Abstract
Abstract. Eruption source parameters (ESP) characterizing volcanic eruption plumes are crucial inputs for atmospheric tephra dispersal models, used for hazard assessment and risk mitigation. We present FPLUME-1.0, a steady-state 1-D (one-dimensional) cross-section-averaged eruption column model based on the buoyant plume theory (BPT). The model accounts for plume bending by wind, entrainment of ambient moisture, effects of water phase changes, particle fallout and re-entrainment, a new parameterization for the air entrainment coefficients and a model for wet aggregation of ash particles in the presence of liquid water or ice. In the occurrence of wet aggregation, the model predicts an effective grain size distribution depleted in fines with respect to that erupted at the vent. Given a wind profile, the model can be used to determine the column height from the eruption mass flow rate or vice versa. The ultimate goal is to improve ash cloud dispersal forecasts by better constraining the ESP (column height, eruption rate and vertical distribution of mass) and the effective particle grain size distribution resulting from eventual wet aggregation within the plume. As test cases we apply the model to the eruptive phase-B of the 4 April 1982 El Chichón volcano eruption (México) and the 6 May 2010 Eyjafjallajökull eruption phase (Iceland). The modular structure of the code facilitates the implementation in the future code versions of more quantitative ash aggregation parameterization as further observations and experiment data will be available for better constraining ash aggregation processes.
Highlights
Volcanic plumes (e.g. Sparks, 1997) are turbulent multiphase flows containing volcanic gas, entrained ambient air and moisture and tephra, consisting on both juvenile, crystal and lithic particles ranging from metre-sized blocks to micron-sized fine ash
Plume models range in complexity from 1-D integral models built upon the buoyant plume theory (BPT) of Morton et al (1956) to sophisticated multiphase Computational Fluid Dynamics (CFD) models (e.g. Suzuki et al, 2005; Esposti Ongaro et al, 2007; Suzuki and Koyaguchi, 2009; Herzog and Graf, 2010; Suzuki and Koyaguchi, 2013)
We present FPLUME-1.0, a steady-state 1-D crosssection-averaged plume model, which accounts for plume bending, entrainment of ambient moisture, effects of water phase changes on the energy budget, particle fallout and reentrainment by turbulent eddies, variable entrainment coefficients fitted from experiments and particle aggregation in presence of liquid water or ice that depends on plume dy
Summary
Volcanic plumes (e.g. Sparks, 1997) are turbulent multiphase flows containing volcanic gas, entrained ambient air and moisture and tephra, consisting on both juvenile (resulting from magma fragmentation), crystal and lithic (resulting from wall rock erosion) particles ranging from metre-sized blocks to micron-sized fine ash (diameter ≤ 63 μm). No plume model tries to predict the formation of ash aggregates in the eruptive column and how it affects the particle grain size distribution erupted at the vent. This can be explained in part because aggregation mechanisms are complex and not fully understood yet, theoretical models have been proposed for wet aggregation (Costa et al, 2010; Folch et al, 2010). The ultimate goal is to improve ash cloud forecasts by better constraining these relevant aspects of the source term In this manuscript, we present first the governing equations for the plume and aggregation models and apply the combined model to two test cases, the eruptive phase-B of the 1982 El Chichón volcano eruption (México) and the 6 May 2010 Eyjafjallajökull eruption phase (Iceland). Fig. 1) are the following (for the meaning of the used symbols see Tables 1 and 2):
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