第 四 紀 研 究 (The Quaternary Research) 30 (2) p. 141-149 July 1991

Recent Progress in Tephra Studies in Japan1)

Hiroshi MACHIDA1)

This paper presents an overview of the development of tephrochronology in Japan, and discusses several problems regarding the Japanese Quaternary. The impact of developments in such subjects as soil science, archaeology, radiometric dating and many other disciplines of Quaternary research has stimulated the tephrochronology in studies of earlier periods. However, recent advances seem more closely related to indigenous factors. Since the early 1970's, systematization of tephrochronology and fundamental characterizations for the identification of widespread tephras, occuring in and around the Japanese Islands, have initiated revision and refinement of regional stratigraphies, revolutionary studies of tephra for determining the nature and effects of explosive eruptions, and new applications to several aspects of Quaternary studies. A compilation of tephra catalogue for the Japan region provides fundamental data for correlations on land and in sea and for determining the recurrence period of cataclysmic explosive volcanism.

I. Volcanoes in Japan as sources Honshu, the Izu-Ogasawara and the Ryukyu of tephra island arcs are characterized by stratovolcanoes with or without calderas, producing a large Plate tectonic models show that the volcanic quantity of lava and tephra of various com- zones of Japan can be divided into two: ast and position. Accordingly, a more or less continu- west (SUGIMURA, 1960).The east volcanic zone ous mantle of tephra exists over some 40% of the lies on the edge of the North American Plate four main islands, resulting in strong control of which is being underthrust by the subducting landforms and subsurface materials. oceanic Pacific Plate. The west zone is being It is for only about 60 years that the tephra has formed by the interaction between the Eurasian received special attention whereas the lava has Plate and the Philippine Sea Plate. Large quan- been the subject of volcanological study for tities of lava and tephra, mainly of rhyolitic and around 100 years in Japan. In this paper I andesitic composition, have erupted throughout review the recent developments in tephrochro- the Quaternary from about 200 volcanic centers, nology emphasizing that tephra is very useful of which about 80 have continued their activity tool for Quaternary research in Japan. into historic times. In the west Japan volcanic zone, Kyushu is II. Recent developments in characterized by clusters of large caldera vol- tephra studies in Japan canoes, which are sites of large-scale explosive The history of tephra studies in Japan can be volcanism producing a number of ignimbrite and divided into four periods: 1) early 1930s to widespread airfall tephra sheets, as mentioned 1950s, 2) 1950s to early 1960s, 3) early 1960s to later. In the east volcanic zone, numbers of late 1970s, 4) late 1970s to the present. large-scale explosive volcanism occurred, Period 1: Pioneer studies on classification, particularly in Hokkaido and northern Honshu mapping, age estimation and other aspects of caldera volcanoes, producing extensive tephra Holocene tephras were carried out with soil sheets. Other volcanic centers or districts in survey in Hokkaido (URAGAMI et al., 1933).

1) Received 5 February 1991. Accepted 13 May 1991. 2) Department of Geography, Faculity of Science, Tokyo Metropolitan University. 142 The Quaternary Research Vol. 30 No. 3 July 1991

