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Analogue experiments to show the effect of buoyancy on surface deformation amplitude above an inflating magma chamber

Alexandra Morand 1, Alison C. Rust1, Alain Burgisser2 , Juliet Biggs1

  • Affiliations: 1School of Earth Sciences, University of Bristol, Bristol, United Kingdom 2ISTerre, Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, Grenoble, France

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 126

  • Programme No: 3.15.31

  • Theme 3 > Session 15

Abstract

At active volcanoes, observed surface deformation results from the complex interaction between the magma and the host rock in the magmatic plumbing system. One common source of deformation is magmatic recharge, resulting in pressurisation of the magma chamber. All active systems, from the most basaltic to the most silicic magmatic composition, are subject to magma chamber replenishment. However, the variation of magma composition implies a variation of its density. In the case of silicic magma, the density can further be decreased by the gas exsolution that occurs at shallow depths. However, the majority of numerical models used to invert surface deformation focus on the effect of over-pressure and neglect the effect of the fluid buoyancy. We present here experiments investigating the effect of buoyancy on surface deformation. Surface deformation, the shear strain pattern and the chamber overpressure are measured throughout the injection of liquid at constant volumetric flux. Then, we use the McTigue (1987) model to predict the surface displacement from the measured overpressure in the chamber, and conversely. We show that predictions are about 7% below the observation when the liquid buoyancy is positive (ẟρ =-81 kg⋅m-3) and 9% above it when the liquid buoyancy is negative (ẟρ =-157 kg⋅m-3). Even if the effect of buoyancy is small, this highlights the possible error made on source overpressure when inverting surface deformation. This call to a careful consideration of the geological context in unrest period at active systems when volume change needs to be precisely estimated.