Antonella Longo

Heterogeneous large total CO2 abundance in the shallow magmatic system of Kilauea volcano, Hawaii

[1] Due to its very low solubility in silicate melts, CO 2 concentrations in melt inclusions (MIs) within crystals are commonly orders of magnitude less than the total concentration in the multiphase magma, strongly limiting the possibility to constrain CO 2 abundance based on the dissolved quantities. Here we develop a statistical method to process MI data, which allows analytical uncertainties to be taken into account together with the peculiar features of the local saturation surface. The method developed leads to retrieve total H 2 O and CO 2 concentrations in magma as well as the gas phase abundance at the time of magma crystallization. Application to a set of 29 high-resolution secondary ion mass spectrometry (SIMS) MI data from a single specimen of the 1842-1844 eruption of Kilauea, Hawaii, reveals the existence of heterogeneous total CO 2 abundance, and of at least 2-6 wt % total CO 2 in some magma batches, two orders of magnitude higher than the dissolved amounts and 30-50 times more abundant than the corresponding total H 2 O content. Heterogeneous total volatile concentrations are interpreted as due to a combination of degassing and gas flushing in magma subject to convective motion at shallow depth where P 1 wt % is likely to characterize the >30 km deep magma, not represented in the analyzed inclusions, from which a CO 2 -rich gas phase exsolves and decouples from the liquid.

Timescales of mingling in shallow magmatic reservoirs

Abstract Arrival of magma from depth into shallow reservoirs has been documented as one of the possible processes leading to eruption. Magma intruding and rising to the surface interacts with the already emplaced, degassed magmas residing at shallower depths, leaving chemical signatures in the erupted products. We performed two-dimensional numerical simulations of the arrival of gas-rich magmas into shallow reservoirs. We solve the fluid dynamics for the two interacting magmas, evaluating the space–time evolution of the physical properties of the mixture. Convection and mingling develop quickly into the chamber and feeding conduit/dyke, leading on longer timescales to a density stratification with the lighter, gas-richer magma, mixed with different proportions of the resident magma, rising to the top of the chamber due to buoyancy. Over timescales of hours, the magmas in the reservoir appear to have mingled throughout, and convective patterns become harder to identify. Our simulations have been performed changing the geometry of the shallow reservoir and the gas content of the initial end-member magmas. Horizontally elongated magma chambers, as well as higher density contrasts between the two magmas, cause faster ascent velocities and also increase the mixing efficiency. Supplementary material: Videos showing the evolution of magma composition with time in the shallow chamber for simulations 1–4 are available at www.geolsoc.org.uk/SUP18819

Signature of magmatic processes in strainmeter records at Campi Flegrei (Italy)

Volcanic unrest at Campi Flegrei caldera, Southern Italy, is characterized by episodes of ground deformation, seismicity and enhanced fumarolic activity; whether its origin is purely hydrothermal or magmatic is highly debated. We have identified ground deformation patterns in strainmeter records from a heightened unrest period in late 2006, closely resembling synthetic signals from numerical simulations of shallow magma chamber replenishment and mixing. Together with other recent findings, our results depict a situation whereby periodic arrivals of deep magma feed a shallow intrusion at 3-4 km depth. These results suggest that the analysis of strainmeter records, coupled with advanced numerical simulations of magma dynamics, could lead to new approaches in imaging subsurface dynamic processes in volcanic areas.

Modeling Free Surface Flows Using Stabilized Finite Element Method

This work aims to develop a numerical wave tank for viscous and inviscid flows. The Navier-Stokes equations are solved by time-discontinuous stabilized space-time finite element method. The numerical scheme tracks the free surface location using fluid velocity. A segregated algorithm is proposed to iteratively couple the fluid flow and mesh deformation problems. The numerical scheme and the developed computer code are validated over three free surface problems: solitary wave propagation, the collision between two counter moving waves, and wave damping in a viscous fluid. The benchmark tests demonstrate that the numerical approach is effective and an attractive tool for simulating viscous and inviscid free surface flows.

Computation of compressible and incompressible flows with a space–time stabilized finite element method

Abstract This paper presents the numerical results of compressible and incompressible flow problems through a unified approach based on a stabilized space–time finite element method. The numerical approach is continuous in space and discontinuous in time. The proposed method starts by the use of a stabilized space–time variational formulation, which allows the use of the same order interpolation functions for all solution variables. The numerical technique is tested through comparison with standard compressible and incompressible flow benchmarks. Compressible flow cases include 1D and 2D shock problems. Incompressible flow cases include lid-driven cavity flow and flow over a backward-facing step computed over a range of R e numbers. The results demonstrate high stability and accuracy of the numerical technique over a wide range of flow regimes, suggesting straightforward extension to many flow cases not yet investigated.

Optimization and homotopy methods for the Gibbs free energy of simple magmatic mixtures

In this paper we consider a mathematical model for magmatic mixtures based on the Gibbs free energy. Different reformulations of the problem are presented and some theoretical results about the existence and number of solutions are derived. Finally, two homotopy methods and a global optimization one are introduced and computationally tested. One of the homotopy methods returns a single solution of the problem, while the other is able to return multiple solutions (often all of them). The global optimization method is a branch-and-reduce one with a theoretical guarantee of detecting all the solutions, although some numerical difficulties, resulting in a loss of a few of them, may have to be faced.

A Numerical Code for the Simulation of Magma-Rocks Dynamics

We present a numerical code for the simulation of the dynamics of compressible to incompressible, multicomponent flows, based on the finite element algorithm by Hauke & Hughes (1998). Balance equations for mass, momentum, energy and composition are solved with space-time Galerkin least-squares and discontinuity-capturing stabilizing techniques. The code is used to study the dynamics of convection and mixing in magmatic systems such as replenishment of magma chambers and volcanic conduits, and it reveals the occurrence of previously not described processes. The fluid-structure interaction of fully coupled magma-rock dynamics is being implemented by using the deforming-spatial domain method by Tezduyar (2006), that intrinsecally includes moving meshes. [ DOI : 10.1685/CSC09237] About DOI