Kazuomi Hirakawa

Antarctic Glacial History Since the Last Glacial Maximum: An Overview of the Record on Land

This overview examines available circum-Antarctic glacial history archives on land, related to developments after the Last Glacial Maximum (LGM). It considers the glacial-stratigraphic and morphologic records and also biostratigraphical information from moss banks, lake sediments and penguin rookeries, with some reference to relevant glacial marine records. It is concluded that Holocene environmental development in Antarctica differed from that in the Northern Hemisphere. The initial deglaciation of the shelf areas surrounding Antarctica took place before 10 000 14 C yrs before present( BP ), and was controlled by rising global sea level. This was followed by the deglaciation of some presently ice-free inner shelf and land areas between 10 000 and 8000 yr BP . Continued deglaciation occurred gradually between 8000 yr BP and 5000 yr BP . Mid-Holocene glacial readvances are recorded from various sites around Antarctica. There are strong indications of a circum-Antarctic climate warmer than today 4700–2000 yr BP . The best dated records from the Antarctic Peninsula and coastal Victoria Land suggest climatic optimums there from 4000–3000 yr BP and 3600–2600 yr BP , respectively. Thereafter Neoglacial readvances are recorded. Relatively limited glacial expansions in Antarctica during the past few hundred years correlate with the Little Ice Age in the Northern Hemisphere.

Circum-Antarctic Coastal Environmental Shifts During the Late Quaternary Reflected by Emerged Marine Deposits

This review assesses the circumpolar occurrence of emerged marine macrofossils and sediments from Antarctic coastal areas in relation to Late Quaternary climate changes. Radiocarbon ages of the macrofossils, which are interpreted in view of the complexities of the Antarctic marine radiocarbon reservoir and resolution of this dating technique, show a bimodal distribution. The data indicate that marine species inhabited coastal environments from at least 35 000 to 20 000 yr BP, during Marine Isotope Stage 3 when extensive iceberg calving created a ‘meltwater lid’ over the Southern Ocean. The general absence of these marine species from 20 000 to 8500 yr BP coincides with the subsequent advance of the Antarctic ice sheets during the Last Glacial Maximum. Synchronous re-appearance of the Antarctic marine fossils in emerged beaches around the continent, all of which have Holocene marine-limit elevations an order of magnitude lower than those in the Arctic, reflect minimal isostatic rebound as relative sea-level rise decelerated. Antarctic coastal marine habitat changes around the continent also coincided with increasing sea-ice extent and outlet glacial advances during the mid-Holocene. In view of the diverse environmental changes that occurred around the Earth during this period, it is suggested that Antarctic coastal areas were responding to a mid-Holocene climatic shift associated with the hydrological cycle. This synthesis of Late Quaternary emerged marine deposits demonstrates the application of evaluating circum-Antarctic phenomena from the glacial-terrestrial-marine transition zone.

Tsunami run-up heights of the 2003 Tokachi-oki earthquake

Tsunami height survey was conducted immediately after the 2003 Tokachi-oki earthquake. Results of the survey show that the largest tsunami height was 4 m to the east of Cape Erimo, around Bansei-onsen, and locally at Mabiro. The results also show that the tsunami height distribution of the 2003 Tokachi-oki earthquake is clearly different from that of the 1952 Tokachi-oki earthquake, suggesting the different source areas of the 1952 and 2003 Tokachioki earthquakes. Numerical simulation of tsunami is carried out using the slip distribution estimated by Yamanaka and Kikuchi (2003). The overall pattern of the observed tsunami height distribution along the coast is explained by the computed ones although the observed tsunami heights are slightly smaller. Large later phase observed at the tide gauge in Urakawa is the edge wave propagating from Cape Erimo along the west coast of the Hidaka area.