Studies of Pleistocene tephras in the Kanto plain, remote districts with one another but also to certral-east Honshu, were started by HARADA approach various stratigraphical and volcanolog- (1943). ical problems as described below. Period 2: Archaeological discovery of Ages of tephrogenic eruptions in the last 1.5ka palaeolithic culture in upper Pleistocene tephra have been determined by historical documenta- sequences of the Kanto and the first use of the 14C tion together with archaeology and dendrochro- dating method stimulated interdisciplinary nology. The majority of tephras ejected tephra studies. In addition, tephra sequences between c. 30ka and 1.5ka BP have been dated were studied in detail together with geomorphic by the 14C method. Moreover, the use of other surfaces and various Quaternary sediments dating techniques, including fission-track, (KANTO LOAM RESEARCH GROUP, 1965) and with uranium series, thermo-luminescence, electron palaeontologic and geomagnetic studies (ITIHARA spin resonance and K-Ar methods, means that et al., 1975). the tephrochronological approach can be Period 3: Progress in tephrostratigraphy, employed beyond the limit of 14C dating. and radiometric dating and other Quaternary Indeed, a number of ages obtained by various research led to the establishment of a standard methods from the same tephra at different chronology for late Quaternary sequences in the localities can be checked with each other, South Kanto and for the early to middle resulting in high-quality age control. Also, the Pleistocene in the Kansai. In addition, sys- strictly identified tephra sequences should play tematization of tephrochronology through an important role in revision and refinement of volcanological interpretations of tephra and various radiometric ages. Fig. 1 is the time- fundamental characterization studies for tephra space diagram of the late-middle Quaternary identification were introduced (NAKAMURA et al., representative tephras and associated marine 1963: KOBAYASHI, 1969). terrace sequences from Kyushu to Hokkaido. Period 4: Discovery of a very widespread The increase in the number of dated marker- tephra layer (MACHIDA and ARAI, 1976) encouraged tephras has greatly contributed to the the volcanological studies on large-scale understanding of Quaternary problems. explosive volcanism and greatly contributed to IV. Widespread marker-tephra layers Quaternary studies over extensive areas, including the Japanese islands and adjacent seas. As a result of progress in characterization and Revision and refinement of proximal strati- identification of tephra, two very widespread graphy were associated with the identification of tephra layers from gigantic explosive volcanism such widespread marker-tephras. Land and of south Kyushu caldera volcanoes, Aira and sea correlation and chronology have been one of Kikai, were discovered and identified in un- the subjects of current studies. usually extensive areas, i.e., throughout Japan and the Sea of Japan as well as over the floor of III. Characterization and age determina- the Pacific Ocean to the south of Honshu tion for identification of tephra (MACHIDA and ARAI, 1976, 1978, 1983). Both Characterization of marker-tephra layers for tephra layers, Aira-Tn ash (AT in abbreviation) identification constitutes the basis for tephra of 22ka and Kikai-Akahoya ash (K-Ah) of 6.3ka, studies and is carried out from various view- provide distinct datum planes available for many points. Recently detailed descriptions have applications of Quaternary sciences in the Japan beengiven, not only of observable specific fea- region. These results encouraged the identifi- tures in the field and mineral assemblages cation of other widespread tephra layers in- available in proximal tephras but also of the cluding those of continental volcano origin (B- refractive indices and chemical compositions Tm and U-Oki). The petrographic characteris- ofvolcanic glass and specified minerals (ARAI, tics of fine-grained tephras have been thoroughly 1972; ARAMAKI and UI, 1976). As a result, it has investigated not only on land but also in cores become possible not only to correlate tephras in from abyssal sediments around Japan. Many 1991年7月 第 四 紀 研 究 第30巻 第3号 143

■ Pleistocene marine formation □ filltop fluvial formation △ glacial till Fig. 1 Time-space diagram of marker-tephras with the representative marine, fluvial and glacial sequence for the last 300ka tephra layers have been successfully identified, this type is closely associated with gigantic the most extensive from the late Quaternary are caldera collapse and should give a cataclysmic shown in Table 1. Fig. 2 shows approximate impact on the environment over extensive areas. outer limits of such widespread tephra layers of 2) Plinian tephra; Air-fall tephra produced by late Quaternary age as hitherto described. plinian eruption. A number of pumice fall The above-mentioned widespread tephras can layers of this type are found throughout Japan. be classified into three types according to The eruptions were often followed by extrusions differences in their mode of ejection and of pyroclastic flow deposits. distribution: 3) Unusually large-scale pyroclastic flow 1) Co-ignimbrite tephra; Air-fall deposits deposits; These are represented by the Aira-Ito predominantly of fine-grained vitric ashes pyroclastic flow of the Aira caldera and the Aso- producing at the same time as huge pyroclastic 4 pyroclastic flow of the Aso caldera, and occur flows (MACHTDA and ARAI, 1976; PARKS and extensively in a concentric pattern centered at WALKER, 1977). The volume of tephra of this the source different from that of plinian tephras. type often exceeds that of the associated Recent tephra studies revealed that such pyroclastic flow deposits. Hence eruption of catalysmic pyroclastic flows can usually be 144 The Quaternary Research Vol. 30 No. 3 July 1991

