(East Asia) Over the Last 86 Kyrs Using Distal Sedimentary Records

Refining the eruptive history of Ulleungdo and Changbaishan volcanoes (East Asia) over the last 86 kyrs using distal sedimentary records

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McLean, D., Albert, P. G., Suzuki, T., Nakagawa, T., Kimura, J.-I., Chang, Q. C., MacLeod, A., Blockley, S., Staff, R. A., Yamada, K., Kitaba, I., Haraguchi, T., Kitagawa, J., SG14 Project Members, and Smith, V. C. (2020) Refining the eruptive history of Ulleungdo and Changbaishan volcanoes (East Asia) over the last 86 kyrs using distal sedimentary records. Journal of Volcanology and Geothermal Research, 389. 106669. ISSN 0377-0273 doi: https://doi.org/10.1016/j.jvolgeores.2019.106669 Available at http://centaur.reading.ac.uk/86408/

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Reading’s research outputs online 1 2 3 4 1 REFINING THE ERUPTIVE HISTORY OF ULLEUNGDO AND 5 2 CHANGBAISHAN VOLCANOES (EAST ASIA) OVER THE LAST 6 3 86 KYRS USING DISTAL SEDIMENTARY RECORDS 7 4 8 9 5 DANIELLE MCLEAN*a, PAUL G ALBERTa, TAKEHIKO SUZUKIb, TAKESHI 10 c d d e,f 11 6 NAKAGAWA , JUN-ICHI KIMURA , QING CHANG , ALISON MACLEOD , 12 7 SIMON BLOCKLEYe, RICHARD A STAFFa,g, KEITARO YAMADAc, IKUKO 13 c h i 14 8 KITABA , TSUYOSHI HARAGUCHI , JUNKO KITAGAWA , SG14 PROJECT 15 9 MEMBERSj AND VICTORIA C SMITHa 16 17 10 18 11 a Research Laboratory for Archaeology and the History of Art, University of Oxford, 19 20 12 Oxford, OX1 3TG, UK 21 13 b Department of Geography, Tokyo Metropolitan University, Tokyo, 192-0397, Japan 22 23 14 c Research Centre for Palaeoclimatology, Ritsumeikan University, Shiga, 525-8577, 24 15 Japan 25 26 16 d Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science 27 17 and Technology, Yokosuka, Japan 28 e 29 18 Department of Geography, Royal Holloway University of London, TW20 OEX, UK 30 19 f Department of Geography and Environmental Science, University of Reading, 31 32 20 RG66AB, UK 33 21 g Scottish Universities Environmental Research Centre, University of Glasgow, East 34 Kilbride, G75 0QF, UK 35 22 36 23 h Osaka City University, Osaka, 558-8585, Japan 37 24 i Fukui Prefectural Satoyama-Satoumi Research Institute, Wakasa, 919-1331 Japan 38 39 25 j www.suigetsu.org 40 26 41 42 27 *Corresponding author: [email protected] 43 28 44 45 29 Highlights: 46 47 30 Distal records show eruptions are more frequent and widespread 48 31 At least 8 Changbaishan eruptions produced widespread ash over the 49 50 32 last 86 kyrs 51 52 33 Explosive eruption of Changbaishan at ca. 42.5 ka dispersed ash >1000 53 34 km 54 55 56 57 58 59 1 60 61 62 63 35 4 Ulleungdo eruptions are now precisely dated using the Lake Suigetsu 64 65 36 chronology 66 67 37 U-Ym tephra is identified in Suigetsu and dated to 40,332 – 39,816 68 38 IntCal13 yrs BP 69 70 39 71 72 40 Abstract 73 74 41 75 76 42 The eruptive histories of Ulleungdo (South Korea) and Changbaishan (North 77 78 43 Korea/China border) volcanoes are not well constrained since their proximal 79 80 81 44 stratigraphies are poorly exposed or largely inaccessible. However, determining 82 83 45 the past behaviour of these volcanoes is critical since future eruptions are likely 84 85 46 to disperse ash over some of the world’s largest metropolitan regions. Alkaline 86 87 47 tephra deposits erupted from both centres are routinely identified in marine 88 89 48 cores extracted from the Sea of Japan, as well as high-resolution lacustrine 90 91 49 records east of the volcanoes. Here, we review the distal ash occurrences 92 93 50 derived from Ulleungdo and Changbaishan and provide new data from the Lake 94 95 51 Suigetsu (central Honshu, Japan) sediment core, in order to provide a more 96 97 52 complete and constrained eruption framework. The intensely-dated Lake 98 99 100 53 Suigetsu archive provides one of the most comprehensive distal eruption 101 102 54 records for both centres, despite being located ca. 500 km E of Ulleungdo and 103 104 55 ca. 1000 km SSE of Changbaishan. The Suigetsu record is utilised to precisely 105 106 56 date and geochemically fingerprint (using major, minor and trace element glass 107 108 57 compositions) ash fall events that reached central Honshu. Here, we identify a 109 110 58 new non-visible (cryptotephra) layer in the Suigetsu sediments, which reveals a 111 112 59 previously unreported explosive event from Changbaishan at 42,750 – 42,323 113 114 60 IntCal13 yrs BP (95.4 % confidence interval). This event is chronologically and 115 116 117 118 119 2 120 121 122 123 61 geochemically distinct from the B-J (Baegdusan-Japan Basin) tephra reported 124 125 126 62 in the Sea of Japan (ca. 50 ka). Furthermore, we also confirm that the 127 128 63 widespread U-Ym tephra erupted from Ulleungdo reached central Japan, and is 129 130 64 herein dated to 40,332 – 39,816 IntCal13 yrs BP (95.4 % confidence interval). 131 132 65 This terrestrial 14C-derived age of the U-Ym can be used to constrain the 133 134 66 chronology of marine records containing the same marker layer. This reviewed 135 136 67 and integrated tephrostratigraphic framework highlights the pivotal role that 137 138 68 distal sedimentary records can play in evaluating the eruptive histories and 139 140 69 hazard potential of Ulleungdo and Changbaishan. 141 142 143 70 144 145 71 Keywords: Ulleungdo, Changbaishan; Glass geochemistry; Eruption history; 146 72 Sedimentary archives; Lake Suigetsu 147 148 73 149 150 74 1. Introduction 151 152 75 153 154 76 Intraplate volcanoes Ulleungdo (South Korea) and Changbaishan (North 155 156 77 Korea/China border) are responsible for two of the largest Holocene eruptions 157 158 78 (≥ Volcanic Explosivity Index (VEI) 6; Newhall and Self, 1982) in East Asia, 159 160 161 79 blanketing large parts of Japan and the surrounding seas in ash (Figure 1; 162 163 80 Machida and Arai, 2003). Fine ash from the AD 946 ‘Millennium Eruption’ (ME) 164 165 81 (Hakozaki et al., 2017; Oppenheimer et al., 2017) of Changbaishan has also 166 167 82 been identified ca. 9000 km from its source in northern Greenland (Sun et al., 168 169 83 2014a), which demonstrates the enormous potential of the volcano to cause 170 171 84 major disruption to airspace across the East Asian and Pacific region. Yet, the 172 173 85 complete eruptive histories of Ulleungdo and Changbaishan are not well 174 175 176 177 178 179 3 180 181 182 183 86 constrained since proximal eruption deposits are poorly exposed and are 184 185 186 87 largely inaccessible. 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 88 219 89 Figure 1. (a) Location of Ulleungdo (South Korea; blue triangle) and Changbaishan 220 90 (North Korea/China; orange triangle) and other sources of Japanese tephras outlined 221 91 in the text (black triangles). Distal sites mentioned in the text are marked by white 222 92 circles; 1 = Marine cores; Lim et al. (2013); 2 = Marine cores; Arai et al. (1981); Chun 223 93 et al. (2007); 3 = Marine cores; Chun et al. (2007); 4 = Lake Biwa; Nagahashi et al. 224 225 94 (2004); 5 = Marine cores; Ikehera et al. (2004); 6 = Yuanchi Lake; Sun et al. (2018); 7 226 95 = Marine cores; Ikehara (2003); 8 = Lake Hane; Sawada et al. (1997); 9 = Marine 227 96 cores; Derkachev et al. (in press); 10 = Hakusan volcano; Higashino et al. (2005); 11 = 228 97 Lake Kushu; Chen et al. (2016, 2019). A white star notates the location of Lake 229 98 Suigetsu, and ocean basins are marked in grey (JB= Japan Basin; YR= Yamato Rise; 230 99 OR= Oki Ridge; UB = Ulleungdo Basin). Dispersal boundaries of the B-Tm (AD 946; 231 100 Oppenheimer et al., 2017), U-Oki (ca. 10 ka) and U-Ym (ca. 40 ka) are marked by 232 101 dashed lines (B-Tm and U-Oki as defined by Machida and Arai, 2003). (b) Location of 233 Lake Suigetsu, which is the largest of the five Mikata lakes, adjacent to Wakasa Bay. 234 102 235 103 The positions of coring campaigns SG06 and SG14 are marked on Lake Suigetsu 236 104 (modified after Nakagawa et al., 2005). 237 238 239 4 240 241 242 243 105 It is likely that proximal evidence of older eruptions, especially those of low- to 244 245 246 106 mid-intensity, have been destroyed, or are now completely buried, following 247 248 107 more recent large magnitude Holocene events. At Changbaishan clear 249 250 108 depositional breaks and soil horizons are not well documented within proximal 251 252 109 eruption successions (e.g., Chen et al., 2016; Sun et al., 2017), making it 253 254 110 unclear how many eruption deposits are preserved. 255 256 111 257 258 112 Distal sedimentary records (e.g., marine and lacustrine sequences) have 259 260 113 proved very important archives of past explosive eruptions, and can be used to 261 262 114 help constrain the frequency and dispersal of tephra-forming events (e.g., Wulf 263 264 115 et al., 2004; Albert et al., 2013; 2018; Smith et al., 2013; Tomlinson et al., 2014; 265 266 116 Ponomareva et al., 2018). Ulleungdo and Changbaishan are the only sources 267 268 117 known to have dispersed alkaline tephra across Japan (Machida and Arai, 269 270 118 2003; Kimura et al., 2015; Albert et al., 2019), and their distal deposits can be 271 272 273 119 easily discriminated from other intraplate sources in the back-arc (e.g., Doki and 274 275 120 Jeju volcanoes; Brenna et al., 2014). Tephra layers preserved in marine cores 276 277 121 extracted from the Sea of Japan (Oki ridge, Yamato and Japan basins; Figure 278 279 122 1), indicate that both Ulleungdo and Changbaishan have been very active 280 281 123 during the Late Quaternary, however the number and precise timing of these 282 283 124 events remains uncertain. This is partly since successive eruption deposits are 284 285 125 difficult to geochemically distinguish, and because marine cores in some 286 287 126 localities are susceptible to reworking processes (e.g., turbidites; Albert et al., 288 289 290 127 2012; Cassidy et al., 2014), and often cannot be precisely dated (i.e., due to 291 292 128 variations in the marine radiocarbon reservoir; Ikehara et al., 2013). 