FIELD EXPERIMENTS ON PHYSICAL WEATHERING AND WIND EROSION IN AN ANTARCTIC COLD DESERT

Field experiments were carried out over a five year period with the aim of understanding contemporary weathering and erosional environments in the Sor Rondane Mountains, an Antarctic cold desert region. These include observations of (1) scaling from rockwalls, (2) disintegration of tuff blocks with or without saline solutions, and (3) abrasion of artificial walls by wind. Monitoring was also made of rock surface temperature and wind speed. Despite frequent temperature oscillations across 0°C, rock scaling due to frost action was generally very slow because of low moisture content in the rockwalls. Exposure to the cold, dry climate led to the rapid disintegration of porous tuff blocks including soluble salts like halite and thenardite. This indicates that rates of weathering are increased greatly with the accumulation of such salts in the bedrock. Although gypsum did not cause any visible damage over four years, its widespread occurrence in heavily damaged rocks demonstrates that increasing gypsum contents may also intensify rock breakdown. The snow-laden katabatic wind resulted in rapid wearing of the windward face of an asbestos board with the peak erosion at 30–40 cm above the ground. Nonetheless, the landforms expected from the unidirectional wind characteristics are by no means common features because of lack of abrasive materials, such as snow and sand particles. These experiments suggest that frost weathering and wind erosion are only locally effective where plenty of moisture or an abrasive material is available, whilst salt weathering and removal of the waste by wind play a major role in constructing erosional landforms over the mountains.

Hydration and refractive indices of Holocene tephra glass in Hokkaido, Northern Japan

Abstract Refractive indices of incompletely hydrated tephra glasses vary widely. Thus, glass refractive index is not a practical indicator for identifying Holocene tephras. Hydration near the surface of tephra glass shards can be removed by either hydrofluoric acid treatment or annealing for 12 h at 400°C. The annealing procedure is a particularly reliable and simple way to dehydrate tephra glasses. Standard deviations ( s ) of refractive indices for glasses after 12 h annealing are small ( s =0.0014–0.0018), in contrast with untreated glasses ( s =0.0034–0.0405). The refractive indices of dehydrated tephra glasses are 0.006–0.014 lower than those of the untreated (hydrated) glasses. Using the 400°C 12-h annealing procedure, values for the refractive indices of eight Holocene tephras in Hokkaido were obtained. These refractive indices are useful indicators for identification and correlation of Holocene tephras.

Late Quaternary glaciations in Japan

A general introduction to the Quaternary glaciations in the Japanese high mountains is presented. Particular attention is paid to the two most significantly-glaciated mountain ranges, and recent knowledge of the glacial history in the Japanese Alps and Hidaka Mountains is presented. Six glacial advances are recognised in the Japanese Alps that occurred during the penultimate glacial cycle, the Last Glaciation, and the Holocene. In the high Japanese mountains, the maximum advance during the Last Glaciation is commonly recognised during Marine Isotope Stage (MIS) 4 with subsequent advances occurring just before 24 ka BP, 18–20 ka PB, 11–10 ka BP and in the early Holocene. In the Hidaka Mountains, recent tephrochronological investigations have revealed the age and extent of the maximum glacier advance during MIS 5a, MIS 3, MIS 2 and MIS 6. Mountain glaciers in Japan were less extensive during the Last Glacial Maximum. This is out of phase with the continental ice sheets in the northern hemisphere.

Chronology and evolution of landforms during the late quaternary in the Tokachi Plain and adjacent areas, Hokkaido, Japan

Summary The succession of various geomorphological processes associated with climatic fluctuations in the late Quaternary and their effects on the landform of the Tokachi Plain are discussed using chronological data on glacial landforms, marine terraces, river terraces, fossil periglacial phenomena and mass movements on the mountain slopes, together with analytical data on the terrace deposits, present river deposits and slope deposits. Three major stages are recognized in the landform evolution after about 60 000 years B.P.. The division of stages is based on the chronology of the fluvial and marine terraces. The stage of the KoI terrace (60 000 – 35 000 or 30 000 years B.P.) is marked by the maximum extent of cirques in the Hidaka Range, vigorous periglacial mass movements on the mountain slopes, and by conspicuous fluvial accumulation in the regions of alluvial fan and upper reaches of each river. This fluvial accumulation seems to have occurred under glacial and periglacial morphogenetic environments. The stage of the KoII — KoIII terraces (35 000 or 30 000 – 10 000 years B.P.) is characterized by the restriction of the glaciers in the Hidaka Range, active solifluction processes on the mountain slopes, remarkable periglacial phenomena, especially sand dune development and involutions, on the terrace surfaces of the Tokachi Plain and a deep incision due to depression in sea level in the lower reaches of the Tokachi River. The stage of the KoIV terrace (10 000 years B.P. — Present) is characterized by wholly different events from the former stages, such as vigorous incision of rivers into the alluvial fans and mountainous regions, accumulation of thick alluvium in the lower reaches of the Tokachi River, and recovery of vegetation on the mountain slopes.

