Lahar characteristics as a function of triggering mechanism at a seasonally snow-clad volcano: contrasting lahars following the 2014 phreatic eruption of Ontake Volcano, Japan

Kataoka, Kyoko S.; Matsumoto, Takane; Saito, Takeshi; Kawashima, Katsuhisa; Nagahashi, Yoshitaka; Iyobe, Tsutomu; Sasaki, Akihiko; Suzuki, Keisuke

doi:10.1186/s40623-018-0873-x

Earth, Planets and Space

Table 3 Grainsize characteristics of ashfall, October rain-triggered lahar and April ROS-triggered lahar deposits, and pre-eruptive fluvial deposits

From: Lahar characteristics as a function of triggering mechanism at a seasonally snow-clad volcano: contrasting lahars following the 2014 phreatic eruption of Ontake Volcano, Japan

Sample name	Distance from source	River system	Position of sampling	Loc.	Lat. (N)	Long. (E)	Gravel (wt%)	Sand (wt%)	Silt (wt%)¹
Pre-eruptive fluvial deposits
On-7	10.6	Nigorigawa/Otakigawa	Pre-eruptive	950	35.803	137.482	3.6	94.9	1.5
On-11	10.6	Nigorigawa/Otakigawa	Pre-eruptive	1207	35.803	137.482	0.2	96.1	3.7
On-14	10.6	Nigorigawa/Otakigawa	Pre-eruptive	1208	35.803	137.482	0.0	96.5	3.6
On-27	4.4	Akagawa	Pre-eruptive	1191	35.853	137.464	79.3	18.3	2.4
On-33	4.1	Akagawa	Pre-eruptive	1192	35.856	137.465	39.8	58.4	1.9
On-39	4.2	Akagawa	Pre-eruptive	S114	35.854	137.464	9.1	86.6	4.4
On-40	4.2	Akagawa	Pre-mudflow event, sand layer	S114	35.854	137.464	0.0	76.4	23.6
On-43	3.0	Akagawa (upstream)	Pre-eruptive	S119	35.864	137.464	47.4	49.6	2.9
October 2014 rain-triggered lahar (cohesive debris flow) deposits
On-13	10.6	Nigorigawa/Otakigawa	Middle-top	1207	35.803	137.482	21.1	52.9	15.6
On-18	4.8	Akagawa	Entire	1199	35.849	137.466	60.4	23.7	10.1
On-29	4.4	Akagawa	Bottom	1191	35.853	137.464	54.1	24.5	13.3
On-30	4.4	Akagawa	Top	1191	35.853	137.464	43.4	30.2	16.1
On-31	4.4	Akagawa	Middle	1191	35.853	137.464	38.6	34.0	16.6
On-34	4.1	Akagawa	Bottom	1192	35.856	137.465	36.6	36.7	15.9
On-35	4.1	Akagawa	Middle	1192	35.856	137.465	44.5	31.4	14.2
On-36	4.1	Akagawa	Top	1192	35.856	137.465	53.1	26.9	12.0
On-41	4.2	Akagawa	Top	S114	35.854	137.464	46.8	28.0	14.9
On-42	4.2	Akagawa	Bottom-middle	S114	35.854	137.464	38.5	32.9	16.7
On-45	3.0	Akagawa (upstream)	Bottom	S119	35.864	137.464	47.5	27.9	14.2
On-46	3.0	Akagawa (upstream)	Middle	S119	35.864	137.464	52.9	24.3	13.6
