagradalsfjall eruption. The deep seismicity has markedly different properties to those earthquakes located in the upper, brittle crust with a lower frequency content and a high b-value suggesting that fluids and/or high temperature gradients could be involved in their initiation. Detailed relocation of the deep seismicity reveals that the locus of the activity shifts southwest after the onset of the eruption, suggesting that although the location of the deep seismicity is unlikely to be the source for the magma which erupted, nevertheless the eruption and the deep earthquakes are linked. We interpret the deep earthquakes to be induced by the intrusion of magma into the lower crust. In such an interpretation, the intruded region could be offset from the conduit that transports the magma from the source region near the base of the crust to the surface.  

How to cite: Greenfield, T., Winder, T., Rawlinson, N., Southern, E., Bacon, C., Ágústsdóttir, T., White, R. S., Brandsdottir, B., Maclennan, J., Horalek, J., Gudnason, E. Á., and Hersir, G. P.: Deep seismicity preceding and during the 2021 Fagradalsfjall eruption, Reykjanes Peninsula, Iceland , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5649, https://doi.org/10.5194/egusphere-egu22-5649, 2022.

09:32–09:39
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EGU22-9802
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ECS
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Presentation form not yet defined
Thorbjörg Ágústsdóttir, Josef Horálek, Egill Árni Gudnason, Jana Doubravová, Gylfi Páll Hersir, Jakub Klicpera, Fridgeir Pétursson, Rögnvaldur Líndal Magnússon, Jiri Málek, Lucia Fojtíková, Tomáš Fischer, Josef Vlček, and Ali Salama

The REYKJANET local seismic network was deployed on the Reykjanes Peninsula, SW Iceland, in 2013; funded by the Czech Academy of Science and supported by Iceland GeoSurvey. The network consists of 15 seismic stations, using Nanometrics Centaur digitizers sampling at a rate of 250 sps with a GPS timestamp. Additionally, 7 stations are equipped with microbarographs. In 2016, REYKJANET was substantially upgraded when short-period seismometers were replaced by Güralp CMG-3ESPC broadband seismometers (eigenperiod T0=30s). The instruments are buried in vaults on concrete pillars and are therefore well coupled with the bedrock. They are powered by batteries recharged by solar and wind power all year round, surviving harsh winter condition and corrosion from geothermal gases. These stations are deployed along the Reykjanes Peninsula, between the Svartsengi and Hengill high temperature geothermal fields, covering an area of about 60x20 km. In the summer of 2021 two new stations were deployed on the eastern part of the Peninsula, each consisting of a Güralp CMG-40T broadband seismometers and a Kinemetrics FBA ES-T EpiSensor also sampling at 250 sps with a GPS timestamp. Since early 2021, data from all REYKJANET stations are streamed in real-time to Iceland GeoSurvey and currently 8 of them are also streamed to the Icelandic Meteorological Office for improved earthquake locations for natural hazard monitoring purposes. Since the deployment of the network in 2013, it has been operated continuously and captured the largest seismic swarms on the Reykjanes Peninsula in 2017, 2019, 2020 and 2021.The REYKJANET network was ideally placed, as the 2021 Fagradalsfjall eruption occurred right in the central part of the network. Here we present the pre-eruptive seismicity of the 2021 Fagradalsfjall eruption in comparison to previous seismic swarms.

The maintenance of REYKJANET, data analysis and interpretation are currently done within the NASPMON project (NAtural Seismicity as a Prospecting and MONitoring tool for geothermal energy extraction), funded through EEA Grants and the Technology Agency of the Czech Republic within the KAPPA Programme.

How to cite: Ágústsdóttir, T., Horálek, J., Gudnason, E. Á., Doubravová, J., Hersir, G. P., Klicpera, J., Pétursson, F., Líndal Magnússon, R., Málek, J., Fojtíková, L., Fischer, T., Vlček, J., and Salama, A.: The REYKJANET local seismic network ideally placed for capturing the 2021 Fagradalsfjall pre-eruptive seismicity: in operation since 2013, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9802, https://doi.org/10.5194/egusphere-egu22-9802, 2022.

09:39–09:46
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EGU22-13504
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ECS
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On-site presentation
Amber Parsons, Conor Bacon, Tim Greenfield, Tom Winder, Thorbjörg Ágústsdóttir, Bryndís Brandsdóttir, Tomas Fischer, Jana Doubravová, Nicholas Rawlinson, Robert White, Egill Árni Gudnason, Gylfi Páll Hersir, and Pavla Hrubcova

Since late 2019, the Reykjanes Peninsula in Iceland has experienced elevated seismic activity, which culminated in a dyke intrusion beneath Fagradalsfjall on 24th February 2021, and an eruption on 19th March. Seismic anisotropy – the directional dependence of seismic wave speed – can be used to study structural properties of the crust, which may be controlled by the state of stress through preferential closure of micro-cracks. This provides an opportunity to investigate changes in crustal stress regime caused by a dyke intrusion, with potential applications in eruption monitoring and forecasting.