293 294 129 295 296 297 298 299 5 300 301 302 303 130 In order to provide new insight into the eruptive histories of Ulleungdo and 304 305 306 131 Changbaishan, this study provides a detailed review of the distal occurrences of 307 308 132 alkaline ash deposited in sedimentary records (marine and lacustrine cores) 309 310 133 spanning the last 86 kyrs (i.e., post-dating the widespread Aso-4 tephra that is 311 312 134 dated to 86.4 ± 1.1 ka using the 40Ar/39Ar method; Albert et al., 2019). We also 313 314 135 provide new tephra data from the intensely-dated Lake Suigetsu archive 315 316 136 (central Honshu, Japan), a record that has significant potential to develop a 317 318 137 comprehensive eruption history for both centres (despite being located 500 km 319 320 138 E of Ulleungdo and 1000 km SSE of Changbaishan). Using the lake sediments, 321 322 323 139 we identify and geochemically characterise two new ash layers erupted from 324 325 140 Ulleungdo and Changbaishan, allowing these eruptive events to be precisely 326 327 141 dated for the first time. New trace element data are also generated for the 328 329 142 previously identified marker layers preserved as cryptotephra in the Holocene 330 331 143 sediments (McLean et al., 2018), offering new possibilities to discriminate 332 333 144 between successive eruption deposits. This reviewed and integrated distal 334 335 145 eruption framework for Ulleungdo and Changbaishan permits critical new insight 336 337 146 into the hazard potential of these active centres. 338 339 147 340 341 342 148 2. Regional setting and proximal volcanic deposits 343 344 149 345 346 150 2.1. Ulleungdo Island, South Korea 347 348 151 349 350 152 Ulleungdo Island (12 km x 10 km) is the sub-aerial portion of a Quaternary 351 352 153 stratovolcano located in the mid-western part of the Sea of Japan (37°30′N, 353 354 154 130°52′E), 130 km east of the Korean Peninsula (Figure 1; Kim, 1985). 355 356 357 358 359 6 360 361 362 363 155 Ulleungdo is the youngest volcano in the back-arc basin, and is known to have 364 365 366 156 erupted intermittently from the Pliocene until the mid-Holocene (Kim et al., 367 368 157 1999; Okuno et al., 2011; Im et al., 2012). Nari caldera is located at the centre 369 370 158 of the island (2.8 km in diameter) and is the source of the most recent phase of 371 372 159 activity (< 19 ka; Kim et al., 2014), erupting rocks that range from alkali basalt to 373 374 160 trachyandesite in composition (Kim, 1985; Brenna et al., 2014; Chen et al., 375 376 161 2018). 377 378 162 379 380 163 The most recent activity of Ulleungdo is exposed at several outcrops near or 381 382 383 164 within Nari caldera. Machida et al. (1984) defined seven pyroclastic units at 384 385 165 extra-caldera outcrops in the north (named in ascending order: U-7 to U-1), 386 387 166 which are comprised of trachytic or phonolitic ash and pumice that were 388 389 167 emplaced as fall deposits and/or by pyroclastic flows (Figure 2). The Holocene 390 391 168 stratigraphy (U-4 to U-2) was further subdivided by Okuno et al. (2011) and 392 393 169 Shiihara et al. (2011) at exposures in the southeast, where the units have also 394 395 170 been geochemically analysed and radiocarbon dated (Figure 2). Two 396 397 171 widespread Japanese tephra marker layers erupted from volcanoes of southern 398 399 172 Kyushu Island are found within the soils that formed between these pumice 400 401 402 173 falls, and are named the Aira-Tanzawa (AT; ca. 30.0 ka) and Kikai-Akahoya (K- 403 404 174 Ah; ca. 7.3 ka) ash. The U-7 to U-5 eruption units are stratigraphically identified 405 406 175 below the AT tephra, and the K-Ah ash is positioned between the U-3 and U-2 407 408 176 eruptions (Shiihara et al., 2011). Radiocarbon dates obtained from buried soils 409 410 177 (ca. 2 cm thick) between units, and charred tree material preserved in the 411 412 178 Holocene deposits suggest that the U-3 eruption occurred ca. 8.3 or 9 ka BP, 413 414 179 respectively, and the U-2 eruption at ca. 5.6 ka BP. 415 416 417 418 419 7 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 180 453 181 454 182 Figure 2. Sedimentological and stratigraphic characteristics of the intra- and extra- 455 183 caldera outcrops on Ulleungdo Island (Machida et al., 1984; Okuno et al., 2010; 456 184 Shiihara et al., 2011; Kim et al., 2014). The radiocarbon ages (s = soil; c = charcoal) 457 185 reported by Okuno et al. (2010) have been recalibrated using IntCal13 (IntCal13 yrs 458 186 BP). Two Japanese tephra layers erupted from volcanoes in Kyushu are identified 459 187 within the soils of the extra-caldera sequences, which include the AT (30 ka) and K-Ah 460 188 (7.3 ka) ash. 461 462 189 463 464 190 Major element glass compositions for Holocene eruptions U-4 to U-2 are known 465 466 191 to be geochemically similar (Machida et al., 1984; Martin Jones, 2012; Shiihara 467 468 192 et al., 2011). Slight geochemical differences between some subunits are 469 470 193 reported by Shiihara et al. (2011), who show that U-4a and U-3c contain glass 471 472 T 194 with lower Al2O3 and higher CaO and FeO . Furthermore, subunits U-3a and U- 473 474 475 476 477 478 479 8 480 481 482 483 195 2a are characterised by slightly lower CaO, TiO and FeOT contents compared 484 2 485 486 196 to the other units. 487 488 197 489 490 198 Intra-caldera outcrops at Nari are ca. 70 m thick, and are composed of un- 491 492 199 welded pyroclastic and epiclastic deposits spanning the last 19 kyrs (Figure 2; 493 494 200 Im et al., 2012; Kim et al., 2014). This sequence is named the Nari Tephra 495 496 201 Formation, and consists of five key eruptive units (in ascending order, N-5 to N- 497 498 202 1), some of which exhibit signs of weathering and soil formation (Figure 2). 499 500 203 Several radiocarbon ages have been obtained from this formation by Im et al. 501 502 503 204 (2012), which have been used to correlate the intra- and extra-caldera 504 505 205 Holocene deposits (U-4 to U-2, and N-4 to N-2) as shown in Figure 2. Kim et al. 506 507 206 (2014) have proposed a detailed succession of eruption styles for the last 19 508 509 207 ka, and suggest that only a few of the events generated sustained eruption 510 511 208 columns or pyroclastic density current (PDC) deposits large enough to overtop 512 513 209 the caldera wall, and therefore extra-caldera sequences may underestimate the 514 515 210 eruption frequency. 516 517 211 518 519 212 2.2. Changbaishan, North Korea/China border 520 521 213 522 523 214 Changbaishan (also referred to as Baitoushan, Paektusan, or Hakutozan) is an 524 525 215 intraplate stratovolcano situated on the border of North Korea and China 526 527 216 (41°00’N, 128°03’E; Figure 1), located on a Neogene trachybasalt lava shield 528 529 217 (the Gaema Plateau). Activity at Changbaishan began in the Middle 530 531 218 Pleistocene, and has been divided into three main episodes: early shield 532 533 219 building, middle cone construction, and a late explosive stage (Wei et al., 2007; 534 535 220 2013). The most recent of which (< 20 ka) culminated with the caldera-forming 536 537 538 539 9 540 541 542 543 221 Millennium Eruption (ME; VEI 7) which ejected ca. 100 km3 of tephra (Dense 544

