Reactivation of Cumbre Vieja volcano: Insights from a paired tephra glass and olivine crystal record

Cumbre Vieja volcano, on La Palma, Canary Islands, Spain, is an excellent natural laboratory for exploring igneous processes at the individual eruption scale (e.g. eruption precursors) and at the larger volcanic-magmatic-system scale (e.g. repose period) because of similar eruptive styles, volumes, and chemical compositions across historical eruptions [1]. To determine the timing and nature of perturbations during pre-eruptive magma assembly and how they may relate to variations in eruption repose and style, we analyze and model the chemical fingerprints of tephra glass and tephra-hosted crystals at the system scale (sampling of all eruptions since 1585) and at the eruption scale (daily sampling of the 2021 eruption). Broadly, the tephra-olivine record is remarkably similar across samples from the 2021, 1971, 1949, 1712, 1677, 1646, and 1585 eruptions: 86% of analyzed crystals (n=85) display a more evolved core composition (Fo80 ± 1.4), followed by a reversely zoned inner rim (Fo82 ± 0.9) and a steeply, normally zoned outer rim (as low as Fo73). Reversely and normally zoned crystal segments respectively show convex and concave Fo–Ni relationships, correspondingly indicating diffusion- and growth-dominated zoning mechanisms. At a finer temporal scale, we observe systematic chemical variability over the first four weeks of the 2021 eruption. At least three distinct chemical flavors can be distinguished thus far: 1) 19-Sept products are most primitive (tephra glass is 46.4 ± 0.3 wt.% SiO₂, containing olivine up to Fo87), 2) 22-Sept products are most evolved (tephra glass is 48.2 ± 0.7 wt.% SiO₂, containing Fo79 ± 0.8 olivine), and 3) products from 22-Sept to 15-Oct become more primitive over time (tephra glass averages 45.9 ± 0.5 wt.% SiO₂ and contains Fo82 ± 1.0 olivine).  Based on these zoning patterns and the application of diffusion chronometry to reverse zones, we propose that episodic injections of primitive melt from depth invade more evolved crystal mushes days to months before and during eruption. Fo-Ni relationships along olivine traverses and thermodynamic decompression models suggest that these crystals are then entrained in an ascending and evolving carrier liquid, crystallizing normally zoned overgrowth rims before eruption.  Our work suggests that primitive melt recharge is a critical mechanism for reactivating and sustaining activity at Cumbre Vieja, and we find that the timings of primitive injections (or recharge events) are not related to repose periods between eruptions. Rather, we propose that it is the timing and volume of primitive melt generation and extraction in the upper mantle that strongly influences volcano reactivation and may influence eruption style and duration.

[1] Longpré and Felpeto (2021), JVGR