Eastern Foot Research Articles

Wide-angle seismic profiling across the middle Izu-Ogasawara arc for understanding boundary structure between the mature and juvenile arcs - KY0609 cruise -

We carried out a deep wide-angle seismic experiment using a large airgun array and total 95 ocean bottom seismo- graphs (OBSs) in the middle Izu-Ogasawara arc area, which was conducted by R/V Kaiyo of Japan Agency for Marine-Earth Science and Technology (JAMSTEC) from August 3, 2006 to September 1, 2006 (UTC) named as KY06-09 cruise. The seis- mic line runs from the Izu-Ogasawara trench to the eastern foot of the Kinan Seamount Chain in the Shikoku basin through the northern tip of the Ogasawara trough, the volcanic front located off south of the Sofugan and the Miocene Nishi-shichito ridge. Most important objective of this cruise is to construct a velocity structure across this area and clarify commonalities and dif fer- ences by comparison of velocity structures obtained with previous studies in the whole of Izu-Ogasawara arc regions. The key structures are the continuity of the crustal layers of the Ogasawara ridge and trough, and the current active arc obtained by p re- vious KY05-02 and KY05-11 cruises. And the high velocity lower crust with P-wave velocity of over 7.0 km/s is also one of the key structures because it was discovered at the arc-backarc transition zones in the western Izu-Ogasawara arc and the Mariana arc. The seismic signals propagated from an airgun array with a total capacity of 12,000 cu.in. were recorded by not only OBSs but also a 12-channnel streamer towed from stern. In this paper, we introduce the seismic experiment, especially the schedule and examples of OBS and reflection data.

Intrasite features distribution as a source of social information: The case of Djaba-Hosséré (Northern Cameroon)

The spatial organization of Dìì settlements has been considered as the reflection of the peculiar social organization of Dìì chiefdoms: a model based on an association of several lineages, most of them being necessary for the working of the whole. The distribution of thousands of surface remains (features and ceramics) located on the eastern foot of the Djaba massif, the site of the eponymous chieftaincy in the early 19th century, together with stratigraphic data, is likely to provide information about the age and the foundation process of a Dìì chiefdom. Following the spatial analysis, we will see that, locally, the growth of political complexity began about the 18th century and that this process may have resulted in the arrival of ‘foreigners’ among one or more of the autochthonous communities, one of what appears to have been strongly involved in metallurgical activities. Archaeological data seems thus to indicate that the foundation myth of the ‘generous foreigner’ shared by most of the Dìì chieftaincies was based on historical events.

The Athenian Prytaneion Discovered?

The author proposes that the Athenian Prytaneion, one of the city's most important civic buildings, was located in the peristyle complex beneath Agia Aikaterini Square, near the ancient Street ofthe Tripods and the Monument ofLysikrates in the modem Plaka. This thesis, which is consistent with Pausanias's topographical account of ancient Athens, is supported by archaeological and epigraphical evidence. The identification of the Prytaneion at the eastern foot of the Acropolis helps to reconstruct the map of Archaic and Classical Athens and illuminates the testimony of Herodotos and Thucydides.

噴出物から推定した有珠山１６６３年噴火の推移

The AD1663 ejecta of Usu volcano, western Hokkaido, northern Japan, have a thickness of approximately 200, cm and are divisible into 7 units on the eastern foot of Usu volcano. The basal deposit, Unit-A, is composed of fine-grained, poorly sorted pumice and ash with well-developed stratification. It contains base surge beds near the sources, and is interpreted as phreatomagmatic in origin. Unit-B is typical in many respects of the product of plinian activity. It is characterized by coarse grain size and wide dispersal, combined with low lithic contents and poor development of internal stratification. This fallout deposit (Usu-b tephra) can be seen in the eastern regions of Usu volcano, and has a thickness of about 4 cm at 200 km from the vent. Unit-C, Unit-E, Unit-F, and Unit-G have characteristics that are satisfactorily interpreted as a consequence of phreatomagmatic activity : fine grain size near source, poor sorting, well-developed stratification and base surge bedforms. Unit-D is typical of phreatic deposits, being composed largely of non-juvenile lithic fragments.According to historical records, the eruption was preceeded by earthquake swarms for 3 days from August 13, 1663. The first eruption (Unit-A) occurred on August 16, followed by an eruption associated with a large amount of pumice and ash (Unit-B) on August 17. The explosive eruptions lasted approximately 20 days.The petrographic properties of the plinian product differ considerably from those of the phreatomagmatic products. The pumice clasts of Unit-B contain abundant glass and little phenocryst (plagioclase, orthopyroxene, and hornblende). The glass has a relatively high refractive index (n = 1.490-1.492) and a low SiO2 content. Orthopyroxene in Unit-B has a relatively high refractive index (γ = 1.735-1.740) and low Mg#. The phreatomagmatic products are rich in massive glass. This glass has a relatively low refractive index (n = 1.475-1.490) and a high SiO2 content, with values differing among horizons. The compositional diversity of the 1663 products indicates the existence of some magma. Presumably, their mixing triggered the 1663 eruption of Usu volcano.

