Hydraulic and numerical study on the generation of a subaqueous landslide-induced tsunami along the coast

By carrying out the hydraulic experiments in a one-dimensional open channel and two-dimensional basin, we clarified the process of how a landslide on a uniform slope causes the generation of a tsunami. The effect of the interactive force that occurs between the debris flow layer and the tsunami is significant in the generation of a tsunami. The continuous flow of the debris into the water makes the wave period of the tsunami short. The present experiments apply numerical simulation using the two-layer model with shear stress models on the bottom and interface, and the results are compared. The simulated debris flow shows good agreement with the measured results and ensures the rushing process into the water. We propose that the model use a Manning coefficient of 0.01 for the smooth slope and 0.015 for the rough slope, and a horizontal viscosity of 0.01 m²/s for the landslide; an interactive force of 0.2 for each layer is recommended. The dispersion effect should be included in the numerical model for the propagation from the shore.     

X-ray CT based numerical analysis of fracture flow for core samples under various confining pressures

The X-ray CT based numerical analysis of fracture flow for core samples, recently developed by the authors, was applied to two granite core samples having either a mated artificial or a mated natural fracture at confining pressures of 5 to 50 MPa. A third-generation medical X-ray CT scanner was used to image the samples within a core holder consisting of an aluminum liner and a carbon fiber overwrap. Fracture models (i.e., aperture distributions) were obtained by the CT images, the resolution of which was coarser than the apertures, and a single-phase flow simulation was performed using a local cubic law-based fracture flow model. Numerical results were evaluated by a fracture porosity measurement and a solution displacement experiment using NaCl and NaI aqueous solutions. These numerical results coincided only qualitatively with the experimental results, primarily due to image noise from the aluminum liner of the core holder. Nevertheless, the numerical results revealed flow paths within the fractures and their changes with confining pressure, whereas the experimental results did not provide such results. Different stress-dependencies in the flow paths were observed between the two samples despite the similar stress-dependency in fracture porosity and permeability. The changes in total area of the flow paths with confining pressure coincided qualitatively with changes in breakthrough points in the solution displacement experiment. Although the data is limited, the results of the present study suggest the importance of analyzing fluid flows within naturally fractured core samples under in situ conditions in order to better understand the fracture flow characteristics in a specific field. As demonstrated herein, X-ray CT-based numerical analysis is effective for addressing this concern. Using a multi-phase flow model, as well as a core holder constructed of an engineered plastic, should provide a useful, non-destructive, and non-contaminative X-ray CT-based fracture flow analysis for core samples under in situ conditions in future studies.     

An improved extraction system to measure carbon‐14 terrestrial ages of meteorites and pairing of the Antarctic Yamato‐75097 group chondrites

Abstract— We examined an improved system for extraction of carbon from meteorites, using a vacuum‐tight RF melting method. Meteorite samples mixed with an iron combustion accelerator, including a specific amount of carbon (0.052%), were combusted in a RF furnace (LECO HF‐10). ¹⁴CO₂ extracted from the meteorite was diluted with a known amount of nearly ¹⁴C‐free CO₂, evolved from the iron accelerator on combustion. The ¹⁴C activities of the recently fallen Holbrook (L6) and Mt. Tazerzait (L5) meteorites were measured by this method. The mean value was 56.5 ± 3.0 dpm/kg, which is similar to the values reported for recently fallen L6 chondrites. Furthermore, terrestrial ages were measured for four Antarctic meteorites: 1.8 ± 0.5 kyr for Yamato (Y‐) 75097 (L6), 1.8 ± 0.5 kyr for Y‐75108 (L6), and 0.1 ± 0.1 kyr for Y‐74192 (H5). For Y‐74190 (L6), an apparent age of 0.8 ± 0.5 kyr was calculated. After consideration of the shielding effect by using ²²Ne/²¹Ne values, we obtained about 1.8 kyr for the terrestrial age of this chondrite. The five samples Y‐74190, Y‐75097, and Y‐75108, together with Y‐75102 (L6) and Y‐75271 (L6), have been reported to be paired and fragments of an L‐chondrite shower (Honda 1981; Takaoka 1987). The result of this work and literature data for the latter two samples confirmed that they are paired. More discussion and experimental work are needed for other recently fallen meteorites, both for L and H chondrites, and a correction for the shielding effect should be done to determine a more reliable terrestrial age.     

