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Table 5 The explored range and best-fit input parameters modelled dispersion of the Tambora-F2 fall deposit using FALL3D

From: Probabilistic Volcanic Ash Hazard Analysis (PVAHA) I: development of the VAPAH tool for emulating multi-scale volcanic ash fall analysis

Modelled dispersion parameters Explored range Tambora-F2a
Tephra mass (1012 kg) 0.1-1.5 1.2
Tephra volume (km3) 0.1-1.5 1.0
Tephra volume DRE (km3)b 0.1-1.5 0.4
Duration (hours) 0-2.8 2.8c
MER (108 kg/s) 1-10 1.3
TGSD-maxima (in Ø units) 0-8 8
Column height (km) 30-43 30
Suzuki coefficients A (−)d 1-4 4
Density of aggregates (kg/m3)e 100-600 300
Diameter of aggregates (in Ø units)e 2-3 2.5
Average deposit density (kg/m3)f Assumed 1100
Aida Indices K/k (−)g Calculated 0.98/1.29
  1. aThese scenarios are the combination of meteorological and volcanological parameters that best reproduce the observed deposits of the Tambora F2 Plinian fall layer
  2. bA density value of 2650 kg/m3 (trachyandesite) was used to convert into DRE volume
  3. cShort eruption duration interpreted to be the result of high magma discharge rate (Sigurdsson and Carey, 1989)
  4. dThe eruption source is described in a purely empirical way in order to reproduce the optimal geometrical shape of the deposits using the Suzuki distribution (in this instance the eruption column acts as a vertical line source)
  5. eAggregation is accounted for using a model similar to that of Cornell et al. (1983) assuming that 50 % of the 63–44 μm (4–4.5Ø) ash, 75 % of the 44–31 μm (4.5-5Ø) ash and 95 % of the sub-31 μm (<5Ø) ash fell as aggregated particles
  6. fThis density value was used to convert deposit thickness, in mass loading and to calculate total tephra volume
  7. gReliability of the best-fit results are shown by the Aida indices (Aida, 1978) for the geometric average (K) and geometric standard deviation (k)