| Summary: | On 19 March 2021, an eruption began in the Fagradalsfjall volcanic system in Iceland, emitting lava for the first time in 781 years on the Reykjanes Peninsula, SW Iceland. The 2021 Geldingardalir eruption contained close to 7000 eruption episodes with unusual diversity in episodic behavior. This research aims to understand episodic and pulsing behavior during lava fountaining episodes typical of Phase IIIA (2 May-10 June), which featured about 6960 lava fountaining episodes. Lava fountaining activity on 4 May was quantified, analyzed, and interpreted, with a focus on videos captured with a 4K camera between 16:00 and 17:00 GMT. From that, a map of pulses was generated, via the quantification of (i) pulse height and duration, (ii) pyroclast exit velocity, and (iii) fountain height. Lava-fountaining episodes displayed maximum heights of 120 to 160 meters and episode durations of 164 to 312 sec. The average exit velocity in each episode recorded by the 4K camera ranged from 16.3 - 20.2 m/s. This study also demonstrates the link between ongoing fountaining activity and volcanic tremor, making the tremor data averaged on a one-minute time scale a good proxy for the frequency of fountaining episodes in Phase IIIA. The tremor episodes start a few tens of seconds before and last a few seconds longer than the visible fountaining. Fountaining on 4 May gave an averaged frequency of 6-8 episodes per hour, with the average duration being 5.5 minutes (+/- 1.1 min) and repose intervals averaging 2.5 minutes (+/- 0.5 min). Þann 19. mars 2021 hófst eldgos í Geldingadölum á Fagradalsfjalli á Reykjanesskaga. Geldingadalagos er fyrsta hraungosið á skaganum í 781 ár og var óvenjulega fjölbreytt þegar kemur að goshegðun og hraunagerðum. Meðal annars voru goshrinurnar um 7000 talsins, sem er það mesta í einu gosi á jörðinni. Í þessari rannsókn er áherslan lögð á að greina goshrinurnar og meðfylgjandi kvikustrókavirkni sem einkenndu virknina 4 maí 2021. Virknin þennan dag er dæmigerð fyrir goshegðunina í Fasa IIIA (2 maí – 10 júní) ...
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