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

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

Modelled dispersion parameters	Explored range	Tambora-F2^a
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	2.8^c
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

^aThese scenarios are the combination of meteorological and volcanological parameters that best reproduce the observed deposits of the Tambora F2 Plinian fall layer
^bA density value of 2650 kg/m³ (trachyandesite) was used to convert into DRE volume
^cShort eruption duration interpreted to be the result of high magma discharge rate (Sigurdsson and Carey, 1989)
^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)
^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
^fThis density value was used to convert deposit thickness, in mass loading and to calculate total tephra volume
^gReliability of the best-fit results are shown by the Aida indices (Aida, 1978) for the geometric average (K) and geometric standard deviation (k)

ISSN: 2191-5040