Bronzealderens kulthuse i Thy – Anlæg med relation til gravkulten

Bronzealderens kulthuse i Thy – Anlæg med relation til gravkulten

東北南部，会津地域周辺における中期更新世テフラの層序と編年

This study shows the revised stratigraphy and correlations of the middle Pleistocene tephras in and around the Aizu area, Northeast Japan. Significant marker tephras in this area are as follows, in descending order of stratigraphy : Nm-SB, TG, Hu-TK, and Kn-KD from volcanoes adjacent to Oze, So-OT, and APm. Stratigraphic positions of Sn-MT and Sn-SK are not clear, but they seem to be positioned near Kn-KD.Nm-SB (110 ka) from Numazawa caldera is mainly a plinian pumice fall deposit distributed in the central to western part of Fukushima Prefecture and northern part of Tochigi Prefecture. Eruption producing Nm-SB associated with ash fall, plinian eruption, and pyroclastic flow or pyroclastic surge. TG (125-135 ka), which is characterized by volcanic glass shards with a low index, was probably derived from the Sunagohara caldera. The distribution of fall-out tephra of TG is similar to that of Nm-SB, and pyroclastic flow deposit of TG is recognized southwest to west of the Numazawa caldera and along the western margin of the Aizu basin. The eruption process of TG comprises plinian eruption, pyroclastic flow, and plinian eruption.So-OT (300-330 ka) is composed of an ignimbrite and a fall-out tephra derived from the Shiobara caldera. This ignimbrite is known as Otahara pyroclastic flow deposit. On the other hand, fall-out tephra of So-OT has been newly identified. APm tephra beds are significant widespread tephras derived from volcano in the Hida mountains at 330-400 ka. This study corrects a correlation of APm in this area, which was shown by Suzuki (1993). Tephras identified as APm in this study are Nm-13, -14, -16 tephras below So-OT.Sn-MT (180-260 ka : FT ages) is composed of an ignimbrite and a fall-out tephra derived from the Sunagohara caldera. The former is part of the Sunagohara-Kubota tephra reported by Yamamoto and Sudo (1996) and the Pyroclastic Flow Deposit I reported by Mizugaki (1993). The latter is the Sunagohara-Kachikata tephra along the western margin of Aizu basin reported by Yamamoto and Sudo (1996), and the Okayaji Volcanic Ash Layer at the eastern foot of Adatara volcano reported by Soda and Saijo (1987). Sn-SK (220 ± 50 ka : FT age), originating from the Sunagohara caldera, was defined by Yamamoto and Sudo (1996). Sn-SK is composed of an ignimbrite and a fall-out tephra characterized by abundant accretionary lapilli. The latter is correlative to the Minowa Volcanic Ash Layer (Soda and Saijo, 1987) distributed at the eastern foot of Adatara volcano.All pyroclastic deposits derived from the Numazawa caldera are Nm-NM (5 ka), Nm-KN (50-55 ka), and Nm-SB (110 ka), and those from the Sunagohara caldera are TG (125-135 ka), Sn-MT (180-260 ka), and Sn-SK (220 ka). This means that, at both caldera, explosive eruptions occurred three times over 260, 000 years, and it appears that the active period of explosive eruptions moved from the Sunagohara caldera to the Numazawa caldera. This resulted in the preservation of volcanic landforms with more dissected caldera landforms at the Sunagohara caldera. Intervals between eruptions at the Numazawa caldera range from 50, 000 to 60, 000 years, and the volumes of the three products are similar, indicating periodic and regular activities with a discharge rate of 0.02-0.06 DRE km3/1, 000 years. On the other hand, the mean interval of eruptions at the Sunagohara caldera is 70, 000 to 40, 000 years, and the discharge rate is estimated to be 0.05-0.08 DRE km3/1, 000 years : the latter is equivalent to or a little larger than that of the Numazawa caldera.

