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