The size range of bubbles that produce ash during explosive volcanic eruptions

Genareau, Kimberly; Mulukutla, Gopal K; Proussevitch, Alexander A; Durant, Adam J; Rose, William I; Sahagian, Dork L

doi:10.1186/2191-5040-2-4

Table 1 Measured characteristics of complex ash particles

From: The size range of bubbles that produce ash during explosive volcanic eruptions

Eruption	Sample	Distance from source (km)	D_MAX (μm)	Grain A.R.	No. of Bubbles/Particles	Mode 1*				Mode 2***			CVF^†	χ²
Eruption	Sample	Distance from source (km)	D_MAX (μm)	Grain A.R.	No. of Bubbles/Particles	Mean (μ)**	Sigma (σ)**	TND (10¹² m^-3)	VF	Mean (μ)**	Sigma (σ)**	TND (10¹² m^-3)
MSH 1980	DZ20-21	157	304	1.3	281/4	−14.53	0.81	539.93	0.544	N/A	N/A	0.077	0.873	0.53
	DZ21-9	250	208	1.6	364/5	−14.42	0.81	415.05	0.325	−10.87	1.27	N/A	0.812	0.22
	BATE7	632	74	1.5	152/10	−14.66	0.88	530.19	0.603	N/A	N/A	N/A	0.890	0.22
	BATE12	634	89	1.7	167/15	−14.18	0.94	130.25	0.620	−10.13	0.54	0.094	0.894	0.28
	BATE17	632	74	2.2	80/4	−14.99	0.96	762.53	0.476	−12.01	0.55	5.590	0.854	0.11
	BATE24	625	71	1.9	99/9	−15.09	1.20	246.11	0.498	N/A	N/A	N/A	0.860	0.31
FUEGO 1974	VF74-25	5	241	1.5	144/16	−13.49	0.74	64.85	0.469	−11.06	0.74	0.64	0.780	0.37
	VF74-4	8	140	1.6	63/15	−14.03	1.06	49.54	0.620	−13.77	0.88	109	0.842	0.06
	VF74-20	10	1805	1.3	135/11	N/A	N/A	N/A	N/A	−12.37	0.64	29.8	N/A	0.16
	VF74-21	10	1336	1.3	76/10	N/A	N/A	N/A	N/A	−12.56	0.67	6.21	N/A	0.19
	VF74-68	16	1303	1.3	324/10	−12.82	0.85	8.86	0.301	−10.00	N/A	N/A	0.710	0.21
	VF74-49	18	896	1.3	293/10	−12.97	1.02	5.34	0.415	N/A	N/A	N/A	0.757	0.22
	VF74-30	32	898	1.4	96/16	−13.01	0.68	27.12	0.276	N/A	N/A	N/A	0.670	0.13
	VF74-42	50	452	1.1	293/10	−13.84	1.03	38.01	0.423	N/A	N/A	N/A	0.761	0.20
	VF74-40	55	194	1.3	145/13	−14.46	1.19	60.43	0.423	N/A	N/A	N/A	0.761	0.26
	VF74-46	57	490	1.4	134/11	−13.49	0.73	67.81	0.234	N/A	N/A	N/A	0.682	0.55

* Log-normal distribution type.
** Log₁₀(m³) units.
*** All distribution parameters for mode # 2 (larger bubble sub-population) are for qualitative purposes only.
^† Cumulative void fraction (CVF) is calculated from the void fraction (VF) of the melt resulting from the smaller bubble population (mode #1) plus the literature values of total crystal-free vesicularity, hypothesized to dominantly reflect the void fraction resulting from the larger bubble population (mode #2). For the MSH samples a value of 0.722 was used (Klug and Cashman 1994) and for the Fuego samples, a value of 0.585 was used (Rose et al. 2008).
Summary of complex ash particle dimensions and bubble size distribution data for Volcán Fuego 1974 and Mount St. Helens 1980 eruptions, showing the distance from source of each sample, the average maximum particle diameter (D_MAX), the average aspect ratio (A.R.) of the ash grains, the number of bubbles measured relative to the number of ash particles examined, the sizes of the two bubble modes, and the total number density (TND) of bubbles. Data for mode 2 is presented for comparative purposes only, as the number of measurable larger bubbles was so much smaller than the number of smaller bubbles that the calculated values cannot be considered statistically reliable. The void fraction (VF) of magma is reliable for the smaller bubble population (mode 1). Using this value, in combination with measured crystal-free vesicularities from the literature, the cumulative void fraction (CVF) is calculated, and represents the void fraction of the magma at the point of fragmentation of the magmatic foam. χ2 is the function fit minimization parameter that must be less than 1.5 to achieve a minimum level of significance.

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