Conditions for detection of ground deformation induced by conduit flow and evolution

Abstract

[1] At mature andesitic volcanoes, magma can reach the surface through the same path for several eruptions thus forming a volcanic conduit. Because of degassing, cooling, and crystallization, magma viscosity increase in the upper part of the conduit may induce the formation of a viscous plug. We conducted numerical simulations to quantify the deformation field caused by this plug emplacement and evolution. Stress continuity between Newtonian magma flow and elastic crust is considered. Plug emplacement causes a ground inflation correlated to a decrease of the magma discharge rate. A parametric study shows that surface displacements depend on three dimensionless numbers: the conduit aspect ratio (radius/length), the length ratio between the plug and the conduit, and the viscosity contrast between the plug and the magma column. Larger displacements are obtained for high-viscosity plugs emplaced in large aspect ratio conduits. We find that only tiltmeters or GPS located close to the vent (a few hundred meters) might record the plug emplacement. At immediate proximity of the vent, plug emplacement might even dominate the deformation signal over dome growth or magma reservoir pressurization effects. For given plug thicknesses and viscosity profiles, our model explains well the amplitude of tilt variations (from 1 to 25 mrad) measured at Montserrat and Mt. St. Helens. We also demonstrate that at Montserrat, even if most of the tilt signal is due to shear stress induced by magma flow, pressurization beneath the plug accounts for 20% of the signal.

Characterization of open and closed volcanic systems in Indonesia and Mexico using InSAR time series

“…Edifice‐wide inflation can only occur at closed volcanic systems where the reservoir pressurization results in significant long‐term ground uplift (months prior to eruption), in contrast to short‐term deformation (days to weeks prior to eruption). At open volcanic systems, magma rises through the established conduit, resulting in limited pressurization of the reservoir and the absence of edifice‐wide long‐term inflation [ Albino et al , ]. Our use of these terms is in contrast to petrological studies in which they refer to the part of the volcanic system between a deep magma source and a shallower reservoir [e.g., Zellmer et al ., ; White et al ., ].…”

“…When magma is supplied to the shallow reservoir, the volcano enters a period of activity characterized by degassing at the vent or growth of a lava dome, reflecting the presence of a permanent or semipermanent conduit [e.g., Wallace , ] (Figure , stage b). In such settings, magma can rise toward the surface without pressurizing the reservoir, explaining the absence of inflation [ Albino et al , ]. Presumably, the system is permanently in a state of near eruption in which eruptions may be triggered by small intrusions into the reservoir, gradual overpressurization of the conduit, or destabilization of the lava dome (Figure , stage c) [ Gottsmann et al ., ].…”

Effects of gas escape and crystallization on the complexity of conduit flow dynamics during lava dome eruptions

“…These variations of overpressure inside the conduit may be detected from geodetic observations such as tilt and GPS measurements. In particular, the measurements around the summit area would be useful for detecting change in the localized overpressure at the shallower level [e.g., Widiwijayanti et al , 2005; Albino et al , 2011]. …”

Topography and Tilt at Volcanoes

“…For tilt produced by conduit pressure or shear stress, in the absence of an available analytical solution, we obtain θ r from 2D axisymmetric models using a constant slope, based on the average dip angle radially away from the summit for each edifice. This mimics the approach of Albino et al (2011), who represent topography using only this first-order approximation. The computation of this average dip angle, and a full description of these 2D axisymmetric models, is included in the Supplementary Material, Section S1.…”