==== Front Data Brief Data Brief Data in Brief 2352-3409 Elsevier S2352-3409(20)31447-5 10.1016/j.dib.2020.106565 106565 Data Article A dataset for distribution and characteristics of Holocene pyroclastic fall deposits along the Pacific coasts in western Hokkaido, Japan Nakanishi Ryo n-ryo@g.ecc.u-tokyo.ac.jpab⁎ Ashi Juichiro ab Okamura Satoshi cd a Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa 277-8564, Japan b Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8561, Japan c Hokkaido University of Education, Sapporo 002-8501, Japan d Hokkaido Soil Research Co-operation, Sapporo 003-0831, Japan ⁎ Corresponding author. n-ryo@g.ecc.u-tokyo.ac.jp 23 11 2020 12 2020 23 11 2020 33 1065655 10 2020 17 11 2020 17 11 2020 © 2020 The Author(s)2020This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).The tephra layers known with eruption ages play an important role in an investigation of tsunami history and archaeology in addition to volcanic history in Hokkaido, Japan. We investigated the event and tephra layers of the Late Holocene in the Pacific coast of western Hokkaido, where the stratigraphy of the Late Holocene has not been clarified. Surveys in coastal peatlands, mostly undisturbed deposits, have allowed for the discovery of thin tephra layers. The newly discovered tephra layers at the unexplored site were used to describe facies, observation under a polarization microscope, refractive index measurement of volcanic glasses, and chemical analysis, and correlated with the reported widespread tephras. We conducted wide-area field surveys and succeeded in revealing a wider distribution of tephra layers than previously known. The distribution of volcanic ash in the coastal area will contribute to the investigations of future volcanic and coastal hazards. Keywords Pyroclastic fall depositTephra stratigraphyUsu volcanoTarumae volcanoKomagatake volcanoHokkaidoLate Holocene ==== Body Specifications Table Subject Stratigraphy; Tephrochronology Specific subject area Volcanology; Geochemistry Type of data Tables and figures How data were acquired Geological fieldwork (sampling procedure) JEOL JXA 8900R (Electron Probe Micro Analyzer: EPMA). JEOL JSM-T330A, Link ISIS300 (Energy Dispersive X-ray Spectrometer: EDS) RIMS 2000 (Refractive Index Measuring System) Data format Raw Parameters for data collection The refractive index of volcanic glass was measured by dehydrating the samples so that the variation due to hydration was reduced. The chemical analysis of volcanic glass by EPMA and EDS was carried out by adjusting the current value and beam diameter to prevent the ionization of light elements. Description of data collection Layer thickness and stratigraphy were described from sampling core and coastal outcrops. The core samples were collected at several nearby sites and checked for variability. Data source location Samples were analyzed at the University of Tokyo, Kashiwa, Japan and Hokkaido University of Education, Sapporo, Japan. Sampling locations are listed in Fig. 1 and Tables 2. Data accessibility All the data sets are available with this article. Value of the Data • Tephra distribution data are commonly used as chronological markers in Hokkaido. • These data can contribute to reconstruct the magnitude and intensity of past explosive eruption in Hokkaido, Japan, and to model possible future eruptive scenarios for hazard assessment. • The data can be used to constrain better the chronology of past coastal hazards (i.e., tsunami, storm) to assist archeological investigations for temporal evolution. 