Stability analysis of the Tajogaite volcano slopes and lahar hazards for reconstruction and land planning in the affected areas, La Palma, Canary Islands

Abstract

<p>Between September and December 2021, a Strombolian fissure eruption with phreatomagmatic pulses occurred in the Westside of the Island of La Palma (Canary Islands, Spain), giving rise to a volcanic edifice called Tajogaite and whose cone reached a height of 1121 m. above sea level (200 m above the pre-eruption topography) with a volume of 34 Mm<sup>3</sup> consisting of the alignment of 6 different craters of 557 meters in length, direction N130ºE.</p><p>In order to analyze the stability of the volcanic edifice and estimate the possible risk of lahars from pyroclastic materials lying on the slopes of the volcano and the surrounding areas, a series of investigations have been carried out consisting on historical series of rainfall data, thickness estimation  of the ashes deposits, laboratory tests on in situ samples, density, friction angle and cohesion of the soils determinations, as well as a geophysical survey using MASW seismic technique geotechnical properties of the slope layers in the first 30 meters of the volcano slopes. Based on these investigations, a stability analysis of the slopes of the volcanic edifice has been carried out considering different rainfall scenarios. Slope stability calculations were carried out using the Slide V6 program, from geotechnical data obtained in laboratory and from limit equilibrium back analysis conditions. Two main scenarios were analyzed including the most probable and the least probable rainfall, corresponding to the return period of  10 years and 50 years respectably.</p><p>Risk of lahars had been indentify as possible for the 50 years return period, as a consequence of both the instability of the cone slopes and the surrounding ash deposits, associated with very intense rains. These data has been incorporated to the land planning of reconstruction development, particularly the adoption of preventive measures in case of intense rainfall, as well as for the design of drainage infrastructures.</p>

Are eruptions reliable precursors to marine volcano collapses?

“…It was not until the recent magmatic unrest at Cumbre Vieja volcano in 2021 that concerns about the possibility of volcano collapse at La Palma reawoke and sparked interest in the scientific community (González, 2022) and the public. The number of scientific publications (Periáñez, 2021;Fernández et al, 2022;González, 2022;Romero et al, 2022) and conference abstracts (Geersen et al, 2023;Miranda-Hardisson et al, 2023;Rodríguez-Losada et al, 2023;Walter et al, 2023) addressing flank instability or collapse at La Palma increased during the 19 months following the eruption. In contrast, only three references were published during the equivalent preceding period (Abadie et al, 2020;Arnaud et al, 2021;Fernández et al, 2021).…”