Fig. 2 Map showing general distribution of the representative marker-tephras of the late Pleistocene in Japan and adjacent areas 1991年7月 第 四 紀 研 究 第30巻 第3号 145

Table 1 Representative large scale eruptions that occurred in and around Japan during the last 300,000 years

FT: fission-track method, U: Uranium-series method, TL: thereto-luminescence method, ST: stratigraphic method. p: plinian eruption, pp: phreatoplinian eruption, i; ignimbrite forming eruption, c: coignimbrite ash fall. pm: pumiceous glass, bw; platy bubble walled glass, af; alkali feldspar, pl; plagioclase, qt; quartz., ol; olivine. opx; orthopyroxene, cpx; clinopyroxene, ho; hornblende, bi; biotite. n, n1, n2, γ; refractive index of glass and phenocrysts. traced as low aspect ratio ignimbrite more than sequences in areas such as the South Kanto, 100km distant from the source (Fig. 1). central Japan, where a standard chronology of Standard ages of most widespread tephras tephra and marine sequences has already been older than the limit of 14Cdating have been given established (MACHIDA, 1975). not only by individual radiometric methods but V. Impact of catastrophic explosive also by stratigraphic and synthetic interpreta- volcanism on the environment tions (Fig, 1). Ages of most widespread tephras and its frequency in the Japan derived from Kyushu calderas, for example, were region during the last 130ka estimated by examining their stratigraphic positions within well-dated Quaternary The Kikai-Akahoya ash represents the biggest 146 The Quaternary Research Vol. 30 No. 3 July 1991 explosive even in the Japanese Holocene. More VI. Tephrochronological applications to than fifty 14C ages for this tephra indicate that the eruption occurred around 6.3ka (MACHIDA Quaternary records and ARAI, 1983). MACHIDA (1984) discussed how Applications of tephrochronology are of many great this volcanic impact was to human beings types: to interpret global and regional Qua- and their environment, on the basis of joint ternary environmental changes on land as well studies between volcanology and archaeology. as in the sea, to disclose the growth history of In fact, this study clearly suggests that a major volcanoes and such problems as the behavior of cultural discontinuity existed between the pre- magma and the nature of eruptive mechanisms tephra Earliest Jomon culture phase and the and to approach to the origin and age of tephric post-tephra Early Jomon phase. This indicates soils and the genesis of clay minerals and their that people with the pre-tephra Jomon culture in controlling factors. In this paper, recent southern Kyushu either dispersed to the studies of sea level and associated changes and northwestern part of Kyushu where volcanic the eruptive history of volcanoes are reviewed. impact was not so severe, or that they totally Sea level studies and associated palaeo- perished in the area. In addition, there is lots