 

A dense seismic network spanning Fagradalsfjall recorded more than 130,000 earthquakes between June 2020 and August 2021; detected and located using QuakeMigrate1. From this dataset, we calculate the seismic anisotropy of the upper crust through shear-wave splitting analysis. Exceptional ray-path coverage allows for imaging at high spatial and temporal resolution. We present these results in relation to the regional stress regime and tectonic structure, and search for changes in anisotropy before, during, and after the dyke intrusion and eruption.

 

1: Winder, T., Bacon, C., Smith, J., Hudson, T., Greenfield, T. and White, R., 2020. QuakeMigrate: a Modular, Open-Source Python Package for Automatic Earthquake Detection and Location. https://doi.org/10.1002/essoar.10505850.1

How to cite: Parsons, A., Bacon, C., Greenfield, T., Winder, T., Ágústsdóttir, T., Brandsdóttir, B., Fischer, T., Doubravová, J., Rawlinson, N., White, R., Gudnason, E. Á., Hersir, G. P., and Hrubcova, P.: Imaging the anisotropic structure of the Reykjanes Peninsula across the 2021 Fagradalsfjall dyke intrusion through local shear-wave splitting analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13504, https://doi.org/10.5194/egusphere-egu22-13504, 2022.

09:46–09:53
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EGU22-12548
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ECS
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Presentation form not yet defined
Hanna Blanck, Benedikt Halldórsson, and Kristín Vogfjord

In the evening hours of 21 December 2021, a seismic sequence started in south-central Reykjanes peninsula in SW-Iceland. Both the science community and the civil protection agency were alarmed due to the proximity of this sequence to the site of the 2021 Fagradalsfjall eruption (March – September 2021), especially as this was the most prominent sequence since the end of the eruption and it showed similar characteristic as the seismic activity that had been observed in the 3 weeks leading up to it. In addition, the December earthquake sequence was located along a NE-SW striking alignment which, together with GPS and InSAR measurements, has been interpreted as a dike intrusion, which also was the origin of the March eruption. We analyse the seismic activity using a small-aperture (D=1.7 km, d=0.5 km) urban seismic array, consisting of 5 Raspberry Shake 4D sensors (1 vertical geophone and 3 MEM accelerometric components) located in the nearby municipality of Grindavík about 10 km WSW from the former eruption site. During the first days of the seismic activity magnitudes reached up to ML 4.8 but on 30 December the activity subsided and then ceased, with only few events reaching more than ML 2, which coincides with the magnitude of completeness of the seismic array.  

We present the first insights into the spatiotemporal characteristics of the sequence provided by array processing of the most intense period of the sequence. To process the array data, we used the SeisComP module AUTOLAMBDA with both the FK and PMCC (Progressive Multi-Channel Correlation) method to obtain back azimuth and slowness pairs of incoming waves. During its first hours, the sequence showed a systematic behaviour in the back azimuthal distribution of the incoming waves. Namely, over a repeated interval of a couple of hours the back azimuthal estimates increase steadily at a rate of 5 to 12°/h after which the source of the activity appears to drop back to the initial azimuthal values, and the cycle repeats. Over the following days, these bursts of oscillating activity become less frequent with relatively calm phases between. These periods of oscillating behaviour show that the seismic activity was systematically migrating southwest to/from northeast and most likely is the signature of a pulsating magma pressure front in the dike itself. This behaviour is similar to some phases during the previous eruption when lava was actively erupting with hours of quiescence in between. These results show that the monitoring of automatic back azimuth and slowness estimates are a useful tool in revealing small-scale systematic behaviour of seismic sequences in the area in real-time. 

How to cite: Blanck, H., Halldórsson, B., and Vogfjord, K.: Array observations of an oscillating seismic sequence in the Reykjanes Peninsula, SW-Iceland, in December 2021 , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12548, https://doi.org/10.5194/egusphere-egu22-12548, 2022.

09:53–10:00
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EGU22-10330
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Highlight
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Virtual presentation
Ásta Rut Hjartardóttir, Tobias Dürig, Michelle Parks, Vincent Drouin, Vigfús Eyjólfsson, Hannah Reynolds, Esther Hlíðar Jensen, Birgir Vilhelm Óskarsson, Joaquín M. C. Belart, Joël Ruch, Nils Gies, Gro B. M. Pedersen, and Páll Einarsson

