Unexpected large eruptions from buoyant magma bodies within viscoelastic crust

Abstract

Large volume effusive eruptions with relatively minor observed precursory signals are at odds with widely used models to interpret volcano deformation. Here we propose a new modelling framework that resolves this discrepancy by accounting for magma buoyancy, viscoelastic crustal properties, and sustained magma channels. At low magma accumulation rates, the stability of deep magma bodies is governed by the magma-host rock density contrast and the magma body thickness. During eruptions, inelastic processes including magma mush erosion and thermal effects, can form a sustained channel that supports magma flow, driven by the pressure difference between the magma body and surface vents. At failure onset, it may be difficult to forecast the final eruption volume; pressure in a magma body may drop well below the lithostatic load, create under-pressure and initiate a caldera collapse, despite only modest precursors.

The cascading origin of the 2018 Kīlauea eruption and implications for future forecasting

“…It may never be possible to determine if or when a particular event, such as a small magma injection, might trigger a sequence of cascading events and culminate in a large eruption. Volcanic systems are highly nonlinear and behave chaotically and unpredictably 83 – 85 ; however, small events can only trigger large events if the state of the volcanic system—such as the volume and pressure of eruptible magma and tectonic stress state—permits it 86 . An important focus of future work should thus be to better understand when systems may be primed such that a small trigger can result in a large eruption.…”

Fault inversion contributes to ground deformation above inflating igneous sills

“…Although inversion of geodetic data that capture ground deformation above intrusions can produce reasonable estimates of emplaced magma volumes by assuming the crust behaves elastically [e.g. Pritchard and Simons 2004;Sigmundsson et al 2020], the geometry of modelled intrusions is typically oversimplified compared to natural examples [Galland 2012]. Furthermore, field-, modelling-, and seismic-based studies demonstrate that viscoelastic and/or plastic deformation of the overburden may accompany and generate space for magma emplacement (e.g.…”

“…sills), particularly at shallow-levels, commonly causes uplift of the overlying rock and free surface [e.g. Biggs et al 2011;Castro et al 2016;Ebmeier et al 2018;Galland 2012; Galland and Scheibert 2013; Hansen and Cartwright 2006;Johnson and Pollard 1973;Pollard and Johnson 1973;Schmiedel et al 2017;Sigmundsson et al 2020;Trude et al 2003]. This overburden uplift generates space for, and thus accommodates, the intruded magma volume.…”

“…By assuming the host rock intruded by magma is elastic, we can analytically or numerically model ground deformation patterns recorded in active volcanic areas to infer intrusion geometries, locations, and dynamics [e.g. Biggs et al 2009;Cannavò et al 2015;Ebmeier et al 2018;Pritchard and Simons 2004;Sigmundsson et al 2020;Sparks et al 2012;van Wyk de Vries et al 2014]. However, numerous studies have demonstrated that host rock deformation can also involve viscoelastic and/or plastic (e.g.…”

“…faulting or compaction) processes [e.g. de Saint-Blanquat et al 2006;Guldstrand et al 2017;Magee et al 2013b;Magee et al 2019a;Magee et al 2017;Morgan et al 2008;Poppe et al 2019;Schmiedel et al 2019;Schmiedel et al 2017;Schofield et al 2012;Sigmundsson et al 2020;Wilson et al 2016]. These viscoelastic and plastic processes can partly generate space for emplacement and thereby reduce the size of forced folds generated by uplift [e.g.…”