of geography and oceanography evidence that the K-Ah eruption induced a 1) Marine-terrestrial sequences in the middle significant change in landforms over a vast area Pleistocene and must have produced a significant decline in In Japan, the Shimosa-Kazusa groups and natural productivity over this same area. their correlatives in the South Kanto and the The bulk volume of the K-Ah tephra including upper part of the Osaka group both represent the plinian pumice, pyroclastic flows and co- standard early to middle Quaternary sequences ignimbrite ash is estimated to be more than and have been studied in detail. These groups 150km3, the size of the 1815 Tambora eruption. are characterized by the cyclic sedimentation Every eruption listed in Table 1 produced a large caused by transgression and regression cor- quantity of 100-1000km3 of ejecta,similar to responding with global climatic changes. By the K-Ah eruption in bulk volume. These erup- the middle 1970s chronological study in both tions can be assessed in terms of Volcanic areas was carried out independently. At the Explosivity Index (VET) on a scale of 7, which end of the 1970s', several important marker- SIMKIN et al. (1981) and NEWHALL and SELF (1982) tephras were identified giving datum planes and proposed. The impact of such large-scale erup- resulting in the correlation of both stratigraphic tions on flora and fauna, as well as human beings sequences (MACHIDA et al., 1980). would be of severe consequence over vast areas. These marker-tephra layers have been dated Tephrochronology should provide fundamental by radiometric and stratigraphic methods. data for determining the recurrence period of This information indicates that three major such cataclysmic explosive volcanism. transgressive-regressive cycles were recorded A catalogue of late Quaternary tephra in Japan during the period from the Brunhes-Matuama and Korea, gives the frequency of very large geomagnetic boundary (c. 700ka) to the Sakura- eruptions, with VEIS 5 to 7, during the last 130ka Kasamori 11 tephra horizon (c. 450ka) in both (MACHIDA,1990). The data indicate that in Japan areas. Also, at least five major cycles can be and adjacent areas, eruptions with index 5, the seen during the next 320ka, from the Sakura- size of the 1980 Mount St. Helens eruption, have Kasamori 11 tephra horizon to the last in- occurred at an average of once per century. terglacial transgression (130ka) in the South Those like Krakatau of 1883, with index 6, have Kanto. occurred twice or thrice per 10ka, whereas those On the basis of recent progress in identifica- of VEI 7, like Tambora of 1815, have occurred tion of marker-tephras in marine and/or ter- perhaps once every 10ka over the last 130ka. restrial sequences at several localities in Japan, it will be possible to discuss sea-level fluctuations and local crustal movements in such areas as 1991年7月 第 四 紀 研 究 第30巻 第3号 147