The Fagradalsfjall eruption started on the 19th of March 2021 on a ~180 m long eruptive fissure, following a dike intrusion which had been ongoing for approximately three weeks. The eruption focused shortly thereafter on two eruptive vents. In April, new fissure openings occurred northeast of the initial eruption on the 5th, 6/7th, 10th, and 13th of April. The northernmost eruption occurred on the 5th of April, approximately 1 km northeast of the initial fissure, whereas the other fissure openings occurred between this and the initial eruptive vents. Stills from web cameras and time-lapse cameras are available for five of the fissure openings. These data show that the eruptions were preceded by steam emitted from cracks in the exact locations where the eruptions started. The time between the first steam observations and the visual appearance of glowing lava ranged between 15 seconds and 1.5 minutes during night observations and 9 to 23 minutes during daytime observations, the difference is likely explained by different lighting conditions. The eruptive vents are located where the north-easterly oriented dike intersected pre-existing north-south oriented strike-slip faults. These strike-slip faults could be identified on both pre-existing aerial photographs and digital elevation models. A high resolution ICEYE interferogram spanning the first day of the eruption in March reveals deformation where the later vent openings occurred in April. This indicates how Interferometric Synthetic Aperture Radar Analysis (InSAR) could be used to predict where subsequent vent openings are likely. This is of great importance for hazard assessment and defining exclusion zones during fissure eruptions.

How to cite: Hjartardóttir, Á. R., Dürig, T., Parks, M., Drouin, V., Eyjólfsson, V., Reynolds, H., Jensen, E. H., Óskarsson, B. V., Belart, J. M. C., Ruch, J., Gies, N., Pedersen, G. B. M., and Einarsson, P.: Eruptive vent openings during the 2021 Fagradalsfjall eruption, Iceland, and their relationship with pre-existing fractures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10330, https://doi.org/10.5194/egusphere-egu22-10330, 2022.

Coffee break
Chairpersons: Halldór Geirsson, Sara Barsotti
10:20–10:23
10:23–10:33
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EGU22-8679
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ECS
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solicited
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Highlight
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Virtual presentation
Vincent Drouin, Valentyn Tolpekin, Michelle Parks, Freysteinn Sigmundsson, Daniel Leeb, Shay Strong, Ásta Rut Hjartardóttir, Halldór Geirsson, Páll Einarsson, and Benedikt Gunnar Ófeigsson

Using ground deformation measurements of high spatial and temporal resolution SAR, the understanding of new vents created during volcanic eruptions can be improved with 3D mapping of the activated shallow magma plumbing system. Interferometric analysis of radar data from ICEYE X-band satellites with daily coherent ground track repeat (GTR) provides unprecedented time series of deformation in relation to the opening of 6 eruptive vents over 26 days in 2021, at Fagradalsfjall, Iceland. Unrest started in this location at the end of February and tens of thousands of earthquakes were recorded during the following four weeks. The seismicity was linked to gradual formation of a magma-filled dike in the crust and triggered seismicity along the plate boundary. On 19 March, an eruptive fissure opened near the center of the dyke. New vents and eruptive fissures opened on the 5th, 7th, 10th, and 13th April. The daily acquisition rate of the ICEYE satellite facilitated the observation of the ground openings associated with each new vents. Each event can be observed individually and with minimal loss of signal caused by new lava emplacement, which would occur if images were acquired at a slower rate. Being able to retrieve deformation near the edge of the fissure ensures that we have the optimal constraints needed for modelling the subsurface magma path. The ICEYE dataset consists of Stripmap acquisitions (30x50km) in the period 3-21 March, and Spotlight acquisitions (5x5 km) from 22 March and onward. Images have a resolution of about 2 m x 3 m, and 0.5 m x 0.25 m, respectively. The descending 1-day interferogram covering each individual event is used to invert for the distributed opening along the dike plane. We find that each fissure was associated with opening of up to 0.5 meters in the topmost 200 m of crust. The conduits propagated vertically at least 50–80 m/h. The new fissure locations were influenced by local conditions and induced stress changes within the shallow crust.

How to cite: Drouin, V., Tolpekin, V., Parks, M., Sigmundsson, F., Leeb, D., Strong, S., Hjartardóttir, Á. R., Geirsson, H., Einarsson, P., and Ófeigsson, B. G.: Conduits feeding new eruptive vents at Fagradajsfjall, Iceland, mapped by high-resolution ICEYE SAR satellite in a daily repeat orbit, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8679, https://doi.org/10.5194/egusphere-egu22-8679, 2022.

10:33–10:40
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EGU22-11995
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Presentation form not yet defined
Joël Ruch, Simon Bufféral, Elisabetta Panza, Stefano Mannini, Birgir Oskarsson, Nils Gies, Celso Alvizuri, and Ásta Rut Hjartardóttir

The Reykjanes Peninsula has recently been subject to a seismo-tectonic unrest triggering widespread ground cracks. This started with a strong seismic swarm from 24 February to 17 March 2021 and culminated in a volcanic eruption on March 19, terminating an 800 years quiescence period in the region. The Peninsula hosts four overlapping and highly oblique rift zones. The structural relations between the plate boundary (N070), the rift zones (N030 to N040) and the barely visible fault zones oriented N175 are challenging to assess, as most structures, beside the rifts, are poorly preserved or absent in the landscape. 