545 3 546 222 Rock Equivalent ca. 25 km ), blanketing the northernmost regions of Japan in 547 548 223 ash (Horn and Schmincke, 2000; Zou et al., 2010; Wei et al., 2013; Sun et al., 549 550 224 2014b; McLean et al., 2016) and injecting 45 Tg of sulphur into the atmosphere 551 552 225 (Iacovino et al., 2016). This eruption produced a ca. 4.5 km wide caldera, which 553 554 226 today contains Lake Tianchi (meaning “Heavenly Lake”; Machida et al., 1990). 555 556 227 The age of the ME has been precisely dated to AD 946, by combining 557 558 228 dendrochronology with the presence of a closely related (AD 994) ‘Miyake 559 560 229 event’ (pronounced radiocarbon peak) preserved in charred tree deposits 561 562 563 230 (Hakozaki et al., 2017; Oppenheimer et al., 2017). The hazard potential of 564 565 231 Changbaishan is considerable and is particularly concerning given that there 566 567 232 has been recent seismic unrest at the crater (Stone, 2010; Xu et al., 2012; Wei 568 569 233 et al., 2013). 570 571 234 572 573 235 The most comprehensively studied proximal outcrop at Changbaishan is at 574 575 236 Twianwenfeng peak, which is on the northern Chinese flank of the summit (e.g., 576 577 237 Chen et al., 2016; Pan et al., 2017; Sun et al., 2017; 2018). There are many 578 579 238 inconsistent interpretations of these Late Quaternary eruption deposits, even 580 581 239 amongst those assigned to the ME (see Pan et al., 2017). Sun et al. (2017) 582 583 240 identify and geochemically characterise five sequential deposits (oldest to 584 585 241 youngest, named NS-1 to NS-5) at Twianwenfeng peak, and suggest that the 586 587 242 three uppermost units (NS-3 to NS-5) are associated with the ME, due to the 588 589 590 243 geochemical (major element glass chemistry) overlap with distal ash deposits, 591 592 244 and that no depositional break is evident between units NS-4 and NS-5. This is 593 594 245 in contrast to other studies that suggest that the youngest unit (NS-5) may 595 596 597 598 599 10 600 601 602 603 246 correlate to post-ME events, which are suggested by historical records in AD 604 605 606 247 1668 or AD 1702 (Cui et al., 1995; Liu et al., 1998). 607 608 248 609 610 249 The ME had two explosive phases, with the initial main phase (ca. 95% by 611 612 250 volume) associated with a ca. 25 km-high Plinian column, producing a 613 614 251 widespread rhyolitic pumice fall unit (Machida et al., 1990; Horn and 615 616 252 Schmincke, 2000), which equates to NS-3 of Sun et al. (2017). This fall unit is 617 618 253 overlain by partially-welded PDC deposits attributed to the partial collapse of the 619 620 254 Plinian column. Trachytic magma was erupted in a late phase of the eruption 621 622 623 255 (i.e., NS-4 and NS-5), forming moderately welded PDC units that overlie the 624 625 256 rhyolitic fall and PDC deposits (Horn and Schmincke, 2000). Chen et al. (2016) 626 627 257 report trace element compositions for the ME at Twianwenfeng peak (therein 628 629 258 named units C-3 to C-1), and show that the rhyolitic fall deposits (C-3 to C-2) 630 631 259 had higher contents of incompatible trace elements (e.g., Th, Ta, Nd, Y) and 632 633 260 lower contents of compatible elements (e.g., Ba, Sr) relative to the upper 634 635 261 trachyte unit (C-1). 636 637 638 262 639 640 641 263 Sun et al. (2017) identify two pre-ME pyroclastic fall deposits at Twianwenfeng 642 643 264 peak, NS-1 (grey fall unit) and NS-2 (yellow fall unit), which are compositionally 644 645 646 265 distinct from the ME deposits. These units are estimated to have been erupted 647 40 39 14 648 266 between 4 – 5 ka based on Ar/ Ar, uranium series disequilibrium, C and 649 650 267 optically stimulated luminescence (OSL) methods (Liu et al., 1998; Wan and 651 652 268 Zheng, 2000; Wang et al., 2001; Yang et al., 2014). 653 654 655 269 656 657 658 659 11 660 661 662 663 270 A large “lava flow” landform, named the Qixiangzhan Comendite that is 5 km 664 665 666 271 long and 400-800 m wide, is observed on the northern summit of Changbaishan 667 668 272 (Yang et al., 2014; Sun et al., 2017). This is widely considered as another pre- 669 40 39 670 273 ME event, although Ar/ Ar ages generated from this deposit span several 671 672 274 thousand years (e.g., Singer et al., 2014; Yang et al., 2014) and its stratigraphic 673 674 275 relationship to the units preserved at Twianwenfeng peak is unclear (Sun et al., 675 676 276 2017). Major element glass compositions of the Qixiangzhan comendite overlap 677 678 277 with those of the rhyolitic phase of the ME (Sun et al., 2018). 679 680 278 681 682 683 279 2.3. Distal marine and lacustrine tephra records 684 685 280 686 687 281 The Sea of Japan (East Sea) is a semi-enclosed marginal sea located between 688 689 282 the Japanese islands and the Asian continent, and is the product of the rear-arc 690 691 283 extension (Figure 1). Due to the prevailing westerly winds, tephra erupted from 692 693 284 Ulleungdo and Changbaishan is typically dispersed to the east and deposited in 694 695 285 the surrounding marine basins (Arai et al., 1981; Chun et al., 1997, 2007; 696 697 286 Ikehara, 2003; Machida and Arai, 2003; Ikehara et al., 2004; Lim et al., 2013, 698 699 287 2014; Derkachev et al., in press). Furthermore, several Japanese tephra layers 700 701 702 288 erupted from volcanoes on Kyushu Island have been dispersed to, and 703 704 289 deposited in the Sea of Japan, including the K-Ah (Kikai), AT (Aira), SAN1 705 706 290 (Kuju) and Aso-4 eruption deposits (Machida and Arai, 2003; Albert et al., 707 708 291 2019). The marine sediments across the Sea of Japan are characterised by 709 710 292 alternations of light and dark coloured sediments, which have been attributed to 711 712 293 millennial-scale palaeoenvironmental changes associated with changes in the 713 714 294 East Asian summer monsoon (Tada, 1999; Ikehara, 2003). These organic rich 715 716 717 718 719 12 720 721 722 723 295 dark-layers are commonly used to date tephra layers that are preserved in the 724 725 726 296 marine sediments (Tada et al., 1999). It has proved very difficult to correlate 727 728 297 between the proximal eruption successions exposed at Ulleungdo and 729 730 298 Changbaishan with those in distal records (Shiihara et al., 2011; Kim et al., 731 732 299 2014; Chen et al., 2016; Pan et al., 2017). Typically, only the largest Holocene 733 734 300 eruptions that reached the Japanese islands have been correlated to specific 735 736 301 eruption units within proximal stratigraphies of these two volcanoes. 737 738 302 739 740 303 The most widespread tephra layer from Changbaishan is associated with the 741 742 743 304 AD 946 ME, and is distally named the Baegdusan-Tomakomai (B-Tm tephra). 744 745 305 The B-Tm tephra was named and characterised using glass refractive indices 746 747 306 and major element compositions (Machida and Arai, 1983; McLean et al., 2016) 748 749 307 at a distal type-locality in Tomakomai Port, Hokkaido (northern Japan), where it 750 751 308 was identified above the Tarumai-c (ca. 50 BC) and below the Tarumai-b (AD 752 753 309 1667) tephra layers from the nearby Tarumae volcano (Machida and Arai, 754 755 310 1983). The B-Tm tephra has since been identified in numerous marine, 756 757 311 lacustrine and archaeological sequences across northern Japan, northeast 758 759 312 China and coastal regions of Russia (see Sun et al., 2014b; McLean et al., 760 761 762 313 2016) and B-Tm glass shards have been identified in the Greenland ice cores 763 764 314 (Sun et al., 2014a). 765 766 315 767 768 316 The most widespread tephra erupted from Ulleungdo is the Ulleung-Oki (U-Oki), 769 770 317 which is correlated to the proximal U-4 deposits on the island (Machida et al., 771 772 318 1984; Okuno et al., 2010; Shiihara et al., 2011; Smith et al., 2011; Kim et al., 773 774 319 2014). The U-Oki tephra has been identified in several marine cores in the Sea 775 776 777 778 779 13 780 781 782 783 320 of Japan, and in archives on the islands of Japan, including Lake Biwa, Lake 784 785 786 321 Suigetsu and Lake Hane (Chun et al., 1997; Domitsu et al., 2002; Nagahashi et 787 788 322 al., 2004; Smith et al., 2011; Figure 1). As outlined further below, several of 789 790 323 these archives contain a younger phonolitic/trachytic ash that post-dates the U- 791 792 324 Oki tephra, and are thought to be distal correlatives of the U-3 eruption of 793 794 325 Ulleungdo. 795 796 326 797 798 327 One of the most comprehensive records of East Asian volcanism is the Lake 799 800 328 Suigetsu sedimentary archive, which is located ca. 500 km E of Ulleungdo and 801 802 803 329 ca. 1000 km SSE of Changbaishan (35°35’0’’N, 135°53’0’’E, 0 m above present 804 805 330 sea level; Figure 1). The sequence spans approximately 150 ka (Nakagawa et 806 807 331 al., 2012), and contains a detailed record of visible and non-visible 808 809 332 (cryptotephra) layers derived from Ulleungdo and Changbaishan eruptions, as 810 811 333 well as over thirty visible tephra layers erupted from sources that span the 812 813 334 length of Japan (Smith et al., 2013; McLean et al., 2016, 2018; Albert et al., 814 815 335 2018, 2019). Despite the difficulties of identifying non-visible layers in a 816 817 336 productive arc setting, cryptotephra layers are precisely preserved and 818 819 337 identified in Lake Suigetsu, partially due to its unique hydrological setting. 820 821 822 338 Suigetsu is a tectonic lake, adequately situated away from the large calderas in 823 824 339 Hokkaido and Kyushu, and so is not inundated with locally sourced volcanic 825 826 340 glass which would preclude the identification of cryptotephra layers deposited 827 828 341 during large distally occurring eruptions. Furthermore, no rivers flow directly into 829 830 342 Lake Suigetsu (Figure 1b) with the water level controlled by input into the other 831 832 343 connected lakes. The fine-grain sedimentation in the lake is often interrupted by 833 834 344 deposits of coarse volcanic ash that fall through the water column. 835 836 837 838 839 14 840 841 842 843 345 844

