Abstract
AbstractMagma decompression rate is one of the most important parameters in controlling eruption dynamics. One way to determine decompression rate is by fitting a volatile elements diffusion profile to a concentration gradient in crystal‐hosted embayments. Previous studies have used a variety of diffusion models, limiting the possibility for inter‐study comparison. Here, we introduce EMBayment‐Estimated Rates (EMBER), a standalone versatile tool that models diffusion of volatile elements along melt embayments. Our model relies on the pdepe function of MATLAB to calculate diffusion profiles of H2O, CO2, and S through the finite difference method. EMBER uses a grid search seeking out the best fits for decompression rates, initial dissolved concentration of each studied volatile and initial exsolved gas content, while setting three constants: temperature along the ascent and pressure at the beginning and end of the ascent. Our model can compute the rate for basaltic, intermediate, and rhyolitic compositions. We applied EMBER to previous studies to evaluate and validate our model. We then reprocessed “homogeneously” the raw data from the literature for a comparison. In other words, the same protocol was used for each diffusion profiles removing the literature‐specific strategies used to constrain unknown parameters. With this comparison, we found a statistically significant positive correlation between maximum magma decompression rates and explosivity of the related eruption. EMBER is expected to help increase the number of volatile diffusion in embayments studies aiming at constraining magma decompression and ascent rates and to facilitate inter‐study comparisons.
Highlights
Magma ascent rate is a fundamental physical parameter in determining the behavior of a volcanic eruption
The Graphical User Interface (GUI) is separated in two parts: the input section, dedicated to generating the grid search and decompression conditions, and the results section dedicated to displaying the results once calculation is terminated (Part 2, panels a, b; Fig. 2)
We present EMBER, a user-friendly GUI program that calculates decompression rates from H2O, CO2 and S concentration profiles along embayments of basaltic to rhyolitic compositions
Summary
Magma ascent rate is a fundamental physical parameter in determining the behavior of a volcanic eruption. Knowing the diffusion coefficient of the species of interest, one can derive an estimate of the magma ascent rate for these eruptions [e.g., Demouchy and Mackwell., 2006; Sparks et al, 2006; Rutherford., 2008] Another method, based on nucleation theory, links the bubble number density in erupted products (measurable from 2D and 3D observations) to the magma decompression rate [Toramaru., 1989, 1995, 2006]. This difference in chemical potential leads to a concentration gradient and to diffusive transport of volatile species from the interior to the mouth of the embayment resulting in a diffusion profile If such a profile is preserved in natural samples, it can be inverted to derive a decompression rate assuming that the elongated tubular shape of the embayment and the relative impermeability of the host crystal led to unidirectional (1D) diffusion and prevented any advective melt motion in the embayment. A numerical model adapted to a wide range of magma compositions is needed to generate multiple diffusion profiles with known parameters and find the synthetic profile which most closely reproduces the measurement
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