To get the full picture of the fracture field generated by the 2021 Reykjanes rifting event, we collected an unprecedented amount of structural data, mapping almost the entire fresh fracture field. Field observations show widespread ground cracks in up to ~7 km distance from the intrusion area with en-echelon metrical segments with a right-lateral sense of shear. Most of these structures are not visible anymore, either covered by lava flows or eroded due to weathering. They are unique testimony of the strong seismicity preceding the eruption and would have remained unnoticed if not caught up by our fixed-wing drone, surveying an area of ~30 km2. We used the resulting high-resolution (<5 cm) orthomosaics and DEMs to study three main NS-oriented fracture zones of 3 to 4 kilometers long, mostly generated by ten earthquakes ranging from M5 to M5.6. Results show metric to decametric en-echelon structures with cracks of very limited extension, even in the vicinity of the eruption site. Two of the three main fracture zones clearly show fault reactivation, suggesting episodicity in the rifting processes. Apart from local sinkholes, the third area has probably also been reactivated, but the loose ground composition did not preserve previous structures.

We further used high-resolution optical image correlation technique to analyze aerial photos and drone imagery acquired before and after the large earthquakes sequence in the three fracture zones. Results show clear NS-oriented shear structures with a right-lateral sense of motion of up to 50 cm. This is in good agreement with moment tensors we computed from waveform data at seismic stations up to 1000 km distance. We observe consistent non-double-couple mechanisms, with tension-crack components oriented northwest-southeast. The orientations suggest strike-slip faulting with nodal planes oriented in the same direction as the main fault traces. We also found that the three fracture zones have sigmoid shapes and their overall extension bounds the near-field deformation of the plate boundary. These sigmoids may suggest a local high geothermal gradient and elasto-plastic deformation affecting the Reykjanes Peninsula, that further decreases toward the South Icelandic Seismic Zone.

How to cite: Ruch, J., Bufféral, S., Panza, E., Mannini, S., Oskarsson, B., Gies, N., Alvizuri, C., and Hjartardóttir, Á. R.: Widespread ground cracks generated during the 2021 Reykjanes oblique rifting event (SW Iceland), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11995, https://doi.org/10.5194/egusphere-egu22-11995, 2022.

10:40–10:47
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EGU22-10343
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ECS
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Presentation form not yet defined
Simon Bufféral, Elisabetta Panza, Stefano Mannini, and Joël Ruch

The dynamics of fault slip in the upper hundreds of meters of Earth’s crust has long been an open question, as their behavior differs from classical elastic dislocation models and their observation still raises challenges. Here, we analyze centimeter-scale ground resolution aerial optical images of the surface ruptures associated with the 8 Mw ≥ 5.0 sub-surface earthquakes that stroke during the Reykjanes seismo-tectonic unrest, starting on February 24, 2021, and ending with the start of an eruption at Fagradasfjall on March 19, 2021. For four major earthquakes, we apply a sub-pixel correlation technique of pre-, syn- and post-crisis aerial and drone orthomosaics to describe the displacement field on surface blocks. We find that surface offsets reached up to 50 cm, with almost pure dextral strike-slip in a NS direction. These orientations contrast with the overall NE-SW-oriented extensional structures originating from magmatic intrusions and appear as a bookshelf faulting system conjugated to the left-lateral strike-slip plate boundary, oriented ~N070.

On hard grounds (e.g.: lava flows), shallow ruptures reached the surface, reactivating pre-existing structures and displaying an en-échelon succession of hectometric-sized fractures. We believe these ruptures are representative of medium-sized faults behavior in the last few hundred meters of the crust. On soft grounds, however, the rupture was only betrayed by meter-sized en-échelon systems, evidenced by thousands of discrete sub-metric surface fractures we were able to observe in the field and map from the orthomosaics. The sharp deformation gradient we imaged indicates that the dislocation drastically decreased above ten to a few tens of meters below the surface. In this layer, diffuse deformation takes on most of the slip deficit, mainly through inelastic processes. As a result, evidence of the February 2021 earthquake did not endure erosion for more than a few months. Except for an isolated sinkhole which allowed us to assume that one fault pre-existed, there were no markers of its presence before the earthquake. We emphasize that this issue must frequently lead to an underestimation of the seismic hazard when performed from surface traces.

How to cite: Bufféral, S., Panza, E., Mannini, S., and Ruch, J.: Sub-surface fault slip dynamics during the 2021 Reykjanes unrest (Iceland), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10343, https://doi.org/10.5194/egusphere-egu22-10343, 2022.

10:47–10:54
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EGU22-11386
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ECS
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Presentation form not yet defined
Páll Einarsson, Ólafur Rögnvaldsson, and Haraldur Ólafsson

During the Fagradalsfjall volcanic eruption in Iceland in 2021, the atmospheric flow was simulated at high-spatial and temporal resolutions with the numerical system WRF, including the WRF-Chem for the simulation of trace gases and aerosols.  The output of the real-time simulations of SO2 has been compared to observations, showing that on time-scales of 12-24 hours, the numerical system has considerable skill, but moving to temporal scales shorter than 6 hours leads to substantial drop in the model performance.  The data and the model output suggest that there may be strong long-lasting horizontal gradients in the trace gases and limited horizontal mixing at times, calling for a more dense network of monitoring of gases from the volcano.  Wind variability on the time scale of minutes up to few hours remains a challenge.

