Post-eruptive Evolution of Lava Fields at the Sundhnúkagígar Crater Row, Svartsengi Volcanic System, Iceland: A Multitemporal Analysis Based on Aerial Stereo Imagery

Subsidence in already emplaced lava can be caused by contraction as they cool, degassing and collapse. In this study, we present preliminary estimates of short-term volume change associated with the January (14 Jan, 07:58 UTC – 16 Jan, 01:08 UTC) and February (8 Feb, 06:03 UTC – 9 Feb, afternoon) 2024 eruptions at the Sundhnúkagígar crater row, Iceland. Surface elevation changes were derived from a series of multi-temporal pre- and post-eruptive Digital Elevation Models (DEMs) based on stereo imagery collected by UAV and manned aircraft, using a photogrammetric workflow in the Agisoft Metashape software. Volume changes were quantified from DEMs of Difference (DoDs) by integrating surface elevation changes over the mapped lava field, accounting for random, spatially correlated, and systematic errors. Positive and negative lava volume estimates represent the areal integration of surface uplift and subsidence respectively, as a result of the eruption, rather than strictly representing net mass addition or removal at a given location. Positive changes may reflect lava emplacement or internal redistribution of previously erupted material, whereas negative changes indicate thermal contraction, lava drainage, degassing, or collapse of the cooling lava surface. All reported volumes refer to changes integrated over the mapped lava field only. During the January eruption, rapid emplacement between 14 and 15 January resulted in a dominance of positive volume change, with 0.463 ± 0.0005 Mm³ of positive and −0.233 ± 0.0004 Mm³ of negative volume change. Between 15 and 17 January (approximately 48 h after eruption onset), volume changes were dominated by surface lowering, with −0.094 ± 0.0009 Mm³ negative versus 0.047 ± 0.0006 Mm³ positive volume change, reflecting contraction and internal redistribution as the dominating processes. From 17 January to 13 February, volume changes were minor, with 0.049 ± 0.001 Mm³ positive and −0.040 ± 0.001 Mm³ negative. For the February eruption, the analysis was constrained by the geological setting and the short repose time between eruptions, as rapid resurfacing of the lava field by subsequent eruptive activity limited the temporal persistence of measurable surface changes. On 8 February, comparison of DEMs acquired at 13:15 and 17:05 UTC shows a dominance of negative volume change, with −1.65 ± 0.01 Mm³ of negative versus 1.35 ± 0.01 Mm³ of positive volume change. Between 8 February (17:05 UTC) and 13 February, negative changes −2.07 ± 0.06 Mm³ exceeded positive changes 1.15 ± 0.04 Mm³.  Ongoing work aims to further refine these results by quantifying vertical surface subsidence rates to better characterize post-eruptive surface change behaviour.