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).