How to cite: Einarsson, P., Rögnvaldsson, Ó., and Ólafsson, H.: Real-time prediction trace gases from the Fagradalsfjall volcanic eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11386, https://doi.org/10.5194/egusphere-egu22-11386, 2022.

10:54–11:01
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EGU22-11537
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ECS
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On-site presentation
Ben Esse, Mike Burton, Catherine Hayer, Sara Barsotti, and Melissa Pfeffer

Effusive eruptions are a significant source of volcanic volatile species, injecting various reactive and climate altering products into the atmosphere, while low-level emissions can be hazardous to human health due to the degradation of local or regional air quality. Quantification of the flux and composition of these emissions also offers an insight into the magmatic processes driving the eruption. These factors mean that gas flux measurements are a key monitoring tool for managing the response to such eruptions. The usual target species for gas flux measurements is sulphur dioxide (SO2) due to its high concentration in volcanic emissions but low ambient concentration, and its ability to be measured with UV and IR spectroscopy from both ground and space.

Fagradalsfjall volcano, Iceland, underwent an effusive eruption between March – September 2021, emitting over 100 million m3 of lava and producing significant SO2 emissions. The eruption progressed through several distinct phases in eruptive style, with different surface activity and gas emission behaviour for each. Satellite instruments have not traditionally been used for monitoring emissions from effusive eruptions such as this, as they often lack the spatial or temporal resolution to detect and quantify low-level effusive emissions. However, the launch of ESA’s Sentinel-5P, carrying the TROPOMI instrument, in October 2017 opened the door for such measurements, offering a step change in sensitivity to tropospheric emissions over previous missions.

Here, we will present measurements of altitude- and time-resolved SO2 fluxes from Fagradalsfjall by combining TROPOMI observations with a back-trajectory analysis toolkit called PlumeTraj. We compare the emissions with other geophysical monitoring streams throughout the eruption and explore changes across the different phases of the eruption. This will demonstrate the ability of TROPOMI and PlumeTraj for quantifying intra-day, low-level SO2 emissions and highlight the potential insight these measurements can provide for future effusive eruptions.

How to cite: Esse, B., Burton, M., Hayer, C., Barsotti, S., and Pfeffer, M.: Quantifying SO2 emissions from the 2021 eruption of Fagradalsfjall, Iceland, with TROPOMI and PlumeTraj, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11537, https://doi.org/10.5194/egusphere-egu22-11537, 2022.

11:01–11:08
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EGU22-3149
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ECS
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Virtual presentation
Jacqueline Grech Licari, William M. Moreland, Thorvaldur Thordarson, Bruce F. Houghton, and Enikö Bali

The 2021 Fagradalsfjall basaltic eruption in Iceland was effusive, but a different eruptive scenario could have unfolded if its location had been shifted a few kilometres to the south to an offshore setting. Namely a shallow marine event similar to the phreatomagmatic stages of the 1211 CE Younger Stampar eruption. The 1211 CE eruption was the initial event of the 1211-1240 Reykjanes Fires and its first stage was a Surtseyan eruption just offshore of the point of Reykjanes. It constructed the ~0.006 km3 Vatnsfellsgígur tuff cone that featured a short-lived dry phase towards the end. A second phreatomagmatic stage took place ca. 500 m off the current Reykjanes coastline to produce the larger Karlsgígur tuff cone (~0.044 km3), with a combined cone/tephra volume of ~0.15 km3. Later, the activity migrated onshore onto a 4km-long fissure with an effusive eruption that generated the Yngri-Stampar crater row and associated lava flow fields. The Vatnsfellsgígur and Karlsgígur tuff cones consist of alternating pyroclastic surge-tephra fall units, intercalated with units formed by simultaneous deposition from surge and fall. The 3.5m-thick Vatnsfellsgígur section is composed of 8 units, whereas the 5.5m-thick Karlsgígur section consists of 9 units. Chemical analysis reveals that the cones are tholeiitic basalt (MgO 6.0-7.5 wt%) with sporadic olivine phenocrysts (Fo78 to Fo84) and dispersed plagioclase macrocrysts with core composition of An87 to An91. Two compositionally distinct groups of plagioclase-hosted melt inclusions are identified: one with composition comparable to the host magma and another more primitive in composition with lower FeO, TiO2 and K2O and higher MgO (ranging from 9-10 wt% and 9-11.5 wt% for Vatnsfellsgígur and Karlsgígur, respectively). This suggests that whilst upper crustal storage zones may have facilitated melt evolution, the erupting magma originated from a deeper, crystal-mush-dominated storage zone. Original and residual sulfur contents of ~2221.7 ± 150 ppm and ~966.2 ± 120 ppm respectively, indicate that ~0.658 ± 0.034 Tg of SO2 were released into the atmosphere during these two stages of phreatomagmatic activity. Moreover, vesicularity measurements on lapilli reveal unimodal, left-skewed vesicularity distributions with modes of 90% and 95% and a range of ~40% for Vatnsfellsgígur and Karlsgígur, respectively. These results indicate that magma had gone through vesicle nucleation to free growth and coalescence and probably initial dry (magmatic) fragmentation prior to contact with external water. The evidence strongly suggests that expansion of exsolved magmatic gases was the driver of explosivity and that the role of external water in these phreatomagmatic stages of the 1211 CE eruption was confined to secondary quench granulation. The analysed juvenile clasts also displayed sharp-bound domains of contrasting vesicularity with boundaries that cross-cut the clast margins. This confirms early mingling of melt batches with different histories of ascent and/or stalling in the shallow conduit. Given such heterogeneity, regions of contrasting vesicularity were analysed separately to construct two vesicle size and number distribution (VSD/VND) datasets. Results from the ongoing micro-textural and additional analysis of volatile degassing shall also be presented here.