845 14 846 346 Since the Lake Suigetsu sediments have been extensively radiocarbon ( C) 847 848 347 dated, and seasonal laminae (varves) are preserved between ca. 10 and 50 ka 849 850 348 (Staff et al., 2011; Bronk Ramsey et al., 2012; Marshall et al., 2012; Schlolaut et 851 852 349 al., 2012), eruptions within the radiocarbon timeframe can be precisely dated if 853 854 350 their associated tephra layers are identified. The Lake Suigetsu 855 856 351 tephrostratigraphic record is therefore utilised in this study to precisely date ash 857 858 352 fall events of Ulleungdo and Changbaishan that reached central Honshu, and 859 860 353 integrate their tephrostratigraphies. 861 862 863 354 864 865 355 3. Tephra identification and analytical methods 866 867 356 868 869 357 3.1. New tephra identification in Lake Suigetsu 870 871 358 872 873 359 The high-resolution and intensely dated sediments of Lake Suigetsu (SG06 and 874 875 360 SG14 cores) have been re-investigated for the presence of thin (i.e., sub 876 877 361 millimetre in thickness) and cryptotephra layers, in order to supplement the 878 879 362 visible tephrostratigraphy as introduced above, and published by Smith et al., 880 881 882 363 (2011, 2013) and Albert et al. (2018, 2019). Cryptotephra extraction procedures 883 884 364 (modified from Turney, 1998; Blockley et al., 2005) were undertaken through 885 886 365 the 12 m of Holocene sediments (≤ 10 ka; McLean et al., 2016, 2018) and more 887 888 366 recently the 14 m of annually laminated (varved) sediments dating to between 889 890 367 ca. 50 and 30 ka, These sections were chosen for analysis as they were 891 892 368 expected to contain low-background levels of volcanic glass, which would not 893 894 369 obscure primary cryptotephra peaks (see McLean et al., 2018). On average, 895 896 897 898 899 15 900 901 902 903 370 through these investigated sediments cryptotephra layers are four times more 904 905 906 371 frequently preserved than visible ash layers. Identified tephra layers in the 907 908 372 Suigetsu sediments are named, and are referred to using their SG06 909 910 373 (correlation model 06 June ‘17) or SG14 (correlation model 30 May ’16) core 911 912 374 composite depth(s) in cm. 913 914 375 915 916 376 The Suigetsu Bayesian age model (Staff et al., 2011; Bronk Ramsey et al., 917 918 377 2012) was used to determine the age for ash layers preserved in the sediments. 919 920 378 The composite Suigetsu sedimentary sequence was modelled on to the 921 922 923 379 IntCal13 timescale (Reimer et al., 2013) implementing three successive cross- 924 925 380 referenced Poisson-process (‘P_Sequence’) depositional models using OxCal 926 14 927 381 (ver. 4.3; Bronk Ramsey, 2008, 2017). These include 775 AMS C dates 928 929 382 obtained from terrestrial plant macrofossils from the upper 38 m (SG06- 930 931 383 Composite Depth (CD) of the SG93 and SG06 cores (Kitagawa and van der 932 933 384 Plicht, 1998a; 1998b, 2000; Staff et al., 2011, 2013a, 2013b; Bronk Ramsey et 934 935 385 al., 2012) and varve counting between 12.88 and 31.67m SG06 CD (Marshall et 936 937 386 al., 2012; Schlolaut et al., 2012). Outside of the varve-counted depth interval, 938 939 387 SG06 event-free depth(s) (EFD, ver. 29th Jan '11) were used within the age 940 941 942 388 model, which excludes instantaneous deposits > 5 mm in thickness, (e.g., 943 944 389 floods, and tephra deposits; Staff et al., 2011; Schlolaut et al., 2012). 945 946 390 947 948 391 3.2. Major and trace element analysis of the glass shards 949 950 392 951 952 393 Major and minor element compositions of individual glass shards extracted from 953 954 394 the Suigetsu visible and cryptotephra layers were measured using a JEOL-8600 955 956 957 958 959 16 960 961 962 963 395 wavelength-dispersive electron microprobe (WDS-EMP) at the Research 964 965 966 396 Laboratory for Archaeology and History of Art (RLAHA), University of Oxford. All 967 968 397 glass analyses used an accelerating voltage of 15 kV, beam current of 6 nA and 969 970 398 10 µm-diameter beam. Peak counting times were 12 s for Na, 50 s for Cl, 60 s 971 972 399 for P, and for 30 s for all other elements. The electron microprobe was 973 974 400 calibrated using a suite of mineral standards, and the PAP absorption correction 975 976 401 method was applied for quantification. The accuracy and precision of these data 977 978 402 were assessed using analyses of the MPI-DING reference glasses from the 979 980 403 Max Plank Institute (Jochum et al., 2006), which were run as secondary 981 982 983 404 standards. Analyses of these secondary standards lie within the standard 984 985 405 deviation of the preferred values and are presented in the Supplementary 986 987 406 Material. All these data were filtered to remove non-glass analyses, and those 988 989 407 with low analytical totals <93%. The raw values were normalised (to 100 %) for 990 991 408 comparative purposes and to account for variable glass hydration, and are 992 993 409 presented as such in all tables and figures. 994 995 410 996 997 411 Trace element compositions of the glass shards >25 µm (i.e. large enough for 998 999 412 analysis) were measured by laser ablation inductively-coupled plasma mass 1000 1001 1002 413 spectrometry (LA-ICP-MS) at the Department of Solid Earth Geochemistry, 1003 1004 414 Japan Agency for Marine-Earth Science and Technology (JAMSTEC). The 1005 1006 415 analytical equipment used include the deep-ultraviolet (200 nm) femtosecond 1007 1008 416 laser ablation system (DUV-FsLA) of OK-Fs2000K (OK Laboratory, Tokyo, 1009 1010 417 Japan) connected to the modified high-sensitivity sector field ICP-MS of 1011 1012 418 Element XR (Thermo Scientific, Bremen, Germany). All analyses used a 25 µm 1013 1014 419 crater diameter and depth, and conditions followed those reported by Kimura 1015 1016 1017 1018 1019 17 1020 1021 1022 1023 420 and Chang (2012). Ten major elements including P O and 33 trace elements 1024 2 5 1025 1026 421 were analysed for each sample, and were also run alongside several MPI-DING 1027 1028 422 reference glasses (Jochum et al., 2006), and the BHVO-2G standard provided 1029 1030 423 by the United States Geological Survey. Accuracies of the BHVO-2G glass 1031 1032 424 analyses are typically < 3 % for most elements, < 5 % for Sc, Ga, Sm, Eu, Gd, 1033 1034 425 U and < 10 % for Ni, Cu, Lu. Full trace element datasets and secondary 1035 1036 426 standard analyses are provided in the Supplementary Material. 1037 1038 427 1039 1040 428 4. Results 1041 1042 1043 429 1044 1045 430 4.1. Suigetsu tephrostratigraphy 1046 1047 431 1048 1049 432 To date, thirty-three visible tephra layers (Smith et al., 2011, 2013; Albert et al., 1050 1051 433 2018; 2019; McLean et al., 2016, 2018) and thirty-four cryptotephra layers 1052 1053 434 (between 50 to 30 ka, and > 10 ka; McLean et al., 2018) have been identified 1054 1055 435 and geochemically fingerprinted in the Lake Suigetsu sediments. The 1056 1057 436 distinctively high alkali content of glass shards (Na O + K O = > 9 wt. %; Figure 1058 2 2 1059 437 3) of eight of these tephra layers indicates that they are not from the Japanese 1060 1061 1062 438 arc volcanoes (Machida and Arai, 2003; Kimura et al., 2015; Albert et al., 2019), 1063 1064 439 and are correlated by McLean et al. (2016, 2018; n = 6) and herein (n = 2) to 1065 1066 440 eruptions from Ulleungdo and Changbaishan. 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 18 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 441 1119 1120 442 Figure 3. The composite Lake Suigetsu tephrostratigraphy and the positioning of 1121 443 Ulleungdo (blue lines), Changbaishan (orange) and other key Japanese (black/grey) 1122 444 tephra layers preserved through the sequence (Smith et al., 2013; McLean et al., 2016, 1123 445 2018; Albert et al., 2018; 2019). The glass shard total alkali content (Na2O + K2O) of 1124 446 these layers is also plotted against eruption age, with Ulleungdo and Changbaishan 1125 tephras containing > 9 wt. %. 1126 447 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 19 1140 1141 1142 1143 448 4.1.1. New Ulleungdo and Changbaishan deposits 1144 1145 1146 449 1147 1148 450 As part of detailed cryptotephra investigations through the Suigetsu sediments 1149 1150 451 dated between ca. 50 to 30 ka, two new alkaline ash layers named SG14-3380 1151 1152 452 and SG14-3216 have been identified. These are positioned between the 1153 1154 453 Sambe-Ikeda (46.4 ka; Albert et al., 2019) and AT (30.0 ka; Smith et al, 2013; 1155 1156 454 Albert et al., 2019) tephras (Figure 3; Table 1). SG14-3380 is a highly 1157 1158 455 concentrated cryptotephra horizon erupted from Changbaishan, and contains 1159 1160 456 over 18,000 shards per gram of dried sediment (Figure 4a.). This eruption is 1161 1162 1163 457 dated to between 42,750 – 42,323 IntCal13 yrs BP (95.4 % confidence interval) 1164 1165 458 using the Suigetsu age model. SG14-3216 is a thin visible (ca. 1 mm) white ash 1166 1167 459 layer (Figure 4b) that is ca. 1.6 m above SG14-3380, and represents an 1168 1169 460 Ulleungdo eruption between 40,332 – 39,816 IntCal13yrs BP (95.4 % 1170 1171 461 confidence interval). 1172 1173 462 1174 1175 463 4.1.2. Previous identifications of Ulleungdo and Changbaishan deposits 1176 1177 464 1178 1179 465 As previously reported by McLean et al. (2018), the Lake Suigetsu Holocene 1180 1181 1182 466 tephrostratigraphy contains three eruptions from Ulleungdo: SG06-1288, SG14- 1183 1184 467 1091 and SG14-0803 that are dated to 10,230 – 10,171 IntCal13 yrs BP, 8,455 1185 1186 468 – 8,367 IntCal13 yrs BP and 5,681 – 5,619 IntCal13 yrs BP (95.4 % confidence 1187 1188 469 interval), respectively (Table 1; Figure 3; Smith et al., 2011; McLean et al., 1189 1190 470 2018). A younger ash layer that also has glass compositions that are similar to 1191 1192 471 eruptions from Ulleungdo (SG14-0433) is dated to 2,737 – 2,620 IntCal13 yrs 1193 1194 472 BP (Table 1; Figure 3). 