1 Data Description Fig. 1 shows the study area and selected stratigraphic columns. Each volcanic ash layer was comprehensively correlated by comparing the layer facies (stratigraphic sequence, grain size, and coloration), mineral compositions, refractive index, and chemical composition of volcanic glass with those reported in Hokkaido [1], [2], [3]. The tephras widely distributed along the Pacific coast of western Hokkaido (Hidaka, Iburi, Uchiura bay, and Kameda Penisula) correspond to Komagatake c2 tephra (Ko-c2: AD1694), Tarumae b tephra (Ta-b: AD1667), Usu b tephra (Us-b: AD1663), Komagatake d tephra (Ko-d: AD1640), Baegdusan Tomakomai tephra (B-Tm: AD946), and Tarumae c2 tephra (Ta-c2: approximately BC400). The Us-b tephra is subdivided into units. The distribution is different between the Plinian eruption deposits (unit B) and the phreatomagmatic deposits (units A, C, E, F, and G: [1,4]). Fig. 2 shows photographs of representative cores and outcrops in each region. Table 1 shows the chemical composition of the confirmed tephra, and Fig. 3 shows the percentage of constituent minerals and the histogram of the refractive index. The scatter plots of K2O and TiO2, which are useful for the identification of volcanic ash [[1], [2], [3], 5], are presented as one of the premises on which we correlated unknown tephras of known age.Fig. 1 Upper: The topographic map (ASTER GDEM Version 3 [12]) of the survey site and the location of the stratigraphic columns. The inset shows the overall map of the study area and the location of Mt. Baegdusan. The solid black lines show the isopach of Baegdusan Tomakomai tephra (B-Tm). Lower: The typical example of stratigraphic columns of each region. The stratigraphic column of Sites 6 and 17 are based on Nakanishi and Okamura [6]. The stratigraphic column of Site 39 is based on Nakanishi et al. [7]. Fig 1Fig. 2 Photographs of cores and the outcrop at Sites 2, 17, 34, and 39. Fig 2 We describe the correlation of each tephra for each region where the combination of tephra layers is similar. In Kameda Peninsula and western Uchiura bay region, volcanic ash layers of Komagatake and B-Tm were identified. B-Tm was easily determined from the unique chemical composition (high potassium) and fine and good sorting grain at all sites. Komagatake tephras (Ko-d and Ko-c2) at Sites 2 and 3, which were difficult to identify from the stratigraphy and mineral compositions, were identified by the scattered plots of SiO2, K2O, and CaO [8]. From western Iburi to eastern Uchiura Bay, we identified B-Tm, Us-b: fine-grained phreatomagmatic units, Ko-c2 as coarse-grain and mafic minerals are widely observed. Ko-d tephra is occasionally found in patches below Us-b. Tokui [2] and Nakamura et al. [9] described in detail the stratigraphy of the eastern part of Iburi to the northern part of Hidaka; thus, we do not report here the details of the stratigraphy of this area. In the southern part of Hidaka, we identified Ta-c2, B-Tm, Us-b, Ta-b, and Ko-c2. Ta-c2 was found below B-Tm as dark orange and fine-grain volcanic ash. Peat layers rarely separate the three tephras deposited in the 17th century are rarely separated because of gaps of only a few years to a few decades. However, they can be distinguished based on the combination since unit B of Us-b is mainly pumice and Ta-b is