THE IDENTIFICATION AND EVOLUTION OF LAVA TUBES WITHIN THE 2021 FAGRADALSFJALL LAVA FLOW FIELD IN ICELAND

The identification of lava tubes and the conditions in which they form are an important subject as it relates to volcanic hazards, lava transport systems, planetary exploration, archaeology, speleology, and multiple other fields of study. The 2021 basaltic eruption of Fagradalsfjall volcano on the Reykjanes Peninsula in Iceland ended a ~800-year hiatus of volcanic activity in the area. We used satellite and airborne remote sensing data to study the evolution of lava tubes by manually mapping flow morphologies in QGIS.

The morphology of the lava field changed significantly over the course of the eruption. March 19–April 5 included the start of the eruption and was dominated by two active vents that infilled Geldingadalir valley. April 5–April 27 had multiple active vents and was dominated by far-reaching incandescent channels that extended the flow field into Meradalir valley and Syðri-Meradalur valley. During April 27–June 28, one active vent was established for the rest of the eruption. The morphology of the lava field was characterized by the formation of a lava pond in Syðri-Meradalur valley and the continued expansion of the lava flow field into Nátthagi valley. June 28–September 2 was characterized by episodic activity at the vent which created discontinuous lava flows that primarily flowed into Meradalir and Syðri-Meradalur. During September 2–September 18, a pause in activity from September 2–11 was followed by the formation of a lava pond in the N of Geldingadalir valley from September 11–15. An upwelling zone in the middle of Geldingadalir appeared on September 15 and ended the eruption when it ceased activity on September 18.

To help determine the source(s) of the upwelling zone, field surveys just north of the upwelling zone were conducted after the end of the eruption. We used a Geometrics MagArrow attached to an unmanned aerial system (UAS) DJI Matrice 600 Pro flying 10 m above ground and a GEM Systems GSM-19 Overhauser walking magnetometer to conduct the surveys. By interpolating the magnetic data collected, possible pathways that the lava traveled to reach the upwelling zone were identified.

The categorization of the morphologies associated with this eruption adds to our knowledge of how to identify lava tubes remotely, especially those in inaccessible locations.