1195 1196 1197 1198 1199 20 1200 1201 1202 1203 473 1204 1205 474 Table 1. Summary of the Ulleungdo and Changbaishan derived tephra layers identified 1206 475 in the Lake Suigetsu (SG06 & SG14) sequence (in bold and shaded grey), along with 1207 476 their stratigraphic positioning relative to key Japanese marker layers. Tephra 1208 477 correlations for SG06 tephra layers are discussed by Smith et al. (2013), McLean et al. 1209 478 (2016) and Albert et al. (2018, 2019) and SG14 tephra layers are correlated in McLean 1210 479 et al. (2018, this study). 1211 480 1212 14Cdate(AD/ IntCal13 SGLabel Tephracode Tephraname Sourcevolcano Sourcelocation 1213 yrsBP) 1214 SG14-0221 Ma-b Mashu-b Mashu Kurile arc, Japan AD 960 - 9921 1215 SG06-0226 B-Tm Baegdusan-Tomakomai Changbaishan NorthKorea/ China AD9462 3 1216 SG14-0239 Iz-Kt Izu-Kozushima-Tenjosan Kozushima Izu arc, Japan AD 838 1 1217 SG14-0433 U-1 Ulleung-1 Ulleungdo SouthKorea 2,737-2,620 SG14-0490 KGP Kawagodaira Pumice Kawagodaira Izu arc, Japan 3,227 - 3,1291 1218 SG14-0803 U-2 Ulleung-2 Ulleungdo SouthKorea 5,681-5,6191 1219 SG14-0840 To-Cu Towada-Chuseri Towada Northern Honshu, Japan 5,986 - 5,8991 1220 SG06-0967 K-Ah Kikai-Akohoya Kikai SouthernKyushu,Japan 7,307-7,1961 1221 SG14-1058 B-Sg-08 Baegdusan-Suigetsu-08 Changbaishan NorthKorea/ China 8,166-8,0991 1222 SG14-1091 U-3 Ulleung-3 Ulleungdo SouthKorea 8,455-8,3671 1223 SG14-1185 1185 - - - 9,372-9,3011 1 1224 SG06-1288 U-Oki/ U-4 Ulleung-4/ Ulleung-Oki Ulleungdo SouthKorea 10,230-10,171 4 1225 SG06-1965 Md-fl Sambe-Midorigaoka fl Sambe SWJapan 19,631 - 19,471 SG06-2650 AT Aira-Tanzawa Aira SouthernKyushu,Japan 30,174 - 30,078 4 1226 SG14-3216 U-Ym Ulleung-Yamato Ulleungdo SouthKorea 40,332-39,8165 1227 SG14-3380 B-Sg-42 Baegdusan-Suigetsu-42 Changbaishan NorthKorea/ China 42,750-42,3235 1228 SG06-3668 SI Sambe-Ikeda Sambe SWJapan 46,566 - 46,162 4 1229 SG06-3912 ACP4 Aso-Central Pumice 4 Aso CentralKyushu,Japan 50,311 - 49,637 4 1230 SG06-4963 Aso-4 Aso-4 Aso CentralKyushu,Japan 86.4 ± 1.1 40Ar/39Ar4 1231 1) McLean et al. (2018); 2) Oppenhemier et al. (2017); Hakozaki et al., 2017; 3) Tsukui et al. (2006); 4) Smith et al. (2013); Albert 1232 481 et al. (2019); 5) This study 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 482 1245 1246 483 Figure 4. (a) Glass shard concentrations (shards per gram of dry sediment) preserved 1247 484 in SG14 core E-35 and the positioning of cryptotephra SG14-3380. Concentration of 1248 485 low-resolution (5 cm) samples are shown in grey and high-resolution samples (1 cm) 1249 486 are overlain in blue. Shard counts for the other Holocene cryptotephra layers are 1250 487 published by McLean et al. (2018). (b) Photograph of visible tephra layer SG14-3216 in 1251 488 Lake Suigetsu Core G-09. 1252 1253 1254 1255 1256 1257 1258 1259 21 1260 1261 1262 1263 489 Two Holocene Changbaishan eruptions are preserved in the sediments: SG14- 1264 1265 1266 490 1058 at 8,166 – 8,099 IntCal13 yrs BP (McLean et al., 2018); and SG06-0226, 1267 1268 491 which has been correlated to the AD 946 B-Tm tephra from the ME (McLean et 1269 1270 492 al., 2016; Hakozaki et al., 2017; Oppenheimer et al., 2017). Several other 1271 1272 493 widespread markers have been identified in the Holocene sediments, which are 1273 1274 494 able to stratigraphically separate eruption events from Ulleungdo and 1275 1276 495 Changbaishan (Figure 3; Table 1). SG14-1185 stratigraphically separates the 1277 1278 496 SG06-1288 and SG14-1091 Ulleungdo layers, and the K-Ah (7.3 ka; Kikai 1279 1280 497 volcano) and To-Cu (5.9 ka; Towada) tephra layers separate SG14-1091 and 1281 1282 1283 498 SG14-0830 (McLean et al., 2018; Table 1; Figure 3). 1284 1285 499 1286 1287 500 4.2. Major and trace element volcanic glass geochemistry 1288 1289 501 1290 1291 502 4.2.1. Ulleungdo glass geochemistry 1292 1293 503 1294 1295 504 The newly analysed glass of SG14-3216 geochemically overlaps with the other 1296 1297 505 previously identified Ulleungdo derived tephra layers preserved in the Suigetsu 1298 1299 506 tephrostratigraphy (e.g., SG06-1288, SG14-1091 and SG14-0803). Collectively 1300 1301 1302 507 they straddle the phonolitic/trachytic boundary on the basis of the Total Alkalis 1303 1304 508 versus Silica (TAS) classification (Le Bas et al., 1986) and contain 60 – 63 wt. 1305 1306 509 % SiO2, ca. 7 wt. % K2O and 19 – 20 wt. % Al2O3 (Table 2; Figure 5). These 1307 1308 510 glasses are characterised by < 2.5 wt. % CaO and contain between 2.5 and 3.5 1309 1310 511 wt. % FeOT. 1311 1312 512 1313 1314 1315 1316 1317 1318 1319 22 1320 1321 1322 1323 513 When normalised to the primitive mantle (Sun and McDonough, 1989), we find 1324 1325 1326 514 the newly obtained trace element compositions of SG14-3216 and SG14-1091 1327 1328 515 show enrichments in the Light Rare Earth Elements (LREE) relative to the 1329 1330 516 Heavy Rare Earth Elements (HREE) (La/Yb = 30 – 35 ppm) and significant 1331 1332 517 depletions in Ba, Sr and Eu that reflect K-feldspar fractionation (Figure 6). The 1333 1334 518 paucity of a depletion in Nb and Ta content within these volcanic glasses, when 1335 1336 519 normalised to the primitive mantle, is inconsistent with subduction related 1337 1338 520 volcanism (Figure 6). 1339 1340 521 1341 1342 1343 522 The four tephra layers with Ulleungdo compositions are difficult to distinguish 1344 1345 523 using their major element glass compositions, but we find that the younger 1346 1347 524 glasses of SG14-0803 are more elevated in CaO (by ca. 0.5 wt. %), compared 1348 1349 525 to the early Holocene and SG14-3216 glass (Figure 5c). In addition, the alkaline 1350 1351 526 glasses of SG14-3216 (59.5 – 62.5 wt. % SiO2 and total alkalis [Na2O + K2O] of 1352 1353 527 11.6 – 14.9 wt. %) can be discriminated from SG14-1091 by larger feldspar- 1354 1355 528 related depletions in Sr, Ba and Eu, that are normalised to primitive mantle 1356 1357 529 compositions (Figure 6). The alkaline glass shards of SG14-0433 (Na O + K O 1358 2 2 1359 530 = 10.4 – 11.0) are also likely to derive from Ulleungdo, but contain ca. 2.5 wt. % 1360 1361 1362 531 lower K2O, and ca. 2 wt. % higher CaO compared to the older eruption events 1363 1364 532 outlined here (Figure 5a; 5c). 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 23 1380 1381 1382 1383 533 Table 2. Average major, minor and trace element glass compositions of the Ulleungdo 1384 534 and Changbaishan tephra layers in the Lake Suigetsu sediment core. 1385 SG14-0433 SG14-0803 SG14-1091 SG06-1288 SG14-3216 1386 McLean et al. 2018 McLean et al. 2018 McLean et al. 2018 Smith et al. 2011 this study wt.(%) Mean ±1σ Mean ±1σ Mean ±1σ Mean ±1σ Mean ±1σ

1387 SiO2 61.76 0.16 60.54 0.63 60.52 0.24 60.85 0.42 60.75 0.67 1388 TiO2 0.79 0.05 0.62 0.07 0.51 0.08 0.50 0.07 0.39 0.07 1389 Al2O3 16.66 0.05 19.48 0.30 19.87 0.22 19.55 0.17 19.85 0.28 FeOT 5.65 0.17 3.16 0.42 2.77 0.24 3.16 0.19 3.12 0.16 1390 MnO 0.23 0.05 0.14 0.10 0.15 0.03 0.14 0.05 0.18 0.05 MgO 1.09 0.06 0.48 0.12 0.23 0.03 0.30 0.06 0.17 0.07 1391 CaO 6.07 0.18 6.60 0.60 6.95 0.40 1.61 0.17 1.34 0.12

1392 Na2O 2.57 0.08 1.99 0.33 1.48 0.14 6.51 0.79 7.28 0.96 1393 K2O 4.59 0.10 6.61 0.21 7.03 0.19 7.07 0.28 6.50 0.33 P2O5 0.36 0.04 0.17 0.05 0.05 0.04 0.10 0.03 0.05 0.03 1394 Cl 0.23 0.03 0.21 0.04 0.40 0.08 0.24 0.03 0.37 0.10 1395 Analytical total 96.85 96.84 97.81 99.72 97.03 n 8 19 24 12 37 1396 SG06-0226 SG14-1058 SG14-3380 1397 McLean et al. 2016 McLean et al. 2018 this study wt.(%) Mean ±1σ Mean ±1σ Mean ±1σ 1398 SiO2 74.89 0.21 75.01 0.18 66.26 0.70

1399 TiO2 0.22 0.04 0.20 0.03 0.60 0.09 1400 Al2O3 10.27 0.10 10.28 0.11 14.97 0.28 FeOT 4.05 0.14 3.89 0.10 5.12 0.14 1401 MnO 0.08 0.05 0.07 0.03 0.15 0.04 1402 MgO 0.02 0.03 0.01 0.01 0.25 0.06 CaO 0.22 0.02 5.30 0.16 1.24 0.17

1403 Na2O 5.36 0.15 0.20 0.02 5.67 0.66 1404 K2O 4.38 0.09 4.50 0.06 5.49 0.09 P2O5 - - 0.01 0.01 0.09 0.03 1405 Cl 0.50 0.03 0.52 0.02 0.16 0.02 1406 Analytical total 96.19 95.54 95.90 1407 n 29 24 14 1408 SG06-0226 SG14-1058 SG14-1091 SG14-3216 SG14-3380 this study this study this study this study this study 1409 ppm Mean ±1σ Mean ±1σ Mean ±1σ Mean ±1σ Mean ±1σ 1410 Rb 396.4 9.8 383.9 23.9 188.7 10.1 195.4 19.1 143.5 8.9 Sr 2.2 0.6 4.4 0.9 59.5 36.2 14.3 10.2 25.0 24.4 1411 Y 143.3 3.9 149.8 11.4 23.5 2.0 26.0 2.9 51.1 3.9 1412 Zr 2415.2 80.0 2302.5 189.8 626.0 50.9 709.6 104.3 741.4 45.8 Nb 286.1 8.9 261.1 21.1 169.8 11.5 175.2 21.2 97.0 5.5 1413 Ba 6.4 0.9 6.6 2.5 99.1 83.5 16.3 13.3 77.3 57.3 1414 La 138.9 4.5 125.2 14.6 86.4 4.3 98.2 9.0 76.4 4.7 Ce 286.9 13.5 243.2 12.3 144.8 6.9 161.7 15.7 154.3 9.6 1415 Pr 31.9 1.2 28.3 1.8 12.8 0.9 14.5 1.2 17.1 1.1 1416 Nd 115.8 4.8 102.3 6.9 39.3 3.5 43.9 4.7 65.6 6.4 Sm 27.6 1.2 26.1 4.5 5.6 1.0 6.4 0.7 12.9 1.9 1417 Eu 0.3 0.1 0.3 0.3 1.5 0.3 0.6 0.2 0.6 0.2 1418 Gd 26.7 1.5 28.0 3.3 5.0 1.4 5.4 1.9 10.7 1.4 Dy 25.3 1.8 25.5 2.2 3.8 0.6 4.4 0.6 9.3 0.9 1419 Er 14.0 0.6 14.0 1.6 2.5 0.5 2.8 0.6 5.1 0.7 1420 Yb 11.4 0.5 11.2 2.0 2.6 0.4 3.1 0.7 4.3 0.6 Hf 55.6 2.3 55.6 5.4 12.0 1.1 13.4 2.1 16.9 1.2 1421 Ta 17.0 1.1 16.4 1.9 9.8 0.7 9.7 1.1 5.6 0.5 1422 Th 49.9 3.1 49.6 5.0 23.5 1.9 25.2 3.2 14.1 1.1 U 10.8 0.7 9.7 0.9 4.8 0.5 5.3 0.9 2.8 0.3 1423 Y/Th 2.9 0.2 3.0 0.1 1.0 1.1 1.0 0.1 3.6 0.2 1424 Zr/Th 48.5 2.5 46.5 2.0 26.6 27.5 28.1 2.3 52.6 3.3 La/Yb 12.1 0.4 11.3 1.4 34.4 6.5 32.7 4.9 18.0 2.4 1425 n 8 5 13 8 10 1426 535 (FeOT = all Fe reported as FeO). Raw dataset and secondary standards are included in the Supplementary Material. 