Top–down control on eruptive style at Masaya volcano inferred from melt composition

Highly explosive Plinian eruptions of basaltic magma are enigmatic because low melt viscosities should inhibit such eruptive style. Masaya volcano, Nicaragua, is a persistently active system capable wide range styles, from open-conduit lava lake activity to voluminous eruptions; it thus an ideal natural laboratory constrain potential controls on eruption Here we report the major, trace, and volatile (CO2, H2O, S, Cl, F) element composition olivine-, plagioclase- clinopyroxene-hosted inclusions as well matrix glasses ejecta two tephra deposits—the 2.1 ka Triple Layer 1.8 Ticuantepe Lapilli—to test whether pre-eruptive contents degassing history may be linked All samples display relatively narrow largely overlapping basaltic–basaltic andesitic compositional (51.7±1.0 wt.% SiO2, 4.8±0.4 MgO) with similar trace signatures (e.g., Ce/Y=0.82±0.10, Ba/La=74±11). However, show systematic differences in contents, forming distinct groups mean H2O 0.6±0.2 (lava lake), 1.1±0.2 (Masaya Layer), 1.9±0.3 (Ticuantepe Lapilli). Together, these generate broad positive correlations between Cl concentrations, maximum values reaching 920 ppm, 1300 ppm 2.3 wt.%, respectively, which compared typical Central American arc magmas. Magma temperature estimates overlap average at 1115±30 °C, while saturation pressures low, mainly <100 MPa, although only record <31 MPa. These observations reiterate compositionally buffered state volcano's magmatic highlighted by previous work demonstrate that — regardless style all magmas undergo variable, but extensive, pressure. Geohygrometry, gas emissions, H2O/Ce–Ba/La systematics suggest initial, undegassed order 3.9–5.5 wt.%. Our results imply not culprit for events Masaya. Instead, propose vigorous supply modulated top–down manner produce whereby temporary sealing conduit instigate transition behavior. In this model, rapid ascent triggered when seal eventually breaks degassing-induced pressurization, yielding high degrees undercooling, microlite growth, dramatic increase viscosity potential. There thin line conditions