DOI: 10.18715/ipgp.2023.lj5wjhw6
title: Codes for calculating the degassing parameters in the reservoir at Shishaldin volcano

description: Three sets of functions written in Matlab are in this folder. The functions have been written by S. Vergniolle, Institut de physique de Paris, France (June 2023) for the submission of a paper on volcanology, and more specifically on the 1999 eruption at Shishaldin (Alaska) for JGR. The title is : « Origin of basaltic Subplinian eruption at Shishaldin volcano (Alaska): A vigourously degassing magma reservoir hosting small bubbles », S. VergniolleThe first set of codes are calculating the magma viscosity from the Giordano’s model (2008 using a code called grdmodel08_SV.m) and the magma composition given in appendix of Rasmussen et al., 2018, found at https://doi.org/10.1016/j.epsl.2018.01.001. My code, which is using the composition of each melt inclusion to calculate the magma viscosity, is called Prog_SV_Visco_Giordano_Shishaldin_JGR.m. The data and results can be found in a matlab file called, visco_Giordano_Shish.mat.The second set of functions analysed the foam height measured in the laboratory experiments. The function Foam_LabExp.m analyses the results from the foam drainage in the laboratory experiments and find the drainage velocity for three values of the initial gas flux. This function gives all the experimental values on the foam top and base, hence on the foam height. This drainage velocity (Kozeny’s equation) gives an estimate on the gas volume fraction in the foam.The third set of functions calculates the errors made on the estimates on the gas volume fraction by selecting each entry parameter within a Gaussian distribution of values. The main function is called monte_carlo_FoamDrainage.m and contains the calculations of all the Gaussian distributions. This function is calling two other functions FoamDrainage.m and EpsilonRatio.m. The function FoamDrainage.m estimates the ratio of gas volume fraction, existing in the Kozeny’s equation, from the measured value of the drainage velocity (Kozeny velocity). The function EpsilonRatio.m gives the value of the gas volume fraction in the foam from the ratio of gas volume fractions. The function randu.m is useful to produce an uniform distribution for some parameters when a Gaussian distribution is not chosen. The fourth set of functions is used to estimate the parameters of the degassing reservoir, bubble diameter, reservoir radius, geometrical coefficient, the diameter of the bubble clusters and their errors. The errors are calculated by selecting each parameter within a Gaussian distribution of values and estimating the characteristics of the degassing parameter. The Gaussian distribution of entry parameters is generated by the function monte_carlo_DegRes_JGR.m. This function calls the direct function FoamStab_Shish_JGR.m, which calculates the characteristics of the degassing parameters for each set of parameter selection. The results of the model and the entry parameters are saved into 2 matlab files, MonteCarlo_ReservoirShish_Tremor.mat for a gas flux based on the tremor increase and MonteCarlo_ReservoirShish_SurfAct.mat for a gas flux based on surface activity and can be used to draw the figure.Using the command « help » with the name of the function gives the main informations on the function. The names of the variables used are commented with % after or before.