1427 536 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 24 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 537 1489 538 Figure 5. Glass shard major (5a – d) and trace (5e – f) element compositions of 1490 539 Ulleungdo (South Korea; shown in blue), Changbaishan (North Korea/China; shown in 1491 540 orange), and key Japanese tephra layers that are preserved in the Lake Suigetsu 1492 1493 541 sediments (shown in grey and black) (Smith et al., 2013; McLean et al., 2016, 2018; 1494 542 Albert et al., 2018, 2019). (d) Total alkali versus silica plot (TAS) with whole-rock 1495 543 classification based on Le Bas et al., 1986). 1496 1497 1498 1499 25 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 544 1534 1535 545 Figure 6. Primitive mantle normalised trace element compositions of glasses of: (a) 1536 546 Ulleungdo tephra layers (SG14-1091 and SG14-3216) in the Lake Suigetsu sequence; 1537 547 (b) Changbaishan tephra layers (SG06-0225, SG14-1058 and SG14-3380) in 1538 548 comparison to proximal ME rhyolitic (C2 – C3) and trachytic (C1) proximal deposits 1539 1540 549 (Chen et al., 2016). Primitive mantle values follow Sun and McDonough (1989). 1541 550 1542 1543 551 4.2.2. Changbaishan glass geochemistry 1544 1545 552 1546 1547 553 The three Changbaishan derived tephra layers (e.g., SG14-3380, SG14-1058 1548 1549 554 and SG06-0226) contain both rhyolitic and trachytic glass compositions (Na2O + 1550 1551 555K 2O = > 9.5 wt. %; Le Bas et al., 1986), with SiO2 ranging from 65.5 to 75.5 wt. 1552 1553 556 % (Table 2; Figure 5d). They contain < 1.6 wt. % CaO, and between 3.7 and 5.4 1554 1555 T 1556 557 wt. % FeO (Figure 5c). New trace element analyses indicate that when 1557 1558 1559 26 1560 1561 1562 1563 558 normalised to primitive mantle compositions, all glasses are enriched in LREE 1564 1565 1566 559 relative to HREE, with La/Yb ratios higher in those of SG14-3880, relative to 1567 1568 560 SG14-1058 and SG06-0226 (Table 2) and show pronounced negative feldspar- 1569 1570 561 related anomalies in Ba, Sr and Eu (Figure 6). 1571 1572 562 1573 1574 563 The newly analysed glasses of SG14-3380 are exclusively trachytic (65.4 – 1575 1576 564 67.9 wt. % SiO2, 14.4 – 15.5 wt. % Al2O3, and Na2O + K2O = 8.7 – 11.7 wt. %) 1577 1578 565 and are compositionally similar to the single trachytic analysis from SG06-0226. 1579 1580 566 Trace element compositions for SG14-3380 are homogenous with 14.1 ± 1.1 1581 1582 1583 567 ppm Th, 144 ± 9.0 ppm Rb, and 51 ± 4 ppm Y (Table 2). Unfortunately, no trace 1584 1585 568 elements could be obtained for the trachytic end-member of SG06-0226 for 1586 1587 569 further comparison with SG14-3380. 1588 1589 570 1590 571 As discussed by McLean et al. (2018), the rhyolitic SG06-0226 glass 1591 1592 1593 572 compositions overlap with SG14-1058 for all major elements (Table 2; Figure 1594 1595 573 5). Both tephras contain glass compositions that are geochemically 1596 1597 574 homogenous, with ca. 75 wt. % SiO2, 10.3 wt. % Al2O3 and ca. 4.4 wt. % K2O, 1598 1599 575 and are characterised by very low CaO concentrations (< 0.3 wt. %). The newly 1600 1601 576 generated trace element compositions of SG14-0226 and SG06-1058 show 1602 1603 577 significant overlap, and are more enriched in incompatible elements (e.g., Th, 1604 1605 578 Ta and Y), whilst depleted in compatible elements (e.g., Sr, Ba, and Eu) relative 1606 1607 579 to the trachytic glass of SG14-3380 (Table 2; Figure 6b). SG06-0226 and 1608 1609 1610 580 SG14-1058 have similar mantle normalised profiles and levels of incompatible 1611 1612 581 trace element enrichment (Figure 6). Glasses of both tephra layers have greater 1613 1614 582 feldspar-related depletions in Ba, Sr and Eu relative to SG14-3380. The SG06- 1615 1616 583 0226 glasses show a significant depletion in Nb, which is not observed in 1617 1618 1619 27 1620 1621 1622 1623 584 SG14-1058 and SG14-3380, which given the intraplate setting of the volcano 1624 1625 1626 585 may relate to late stage, high-level fractionation processes. 1627 1628 586 1629 1630 587 1631 1632 588 5. Review of Ulleungdo and Changbaishan eruption framework 1633 1634 589 1635 1636 590 Here, the distal ash deposits erupted from Ulleungdo and Changbaishan are 1637 1638 591 outlined and reviewed using the relative stratigraphy, geochemical glass 1639 1640 592 compositions and eruption chronology. Published occurrences are centred on 1641 1642 1643 593 the Lake Suigetsu tephrostratigraphy to provide an integrated framework that is 1644 1645 594 constrained by numerous widespread ash layers erupted from Japanese 1646 1647 595 volcanoes (Figure 7). There are no pre-50 ka visible ash layers in Lake 1648 1649 596 Suigetsu with Ulleungdo or Changbaishan compositions, but we should 1650 1651 597 highlight that cryptotephra extraction techniques have not yet been carried out 1652 1653 598 on these older sediments. It is possible that there are other pre-50 ka Ulleungdo 1654 1655 599 or Changbaishan layers preserved cryptically in Lake Suigetsu. 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 28 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 600 Figure 7. Summary tephrostratigraphy of proximal and distal archives that contain ash 1725 601 erupted from Ulleungdo (blue boxes) and Changbaishan (orange boxes) (see Figure 1 1726 602 for archive location). Widespread Japanese tephra layers, which provide valuable 1727 603 chronostratigraphic markers, are also shown in grey boxes. Alkali-rich ashes erupted 1728 604 from Ulleungdo and Changbaishan are routinely identified in marine cores extracted 1729 605 from the Sea of Japan (East Sea) and high resolution lake archives in Japan. 1 = Chun 1730 606 et al. (1997); 2 = Lim et al. (2013); 3 = Chun et al. (2007); 4 = Arai et al. (1981); 5 = 1731 607 Nakajima et al. (1996); 6 = Ikehara et al. (2004); 7 = Derkachev et al. (in press); 8 = 1732 608 Ikehara (2003); 9 = Sawada et al. (1997); 10 = Higashino et al. (2005); 11 = Nagahashi 1733 609 et al. (2004); 12 = Smith et al. (2011; 2013), Albert et al. (2018; 2019), McLean et al. 1734 610 (2016; 2018; this study). Due to the paucity of glass data from pre-Holocene eruptions 1735 611 of Ulleungdo and Changbaishan, these units cannot be correlated to distal ash 1736 612 deposits elsewhere. 1737 1738 1739 29 1740 1741 1742 1743 613 5.1. Ulleungdo eruption history 1744 1745 1746 614 1747 1748 615 Ulleungdo has erupted explosively at least five times over the last 86 kyrs (since 1749 1750 616 the eruption of the Aso-4 tephra) with associated widespread ash fall events 1751 1752 617 recognised by the ca. 60 – 61 ka U-Sado tephra (Lim et al., 2013); the ca. 40.1 1753 1754 618 ka U-Ym tephra (this study); the ca. 10 ka U-Oki/U-4 tephra (Smith et al., 2011; 1755 1756 619 2013); ca. 8.4 ka U-3 tephra (McLean et al., 2018); and the ca. 5.7 ka U-2 1757 1758 620 tephra (McLean et al., 2018). The known distal deposits of these events and 1759 1760 621 possible proximal correlations are illustrated in Figure 7 and discussed further 1761 1762 1763 622 below. 1764 1765 623 1766 1767 624 5.1.1. Post 86 ka (Aso-4) Ulleungdo eruptions 1768 1769 625 1770 1771 626 Distal ash layers erupted from Ulleungdo were identified stratigraphically below 1772 1773 627 the AT tephra (30 ka) in marine sediments obtained from the Oki ridge (Arai et 1774 1775 628 al., 1981) and Yamato Basin (Ikehara et al., 2004). These pre-AT Ulleungdo 1776 1777 629 tephra layers were originally considered to be from a single eruption, but the 1778 1779 630 age was controversial. However, Chun et al. (2007) clarified the issue by 1780 1781 631 identifying two separate alkaline ash deposits in marine core MD01-2407 1782 1783 1784 632 (Figure 1), which they named SKPI and SKPII, and were dated to 40 – 41 ka 1785 1786 633 and 60 – 61 ka, respectively, based on correlations with the regional-scale 1787 1788 634 thinly-laminated marine stratigraphy (Tada, 1999; Chun et al., 2007). 1789 1790 635 1791 1792 1793 1794 1795 1796 1797 1798 1799 30 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 636 1831 1832 637 Figure 8. Glass shard major and trace element compositions of Ulleungdo (SG14- 1833 638 0803; SG14-1091; SG06-1288; SG14-3216) and Changbaishan (SG06-0226; SG14- 1834 639 1058; SG14-3380) tephra layers preserved in the Lake Suigetsu archive, compared to 1835 640 other proximal (Chen et al., 2016; Sun et al., 2017, 2018) and distal occurrences 1836 1837 641 (Ikehara et al., 2004; Lim et al., 2013; Derkachev et al. (in press). Error bars represent 1838 642 2 x standard deviations of repeat analysis of the StHs6/80-G MPI-DING reference 1839 643 glass analyses, error bars for (d) are smaller than the data symbols. 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 31 1860 1861 1862 1863 645 Lim et al. (2013) also identified two equivalent cryptotephra layers in several 1864 1865 1866 646 other marine cores northeast of Ulleungdo (e.g., GH86-2-N, GH89-2-25, GH89- 1867 1868 647 2-26 and GH89-2-28), which were stratigraphically positioned between the 1869 1870 648 rhyolitic Aso-4 and AT tephra. These distal tephra layers were therein named 1871 1872 649 the Ulleung-Yamato (U-Ym) and Ulleung-Sado-Oki (U-Sado), and are 1873 1874 650 considered to be equivalent to SKP-I and SKP-II, respectively (Figure 7). 