金剛断層系の平均変位速度分布と奈良盆地南西縁地域における地形発達

The Nara basin, located in the central part of the Kinki triangle in central Japan, mainly consists of Plio-Pleistocene sediments (Osaka group), Pleistocene terrace deposits, and Holocene alluvial deposits.The upper most part of the Osaka group extending in this area consist of fluvial deposits, and is correlated with the Ma3, which is includes the Azuki tephra.The terrace surfaces have developed along the eastern foot of the Kongo-katsuragi Range, in the southwestern part of the basin. Based on the distribution of surface heights and stratigraphies, these terraces are classified into the H, Ml, M2, M3, Li, and L2 surfaces in descending order.The Kongo fault system striking in the north-south direction extends along the eastern foot of the Kongo-katsuragi Range. This fault system consists of the Yamaguchi, Kongo, Nakato, and Yamada faults. These faults have displaced fluvial terrace surfaces, and the slip rates of the vertical component are about 0.03-0.3 m/ky.The Median Tectonic Line striking in the west-east direction and extending southward of the Nara basin, separates the Izumi Range and the Kinokawa lowland. The Shobudani fault, one of the fault systems of the Median Tectonic Line, had a tendency of reverse faulting activity in the former half of the Quaternary. On the contrary, right lateral faulting activity of the Gojodani fault started from the middle Pleistocene, and this tectonic movement has continued to the present along the Median Tectonic Line.Based on the stratigraphy of the Osaka group and fault activity around the study area, the fact that the Nara basin was divided from the Kinokawa lowland by reverse faulting of the Shoubudani fault at least the early Pleistocene, was, clarified. This faulting also formed the, present drainage pattern and the watershed located in the southwestern part of the Nara basin.Fault activity of the Kongo fault system started after the middle Pleistocene. The central part of the fault system shows the highest slip rate. On the contrary, the slip rate at the tips of fault system show a small value compared with the slip rate in the central part of the fault system. Both the height distribution of the terraces and that of the Kongo-katsuragi range, extending to the southwestern part of the Nara basin, have same trend in comparison with the distribution of slip rate along the Kongo fault system.In conclusion, tectonic movement with faulting of the Kongo fault system has affected the formation of landforms in the southwestern margin of the Nara basin.

Soil Classification of the Soils Developed at the Eastern Foot of Mt. Nantai by means of Unified Soil Classification System of Japan -2nd Approximation(2002)- and Correlation with Soil Classification of National Soil Survey

Soil Classification of the Soils Developed at the Eastern Foot of Mt. Nantai by means of Unified Soil Classification System of Japan -2nd Approximation(2002)- and Correlation with Soil Classification of National Soil Survey

Hydrogeological survey and satellite remote sensing in the Dunhuang area

Mogao Grottos are located at the eastern foot of the Mingsha Mountain, 25 km southeast of Dunhuang City. The caves were excavated into the cliff on the west bank of the Daquan River. The wall paintings in the caves are subject to the severe deterioration generated by recrystallization of salt. It relates with the movement of water/moisture in rock formation. Through the satellite image analysis and geological survey, it has been clarified that the movement of ground water is governed by the fault system. The geographical nature is specified by the aggressive tectonic movement from the south.

Observational Study on the Initial Formation Process of the Mei-yu Frontal Disturbance in the Eastern Foot of the Tibetan Plateau in Middle-Late June 1992

In this research, a case study is conducted on the formation process of the Mei-yu frontal disturbance in the eastern foot of the Tibetan Plateau. The target period is middle-late June of 1992, during which the Mei-yu front is re-intensified after the decaying phase observed in middle June. The re-intensification process of the Mei-yu front occurs in accordance with the approach of the migrating upper level trough to the north of the Plateau. When the upper level trough is situated to the northwest or north of the Plateau, the lower level high pressure area becomes apparent. Subsequently, the low pressure area on the northeast of the Plateau deepens. At the same time, a shallow cold air mass observed below the 700 hPa level formed in the southeast of the low pressure area. The appearance of the cold air mass might be related to the development of low and high pressure systems to the north-northeast of the Plateau. Concurrently, a lower level strong westerly wind appears along the northern periphery of the Plateau, and turns into northwesterly or northerly wind along the eastern periphery of the Plateau. A shear line formed in the northeastern or eastern foot of the Plateau between this northwesterly wind and the southerly wind prevailing over the North-Middle China Plain. This shear line in the lower layer changed into the Mei-yu frontal disturbance after∼:00UTC 21 June. Note that the wind system along the northern-eastern periphery of the Plateau mentioned above is considered to be an ageostrophic wind system, accompanied by the transient small scale low and high pressure systems that migrate clockwise along the northern-eastern periphery of the Plateau. The synchronic appearance of the cold air mass and the shear line is considered to be an effective trigger for the formation of the initial Mei-yu frontal disturbance. Further, the coupling of the upper level migrating trough and the lower level shear line also can be important for the evolution of the Meiyu frontal disturbance.

