Uas-Based Multitemporal Remote Sensing Of The 2021 Tajogaite Eruption (La Palma Island, Spain)

Volcanic eruptions shape the landscape. While some events may locally cause mass loss following e.g. gravitational failure, explosive excavation or collapse following magma withdrawal, constructive processes are by far the most abundant: volcanic deposits can create new land, cover the landscape and create new cones around the vents.

The 2021 Tajogaite eruption (La Palma, Spain, 19 September - 13 December 2021) produced a cinder cone that was initially (January 2022) 187 m taller than the pre-eruption topography. The cone is likely welded in some parts but is covered by unconsolidated deposits. This volcanic edifice offered a unique opportunity to monitor its shape evolution after the eruption.

To this end, we are using six datasets of UAS surveys with optical cameras between March 2022 and July 2024. Structure-from-Motion (SfM) photogrammetry allowed us to produce high-resolution (up to 0.2 m/pixel) DSMs (Digital Surface Models) and orthophotomosaics (up to 0.1 m/pixel). This unprecedented and unique dataset, moreover, allows us to constrain these changes at high temporal and spatial resolution. Over the course of our observation period, our conservative approach reveals that the cone "shrank" by more than 10 m in height and lost almost 1*10⁶ m³ of volume. The rate of these changes was highest at the beginning (6,2 cm height loss per day between 28 January and 21 March 2022) and declined exponentially. Towards the end of the observation period reported here (7 August 2023 to 18 July 2024), the average rate was 0,3 cm per day. These quantifications showed that surface processes (wind, rain) accounted for approximately 10% of volume loss, with approximately 75*10³ m³ being redeposited at the base of the cone. Satellite data show that there is no significant westward movement of the entire cone. Accordingly, most of the observed shape change of the Tajogaite cone is due to intrinsic processes, such as 1) decrease of magmatic pressure, 2) volume loss due to outgassing and cooling and 3) compaction of tephra deposits. The contribution of these individual processes will be discussed.