1875 1876 651 1877 1878 652 The Lake Suigetsu sediments verify that an ash fall event from Ulleungdo 1879 1880 653 occurred at 40,332 – 39,816 IntCal13 yrs BP (95.4 % confidence interval). This 1881 1882 1883 654 1 mm thick ash layer (SG14-3216; Figure 4) contains volcanic glass that 1884 1885 655 compositionally overlaps the other Ulleungdo-derived tephra deposits preserved 1886 1887 656 in the Suigetsu sequence (e.g. SG06-1288, SG14-1091), and other distal and 1888 1889 657 proximal occurrences of the U-Oki tephra (Figure 5; Figure 8; Furuta et al., 1890 1891 658 1986; Nagahashi et al., 2004; Chun et al., 2007; Park et al., 2003, 2007). 1892 1893 659 1894 1895 660 Although grain-specific glass compositional datasets for the U-Ym tephra 1896 1897 661 preserved in the Sea of Japan have not been published for comparison, the 1898 1899 662 broad geochemical and chronological data and the stratigraphic position is 1900 1901 1902 663 consistent with SG14-3216, meaning this ash must also correlate to the same 1903 1904 664 eruption of Ulleungdo. The Suigetsu-derived deposit age of 40,332 – 39,816 1905 1906 665 IntCal13 yrs BP (95.4 % confidence interval) provides the most precise eruption 1907 1908 666 age, and this date can now be imported into other site-specific age models that 1909 1910 667 contain this marker. 1911 1912 668 1913 1914 1915 1916 1917 1918 1919 32 1920 1921 1922 1923 669 No other distal ash occurrences have been reported that are chronologically or 1924 1925 1926 670 geochemically consistent with the ca. 19 ka eruption (proximal unit N-5; Kim et 1927 1928 671 al., 2014), suggesting that this eruption of Ulleungdo was probably not 1929 1930 672 widespread. 1931 1932 673 1933 1934 674 5.1.2. Holocene Ulleungdo eruptions 1935 1936 675 1937 1938 676 As previously outlined, the largest known Plinian eruption from Ulleungdo 1939 1940 677 generated the U-Oki tephra layer that is dated to 10,230 – 10,171 IntCal13 yrs 1941 1942 1943 678 BP (95.4 % confidence interval; Smith et al., 2011, 2013). The U-Oki ash is 1944 1945 679 found in several high-resolution sedimentary records in Japan, including Lake 1946 1947 680 Biwa (BT-4; Nagahashi et al., 2004) and Lake Suigetsu (SG06-1288; Smith et 1948 1949 681 al., 2011) (Figure 7). This U-Oki tephra is the only distal tephra that has been 1950 1951 682 correlated to proximal deposits on Ulleungdo, and equates to the proximal U-4 1952 1953 683 unit of Shiihara et al. (2011). 1954 1955 684 1956 1957 685 Lake Suigetsu tephra layers SG14-1091 (ca. 8.4 ka) and SG14-0803 (ca. 5.7 1958 1959 686 ka) overlay the U-Oki tephra and are considered distal equivalents of proximal 1960 1961 1962 687 deposits U-3 and U-2, respectively, due to their close agreement to the proximal 1963 1964 688 radiocarbon dates of soils between fall units (Okuno et al., 2010). Furthermore, 1965 1966 689 the K-Ah tephra is stratigraphically positioned between the U-3 (SG14-1091) 1967 1968 690 and U-2 (SG14-0803) deposits (Shiihara et al., 2011). Distal equivalents of the 1969 1970 691 U-3 eruption have been reported in the Sea of Japan (TRG1 sediment core; 1971 1972 692 Domitsu et al., 2002), Lake Biwa (Nagahashi et al., 2004), and close to 1973 1974 693 Hakusan volcano in central Honshu (Higashino et al., 2005). In comparison, 1975 1976 1977 1978 1979 33 1980 1981 1982 1983 694 SG14-0803 is the only known distal equivalent of the U-2 tephra, indicating that 1984 1985 1986 695 it was either a lower magnitude event or the eruption plume was dispersed in a 1987 1988 696 different direction. 1989 1990 697 1991 1992 698 The proximal deposits of the youngest U-1 eruption of Ulleungdo suggest it was 1993 1994 699 a small strombolian-type eruption with a lava dome extrusion (Kim et al., 2014). 1995 1996 700 Whole rock trace element data reported for this youngest event have a distinct 1997 1998 701 tephriphonolite composition (Brenna et al., 2014). Similarly, distal SG14-0433 1999 2000 702 glass compositions are distinct from those of other Ulleungdo derived tephras in 2001 2002 2003 703 Suigetsu. Unfortunately, the lack of proximal glass chemistry for the U-1 unit 2004 2005 704 means that this correlation cannot be confirmed but it is likely that the SG14- 2006 2007 705 0433 layer at 2,737 – 2,620 IntCal13 yrs BP (95.4 % confidence interval) 2008 2009 706 correlates to the U-1 eruption. 2010 2011 707 2012 2013 708 5.2. Changbaishan eruption history 2014 2015 709 2016 2017 710 The newly identified Changbaishan-derived tephra layer outlined here, in 2018 2019 711 addition to the previously recognised layers, indicate that at least eight 2020 2021 2022 712 explosive eruptions have produced widespread ash dispersals over the last 86 2023 2024 713 kyrs. These include the: ca. 85.8 ka B-Ym tephra (Lim et al., 2013); ca. 67.6 ka 2025 2026 714 B-Sado tephra (Lim et al., 2013); ca. 50.5 ka B-J tephra (Ikehara et al., 2014; 2027 2028 715 Lim et al., 2013); ca. 42.5 ka B-Sg-42 tephra (this study), ca. 38 ka B-Un1 2029 2030 716 tephra (Derkachev et al., in press), ca. 25 ka B-V tephra (Machida and Arai, 2031 2032 717 2003); ca. 8.1 ka B-Sg-08 tephra (McLean et al., 2018); and AD 946 B-Tm 2033 2034 718 tephra associated with the ME (McLean et al., 2016; Hakozaki et al., 2017; 2035 2036 2037 2038 2039 34 2040 2041 2042 2043 719 Oppenheimer et al., 2017). All the known distal ash deposits associated with 2044 2045 2046 720 eruptions at Changbaishan and possible correlations to proximal units on the 2047 2048 721 volcano are summarised in Figure 7 and are discussed below. 2049 2050 722 2051 2052 723 5.2.1. Post 86 ka (Aso-4) Changbaishan eruptions 2053 2054 724 2055 2056 725 To date, at least four individual tephra layers originating from Changbaishan 2057 2058 726 have been recognised in marine cores stratigraphically positioned between the 2059 2060 727 Aso-4 and AT tephra layers (Figure 7). The two oldest, Baegdusan-Yamato 2061 2062 2063 728 Basin (B-Ym; ca. 85.8 ka) and Baegdusan-Sado-Oki (B-Sado; ca. 67.6 ka) 2064 2065 729 tephras, have been identified as cryptotephra horizons in both the GH89-2-26 2066 2067 730 and GH89-2-28 marine cores (Figure 7; Lim et al., 2013). Lim et al. (2013) 2068 2069 731 report that the B-Ym and B-Sado glass shards are trachytic in composition 2070 2071 732 (Figure 8). More recently, Derkachev et al. (in press) also identify visible 2072 2073 733 deposits in several marine cores across the Yamato and Pervenets Rise (e.g., 2074 2075 734 cores Lv53-25, Lv53-20, Lv53-27, and Lv53-29) that they correlate to the B- 2076 2077 735 Sado tephra. The constructed age models for these marine cores suggest an 2078 2079 736 eruption age ca. 71 ka (Derkachev et al., in press). 2080 2081 2082 737 2083 2084 738 The Baegdusan-Japan (B-J) tephra is found between Ulleungdo U-Ym and U- 2085 2086 739 Sado tephra layers (Figure 7), and estimated to have been erupted at ca. 50 ka 2087 2088 740 based on correlations with the regional-scale thinly laminated layer 2089 2090 741 stratigraphy (Ikehara et al., 2004; Lim et al., 2013; Derkachev et al., in press). 2091 2092 742 Ikehara et al. (2004) and Lim et al. (2013) report a homogenous rhyolitic 2093 2094 743 composition for the B-J tephra, with ca. 71.2 wt. % SiO2, ca. 12.0 wt. % Al2O3, 2095 2096 2097 2098 2099 35 2100 2101 2102 2103 744 and total alkalis of 11.1 wt. % (Figure 8). It contrasts with the exclusively 2104 2105 2106 745 trachytic glass compositions of the older ca. 67.6 ka B-Sado tephra (Lim et al., 2107 2108 746 2013). 2109 2110 747 2111 2112 748 Derkachev et al. (in press) report a 5 mm thick volcanic ash layer in a sequence 2113 2114 749 (Lv53-23 at 211 cm) from the Yamato Rise, about 270 km SE of Changbaishan, 2115 2116 750 in the Sea of Japan. This deposit is therein named the Baegdusan-Unknown (B- 2117 2118 751 Un1) tephra and represents another explosive event dated to around 38.3 ka. 2119 2120 752 The glass chemistry of this layer is somewhat distinct, containing ca. 73.9 wt. 2121 2122 2123 753 %, ca. 13.5 wt. % Al2O3, and total alkalis of 8.2 wt. % 2124 2125 754 2126 2127 755 The Lake Suigetsu sediments also provide evidence of another explosive 2128 2129 756 eruption of Changbaishan chronologically occurring between the B-J and B-Un1 2130 2131 757 event. A cryptotephra layer (SG14-3380) is found ca. 1.6 m below the U-Ym 2132 2133 758 tephra (SG14-3216) and this depth corresponds to a date of 42,750 – 42,323 2134 2135 759 IntCal13 yrs BP (95.4 % confidence interval). The glass compositions of SG14- 2136 2137 760 3380 are exclusively trachytic and geochemically overlap with proximal units 2138 2139 761 assigned to the late phase of the ME (e.g., NS-4 and NS-5 proximal deposits; 2140 2141 2142 762 Sun et al., 2017) (Figure 8) and other distal occurrences of the trachytic end 2143 2144 763 member of the B-Tm ash (e.g., Okuno et al., 2011; Hughes et al., 2013; Sun et 2145 2146 764 al., 2015; Chen et al., 2016). SG14-3380 does not geochemically overlap with 2147 2148 765 the reported composition of the ca. 38 ka B-Un1 tephra reported in the Yamato 2149 2150 766 Rise (Derkachev et al., in press), or the ca. 50.5 ka B-J tephra (Ikehara et al., 2151 2152 767 2004; Lim et al., 2013) clearly indicating that they represent separate eruptions 2153 2154 768 of Changbaishan. Here, we name the Suigetsu distal ash of this Changbaishan 2155 2156 2157 2158 2159 36 2160 2161 2162 2163 769 eruption (ca. 42 ka) as the Baegdusan-Suigetsu-42 (B-Sg-42) tephra, following 2164 2165 2166 770 the convention of naming proximally undefined distal deposits using the type- 2167 2168 771 locality. 