Field Survey of the 2003 Tokachi-Oki Earthquake Tsunami and Simulation at the Ootsu Harbor Located at the Pacific Coast of Hokkaido, Japan

Field survey for the 2003 Tokachi-oki earthquake tsunami was conducted by the scientists from all over Japan [Tanioka et al., 2004a, b]. Large tsunami heights of about 4 m were observed at Hyakuninhama to the east of Cape Erimo and along the beach between Horokayanto and Oikamanai. Those places are close to the source region of the earthquake. In general, tsunami heights gradually decreased to the east and to the west away from those two locations except at Mabiro where a large tsunami height of about 4m was locally observed. The most intensive tsunami survey was conducted at the Ootsu harbor. The survey results indicate that the quay of the harbor was completely submerged by the tsunami, but the road around the harbor was not. Numerical computation of the 2003 Tokachi-oki tsunami was carried out by solving the nonlinear shallow water equations with a moving boundary condition near the Ootsu harbor. The computed tsunami at the Ootsu harbor well explains the above observations.

Holocene Antarctic's coastal environment, ice sheet, and sea levels explored

Efforts are in the works to resolve a several-decade-long debate over the size and extent of the Antarctic ice sheet and its role in sea levels during the last glacial cycle. Researchers also want to find out more about the nature of environmental changes around the Antarctic coast throughout the Holocene, the sensitivity of the ice sheet to warm periods, and the significance of pre-Holocene marine fossils there. Scientists concerned with these issues presented their research priorities last fall at an Antarctic ice margin evolution (ANTIME) workshop, “Circum-Antarctic Coastal Environmental Variability and Sea Level History During the Late Quaternary.” These workshop participants included coastal and glacial geomorphologists, geochemists, and paleoecologists.

Geomorphological Examination on the Fortified Camps (Ezo-Jinya) in Hokkaido of the Nineteenth Century

I.はじめに 江戸時代後半,箱館奉行による蝦夷地の直接統治と 東北諸藩(弘前・盛岡・仙台・会津・秋田・鶴岡)お よび松前藩による蝦夷地沿岸部の防備という蝦夷地政 策にもとづいて,幕府の箱館奉行所の亀田土塁,東北 諸藩による陣屋・囲郭が沿岸各地に建設された。それ らの奉行所・陣屋・囲郭の建設計画図や各藩の警備担 当地の沿岸図など多種多様な絵地図が作成,筆写され 現存する。これらの絵地図からは,陣屋の立地・選定 にあたって影響を与えたに違いない地形,気候・気象 環境など自然地理的側面ついて分析をおこなうことは 不可能と言ってよい。しかし,ほとんど未開拓の蝦夷 地において,東北諸藩が陣屋設営に当たって陣屋とそ の周辺の自然環境,とくに地形条件に配慮したか否か, さらにどのように対処したかに関する自然地理学的な 検討・視点があってしかるべきであろう。 このような観点からの検討を可能にする唯一の史料 が,盛岡藩の『松前持場見分帳』である。『松前持場 見分帳』は,盛岡藩が幕府の命令に従って藩士を派遣 し,函館周辺と東蝦夷地の持場(現在の渡島半島太平 洋沿岸から室蘭,白老近傍に至る沿岸)について現地 踏査(見分)をおこない,その結果を幕府(函館奉行 所)に提出したものである。ここでは,陣屋とその周 辺の地形的条件について,1衛星画像などから作成し た 3D地形表現を基礎資料として列挙・提示し,2盛 岡藩士による『松前持場見分帳』の記載に依拠しつつ, 3D地形画像を用いて解釈・検討する。 陣屋とその周辺の地形について,現在の地形学的知 見や解釈を記述することは困難ではない。しかし,単 なる地形環境の記述では,陣屋の立地に関する論点は 明確にはならず,意義に欠けると言わざるを得ない。 『松前持場見分帳』のような史料は,当該陣屋以外の 蝦夷地陣については存在しない。したがって,『松前 持場見分帳』の記載を参考にしながら,他の資料(地 形図や衛星画像およびそれらの 3D表現)を比較・検 討の基礎とすれば,全ての蝦夷地陣屋の自然地理的な 立地条件についての洞察が多少とも可能になると考え られる。以下,この報告において掲載する地形の 3D 画像の意義は,この点をおいて他にない。 検討対象とする陣屋は,砂原,長万部,室蘭および 白老 に限る。函館周辺の陣屋については,3D地形 表現の例を示し,地形に関するコメントを付すに止め る。これは『松前持場見分帳』では,函館周辺につい ての見分記載に多くが充てられているが,それらは主 として警衛上の見解であって,陣屋の地形的立地条件 に関わる記述は少ないためである。