Tanegashima, Miyazaki, Oga, etc (OTA and Hb (100-120ka), etc (Fig. 1, Table 1). Such MACHIDA, 1987). correlationof marine terraces clearlyindicates 2) Sea level changes in the late Pleistocene and the difference in rates of regional tectonic Holocene deformations (OTA and MACHIDA, 1987). The most prominent marine formation in the Determination of ages of low sea levels South Kanto, the Shimosueyoshi terrace for- indicating glaciation, and evaluation of their mation provides considerable evidence that it magnitude is more difficult than of those for was formed in the interglacial stage. However, higher sea levels. However, on the eastern there were some arguments about the age of this coast of Tokyo Bay, problems can be approached stage: whether it can be assigned to the last by investigating fluvial sediments buried under interglacial or the penultimate one, and how old marine deposits. In addition, a comparison of it is. In 1971, a solution to this problem was fossil assemblages between periods, and provided by tephrochronological studies (MACHIDA investigation of the strata yielding large con- and SUZUKI, 1971). The transgression seems to tinental vertebrates indicates that land bridge have attained its culmination around 130ka connections with the continent occurred three because the TAu-12 tephra of Hakone origin times within the last 300ka (SUGIHARA et al., 1978). dated to around 143-147ka by the fission-track Of the periods of maximum lowering of sea method occurs within the marine formation of levels, those at c. 250ka and c. 150-140ka this stage and the K1P-6 tephra of Hakone, with would be the periods of greatest magnitude. an age of around 128ka, covered the palaeo- The Aira-Tn ash with a 14C age of around shoreline and terrace of the Shimosueyoshi 22ka, should be the most useful marker of the stage. last glaciation. A unique chronostratigraphic The standard sections for younger marine horizon of it suggests that the coldest climate and terraces are located in the Miura Peninsula, the lowest sea level occurred soon after this South Kanto, where three late Pleistocene tephrogenic eruption. In addition, the marked terraces are observed and named as the decrease of 18O values of the planktonic fora- Hikihashi, Obaradai and Misaki terraces. The miniferal tests indicates a continuous decrease ages of formation of each terrace were estimated in the salinity of the Sea of Japan, caused by 105ka, 80ka and 60ka respectively on the basis palaeo-geographic checking of the inflow of of the stratigraphical relation with several water from the open sea (ARAIet al., 1981). marker-tephra layers, dated by fission-track The Kikai-Akahoya ash, the most notable method (MACHIDA and SUZUKI, 1971; MACHIDA,time-marker in the Japanese Holocene, occurs in 1975). Recent observations indicate that marine deposits at various localities in relatively low sea level stands prior to the southwestern and central Japan. It is of critical formation of each terrace are highly likely age (6.3ka) for the understanding of different probable (Fig. 1). environments associated with the postglacial In the coastal areas of Japan, there are many transgression, as well as local tectonic places where a series of marine terraces has movement. Vertical changes in the foraminif- developed. No ages for these are known except eral and oxygen isotope characteristics in the for the above-mentioned South Kanto and for the cores bearing this tephra, and the underlying Ryukyu terraces, composed of datable coral Ulreung-Oki ash (c. 9.3ka) from the southern limestone. With the recent identification of part of the Sea of Japan, clearly indicate that an several widespread marker-tephra layers, abundant inflow of the warm current water from marine terraces of the late Pleistocene in almost the Pacific Ocean and East China Sea began all coastal plains of Japan can be readily iden- around 8ka, between these two tephrogenic tified by direct tephrostratigraphic control. eruptions (ARAI et al., 1981). This may have The principal time-markers are Aso-4 (c. 70ka), largely depended on widening of the two straits, K-Tz (c.75ka), On-PmI (c.80ka), Ata (85- Tsushima and Tsugaru, caused by the sea-level 90ka), SK (80-90ka), Toya (90-100ka), Kc- rise. 148 The Quaternary Research Vol. 30 No. 3 July 1991

