A lesson from a magnificent eruption: year 2021, La Palma, Canary Islands

Abstract

AbstractThe exceptionally dynamic eruption of La Palma in 2021 represents a unique window to look deep into the lithosphere and the mechanics of an eruptive process. Magma ascent is powered by overpressure (dynamic/lithostatic pressure > 1), meaning that thermodynamically estimated pressure cannot be directly converted to depth. The problem is that the amount of overpressure is still unknown. We use classical rock mechanics and fluid flow laws to analyse geophysical and thermodynamic data, and infer high values of overpressure (> 1.5). A large pressure gradient between surface vents and magma reservoirs was established in the early days of eruption, which violently sucked magma from the deeper sources and greatly increased magma velocity that induced brittle behaviour of the lithosphere at depths of 40 km (deepest earthquake). Supersonic explosions and lava fountains hundreds of meters tall were the surface witness of the inferred high overpressure. The non-acknowledgement of significant overpressure in the volcanic process has two undesirable effects: (1) the lithospheric structure, magma ponding levels, volumes, and plumbing system may be misplaced by several kilometres; (2) it hampers the understanding of the mechanics of the whole process and, therefore, of a better knowledge of hazard and risk.