Confort 15 (Conflow improvement)

By Silvia Campagnola1, Claudia Romano1, Larry G Mastin2, Alessandro Vona1

1. Roma Tre University 2. U.S. Geological Survey--Cascades Volcano Observatory

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Abstract

We present an updated version of the Conflow model, an open-source numerical model for flow in eruptive conduits during steady-state pyroclastic eruptions (Mastin and Ghiorso, 2000). 

In the Confort 15 program, several updates were considered:

  1. The rheological parameters of the model are improved, by inserting the most recent equations describing both the liquid viscosity and crystal-bearing rheology. The earliest models for predicting the viscosity of geologically-relevant silicate melts, including the one applied in the original Conflow model, adopted a strictly Arrhenian temperature dependence and were based on a relatively small number of high-T experiments (for melts containing less than 70 wt.% SiO2). Here, we insert the most recent generation of multicomponent chemical models for predicting the viscosity of naturally-occurring silicate melts, which adopt a non-Arrhenian T-dependence. With this improvement, Confort 15 can be applied to all natural magma compositions, including the peralkaline melts excluded in the original version.
  2. The evaluation of crystal-bearing rheology is improved by computing the effect of crystal shape on the rheology of natural magmatic suspensions and expanding the crystal content range in which it could originally be modeled (the original Conflow model is applicable to magmatic mixtures with up to 30 vol% crystal content). This improvement allows investigation of the effect of suspended crystals on magma viscosity, which can increase the viscosity through both hydrodynamic and mechanical interaction among solid particles.
  3. Volcanological studies of the juvenile products (crystal and vesicle size distribution) of the investigated eruption are directly incorporated into the modeling procedure. Textural-derived Vesicle Number Densities are used to estimate, through Toramaru (1995, 2006) equations, maximum decompression rates experienced during ascent.
  4. Both degassing under equilibrium and disequilibrium conditions are considered. The effect of different fragmentation criteria on the conduit flow analyses are evaluated, in terms of maximum volume fraction criterion (“porosity criterion”, e.g. Sparks, 1978; Wilson et al., 1978; Houghton and Wilson, 1989), brittle fragmentation criterion (Dingwell and Webb, 1989; Papale, 1999), and, wherever degassing under disequilibrium conditions is considered, overpressure fragmentation criterion (Alidibirov, 1994; Spieler et al., 2004). 

Also a PDF manual could be downloaded

Cite this work

Researchers should cite this work as follows:

  • Silvia Campagnola; Claudia Romano; Larry G Mastin; Alessandro Vona (2016), "Confort 15 (Conflow improvement)," https://vhub.org/resources/3743.

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