Ｄｕｎｈｕａｎｇ，莫高窟周辺の地質と水文―リモートセンシングと断層調査

Mogao Grottos are located at the eastern foot of the Mingsha Dunes, 25km southeast of Dunhuang town. It faces east toward Sanwei Mountain, one range of Qilian Mountains, and in front of it Daquan River runs.The caves were excavated into the cliff on the west bank of the Daquan River. The stratum in which the caves were excavated is the alluvial and pluvial Jiuquan conglomerate in which there is argillaceous and calcareous cementation. The wall paintings in the caves are subject to the severe deterioration generated by recrystallization of salt. It relates with the movement of water/moisture in rock formation. The basement of Mogao Area consists of granite and gneiss formed in the Pre-Cambrian Age. Through the satellite image analysis and geological survey, it has been clarified that the movement of ground water is governed by the fault system and the geographical nature is specified by the aggressive tectonic movement from the south.

Growth mechanism of the 1944 lava dome of Usu volcano in Hokkaido, Japan

Usu volcano has erupted eight times since 1663. The last four eruptions took place in the 20th century, and were monitored using standard instruments. Only the 1944 eruption produced a lava dome with a mound. However, growth of the lava dome and the mound beneath have not been discussed quantitatively because direct data of the dome formation were not obtained. During the early period of the 1944 eruption, T. Minakami repeated precise levels along the road traversing the eastern foot of Usu volcano which had grown to a part of the new dome (Showa-shinzan). The surveying period covered the stages of precursory upheaval, mound upheaval, explosions, and finally, lava dome extrusion. Though the surveying route grazed the upheaving mound, the results of the precise levels prove to be extremely useful in deriving a pseudo growth curve for the mound and the lava dome. The growth curves afford us important information on ground upheavals and lava dome extrusions. Such knowledge can not be obtained by model experiments or theoretical simulations.