2169 2170 772 2171 2172 773 A post-AT distal tephra named the Baegdusan-Vladivostok (B-V) ash was found 2173 2174 774 in the Primorye regions of Russia, and in the north-eastern part of the Japan 2175 2176 775 Sea (Figure 1; Machida and Arai, 2003; Ikehara, 2003; Derkachev et al., in 2177 2178 776 press). The eruption age is estimated to ca. 29 ka (Derkachev et al., in press). 2179 2180 777 2181 2182 2183 778 5.2.2. Holocene Changbaishan eruptions 2184 2185 779 2186 2187 780 An eruption from Changbaishan was identified in Lake Suigetsu (SG14-1058) at 2188 2189 781 8,166 – 8,099 IntCal13 yrs BP (95.4 % confidence interval; McLean et al., 2018) 2190 2191 782 and was the first known discovery of a large early Holocene eruption from this 2192 2193 783 volcano. A visible patchy grey peralkaline tephra has since been identified in 2194 2195 784 Lake Yuanchi, located ca. 30 km east of Changbaishan in China, which is dated 2196 2197 785 to a similar age as the Suigetsu layer, 8,831 – 8,100 IntCal13 yrs BP (95.4 % 2198 2199 786 confidence interval; Sun et al., 2018). The major element glass compositions of 2200 2201 2202 787 this Yuanchi tephra broadly overlap with those of SG14-1058 (Figure 8c), 2203 2204 788 although some offsets, which are close to instrumental/analytical uncertainty, 2205 2206 789 are observed. Sun et al. (2018) also suggest the Suigetsu SG14-1058 and 2207 2208 790 Yuanchi tephra are distal deposits from the eruption that produced the 2209 2210 791 Qixiangzhan comendite lava flow, but it is not known if there was an explosive 2211 2212 792 phase associated with this eruption, and the stratigraphic relationship between 2213 2214 793 the Qixiangzhan comendite and the explosive pre-ME fall deposits is not 2215 2216 2217 2218 2219 37 2220 2221 2222 2223 794 known. Furthermore, the chronological uncertainty on 40Ar/39Ar ages for the 2224 2225 2226 795 Qixiangzhan comendite mean that it could be a separate eruption (e.g., Singer 2227 2228 796 et al., 2014; Yang et al., 2014). When normalised to mantle concentrations, we 2229 2230 797 find that SG14-1058 only shows a minor depletion in Nb, unlike SG06-0226 (B- 2231 2232 798 Tm ash) and C-3 unit (Chen et al., 2016), which could help identify the proximal 2233 2234 799 deposit. We suggest that the distal ash erupted from Changbaishan at ca. 8.1 2235 2236 800 ka (e.g., SG14-1508) is named Baegdusan-Suigetsu-08 (B-Sg-08). 2237 2238 801 2239 2240 802 No distal ash deposits have been identified that geochemically or 2241 2242 2243 803 chronologically overlap with the pre-ME proximal deposits of NS-4 and NS-5 2244 2245 804 that are dated to ca. 4 – 5 ka (Sun et al., 2017). Similarly, even in the high- 2246 2247 805 resolution archives in northern Japan (e.g., Lake Kushu; Chen et al., 2019) 2248 2249 806 there are no clear isochrons representing post-ME ash eruptions of 2250 2251 807 Changbaishan. 2252 2253 808 2254 2255 809 6. Conclusions 2256 2257 810 2258 2259 811 Distal records can provide useful information on past eruption activity from 2260 2261 2262 812 volcanoes whose deposits are inaccessible for various reasons, e.g., burial or 2263 2264 813 deposition into dynamic ocean environments. The new occurrences reported 2265 2266 814 here and considered with other known distal alkali-rich ash units found in 2267 2268 815 marine and lacustrine cores (spanning the last 86 kyrs) in the East Asian/Pacific 2269 2270 816 region provide an improved eruption framework for intraplate volcanoes, 2271 2272 817 Ulleungdo and Changbaishan. This framework shows that there are numerous 2273 2274 2275 2276 2277 2278 2279 38 2280 2281 2282 2283 818 explosive eruptions responsible for distal ash fall events that are only cryptically 2284 2285 2286 819 recorded in the geological record. 2287 2288 820 2289 2290 821 Ulleungdo has erupted explosively at least five times over the last 86 kyrs (since 2291 2292 822 the deposition of the Aso-4 tephra) and these are: the 60 – 61 ka U-Sado 2293 2294 823 tephra (Lim et al., 2013); the ca. 40.1 ka U-Ym tephra (this study); the ca. 10 ka 2295 2296 824 U-Oki/U-4 tephra (Smith et al., 2011; 2013); ca. 8.4 ka tephra (U-3; McLean et 2297 2298 825 al., 2018); and the ca. 5.7 ka U-2 tephra (McLean et al., 2018). Furthermore, it 2299 2300 826 is likely that a younger eruption from Ulleungdo occurred ca. 2.7 ka, but 2301 2302 2303 827 chemical analyses of proximal deposits are required to confirm the correlation. 2304 2305 828 This age would be consistent with an eruption repose interval of <3 ka 2306 2307 829 throughout the Holocene. 2308 2309 830 2310 2311 831 The new Changbaishan-derived tephra layers identified in the Suigetsu 2312 2313 832 sediments indicate that at least eight explosive eruptions have produced 2314 2315 833 significant ash dispersals over the last 86 kyrs which include the: ca. 85.8 ka B- 2316 2317 834 Ym (Lim et al., 2013); ca. 70 ka B-Sado (Lim et al., 2013; Derkachev et al., in 2318 2319 835 press); ca. 50.5 ka B-J tephra (Ikehara et al., 2014; Lim et al., 2013; Derkachev 2320 2321 2322 836 et al., in press); ca. 42.5 ka B-Sg-42 (this study), ca. 38 ka B-Un1 (Derkachev et 2323 2324 837 al., in press), ca. 25 ka B-V (Machida and Arai, 2003); ca. 8.1 ka B-Sg-08 2325 2326 838 (McLean et al., 2018); and AD 946 B-Tm tephra associated with the ME 2327 2328 839 (Hakozaki et al., 2017; Oppenheimer et al., 2017). It is possible that additional 2329 2330 840 ash fall events will be discovered in other distal records in the future, as there 2331 2332 841 are some proximal units near Changbaishan (e.g., the compositionally distinct 2333 2334 2335 2336 2337 2338 2339 39 2340 2341 2342 2343 842 NS-4 and NS-5 layers; Sun et al., 2017) that have not yet been correlated to 2344 2345 2346 843 distal markers. 2347 2348 844 2349 2350 845 Even though Lake Suigetsu is located ca. 500 km E of Ulleungdo and ca. 1000 2351 2352 846 km SSE of Changbaishan (i.e., not downwind of the current prevailing winds), 2353 2354 847 tephra from these volcanoes is clearly preserved in the sediments. The 2355 2356 848 eruptions responsible for the B-Sg-42 and B-Sg-08 distal tephra must have 2357 2358 849 been large eruption events (i.e., greater than VEI 5-6), based on the shard 2359 2360 850 concentrations preserved in Suigetsu (>18,000 shards per gram of dried 2361 2362 2363 851 sediment). Unfortunately, it is not possible to get better constraints on volume 2364 2365 852 and magnitude of these events given that they have not yet been found as 2366 2367 853 visible layers and have not been identified in multiple locations. The precise 2368 2369 854 ages provided in this paper from the Lake Suigetsu chronology may help locate 2370 2371 855 these deposits in other records, which may provide more information about the 2372 2373 856 eruptions and the dispersal of the events. Critically, these tephra occurrences 2374 2375 857 demonstrate that both Ulleungdo and Changbaishan have been more active 2376 2377 858 than previously thought, and the ash plumes from these explosive eruptions 2378 2379 859 were widespread. 2380 2381 2382 860 2383 2384 861 2385 2386 862 Acknowledgements 2387 2388 863 The SG14 (formally ’Fukui-SG14’) sediment coring campaign was funded by the 2389 2390 864 Fukui Prefectural government, and the coring was conducted by the team of 2391 2392 865 Seibushisui Co. Ltd. Japan, led by Mr. Atsumi Kitamura. KAKENHI grants by 2393 2394 866 MEXT, Japan (15H021443 and 18H03744 to TN) as well as grants by Casio 2395 2396 2397 2398 2399 40 2400 2401 2402 2403 867 Science Promotion Foundation were used to purchase laboratory equipment 2404 2405 2406 868 and consumables during the project. Trace element analysis was funded by the 2407 2408 869 Japan Society for the Promotion of Science (JSPS) 2018 Summer Program. DM 2409 2410 870 was funded by NERC (grant: NE/L002612/1) and part of the Environmental 2411 2412 871 Research Doctoral Training Program at the University of Oxford. PGA and RAS 2413 2414 872 were supported by Early Career Fellowships from the Leverhulme Trust (grant: 2415 2416 873 ECF-2014-438 and ECF-2015-396). Geochemical bi-plots were generated 2417 2418 874 using the RESET plot function (https://c14.arch.ox.ac.uk). We would like to 2419 2420 875 thank the two anonymous reviewers for their feedback on an earlier version of 2421 2422 2423 876 the manuscript. 2424 2425 877 2426 2427 878 References 2428 2429 879 2430 2431 880 Albert, P. G., Tomlinson, E. L., Smith, V. C., Di Roberto, A., Todman, A., Rosi, 2432 2433 881 M., Marani, M., Muller, W. and Menzies, M. A. 2012. Marine-continental tephra 2434 882 correlations: volcanic glass geochemistry from the Marsili Basin and the Aeolian 2435 2436 883 Islands, Southern Tyrrhenian Sea, Italy. 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