On-47	3.0	Akagawa (upstream)	Top	S119	35.864	137.464	39.8	30.7	17.9
On-50	4.7	Akagawa	Middle	1227	35.850	137.465	52.6	26.6	12.9
On-58	6.3	Nigorigawa	Middle	1232	35.837	137.469	68.1	22.7	6.0
October 2014 rain-triggered lahar (cohesive debris flow) deposits: sole fine layer
On-12	10.6	Nigorigawa/Otakigawa	Sole layer	1207	35.803	137.482	0.0	47.4	33.4
On-28	4.4	Akagawa	Sole layer	1191	35.853	137.464	0.0	40.3	35.3
April 2015 rain-on-snow-triggered lahar deposits
On-15	10.6	Nigorigawa/Otakigawa	Lower	1208	35.803	137.482	0.0	96.2	3.8
On-16	10.6	Nigorigawa/Otakigawa	Upper	1208	35.803	137.482	0.0	95.7	4.3
On-19	4.8	Akagawa	Over bank (peak flow) facies	1199	35.849	137.466	80.7	18.1	1.3
On-20	4.8	Akagawa	Flow waning stage	1199	35.849	137.466	40.9	57.4	1.7
On-48	10.6	Nigorigawa/Otakigawa	Surface (bar top)	1206	35.803	137.481	0.0	94.1	5.9
On-51	4.7	Akagawa	Top	1227	35.850	137.465	35.5	61.6	2.9
On-52	4.7	Akagawa	Middle	1227	35.850	137.465	67.2	30.3	2.5
On-53	4.7	Akagawa	Bottom	1227	35.850	137.465	54.0	43.6	2.4
On-54	7.3	Nigorigawa/Denjogawa	Upper	1228	35.828	137.471	74.5	25.1	0.4
On-55	7.3	Nigorigawa/Denjogawa	Lower	1228	35.828	137.471	24.0	75.2	0.8
On-56	7.3	Nigorigawa/Denjogawa	Top	1229	35.828	137.471	1.6	97.1	1.3
On-57	7.3	Nigorigawa/Denjogawa	Middle	1229	35.828	137.471	18.0	81.3	0.7
April 2015 rain-on-snow-triggered lahar deposits (mud drape)
On-21	4.8	Akagawa	Entire	1199	35.849	137.466	0.0	28.0	48.2
On-32	4.4	Akagawa	Entire	1191	35.853	137.464	0.0	22.1	46.9
September 2014 Primary deposits
On-64	–	Nearby the summit	Ashfall lower	1289	35.895	137.488	0.0	12.0	52.0
On-65	–	Nearby the summit	Ashfall upper (aggregates)	1289	35.895	137.488	0.0	15.2	50.1
On-66	–	Nearby the summit	Ashfall uppermost (aggregates+reworked)	1289	35.895	137.488	0.0	19.5	48.9
On-44	3.0	Akagawa (upstream)	Ashcloud deposits?	S119	35.864	137.464	0.0	18.9	64.3
Shirakawa River deposits
On-22	–	Shirakawa	Pre-eruptive fluvial deposits	1202	35.854	137.462	3.8	94.0	2.1
On-23	–	Shirakawa	Post-eruptive reworked ash	1202	35.854	137.462	0.0	39.7	48.0
On-24	–	Shirakawa	October 2014 runoff?	1202	35.854	137.462	0.0	51.2	48.7
On-25	–	Shirakawa	October 2014 runoff?	1202	35.854	137.462	0.0	72.0	28.0
On-26	–	Shirakawa	Rain-on-snow runoff/entire	1202	35.854	137.462	0.2	86.3	13.5