Snow Mountain Passage by James D. Houston

3 8 6 WAL 3 7 .3 F a l l 2 0 0 2 research to render each character an aura of authenticity. Moreover, the profes­ sions and obsessions are made relevant to the themes of each story. The stories in Yellow show a promising writer with an inexhaustible range. Snow Mountain Passage. By James D. Houston. N ew York: Alfred A . Knopf, 2001. 317 pages, $24-00/$l4.00. Reviewed by David Fenimore University of N evada, Reno Houston’sseventh novel is based on one ofthe most familiar episodes in the history of western emigration. The Donner Party arrived at the eastern foot of the Sierra Nevada in late October 1846, only a few days after snow closed the eponymous pass. As more storms rolled in, they hunkered down for the winter, eating ox hides, bootlaces, and, finally, to a more limited extent than popular tra­ dition would have it, the bodies of their deceased companions. Thirty-five out of eighty-one died, plus several members of the first few rescue parties. Survivor James Reed provides Houston’s principal point-of-view character, based on well-known facts: banished from the emigrant train for killing a team­ ster in self-defense, Reed rode ahead and crossed into California in time to join the Mexican War. In the springhe returned with one ofthe rescue parties, bring­ ing his family safely over into San Jose. Dramatic scenes of starvation and can­ nibalism during the winter at Donner Lake—usually the focus of historical as well as fictional accounts—are here related in impressionistic flashbacks by his daughter Patty Reed, who was eight years old in 1846-47 but now looks back as an elderly woman rocking on her porch overlooking the Pacific Ocean. Unlike previous versions of the Donner story, which tend to dwell on those grisly and sometimes fanciful details, Houston concerns himself more with the natural and multicultural environment of a wild and distant frontier. The Reeds and other, less sympathetic Anglo characters move across an enormous and mys­ terious California landscape, fertile and full ofpromise. The Mexican Californios are treated with contempt by the settlers and the U.S. Army (but not by Reed), and the Indians are displaced, exploited, and, in two cases, killed for food. Houston incorporates many such historical details to paint an unromanti­ cized, revisionist portrait of early California. When Reed finally arrives at Captain John A. Sutter’s fort, the primary goal and sanctuary for overland emi­ grants, he is greeted by the head of a Mokolumne chief impaled on the gatepost, staring at him through pecked-out eye sockets. One image like this tells more about the Golden State than all the ersatz scenes of bloodsmeared children eat­ ing their parents’ livers that are so often retailed as Donner Party history. Thankfully, Houston steers clear of the social Darwinism, manufactured heroes, and fabricated gore on sale in the best-known narrative of the Donner Party, George R. Stewart’s Ordeal by Hunger (rev. ed. 1960). As recent scholar­ ship has shown, Stewart used questionable sources, including sensational news­ BOOK REVIEW S 3 8 7 paper accounts published, in certain cases, before all the survivors had arrived at Sutter’s. In some ways, his purported nonfiction is less reliable a history than Houston’s novel. But as is often the case in western novels, Houston’s meticu­ lously rendered setting at last steals the limelight from his plot as well as from his historical and fictional cast of characters. In one scene, Reed confronts the swollen Sacramento River, the surging confluence of all the creeks and rivers that channel water from the mountain ranges east and west to make the broad stream that divides the valley. . . . The Sacramento flows on south to the delta, and the Feather River is a brown flood pouring into the Sacramento, and the Bear River dumps into the Feather, spilling down out of the foothills. (252, 258) Bound for the high country, Reed and his fellow rescuers celebrate this vision of California’s world-class watershed by passing a bottle around the campfire. One man shows offa little wooden whistle he’sbought at Sutter’s Fort forhis...

Neotectonics of the Min Shan, China: Implications for mechanisms driving Quaternary deformation along the eastern margin of the Tibetan Plateau

The Min Shan region, located along the eastern margin of the Tibetan Plateau north of the Sichuan Basin, provides an important natural laboratory in which to study the rates and patterns of deformation and their relationship to mountain building at the margin of the plateau. The topographic margin of the plateau is coincident with a north-trending mountain range, the Min Shan, that stands nearly 2 km above the mean elevation of the plateau (~3500 m in this region). We exploit the preservation of a series of variably deformed Quaternary sediments along the western flank of the range to investigate the Pleistocene-Holocene deformation field within the Min Shan region. Mapping and field observations of remnant alluvial fans of late Pleistocene age indicate that deformation within the Min Shan involved substantial (~10°), rapid, down-to-the-northwest tilting. The geometry of the deposits and the partial preservation of an erosion surface beneath the basin suggest that much of the modern relief of the Min Shan relative to the Tibetan Plateau is a consequence of this late Pleistocene tilting. Rates of tilting inferred from luminescence dating of interbedded loess have been remarkably rapid (~10 ‐8 rad/yr). Similarly rapid rates of Holocene differential rock uplift are inferred from tilted lacustrine sediments in the southwestern part of the range. The range is bounded on the west by the Min Jiang fault zone, an east-vergent reverse fault. However, Holocene alluvial terraces in headwaters of the Min River are preserved across the fault in several places, indicating that displacement rates on the Min Jiang fault are <1 mm/yr. Active faulting only occurs along the eastern foot of the range (Huya fault) for a short distance (~60 km), despite 3 km of relief on the eastern range front. The relationship between these structures and the tilting observed in the Min Jiang basin is enigmatic; the faults do not appear to exert a strong control on the rates and pattern of deformation within the basin. A simple flexural model demonstrates that rates of tilting on the western flank of the Min Shan are too high to be simply attributed to an isostatic response to surficial loading and unloading of the lithosphere. Present-day horizontal shortening across the Min Shan is geodetically determined to be less than 2‐3 mm/yr, suggesting that only a small part of the observed tilting can be attributed to horizontal shortening. Thus, tilting and concomitant differential rock uplift in the Min Shan appear to require an additional driving component. We suggest that Quaternary deformation along the western Min Shan may reflect the surface response to thickening of a weak lower crust at the margin of the Tibetan Plateau.