fine-grain in contrast. The identification supported by the K2O-TiO2 diagrams is plotted in different areas due to the different source volcanoes of each tephra. Fig. 4 and Table 2 show the layer thickness distribution of tephras at each study site.Table 1 Major element analyses of volcaniclastic glass. The result for each oxide is shown as the mean and deviation of normalized weight% and, N is a number of analyzed glass shards. Table 1 Normalized average (%) Standard deviation Sample ID Site Tephra name SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Raw total N SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Raw total Analysis equipment AT AT 78.65 0.12 11.90 1.26 0.03 0.13 1.10 3.47 3.33 93.0 10 0.07 0.00 0.03 0.03 0.00 0.00 0.01 0.06 0.02 0.66 EPMA a 2 Ko-d 75.86 0.41 12.55 2.47 0.09 0.55 2.63 3.69 1.75 97.7 11 0.52 0.01 0.25 0.12 0.01 0.08 0.18 0.05 0.04 0.14 EPMA b 3 Ko-c2 77.19 0.44 12.03 2.39 0.10 0.49 2.33 3.23 1.80 95.3 10 0.15 0.01 0.07 0.04 0.01 0.01 0.03 0.21 0.04 0.06 EPMA c 3 B-Tm 70.06 0.34 13.49 4.69 0.13 0.10 0.90 5.07 5.22 96.5 12 0.98 0.02 0.52 0.11 0.01 0.01 0.11 0.22 0.15 0.24 EPMA d 12 Ko-d 76.34 0.43 12.34 2.43 0.10 0.48 2.48 3.65 1.75 97.2 10 0.15 0.01 0.13 0.05 0.01 0.02 0.06 0.06 0.02 0.06 EPMA e 24 Ko-d 76.41 0.43 12.25 2.48 0.09 0.52 2.43 3.69 1.71 97.3 11 0.05 0.01 0.03 0.02 0.01 0.01 0.03 0.07 0.03 0.03 EPMA f 31 Us-b (B) 77.35 0.13 12.89 2.00 0.14 0.25 1.81 4.27 1.15 95.5 10 0.48 0.00 0.17 0.05 0.01 0.01 0.03 0.14 0.02 0.67 EPMA g 31 B-Tm 73.03 0.28 11.88 4.07 0.10 0.09 0.72 5.39 4.43 95.8 10 0.84 0.03 0.66 0.27 0.01 0.04 0.19 0.21 0.38 1.08 EPMA h 32 Ko-c2 76.82 0.41 12.16 2.30 0.09 0.45 2.30 3.63 1.84 97.1 10 0.20 0.01 0.10 0.04 0.00 0.01 0.09 0.04 0.03 0.06 EPMA i 32 Ta-b 77.29 0.25 12.36 1.95 0.10 0.34 1.94 3.82 1.95 94.0 10 0.65 0.04 0.09 0.08 0.02 0.03 0.11 0.11 0.16 0.68 EPMA j 32 Us-b (B) 77.17 0.12 12.96 1.92 0.16 0.25 1.85 4.41 1.17 94.9 10 0.71 0.00 0.12 0.01 0.01 0.00 0.02 0.10 0.01 0.93 EPMA k 34 Ko-c2 76.44 0.44 12.41 2.48 0.10 0.49 2.50 3.35 1.79 97.0 10 0.54 0.01 0.26 0.08 0.01 0.02 0.17 0.17 0.04 0.14 EPMA l 34 Ko-f? 75.05 0.54 12.56 2.83 0.11 0.62 2.63 3.91 1.75 97.4 11 0.09 0.01 0.05 0.03 0.01 0.01 0.04 0.07 0.02 0.04 EPMA m 34 Ko-g? 74.32 0.55 13.03 2.95 0.11 0.66 3.03 3.69 1.67 97.5 11 0.27 0.01 0.22 0.06 0.00 0.01 0.12 0.05 0.04 0.09 EPMA n 42 Us-b 75.31 0.15 14.43 1.67 0.12 0.26 2.54 4.50 1.02 95.8 10 0.72 0.04 0.52 0.16 0.01 0.06 0.24 0.13 0.06 0.21 EPMA o 42 B-Tm 66.41 0.37 12.67 4.40 0.11 0.17 1.01 5.04 4.75 95.0 10 1.15 0.07 0.64 0.17 0.01 0.10 0.24 0.27 0.16 1.20 EPMA p 42 Ta-c2 76.37 0.30 12.50 2.02 0.06 0.36 2.45 3.73 2.21 95.6 10 0.83 0.02 0.31 0.06 0.01 0.02 0.22 0.08 0.06 0.71 EPMA q 2 B-Tm 71.77 0.36 14.13 4.15 0.06 0.10 1.12 3.15 5.07 100.2 10 1.42 0.05 0.72 0.42 0.04 0.04 0.36 0.32 0.41 0.42 EDS r 9 Ko-d 75.81 0.50 13.47 2.38 0.15 0.49 2.47 2.74 2.00 100.4 9 0.14 0.04 0.16 0.08 0.06 0.03 0.10 0.13 0.03 0.08 EDS s 17 Ko-d 75.98 0.55 12.52 2.16 0.10 0.55 2.10 3.13 2.04 98.5 10 0.38 0.05 0.10 0.10 0.05 0.06 0.07 0.19 0.08 0.12 EDS t 32 Ta-c2 77.10 0.39 12.61 1.90 0.08 0.29 1.85 3.41 2.37 93.5 9 0.53 0.03 0.23 0.13 0.04 0.04 0.14 0.12 0.05 0.15 EDS u 33 B-Tm 70.00 0.32 14.44 3.68 0.11 0.08 0.60 5.46 5.31 95.5 11 1.30 0.10 0.70 0.42 0.03 0.09 0.24 0.39 0.28 0.40 EDS v 39 Us-b (B) 77.55 0.18 13.26 1.88 0.12 0.34 1.57 3.83 1.27 96.1 10 1.30 0.04 0.73 0.09 0.04 0.02 0.19 0.44 0.09 0.33 EDS w 39 Us-b (B) 76.03 0.19 13.75 1.86 