Total grain-size distribution of four subplinian–Plinian tephras from Hekla volcano, Iceland: Implications for sedimentation dynamics and eruption source parameters

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.

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Reproducing pyroclastic density currents deposits of the AD 79 eruption of the Somma-Vesuvius volcano using the box-model approach

10.5194/se-2020-138 ◽

2020 ◽

Author(s):

Alessandro Tadini ◽

Andrea Bevilacqua ◽

Augusto Neri ◽

Raffaello Cioni ◽

Giovanni Biagioli ◽

...

Keyword(s):

Grain Size ◽

Size Distribution ◽

Grain Size Distribution ◽

Solid Particles ◽

Box Model ◽

Density Currents ◽

Input Parameters ◽

Vesuvius Volcano ◽

Total Grain Size Distribution ◽

Model Approach

Abstract. In this study we use PyBox, a new numerical implementation of the box-model approach, to reproduce pyroclastic density current (PDC) deposits from the Somma-Vesuvius volcano (Italy). Our simplified model assumes inertial flow front dynamics and mass deposition equations, and axisymmetric conditions inside circular sectors. Tephra volume and density, and Total Grain Size Distribution of EU3pf and EU4b/c, two well-studied PDC units from different phases of the AD 79 Pompeii eruption of Somma-Vesuvius (Italy) are used as input parameters. Such units correspond to the deposits from variably dilute, turbulent PDCs. We perform a quantitative comparison and uncertainty quantification of numerical model outputs with respect to the observed data of unit thickness, inundation areas, and grain size distribution as a function of the radial distance to the source. The simulations that we performed with PyBox were done considering: (i) polydisperse conditions, given by the total grain size distribution of the deposit, or monodisperse conditions, given by the mean Sauter diameter of the deposit; (ii) round-angle axisymmetrical collapses or divided in two circular sectors. We obtain a range of plausible initial volume concentrations of solid particles from 2.5 % to 6 %, depending on the unit and the circular sector. Optimal modelling results of flow extent and deposit thickness are reached on the EU4b/c unit in a polydisperse and sectorialized situation, indicating that using total grain size distribution and particle densities as close as possible to the real conditions significantly improve the performance of the PyBox code. The study findings suggest that the box model simplified approaches adopted have promising applications in constraining the plausible range of the input parameters of more computationally expensive models.

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FPLUME-1.0: An integrated volcanic plume model accounting for ash aggregation

Geoscientific Model Development Discussions ◽

10.5194/gmdd-8-8009-2015 ◽

2015 ◽

Vol 8 (9) ◽

pp. 8009-8062 ◽

Cited By ~ 2

Author(s):

A. Folch ◽

A. Costa ◽

G. Macedonio

Keyword(s):

Grain Size ◽

Size Distribution ◽

Grain Size Distribution ◽

Risk Mitigation ◽

Source Parameters ◽

Air Entrainment ◽

Phase Changes ◽

Column Height ◽

Volcanic Plume ◽

Eruption Column

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 cross-section averaged eruption column model based on the Buoyant Plume Theory (BPT). The model accounts for plume bent over 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 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).

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