How to cite: Grech Licari, J., Moreland, W. M., Thordarson, T., Houghton, B. F., and Bali, E.: Shallow conduit processes and sulfur release in the phreatomagmatic stages of the 1211 CE Younger Stampar eruption, Iceland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3149, https://doi.org/10.5194/egusphere-egu22-3149, 2022.

11:08–11:15
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EGU22-3140
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ECS
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On-site presentation
Eva P. S. Eibl, Thorvaldur Thórðarson, Ármann Höskuldsson, Egill Á. Gudnason, Thoralf Dietrich, Gylfi Páll Hersir, and Thorbjörg Ágústsdóttir

The Fagradalsfjall eruption on the Reykjanes peninsula, Iceland, lasted from 19 March to 18 September 2021. While it continuously effused lava at the beginning, it opened up 7 further vents in April and focused the activity from late April on Vent 5. Surprisingly the continuous effusion changed to pulses of lava effusion (as lava fountains or vigorous overflow) between 2 May and 14 June that was seismically recorded as tremor pulses. We examined the frequency of 6939 lava fountaining pulses based on seismological data recorded at NUPH at the SE corner of Núpshlíðarháls 5.5 km southeast of the active vent.

We subdivide the time period into 6 episodes based on sudden changes in the pattern. In this presentation we present the different fountaining patterns and systematic changes and discuss their origin. Our comparison with vent height, vent stability and lava effusion style, led us to conclude that the changes in the pulsing behaviour might be caused by collapses from the crater walls. The system is clearly unstable and evolving with time.

How to cite: Eibl, E. P. S., Thórðarson, T., Höskuldsson, Á., Gudnason, E. Á., Dietrich, T., Hersir, G. P., and Ágústsdóttir, T.: Crater Rim Collapses Affect the Lava Fountaining Frequency during the Fagradalsfjall Eruption, Iceland 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3140, https://doi.org/10.5194/egusphere-egu22-3140, 2022.

11:15–11:22
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EGU22-12260
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Virtual presentation
Talfan Barnie, Manuel Titos, Tryggvi Hjörvar, Bergur Bergsson, Sighvatur Pálsson, Björn Oddson, Sara Barsotti, Melissa Pfeffer, Sibylle von Löwis of Menar, Eysteinn Sigurðsson, and Þórður Arason

The 2021 Fagradalsfjall basaltic fissural eruption in Iceland was closely studied due to its proximity to Reykjavík, which allowed easy installation and maintenance of monitoring equipment. Here we present the results from a network of calibrated webcameras maintained by the Icelandic Meteorological Office and Department of Civil Protection and Emergency Management which were used to monitor volcanic plume height and fire fountain height. A number of different camera designs optimised for different power and communications constraints were used, some built in house at IMO, and they will be presented here. To make a 3D height measurement from a 2D web camera image requires extra geometric constraints, which are provided by assuming the vent location and wind direction, in a similar manner to the method applied at Etna. We have implemented this technique as a react.js single page app, which is kept updated by a messaging queue system which pushes new images through the servers at IMO. Additionally, the webcameras have to be calibrated, in that the geometry of the camera and lens distortion parameters have to be known - this is either perfomed in the laboratory, or where the cameras were not available before installation, using one of a number of vicarious calibration techniques developed for this purpose. The resulting plume heights were used to constrain SO2 dispersion models that were the basis for air quality forecasts during the eruption. 

How to cite: Barnie, T., Titos, M., Hjörvar, T., Bergsson, B., Pálsson, S., Oddson, B., Barsotti, S., Pfeffer, M., von Löwis of Menar, S., Sigurðsson, E., and Arason, Þ.: Monitoring volcanic plume height and fountain height using webcameras at the 2021 Fagradalsfjall eruption in Iceland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12260, https://doi.org/10.5194/egusphere-egu22-12260, 2022.