Sample name	Clay (wt%)	Clay in matrix (wt%)²	Median grainsize Mdφ³	Mean grainsize Mz	Sorting σ_I	Skewness Sk_I	Kurtosis K_G	Method⁴
Pre-eruptive fluvial deposits
On-7			2.02	1.96	1.04	− 0.15	1.26	a
On-11			2.28	2.26	0.85	0.03	1.09	a
On-14			2.28	2.25	0.93	− 0.02	1.08	a
On-27			− 4.28	− 3.04	2.33	0.80	1.15	a
On-33			− 0.57	− 0.68	1.79	− 0.04	1.05	a
On-39			1.10	1.10	1.60	− 0.01	1.16	a
On-40			3.26	3.40	1.03	0.24	1.10	a
On-43			− 0.89	− 0.84	1.60	0.17	1.01	a
October 2014 rain-triggered lahar (cohesive debris flow) deposits
On-13	10.5	13.3	0.87	2.10	3.76	0.46	0.93	b
On-18	5.8	14.7	− 2.52	− 1.05	4.14	0.58	0.90	b
On-29	8.1	17.6	− 1.84	− 0.23	4.29	0.69	0.57	b
On-30	10.4	18.4	0.04	0.82	4.91	0.26	0.71	b
On-31	10.8	17.6	0.60	1.28	4.73	0.22	0.77	b
On-34	10.8	17.0	0.54	1.27	4.68	0.24	0.82	b
On-35	9.9	17.9	− 0.21	0.41	5.02	0.25	0.67	b
On-36	8.0	17.1	− 1.55	− 0.35	4.73	0.42	0.74	b
On-41	10.3	19.3	− 0.51	0.38	5.07	0.30	0.65	b
On-42	12.0	19.4	0.59	1.29	4.91	0.23	0.72	b
On-45	10.4	19.9	− 0.59	0.65	4.43	0.54	0.53	b
On-46	9.2	19.6	− 1.47	0.15	4.33	0.67	0.55	b
On-47	11.7	19.4	0.50	1.27	4.87	0.24	0.69	b
On-50	8.0	16.8	− 1.49	− 0.23	4.48	0.53	0.70	b
On-58	3.3	10.2	− 3.28	− 2.10	3.33	0.64	1.06	b
October 2014 rain-triggered lahar (cohesive debris flow) deposits: sole fine layer
On-12	19.3	19.3	4.29	4.74	3.18	0.19	0.78	c
On-28	24.3	24.3	5.40	5.38	3.08	0.02	0.70	c
April 2015 rain-on-snow-triggered lahar deposits
On-15			2.51	2.52	0.78	0.03	1.17	a
On-16			2.38	2.36	0.76	0.06	1.22	a
On-19			− 3.17	− 2.92	1.87	0.52	0.73	a
On-20			− 0.50	− 0.45	2.04	0.07	0.90	a
On-48			2.14	2.16	1.08	0.05	1.11	a
On-51			− 0.26	− 0.39	1.93	− 0.05	1.00	a
On-52			− 2.51	− 1.99	2.56	0.32	0.82	a
On-53			− 1.17	− 1.04	1.72	0.18	1.10	a
On-54			− 3.87	− 2.81	2.07	0.77	0.58	a
On-55			− 0.01	− 0.18	1.63	− 0.25	1.44	a
On-56			1.26	1.21	0.89	− 0.04	1.20	a
On-57			0.25	0.16	1.30	− 0.13	1.13	a
April 2015 rain-on-snow-triggered lahar deposits (mud drape)
On-21	23.8	23.8	5.52	5.85	2.50	0.20	0.77	c
On-32	31.0	31.0	6.37	6.36	2.59	0.02	0.76	c
September 2014 primary deposits
On-64	36.0	36.0	7.10	6.92	2.31	− 0.09	0.84	c
On-65	34.7	34.7	6.99	6.78	2.47	− 0.11	0.86	c
On-66	31.6	31.6	6.70	6.43	2.65	− 0.13	0.89	c
On-44	16.7	16.7	5.06	5.69	2.08	0.46	1.10	c
Shirakawa River deposits
On-22			1.27	1.28	1.26	0.01	1.06	a
On-23	12.3	12.3	4.44	4.78	2.35	0.28	1.32	c
On-24			3.97	4.21	0.95	0.32	0.79	a
On-25			3.41	3.54	1.03	0.21	1.04	a
On-26			2.43	2.50	1.39	0.13	1.23	a

¹Silt indicates particles of < 0.063 mm when manual sieving methods
²Clay/(sand + silt + clay)
³Grain characters based on Folk (1974)
⁴Methods: a) dry sieving, b) wet sieving and laser analyzer, and c) laser analyzer

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