Eruptive history of volcanoes H. (1981) Late Quaternary tephrochronology and Establishment of the chronostratigraphy of palaeo-oceanography of the sediments of the Japan widespread tephras and local tephras enables us Sea. The Quat. Res. (Daiyonki-Kenkyu), 20, p. 209- to interpret the eruptive history of the principal 230. ARAI, F., MACHIDA, H., OKUMURA, K., MIYAUCHI, T., SODA, volcanoes of Japan (MACHIDA,1980). Among the T. and YAMAGATA, K. (1986) Catalog for late stratovolcanoes such active ones as Sakurajima, Quaternary marker-tephras in Japan II-Tephras the central cones of Aso, Asama and Izu-Oshima occurring in Northeast Honshu and Hokkaido-Geogr. have grown up only in the last several tens of Rept. Tokyo Metropol. Univ., 21, p. 57-84. thousands of years or less. The larger the size ARAMAKI, S. andUI, T. (1976) Pyroclastic deposits in of the cone, the longer the period of activity and southern Kyushu-A correlation by the Ca-Mg-Fe the greater the number of tephra sheets. The ratios of the phenocrystic minerals. Bull. Earthq. eruptions were not generally explosive but Res. Inst., 51, p. 151-182. occurred at frequent intervals, so that the FURUTA, T., FUJIOKA, K. and ARAI, F. (1986) Widespread tephras of any one cycle of eruption have a submarine tephras around Japan-Petrographic and chemical properties. Marine Geology, 72, p. 125- comparatively small volume. For large 142. composite volcanoes, the larger the size, the HARADA, M. (1943) Studies on the genesis of Kanto loam. longer the period of activity, often dating back to Rept. Dept. Pedology, Univ. Tokyo, 3, p. 1-140. the middle Pleistocene as in the cases of Hakone, HAYASHI, M. and MIURA, K. (1987) Stratigraphy and Daisen, Akagi, Yatsugatake and Ontake. distribution of tephra arising from Sambe volcano. Tephrostratigraphic studies suggest that most Regional Studies of Sa'in, 3, p. 43-66. of the large caldera volcanoes have a history of ITIHARA, M., YOSHIKAWA, S., INOUE, K., HAYASHI, T., repeated cataclysmic eruptions, as mentioned TATEISHI, T. and NAKAJIMA, K. (1975) Stratigraphy of earlier. the Plio-Pleistocene Osaka Group in the Sennan- Deep sea tephrochronology Senpoku areas, south of Osaka, Japan-A standard Identification of marker-tephra layers in deep stratigraphy of the Osaka Group-. J. Geosci., Osaka City Univ. 19, p. 1-29. sea sediments provides useful data for KANTO RESEARCH GROUP (1965) Kanto loam formations- determining the ages of sediments and for their origin and nature, isopach map, geological map, isotope stratigraphy, consequently indicating atlas of columnar sections. 378pp Tsukiji-shokan, environmental changes (ARAI et al., 1981; MACHIDA Tokyo. and ARAI, 1988; FURUTA et al., 1988). In addition, KATSUI, Y. (1959) On the Shikotsu pumice fall deposit. Bull. some revision and refinement of ages and Vollcanol. Soc. Japan, Ser. 2, 4, p. 33-48. magnitude of eruption would be given by deep KOBAYASHI K., MINAGAWA, K., MACIDA, M., SHIMIZU, H. and sea tephras. The abyssal sediment of the Sea of KITAZAWA, K. (1968) The Ontake pumice-fall deposit Pm- Japan was studied in more detail to obtain 1 as a late Pleistocene time-marker in central Japan. important information on palaeo-oceanography J. Fac. Sci. Shinshu Univ., 3, p. 171-198. in the post-glacial, as mentioned earlier. KOBAYASHI, K. (1969) Methodsof identification of par- ticular tephra layers. Etude sur le Quaternaire dans le However, little is known for older periods, not Monde, p. 981-984. only in the Sea of Japan but also in the Pacific MACHIDA, H. (1975) Pleistocene sea levelof South Kanto, Ocean. The joint study of tephrochronology Japan, analysed by tephrochronology. In R.P. and palaeo-oceanography is one of the important SUGGATE and M.M. CRESSWELL (eds.): Quaternary topics of current research. Studies. Royal Soc. New Zealand Bull., 13, p. 215-222. MACHIDA, H. (1980) Tephra and its implications with References regard to the Japanese Quaternary period. In ARAI, F. (1972) Identification of particular tephras by ASSOC. JAPAN. GEOGR.: Geography of Japan, p. 29-53. means of refractive indices of orthopyroxenes or MACHIDA,H. (1984) The significance of explosive hornblendes-A fundamental study of tephrochro- volcanism in the prehistory of Japan. Geol. Survey nology. The Quat. Res. (Daiyonki-Kenkyu), 11, p. 254- Japan, Rept., 263, p. 301-313. 270. MACHIDA,H. (1990) Frequency and magnitude of ARAI, F., OBA, T., KITAZATO, H., HORIBE, Y. and MACHIDA,catastrophic volcanism in the Japan region during 1991年7月 第 四 紀 研 究 第30巻 第3号 149