11:22–11:29
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EGU22-13095
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Presentation form not yet defined
Aerosol chemistry of the 2021 Fagradalsfjall eruption – following major and trace elements from source to exposed communities
(withdrawn)
Evgenia Ilyinskaya, Melissa Pfeffer, Andri Stefansson, Barbara Kleine, Penny Wieser, Emma Liu, Marie Edmonds, Tamsin Mather, Emily Mason, Mike Burton, and Sara Barsotti
11:29–11:36
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EGU22-9846
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ECS
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On-site presentation
Madeleine Stow, Julie Prytulak, Kevin Burton, Geoff Nowell, Edward Marshall, Maja Rasmussen, Simon Matthews, Eemu Ranta, and Alberto Caracciolo

Lavas from the 2021 Fagradalsfjall eruption, Iceland, show remarkable, day to month scale temporal variations in trace element and radiogenic isotopic compositions. Changes have been attributed to variation in the depth and degree of melting and/or source lithology, with progressive melting of a deeper, more enriched source as the eruption proceeded [1]. Distinguishing melting processes from source composition can be difficult to untangle using trace elements alone. Radiogenic isotopes are unaffected by the melting processes, but pinpointing lithological variations requires that the radiogenic isotopic compositions of the (unknown) endmembers are distinct and fairly restricted to be able to calculate relative contribution(s) to a lava.

Stable isotopic composition may provide another perspective on the cause of the clear temporal chemical trends in the eruption. For example, it has been proposed that Fe stable isotopes may detect the contribution of distinct mantle lithologies to a lava, due to the contrasting bonding environment of Fe in mantle minerals. Both empirical and theoretical studies show that at equilibrium, pyroxenite should be enriched in heavy Fe isotopes compared to typical mantle peridotite [e.g. 2]. Due to limited (<0.1‰) isotopic fractionation during mantle melting, unevolved basalts should capture this lithological variation. However, more recent theoretical work has argued that unrealistically high proportions of pyroxenite are needed to cause resolvable variations in basalt Fe isotopic composition [3]. Zinc stable isotopes provide a complementary system, with variation in Zn isotopic composition detected between garnet and spinel bearing lithologies [4], and without the added complexities of redox-driven fractionation that may affect Fe isotopes. The basaltic Fagradalsfjall eruption thus provides a unique time series to test whether the changes in trace element chemistry of the erupted lavas is mirrored by Fe-Zn isotopic variation. Variation in degree of melting alone is not expected to cause significant Fe-Zn isotopic fractionation, whereas a change in contribution to the lavas from pyroxene and/or garnet bearing lithologies may be reflected in the Fe-Zn isotopic composition. By combining redox sensitive (Fe) and redox insensitive (Zn) isotope systems we can potentially investigate magmatic processes in terms of the redox evolution of the source. We will present the Fe and Zn isotopic compositions of 15 fresh, glassy basaltic lavas collected during the first 4 months of the eruption. We will discuss the possible cause(s) of isotopic variations and how this adds to our understanding of the Fagradalsfjall eruption, specifically. Finally, this timeseries allows us to re-visit and evaluate the efficacy of using Fe-Zn isotopes to determine variations in mantle lithology.

[1] Marshall et al. (2021), AGU FM Abstract [2] Williams and Bizimis (2014), EPSL, 404, 396-407 [3] Soderman et al. (2021), GCA, 318, 388-414 [4] Wang et al. (2017), GCA, 198, 151-167

How to cite: Stow, M., Prytulak, J., Burton, K., Nowell, G., Marshall, E., Rasmussen, M., Matthews, S., Ranta, E., and Caracciolo, A.: Temporal Fe-Zn isotopic variations in the chemically heterogeneous Fagradalsfjall eruption, 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9846, https://doi.org/10.5194/egusphere-egu22-9846, 2022.

11:36–11:43
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EGU22-12772
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ECS
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On-site presentation
William Wenrich, Eniko Bali, Edward W. Marshall, and Gudmundur Gudfinnssonn