0.18 0.26 1.76 4.29 1.13 99.2 10 0.29 0.04 0.06 0.07 0.04 0.03 0.04 0.15 0.03 0.08 EDS x 39 B-Tm 71.75 0.31 13.34 4.13 0.07 0.01 0.69 4.95 4.76 98.7 10 1.49 0.05 0.78 0.54 0.05 0.02 0.36 0.18 0.18 0.41 EDS y 39 B-Tm 69.49 0.33 14.87 3.70 −0.03 0.07 0.63 5.90 5.04 96.7 10 1.14 0.05 0.78 0.55 0.03 0.02 0.13 0.66 0.22 0.40 EDS z 39 Ta-c2 77.14 0.37 12.50 1.95 0.05 0.38 1.95 3.19 2.48 93.1 10 0.22 0.05 0.22 0.12 0.03 0.04 0.10 0.11 0.08 0.11 EDS α 39 Ta-c2 76.49 0.36 13.08 1.63 0.08 0.35 2.35 3.52 2.13 95.5 11 0.59 0.03 0.34 0.13 0.05 0.05 0.23 0.14 0.14 0.19 EDS Fig. 3 Left: Histograms of refractive index for volcanic glass and mineral composition. For comparison, the refractive index of the volcanic glass of Nakamura [1] is shown. Right: Variation diagrams for TiO2-K2O contents of glass shards by EPMA and EDS. Each symbol shows the mean and deviation in normalized wt%. Fields of referenced volcanic glass by Tokui [2], Aoki and Machida [5], Furukawa and Nanayama [3], and Nakamura [1] are color shaded. AT is a working standard sample analyzed in each analysis. Scatter plots for SiO2-K2O and SiO2-CaO contents of glass shards by EPMA to identify for historical Komagatake tephras. Fig 3Fig. 4 The open circles and black or blue numbers show the location of survey sites and thickness (cm) distribution of each widespread tephra revealed by this study, respectively. Cross marks show patchy tephra layers or thickness less than 1 cm. For comparison, the isopachs of each tephra from Nakamura [1] are shown as gray solid and dashed lines. Gray numbers and cross marks indicate the tephra thickness distribution reported by Tokui (1993), Furukawa and Nanayama [3], and Nakamura [1]. Fig 4Table 2 Latitude and longitude of the sampling site and thickness of the tephra layers. Bold letters indicate that pumice are the main component. Table 2 Tephra layer thickness (cm) Number of checked cores Site Place names Latitude Longitude Ko-c2 Ta-b Us-b B (F) Ko-d B-Tm Ta-c2 1 Shiriuchi 41.63015 140.42718 2–3 3 2 Hinohama 41.78051 141.10008 3–4 1–4 10 3 Todohokke 41.83841 141.13871 4–8 2–4 6 4 Washimoki 42.12321 140.52544 90 1 5 Nodaoi 42.21278 140.39756 15 2 6 Yakumo 42.28111 140.26867 12–15 10 7 Hanaura 42.30084 140.27149 8–17 2 15 8 Yamazaki 42.31947 140.27407 3–6 2 5 9 Nakanosawa 42.48374 140.35288 3–5 patch–1 17 10 Oshamanbe 42.53681 140.39934 1–3 1 4 11 Kyoritsu 42.5546 140.4197 2 1 1 12 Arutori 42.50259 140.79817 (16–50) patch 2 5 13 Nakamareppu 42.4368 140.88948 (1) 1 14 Mareppu 42.41995 140.90502 (2–12) 3 15 Kogane 42.39475 140.91097 (3–4) patch 1 5 16 Ishikawa 42.38394 140.91697 (1) 1 17 Wakayama 42.38551 141.07627 2–8 (1–4) patch 1 102 18 Tomiura 42.44016 141.1509 1–2 4(6) patch 1 11 19 Kojohama 42.46612 141.22053 7–25 5 20 Takeura 42.48162 141.24172 23–52 10 21 Hagino 42.52094 141.29922 74–126 7 22 Ishiyama 42.54912 141.34445 104–122 11 23 Shadai 42.55974 141.37612 2–3 5 30–71 1 33 24 Tarumai 42.59322 141.45847 1–2 3–6 18–28 patch 7 25 Atsuma 42.61677 141.7819 68 3 1 6–8 1 26 Taura 42.58127 141.90511 20 13 3 10 1 27 Shiomi 42.55456 141.93927 2–4 7–21 38–55 patch–1 3–4 9 28 Tomikawa 42.49727 142.01894 4 15–51 7 29 Monbetsu 42.48384 142.04563 patch 2–7 20–35 patch–3 9 30 Toyosato 42.47317 142.11813 10–17 patch–2 3 31 Kabari 42.44806 142.19574 16–34 patch–2 patch–3 21 32 Urawa 42.30936 142.43231 2 patch–2 4–8 patch–3 patch 20 33 Higashisizunai 42.30414 142.4541 patch 4 patch–2 patch–3 7 34 Harutachi 42.26573 142.51294 