Linking surface deformation to thermal and mechanical magma chamber processes

Abstract

Surface deformation at active volcanoes reflects a wide variety of magmatic and crustal processes, and the typical kinematic models employed to interpret these geodetic data are highly nonunique. This work presents a new model for surface deformation linked to magma chamber evolution in response to magma injection, eruptions, cooling and crystallization, volatile exsolution, and viscoelastic deformation of the crust. The model is applied to investigate surface displacements during 1) magma chamber crystallization and second boiling without magma injection; 2) a single episode of magma injection to the chamber; and 3) steady magma injection over multiple eruption cycles. Results indicate that the magnitude of surface velocities associated with crystallization and second boiling should not exceed ∼1 mm/yr unless the magma cooling rate is substantially elevated above normal conductive cooling rates. The surface response to an episode of magma injection depends on magma compressibility and how the timescale of injection compares to the timescale for viscous relaxation. When the injection time is short compared to the relaxation time, and when the magma is equally or less compressible compared to the wall rocks, post-injection deflation can occur without any volume contraction of the chamber. For more compressible magmas, or longer-duration injections, inflation continues over a protracted time following injection. Over multiple eruption cycles, uplift accumulates when more magma is added to the chamber than lost by eruptions; because both the eruption frequency and uplift rate are sensitive to the time-averaged magma supply and chamber volume, geologic data from the eruptive record can be integrated with geodetic data to place tighter constraints on the size and state of subvolcanic magma systems.