The 2021 Fagradalsfjall lava brought a number of mineral clusters/xenoliths <6cm in diameter to the surface. Of the >40 samples collected from the field, eight xenoliths and one plagioclase megacryst were analyzed by stereo- and petrographic microscopes and the electron microprobe. In hand specimen, the xenoliths were sub-rounded to rounded, and were olivine and clinopyroxene bearing anorthositic gabbros and anorthosites. During thin section characterization, deformed and undeformed textural types were distinguished. In deformed xenoliths, deformation textures such as undulose extinction, deformed albite twinning, and triple junctions were observed in plagioclases. Plagioclase in deformed samples was typically unzoned and had bimodal crystal size distribution. Olivines had normal zoning where they were in contact with interstitial melt and more pronounced zoning was observed on the edges on the clusters. Undeformed samples did not show deformation features and had ophitic and poikilitic texture. Clinopyroxene in undeformed xenoliths was commonly observed interstitially as well as discrete subhedral crystals. The interstitial clinopyroxene resorbed the edges of plagioclase and olivine and had uniform extinction in all but one sample. 
Electron microprobe results show that the compositional variation of minerals within the xenoliths overlaps and exceeds the compositional variation of the host lava macrocryst cargo. Olivine forsterite, plag anorthite, Cpx Mg#, and Cr# content ranged from 80-89, 76-89, 82-87, and 6-18, respectively in mineral cores and 59-86, 65-86, 71-87, and 0.4-12, respectively, in zoned rims. Mineral compositions overlap in both deformed and undeformed samples. In general, undeformed samples cover a broader range compared to deformed ones, the latter being much more uniformly primitive. One deformed sample is an outlier with significantly lower forsterite (~73-79), anorthite (~66-71), and Mg# (~74) in clinopyroxene compared to the rest of the clusters and lava phenocrysts.
Plagioclases in most xenoliths contained devitrified silicate melt inclusions. Melt compositions after post entrapment corrections are in equilibrium with their host plagioclases according to Putirka (2008). The calculated temperatures based on plagioclase melt pairs indicate a difference in crystallization environment between the clusters that overlap the lava phenocrysts and the evolved outlier. The average crystallization temperatures for most xenoliths is 1222°C, whereas for the deformed one is 1191°C, respectively. With an error of ±23°C, these two temperatures could be from separate sources.

How to cite: Wenrich, W., Bali, E., Marshall, E. W., and Gudfinnssonn, G.: Origin of gabbro and anorthosite mineral clusters in Fagradalsfjall lavas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12772, https://doi.org/10.5194/egusphere-egu22-12772, 2022.

11:43–11:50
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EGU22-8479
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On-site presentation
Olgeir Sigmarsson, Edward W. Marshall, Chantal Bosq, Delphine Auclair, Maja B. Rasmussen, Barbara I. Kleine, Eemu J. Ranta, Simon Matthews, Sæmundur A. Halldórsson, Matthew G. Jackson, Gudmundur H. Gudfinnsson, Enikö Bali, Andri Stefánsson, and Magnús T. Gudmundsson

Mantle melting processes and the characteristics of the source lithologies are mostly derived from basalt compositions of the mid-ocean ridge system and from oceanic islands. However, these basalts are in most cases the products of crustal processes resulting from magma storage, mixing, differentiation and crustal interaction. In Iceland, magma mixing and homogenization in thoroughly stirred magma reservoirs appear to be the norm, leading to restricted variations of Sr and Nd isotope ratio for a given volcanic system. In contrast, more primitive basalts were erupted during the 2021 Fagradalsfjall eruption on the Reykjanes Peninsula with a large spread in isotope ratios. A strong negative correlation between Sr and Nd isotopes is observed from ratios that span a range from a depleted mantle composition to values akin to the Icelandic mantle such as that of the basalts of the Grímsvötn volcanic system. The isotope ratios are also correlated with the measured discharge rate during the eruption, with a depleted Sr isotope ratio appearing during the period of low discharge (around 5 m3/s) for the first month and a half of the eruption. In early May, the magma flux doubled and basalts with more radiogenic Sr isotope composition were produced. During the summer 2021, the Sr isotope ratios declined, due to lower proportions of melts from undepleted mantle source in the basalt mixture erupted. Whether the eruption ended when melts from the enriched mantle was exhausted or not remains to be elucidated, but clearly the highest eruption discharge rate resulted from melts of a more fertile mantle source.

The variable proportions of depleted versus enriched melts in the eruption products demonstrate the absence of a magma reservoir in which homogenization could take place, and from which decreasing discharge rate with time would be expected.  Instead, the initially low and steady and then increasing magma extrusion rate measured, strongly indicate direct mantle melt ascent to surface, which is also supported by the primitive mineralogy of the high-MgO basalt produced. Leaky-transform faults on the mid-ocean ridge system are characterized by eruptions of primitive basalts on intra-transform spreading centres (e.g. Garrett and Siqueiros fracture zones in the East Pacific). The Fagradalsfjall complex appears to be of similar nature, and the primitive magma and the important compositional and temporal variations demonstrate the effect of mantle source composition and associated processes on the eruption behaviour, as reflected in the magma discharge rate.

How to cite: Sigmarsson, O., Marshall, E. W., Bosq, C., Auclair, D., Rasmussen, M. B., Kleine, B. I., Ranta, E. J., Matthews, S., Halldórsson, S. A., Jackson, M. G., Gudfinnsson, G. H., Bali, E., Stefánsson, A., and Gudmundsson, M. T.: Basalt production controlled by mantle source fertility at Fagradalsfjall, Iceland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8479, https://doi.org/10.5194/egusphere-egu22-8479, 2022.