Body waveform inversion for the source process of the February 3, 1996 Lijiang, Yunnan earthquake

The source process of February 3, 1996 Lijiang earthquake in Yunnan was studied by body waveform inversion using teleseismic data from IRIS. Two normal double-couple subevents with different strikes were obtained. The difference of the onset time between these two subevents, which are 15 km apart in space, is 7 s. The total seismic moment is 3.81 × 1018 Nm (Mw=6.3). The total fault area S is about 720 km2 from the aftershock data and the average dislocation is about ū=0.18 m. Considering both the result of inversion and tectonic environment around the source, the first rupture might result from the extension along the NNW directed Zhongdian-Yongsheng fault belt where an earthquake of M=6.4 occurred in 1966. Then, the second started along the NE directed the eastern foot of Snow Mountain fault where rupture seemed to be able to propagate more easily.

The Yaqui of Guadalupe, Arizona: A Century of Cultural Survival through Trilingualism

The Valley of the Sun is a large basin in which two major Sonoran Desert water systems, the Salt and Gila rivers, combine, enabling large-scale human settlement in central Arizona. The agricultural potential of this natural resource has sustained a stable population base since prehistoric times. Today it is home to a number of small cities that comprise the Phoenix metropolitan urban sprawl and more than half of the residents of the state of Arizona. Located at the far eastern foot of South Mountain, the southern natural boundary of the Valley, is Guadalupe, an urban anomaly that seems strangely juxtaposed in this widely spread, low density urban landscape fashioned by the advent of the automobile culture. Founded by Yaqui refugees from Sonora just after the turn of the century, the small one-square-mile desert settlement was not much more than a refugee camp, an innocuous cluster of extremely humble dwellings on the lightly populated Valley’s periphery. This was about to change. Just two years Guadalupe came into being, the small but significant city of Phoenix became the capital of the new state of Arizona. The peripheral Octaviana V. Trujillo, a former chairwoman of the Pascua Yaqui Tribe of Arizona, works in the area of multicultural and indigenous peoples education program development. Presently, she is the director of the Center for Indian Education and editor of the Journal of American Indian Education at Arizona State University.

Letter from Yekaterinburg.

The Russian city of Yekaterinburg, known as Sverdlovsk before the influence of perestroika, lies at the eastern foot of the Ural Mountains on the border between Europe and Asia. It was the site of large armaments factories, most of which are now closed, but the area continues to feel the aftermath of their heavy pollution. The annual Congress of the Russian Society of Internal Medicine was held here in 1995 and was attended by physicians from all corners of this vast country. Leaders in the field of internal medicine from Russia presented state-of-the-art papers on many aspects of the theme of the conference, Emergencies in Internal Medicine. The problem of the acquired immunodeficiency syndrome was also discussed, but this subject is still taboo as far as the official health authorities are concerned. The Russian physicians talked about how they deplored the great shortage of disposable medical equipment. One of the most serious health problems in Russia is alcoholism; surprisingly, this problem was hardly mentioned at the congress. An open international exchange of information is again possible in Russia, but financial considerations restrict attendance at meetings abroad and the availability of professional journals domestically.

Damage to River Levees and Revetments

ABSTRACT Levees with masonry and concrete-block walls underwent collapse and destortion between the central Kobe and Nishinomiya where the most severe damage was sustaind. In a coastal area, levees sustained characteristic deformation of the soft ground. In a reclaimed land liquefaction of the fill brought about excessive deformation in revetments of levees. Levees in the Muko River on the eastern foot of Mt. Rokko suffered from settlement, distortion and cracks. The Ina, Mo, Kanzaki, nakajima, Samondo, Aji and Shorenji Rivers were damaged where a thick soft sandy deposits underlay and old meanders were also found in some locations. In a port area, excessive distortion and cracks occurred in levees, while heavy concrete revetments supported by long piles which resist against the storm surge were little damaged. This paper outlines the structural, geological and geotechnical aspects of earthquake damage to levees in Hanshin region but damage to the Yodo River is excluded.

