Reconstruction of a phreatic eruption on 27 September 2014 at Ontake volcano, central Japan, based on proximal pyroclastic density current and fallout deposits

Earth, Planets and Space

Table 1 Estimated volume and mass of Ontake eruption on 27 September 2014

Event date	Method^a	Case^b	Volume^c (×10⁶ m³)	Mass (×10⁹ kg)
Fallout deposit and proximal pyroclastic density current deposit
27 September	a	1	0.77–1.1 (0.31–0.46)	0.77–1.1
27 September	a	2	0.67–1.3 (0.27–0.52)	0.67–1.3
27 September	b	1	0.70–1.2 (0.28–0.49)	0.70–1.2
27 September	b	2	0.77–1.4 (0.31–0.54)	0.77–1.4
27 September	c	1	0.63–1.4 (0.25–0.56)	0.63–1.4
27 September	c	2	0.74–1.2 (0.30–0.48)	0.74–1.2

Event date	Method^d		Volume^c (×10⁶ m³)	Mass (×10⁹ kg)
Pyroclastic density current deposit in S and W slopes
27 September	d	Max	0.072 (0.029)	0.072
27 September	d	Min	0.036 (0.015)	0.036
27 September	e	Max	0.03 (0.01)	0.03
27 September	e	Min	0.005 (0.002)	0.005

^aMethod for fallout: (a) integrating log[mass per unit area (kg/m²)] versus log[area (m²)], (b) exponential fitting for log[thickness (m)] versus [area (m²)]^1/2, (c) Weibull fitting for log[mass per unit area (kg/m²)] versus [area (m²)]^1/2
^bCase: Cases 1 and 2 represent calculations that include and exclude proximal isopach data, respectively
^cVolume in parentheses is DRE (dense rock equivalence) value
^dMethod for PDC: (d) 2 cm and 1 cm in average thickness were assumed for maximum and minimum cases, respectively, (e) Scaling analyses using a depth-averaged gravity flow model