1 patch–1 3 1–2 2 7 35 Kerimai W 42.22778 142.61414 patch 1–4 1–2 4 36 Kerimai E 42.21743 142.64155 1–2 1 4 4 37 Hamahagifushi 42.20869 142.66531 1 2 1 38 Efue 42.19227 142.72283 patch–1 patch 1–2 2–3 4 39 Utoma 42.13652 142.85985 patch–2 patch–4 patch–4 30 40 Nishisamani 42.13736 142.91001 1 2 4 41 Tomabetsu 41.98969 143.24526 1–4 patch–3 7 42 Syoya 41.99826 143.25279 patch 2–5 patch 17 2 Experimental Design, Materials and Methods 2.1 Field survey A total of 431 samples from cores and outcrops were obtained at the 42 sites along the Pacific coast by using a handy Geoslicer and a Peat Sampler (diameter of 7 cm) with lengths of either 0.6 m or 2.5 m. Photographs were taken of each core sample, and sedimentary facies (stratigraphic sequence, thickness, and presence of pumice) were described. 2.2 Sample preparation To separate volcanic glass and rock-forming minerals from the clay, each sample was vibrated in an ultrasonic cleaning device and the clay components were removed with water elutriation. Samples were dried at 70 °C. The dried samples were divided into 0.063–0.125 phi and 0.125–0.25 phi using a sieve. Refractive index measurements and microscopic observations were conducted for samples of 0.063–0.125 phi and 0.125–0.25 phi, respectively. The samples measuring the glass refractive index were dehydrated by annealing at 400 °C for 12 h in an electric furnace [9]. 2.3 Measurement of refractive index and mineral composition At least 200 grains were counted under a polarization microscope to examine the mineral composition. The refractive index of volcanic glass shards was measured with a Refractive Index Measuring System (RIMS 2000: Kyoto Fission Track Co., Ltd.). This method is possible to measure with an overall accuracy of ±2 × 10−4 and a precision of ±1 × 10−4 [10]. 2.4 Chemical analysis of volcanic glass Chemical analysis of volcanic glass was performed using a JEOL JXA 8900R Electron Probe Micro Analyzer (EPMA) and a JEOL JSM-T330A (Link ISIS300) Energy Dispersive X-ray Spectrometer (EDS). EPMA operating conditions were 15 kV acceleration voltage, 7 nA beam current, beam scanned area of 10 μm, and counting time was 10–60 s at the peak position and 5–30 s at the background-position [11]. EDS operating conditions were 15 kV acceleration voltage, 1.1 nA specimen current, and the beam scanned an area of 3 μm. All analysis results were corrected using the oxide ZAF method. The AT tephra from Aira Caldera was used as an in-house standard to check any difference between the reference values [5]. The mean values of approximately 10 grain with a detection analysis values more than 90% by weight, and it was normalized to 100%. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships which have, or could be perceived to have, influenced the work reported in this article. Acknowledgments We are grateful to Satomi Kato (the curator of Samani town), Shinya Ishikawa (Erimo town), for allowing us to conduct field surveys. We thank Asuka Yamaguchi and Katsunori Akizawa (the University of Tokyo) for guidance on EPMA analysis. This work was supported by the Fukada field research subsidy and, we received funding from Yuji MIKI through crowdfunding through academist, inc. This research was supported by Grant-in-Aid from the 10.13039/501100001691Japan Society for the Promotion of Science to R. Nakanishi (20J21239). ==== Refs References 1 Nakamura Y. 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