DISTRIBUTION OF AEROSOL EXTINCTION IN THE LOWER TROPOSPHERE BY MICRO-PULSE LIDAR OBSERVATION

The profiles of aerosol extinction coefficients are investigated by micro-pulse lidar(MPL)combined with the meteorological data in the lower troposphere at Meteorological ResearchInstitute(MRI).Japan.Larger extinction values of aerosol are demonstrated in the nocturnalstable air layer with larger Richardson number,and light wind velocities are favorable for aerosolconcentrating in the planetary boundary layer(PBL).But aerosol extinction coefficients showlarger values over the altitudes of 2.0 to 5.0km where correspond to higher relative humidity(RH).The tops of PBL identified by the aerosol extinction profiles almost agree with ones byradiosonde data.The diurnal variations of aerosol extinction profiles are clearly displayed,intensive aerosol layers usually are formed over the period of mid-morning to 1400 Loeal Time(LT).then elapse in the cloudless late afternoon and nighttime.Thermal eonvection or turbulenttransport from the surfaee probably dominates these temporal and spatial changes of aerosoldistribution.     

DISTRIBUTION OF AEROSOL EXTINCTION IN THE LOWER TROPOSPHERE BY MICRO-PULSE LIDAR OBSERVATION*

The profiles of aerosol extinction coefficients are investigated by micro-pulse lidar(MPL) combined with the meteorological data in the lower troposphere at Meteorological Research Institute(MRI).Japan.Larger extinction values of aerosol are demonstrated in the nocturnal stable air layer with larger Richardson number,and light wind velocities are favorable for aerosol concentrating in the planetary boundary layer(PBL).But aerosol extinction coefficients show larger values over the altitudes of 2.0 to 5.0km where correspond to higher relative humidity(RH).The tops of PBL identified by the aerosol extinction profiles almost agree with ones by radiosonde data.The diurnal variations of aerosol extinction profiles are clearly displayed,intensive aerosol layers usually are formed over the period of mid-morning to 1400 Loeal Time(LT).then elapse in the cloudless late afternoon and nighttime.Thermal eonvection or turbulent transport from the surfaee probably dominates these temporal and spatial changes of aerosol distribution.     

On the number ratio of horizontal branch stars to red giant stars in globular clusters

The number ratios of horizontal branch stars to red giant stars were obtained for globular clusters and Draco dwarf galaxy and the helium abundance was estimated using model results without semiconvection zone (SCZ) and with fully developed one. The analysis was confined to the four clusters (M4, M5, M13, and 47 Tuc) and the Draco galaxy, for which fairly precise star counts had been carried out. The effect of the difference in radial distribution between horizontal and red giant branch stars were taken into account, if necessary. The statistically significant difference inR exists among these objects. The cause may be the difference in the helium abundance and/or in the development of the SCZ. In the case of the fully developed SCZ, the helium abundance for M5 and Draco is appreciably smaller than the value given by the big-bang cosmology. It may be taken as an evidence against the full development of the SCZ for the horizontal branch stars in these objects.     

Change in Extent of Meadows and Shrub Fields in the Central Western Cascade Range,Oregon∗

We examined change in areal extent of mountain meadows and fields of deciduous shrubs and conifer saplings in the central western Cascade Range of Oregon, based on analysis of aerial photographs taken in 1946 and 2000. These nonforest vegetation patches are distinctive habitats in dominantly forested landscapes, such as the Cascades, and change in extent of these habitats is of interest to scientists and land managers. We mapped and dated even-aged forest stands of probable postfire origin around the nonforest patches, using tree-ring analysis and interpretation of aerial photographs. We used these and archival data to interpret possible influences of past wildfire and sheep grazing on the extent of nonforest patches. The total area of nonforest vegetation patches decreased from 5.5 percent of the study area in 1946 to 2.5 percent in 2000. Significantly more cases of contracted patches were observed for mesic and xeric meadows which have adjacent forest established after wildfire in the approximately 150 years preceding 1946. A higher proportion of mesic (47 percent, n = 47) than xeric (17 percent, n= 115) meadows contracted between 1946 and 2000. Broad-leaved shrub fields were unchanged, probably because of topo-edaphic controls, dense cover of shrubs, and snow effects; but all fields of conifer saplings underwent succession to forest. We observed no strong influences of sheep grazing on the extent of meadows.