Depositional features and transportation mechanism of valley-filling Iwasegawa and Kaida debris avalanches, Japan

 The depositional features of two valley-filling debris avalanche deposits were studied to reveal their transportation and depositional mechanisms. The valley-filling Iwasegawa debris avalanche deposit (ca. 0.1 km³) is distributed along the valleys at the southeastern foot of Tashirodake Volcano, northern Honshu, Japan. Debris-avalanche blocks range in size from <35 m proximally to <10 m in the distal zone and consist dominantly of fragile materials. Debris-avalanche matrix percentages increase from 35–60% in the proximal zone to 95% in the distal zone. The debris-avalanche matrix is greater in volume (80–90%) at the bottom and margins of the deposit. Normal grading of large clasts and reverse grading of wood logs and branches occur within the debris-avalanche matrix. Preferred orientation of 311 wood logs and branches within the deposit coincide with the interpreted local flow direction. The basal part of the deposit is characterized by (1) erosional features and incorporated clasts of underlying material; (2) a higher proportion (30–50%) of incorporated clasts than the upper part; and (3) reverse grading of clasts. The valley-filling Kaida debris avalanche deposit (50 000 y B.P., >0.3 km³) is distributed along the valleys at the eastern-southeastern foot of Ontake Volcano, central Japan. Debris-avalanche blocks range in size from <25 m proximally to <7 m in the medial zone. Debris-avalanche matrix percentages increase from 50–70% in the proximal zone to 80% in the distal zone. The debris-avalanche matrix is more abundant (80–90%) at the bottom part of the deposit. Deformation structures observed in the debris-avalanche blocks include elongation, folding, conjugate reverse faults, and numerous minor faults in unconsolidated materials. Lithic components within the debris-avalanche matrix tend to have a higher percentage of plucked clasts from the adjacent underlying formations. A Bingham "plug flow" model is consistent with the transportation and depositional mechanisms of the valley-filling debris avalanches. In the plug of the debris avalanche, fragile blocks were transported without major rupturing due to relatively small shear stresses in regions of small strain rate. The debris-avalanche matrix was mainly produced by shearing at the bottom and margins of the avalanche. Valley-filling debris avalanches tend to have smaller debris-avalanche blocks and larger amounts of debris-avalanche matrix than do unconfined debris avalanches. These differences may be due to disaggregation of debris-avalanche blocks by shearing against valley walls and interaction between debris-avalanche blocks and valley walls. Oriented wood logs and branches, reverse grading of clasts at the base, and a higher proportion of incorporated clasts at the base are interpreted to result from shearing along the bottom and valley walls. Received: 25 March 1998 / Accepted: 10 October 1998     

Relation between the concentrations of DMS in surface seawater and air in the temperate North Pacific region

The concentrations of DMS were simultaneously measured in both water and air at the sea surface on board a vessel during a trans-Pacific cruise around 40° N in August 1988. Those in the surface seawater varied widely with a mean of 162 ng S/1 and a standard deviation of 134 ng S/1 (n=37), but the variation was not a mere fluctuation and the high concentration (376 ng S/1) was found in the area between 145° W and 170° W. The atmospheric DMS concentration varied more widely with a mean value of 177 ng S/m³ and a standard deviation of 203 ng S/m³ (n=23). The diurnal variation of DMS was not significant in the air near the sea surface. However, the concentrations in the surface water was fairly well correlated with those in the surface air. The correlation coefficient (r ²=0.86) was larger than that between the atmospheric concentration and outflux of DMS (r ²=0.64). These findings mean that the turnover time of DMS in the atmosphere is not extremely short. Based on the linear relation between the atmospheric and seawater DMS, the turnover time of the atmospheric DMS has been calculated to be 0.9 days with an uncertainty of around 50%. The oxidation rate agrees fairly well with that expected from the OH radical concentration in the marine atmosphere.     

日本结构控制的工程应用

提出了包括基础隔震系统、质量阻尼系统和其他阻尼器的结构振动控制系统,阐述了结构控制系统在日本的实际工程应用,同时还介绍了于2000年11月召开的第二届日本结构控制学术会议的情况.     

Fractionation of azaarenes during oil migration

A comparative study of alkylbenzoquinolines in crude oils and rock extracts (bitumens) from Japan and Sumatra shows that the ratios of nitrogen-masked isomers (NMIs) to nitrogen-exposed isomers (NEIs), and the ratio of higher homologs to lower homologs is higher in crude oils than in corresponding bitumens. Also, a regular increase in the ratios of NMIs to NEIs with increasing migration distance is observed for a series of crude oils from the Sarukawa Oil Field, northeastern Japan. These results are attributed to the preferential migration of NMIs caused by their weak adsorption on clay minerals and/or their low solubility in interstitial water, and the selective removal of lower honologs caused by their irreversible adsorption onto clays during oil migration, which are regarded as geochromatographic phenomena. It is suggested that those ratios can be used to estimate the degree of fractionation of oils during primary and secondary migration.     