Pyroclastic flows from the 1991 eruption of Unzen volcano, Japan

Pyroclastic flows from Unzen were generated by gravitational collapse of the growing lava dome. As soon as the parental lobe failed at the edge of the dome, spontaneous shattering of lava occurred and induced a gravity flow of blocks and finer debris. The flows had a overhanging, tongue-like head and cone- or rollershaped vortices expanding outward and upward. Most of the flows traveled from 1 to 3 km, but some flows reached more than 4 km, burning houses and killing people in the evacuated zone of Kita-kamikoba on the eastern foot of the volcano. The velocities of the flows ranged from 15 to 25 m/s on the gentle middle flank. Observations of the flows and their deposits suggest that they consisted of a dense basal avalanche and an overlying turbulent ash cloud. The basal avalanche swept down a topographic low and formed to tongue-like lobe having well-defined levees; it is presumed to have moved as a non-Newtonian fluid. The measured velocities and runout distances of the flows can be matched to a Bingham model for the basal avalanche by the addition of turbulent resistance. The rheologic model parameters for the 29 May flow are as follows: the density is 1300 kg/m3, the yield strength is 850 Pa, the viscosity is 90 Pa s, and the thickness of the avalanche is 2 m. The ash cloud is interpreted as a turbulent mixing layer above the basal avalanche. The buoyant portions of the cloud produced ash-fall deposits, whereas the dense portions moved as a surge separated from the parental avalanche. The ash-cloud surges formed a wide devastated zone covered by very thin debris. The initial velocities of the 3 June surges, when they detached from avalanches, are determined by the runout distance and the angle of the energy-line slope. A comparison between the estimated velocities of the 3 June avalanches and the surges indicates that the surges that extended steep slopes along the avalanche path, detached directly from the turbulent heads of the avalanches. The over-running surge that reached Kita-Kamikoba had an estimated velocity higher than that of the avalanche; this farther-travelled surge is presumed to have been generated by collapse of a rising ash-cloud plume.

南関東の完新世火山灰土壌の母材 一次鉱物組成と元素組成による判定

Volcanic ash soils occur widely on South Kanto district. The surface soil has black color and high humus content. The parent material is derived from Holocene volcanic ash. There are some buried humic horizons resulted from a succession of volcanic ash accumulation and plant residue supply leading to the accumulation of soil organic matter or humus. It has commonly been considered that Mt. Fuji supplied parent material of those soils.A huge amount of Holocene volcanic ejecta (tephra) with a large particle size accumulates at the eastern foot of Mt. Fuji, Tephrochronological studies enabled us to identify each scoria layers.However, little information of the tephrochronological study is available for soils formed in the region away from Mt. Fuji, such as on Musashino Plateau. A small amount of volcanic ash accumulation with a small particle size, compared with those in the eastern piedmont region close to Mt. Fuji promoted soil formation in this region, it is difficult to identify the characteristic tephra on Musashino Plateau on the contrary to the tephra of piedmont region which can easily be identified. Furthermore, it is assumed that more than one volcano in addition to Mt. Fuji such as Mt. Asama and Mt. Haruna supplied volcanic ash with a different rock type from that of Mt. Fuji in Musashino Plateau region. It is important to claryfy to what extent other volcanoes contributed in south Kanto district as a source volcano of the parent material of soils.In this paper, we compared morphological features, primary mineral composition, and element composition of three profiles which were locatd in Fujisawa City, Kanagawa, Fuchu City, Tokyo, Hidaka Town, Saitama respectivery. They are located almost in the same ditsance but the different direction from Mt. Fuji.At first, we directed our attention to buried humic horizon which was often identified as a horizon where it covered the archaeological site and remnants of the Nara-Heian period in Fuchu City, Tokyo. The horizon has some morphological and mineralogical characteristics; most blackish color in the solum, fine granular structure, and high olivine content. We gave the horizon tentative name as H-1BB (Holocene 1st Black Band).The results are summarized as follows:(1) On the basis of primary mineral composition, following were concluded: The dominance of heavy minerals and high content of olivine indicated that, parent material of Fujisawa pedon was supplied from Mt. Fuji. The dominance of light minerals, high content of non-colored volcanic glass and clinopyroxene, parent material of Hidaka pedon was supplied from Mt. Asama, Fuchu pedon indicated the transitional character between Fujisawa and Hidaka.(2) H-1BB is identified morphologically in all profiles based on relatively strong blackish color and structure. There was high content of transparent olivine in this horizon in every pedon. Because Fujisawa pedon indicated the highest olivine content, We assumed that H-1BB in three pedons were derived from more or less the same parent material erupted from Mt. Fuji.(3) From the viewpoint of chemical classification of volcanic rock, Si contents themselves, didn't directly reflect primary mineral composition of these soils. However, the profile which abounded in the parent material from Mt. Fuji had high Ca and Sr content. H-1BB in three profiles had high Ca and low K proportion in base element.