the past 130ka: Implications for human occupance NEWHALL, C.G. and SELF, S. (1982) The volcanic of volcanic regions. Geol. Soc. Australian Symposium explosivity index (VET): An estimate of explosive Proc., 1, p. 27-36. magnitude for historical volcanism. J. Geophys. MACHIDA, H. and SUZUKI, M. (1971) A chronology of Res., 87, (C2), p. 1231-1238. the late Pleistocene tephras as established by OKUMURA, K.(1988) Recurrence of large pyroclastic fission-track dating. Kagaku, 41, p. 263-270. flows and innovation of volcanic activity in eastern MACHIDA, H. and ARAI, F. (1976) The discovery and Hokkaido, Japan. Proc. Kagoshima Intern. Conf. significance of the very widespread tephra: The Volcanoes, p. 518-521. Aira-Tn ash. Kagaku, 46, p. 339-347. ONO, K., MATSUMOTO, Y., MIYAHISA, M., TERAOKA, Y. and MACHIDA, H. and ARAI, F. (1978) Akahoya ash-A KAMBE, N. (1977) Geologyof the Taketa district. Geol. widespread marker erupted from Kikai caldera, Surv. Japan, 156pp. southern Kyushu, Japan. The Quat. Res. (Daiyonki- OTA, Y. and MACHIDA, H. (1987) Quaternary sea level Kenkyu), 17, p. 143-163. changes in Japan. In M.J. TOOLEY and I. SHENNAN MACHIDA, H. and ARAI, F (1979) Daisen Kurayoshi (eds.): Sea-level Changes., p. 182-224, Blackwell, pumice: Stratigraphy, distribution and implication London. to late Pleistocene events in central Japan. J. Geogr. SPARKS, and WALKER, G. (1977) The significance of Tokyo, 88, p. 313-330. vitric-enriched air-fall associated with crystal- MACHIDA,H., ARAI, F. and SUGIHARA,S. (1980) enriched ignimbrites. J. Volcanol. Geotherm. Res., 2, Tephrochronological study on the middle Pleisto- p. 329-341. cene deposits in the Kanto and Kinki districts, Japan. SIMKIN, T., SIEBERT, L., McCLELLAND, L., MELSON, W.G., The Quat. Res. (Daiyonki-Kenkru), 19, p. 233-261. BRIDGE, D., NEWHALL, C.G. and LATTER, J. (1981) MACHIDA, H. and ARAI, F. (1983) Extensive ash falls in Volcanoes of the world. Smithsonian Inst., and around the Sea of Japan from large late Hatchinson Ross., 233p. Quaternary eruptions. J. Volcanol. Geotherm. Res., SUGIHARA, S., ARAI, F. and MACHIDA, H. (1978) 18, p. 151-164. Tephrochronology of the middle to late Pleistocene MACHIDA, H., ARAI, F., Lee, B., MORIWAKI, H. and FURUTA, sediments in the northern part of the Boso T. (1984) Late Quaternary tephras in Ulreung-do Peninsula, Central Japan. J. Geol. Japan, 84, island, Korea. J. Geogr. Tokyo, 93, p. 1-14. p. 583-600. MACHIDA, H., ARAI, F. and MOMOSE, M. (1985) Aso-4 ash: SUGIMURA, A. (1960) Zonal arrangement of some A widespread tephra and its implications to the geophysical and petrological features in Japan events of late Pleistocene in and around Japan. Bull. and its environs. J. Fac. Sci., Univ. Tokyo, Sec. II, 12, Volcanol. Soc. Japan, Ser. 2, 30, p. 49-70. p. 133-153. MACHIDA, H., ARAI, F., MIYAUCHI, T, and OKUMURA, K. TOYOKURA, I., OMURA, K., ARAI, F., MACHIDA, H., TAKASE, (1987) Toya ash-A widespread late Quaternary S., NAKADAIRA, K. and ITO, T. (1991) Identification of time-marker in Northern Japan-The Quat. Res. the Sambe Kisuki tephra found in marine terrace (Daiyonki-Kenkyu), 26, p. 129-145. deposits along coastal areas of Hokuriku district, and MACHIDA, H. and ARAI, F. (1988) A review of late its implications. The Quat. Res. (Daiyonki-Kenkyu), 30, Quaternary deep-sea tephras around Japan. Quat. p. 79-90. Res. (Daiyonki-Kenkyu), 26, p. 227-242. URAGAMI, K., YAMADA, S, and NAGANUMA, Y.(1933) NAKAMURA, K. ARAMAKI, S. and MURAI, I. (1963) Vol- Studies on the volcanic ashes in Hokkaido. Bull. canic eruption and nature of the pyroclastic depos- Volcanol. Soc., 1, p. 44-60. its. The Quat. Res. (Daiyonki-Kenkyu), 3, p. 13-30.