Temporal Change of Dissolved Inorganic Carbon in the Subsurface Water at Station KNOT (44°N, 155°E) in the Western North Pacific Subpolar Region

The dissolved inorganic carbon (DIC) and related chemical species have been measured from 1992 to 2001 at Station KNOT (44°N, 155°E) in the western North Pacific subpolar region. DIC (1.3∼2.3 µ mol/kg/yr) and apparent oxygen utilization (AOU, 0.7∼1.8 µmol/kg/yr) have increased while total alkalinity remained constant in the intermediate water (26.9∼27.3σ_θ). The increases of DIC in the upper intermediate water (26.9∼27.1σ_θ) were higher than those in the lower one (27.2∼ 27.3σ_θ). The temporal change of DIC would be controlled by the increase of anthropogenic CO₂, the decomposition of organic matter and the non-anthropogenic CO₂ absorbed at the region of intermediate water formation. We estimated the increase of anthropogenic CO₂ to be only 0.5∼0.7 µmol/kg/yr under equilibrium with the atmospheric CO₂ content. The effect of decomposition was estimated to be 0.8 ± 0.7 µmol/kg/yr from AOU increase. The remainder of non-anthropogenic CO₂ had increased by 0.6 ± 1.1 µmol/kg/yr. We suggest that the non-anthropogenic CO₂ increase is controlled by the accumulation of CO₂ liberated back to atmosphere at the region of intermediate water formation due to the decrease of difference between DIC in the winter mixed layer and DIC under equilibrium with the atmospheric CO₂ content, and the reduction of diapycnal vertical water exchange between mixed layer and pycnocline waters. In future, more accurate and longer time series data will be required to confirm our results.     

Influence of submarine fumaroles on the distribution of mercury in the sediment of Kagoshima Bay,Japan

To estimate the influence of mercury emitted from submarine fumaroles, the horizontal and vertical distribution of mercury in sediment of Kagoshima Bay was studied. The fumaroles are located in the northern bay head area, and the sediment samples had been taken from 52 points throughout the bay with a gravity core sampler. The core samples obtained were cut at a thickness of 1–2 cm and used for measurements. The total concentration of mercury in surface sediment in the northern and central areas of the bay was 51–679 μg kg^− 1 (average 199 μg kg^− 1, n = 22) and 23–100 μg kg^− 1 (average 55 μg kg^− 1, n = 30), respectively. The highest value was obtained in the vicinity of the fumaroles. The mercury concentration in sediment near the fumaroles varied with depth, which may reflect the variation in fumarolic activity. A successive extraction method was applied to the speciation of mercury in the sediment. The results showed that sediment taken in the vicinity of submarine fumaroles contained a higher percentage of mercury bound with organic matter.     

Vanishing Island States and sovereignty

Sea level rise could bring about an event that has not previously been seen in modern history, that of the physical disappearance of some low-lying Island States. The objective of this paper is to examine what are the likely scenarios for some of these islands in the course of the next century, and analyse for each scenario if these Island States could continue to claim an Exclusive Economic Zone or not. Also, it will analyse the possibility that Island States could continue having some sort of status analogous to statehood even if it was to lose all territory. Finally, the idea of a “government-in-exile” will be discussed, where the State could retain its identity waiting for a future re-emergence of the island.     

Global mapping of the degree of space weathering on asteroid 25143 Itokawa by Hayabusa/AMICA observations

Abstract— We obtained color images of near‐Earth asteroid 25143 Itokawa by the Hayabusa multiband imaging camera to characterize the regional color properties. Images were obtained for the whole disk from the gate position (GP) and home position (HP) at a spatial resolution of 0.8–3.7 m/pixel. Whole‐disk spectra are adjusted to the telescopic data obtained by the University of Hawai'i's 88‐inch telescope using the Eight Color Asteroid Survey (ECAS) system. The disk‐resolved measurements show large variations in the three visible channels. We present a map of an index related to the degree of space weathering, which has been newly developed based on laboratory measurements. We find large variations in the degree of space weathering on Itokawa. Fresh materials are observed in regions of steep slopes and craters, whereas mature materials are ubiquitously distributed. This result suggests that pristine ordinary chondrite‐like materials have been exposed through weathered layers by excavation. By also examining close‐up images obtained during touchdown rehearsal, we find that most rocks in Itokawa's rough terrains are weathered. Instead of a regolith blanket, the surface of this small asteroid is covered with weathered rocks and gravels.