1. Introduction
Effusion rates and volumes of lava flows are key eruption parameters necessary for evaluation of hazards posed by basaltic eruptions. Various methods exist to monitor and quantify near-real time effusion rate ranging from localized channel and tube estimates of instantaneous effusion rate to time-averaged discharge rate (TADR) based on satellite-based thermal data and synthetic aperture radar data (see Harris et al., 2007, Poland, 2014 and references therein). Photogrammetric methods are more recurrently and effectively applied in monitoring effusive eruptions (e.g., Dietterich et al. 2021). This study presents a significant achievement in full-scale monitoring of a lava field with photogrammetric methods that yielded daily to weekly 3-D models and effective near real-time processing and presentation of results. We show how near real-time photogrammetric monitoring in the Fagradalsfjall 2021 eruption provided key information necessary for evaluating hazards and delivering data products to Civil Protection, local police, and the public.
On March 19, 2021, an eruption started at Mt. Fagradalsfjall ending a 781-year eruption hiatus on the Reykjanes Peninsula, Iceland (Fig. 1). Fagradalsfjall is a broad hyaloclastite tuya located within an oblique spreading zone, characterized by volcanic systems and strike-slip faults that are associated with the Mid-Atlantic plate boundary (e.g., Klein et al., 1977; Gee, 1998; Clifton and Kattenhorn, 2006; Einarsson et al., 2020, Sæmundsson et al., 2020). Eruptions in Reykjanes occur from eruptive fissures, that may focus onto a single vent to form lava shields. When occuring under a glacier, these eruption types form cones, tindars or tuyas (e.g., Jones, 1969, Pedersen and Grosse, 2014). At least in the last four thousand years, volcanic activity on the Reykjanes Peninsula has been episodic, with multiple eruptions occurring over several hundred years followed by ~800–1000 years of quiescence. The last eruptive period ended in 1240 CE (Sæmundsson et al., 2020).