Pre-eruptive conditions and triggering mechanism of the ~ 16 ka Santa Bárbara explosive eruption of Sete Cidades Volcano (São Miguel, Azores)

Biased Volcanic Hazard Assessment Due to Incomplete Eruption Records on Ocean Islands: An Example of Sete Cidades Volcano, Azores

“…Samples from SBF outcrops A and B, and Ponta do Cintrão outcrop C (7C01 to 7C06, see Figure 1 for location) overlap in all major elements, while sample 7C07 from outcrop D is distinguished on the basis of a higher SiO 2 content and lower CaO, MgO, and TiO 2 ( Figure 5 and Table 3). Recently published glass major elements from pumices clasts (with and without flow bands) of the SBF (Laeger et al, 2019) overlap with our samples 7C01-7C06. The observed spread is due to the focus of Laeger et al (2019) on the analysis of banded pumice clasts, which contain filaments of a less evolved composition, due to magma mixing/mingling.…”

“…Recently published glass major elements from pumices clasts (with and without flow bands) of the SBF (Laeger et al, 2019) overlap with our samples 7C01-7C06. The observed spread is due to the focus of Laeger et al (2019) on the analysis of banded pumice clasts, which contain filaments of a less evolved composition, due to magma mixing/mingling. Glass geochemistry data from Fogo and Furnas volcanoes (Johansson et al, 2017) are also shown for comparison and clearly reveal different compositions ( Figure 5).…”

“…They are variable in size and shape, ranging from single (sub-)millimetersized, scoriaceous fragments to MME-enriched areas up to 10 cm in large pumice clasts. The MME are microcrystalline and poorly vesicular, commonly showing diktytaxitic texture (Figures 4C,D) interpreted as evidence of quench crystallization (see Paredes-Mariño et al, 2017;Porreca et al, 2018;Laeger et al, 2019). In many pumice clasts the interior wall of large bubbles is dotted with angular MME.…”

“…The resulting fragments (MME) served as favorable sites for bubble nucleation and growth. The combined effect of thermodynamic instability and volatile exsolution, leading to increase in the magmatic pressure of the reservoir, acted as the eruption trigger and subsequent enhancement of the explosivity (see Paredes-Mariño et al, 2017;Porreca et al, 2018;Laeger et al, 2019).…”

“…Samples 7C01 through 7C06 (macroscopically homogeneous pumices, colored circles) form clusters owing to the genetic relationship; sample 7C07 (black circles) is compositionally different. Gray circles (banded pumices of the SBF, Laeger et al, 2019) show larger spread owing to magma mixing/mingling. Comparative samples from Fogo (Fogo A and Fogo 1563) and Furnas (Furnas 1630) volcanoes (Johansson et al, 2017).…”