A new model for predicting three-dimensional beach changes by expanding Hsu and Evans' equation

The empirical bay shape model proposed by Hsu and Evans in 1989 for predicting the static planform of a pocket beach is expanded to enable the calculation of three-dimensional beach changes on a pocket beach with a seawall. The original formulation was developed on the basis of a second-order regression analysis. Unlike the one-line model of shoreline changes, the model of Hsu and Evans does not require repeated calculations of the wave field and shoreline position, because it was derived on the assumption of null sediment movement within a pocket beach in static equilibrium, hence without the need of applying the continuity condition of total sand volume in the calculation. The expanded model proposed by the present authors satisfies the total sand budget on a pocket beach, by taking into account the concept of depth change due to longshore sand transport. Model tests were carried out and the new model was further applied to the beach changes at Kemigawa on the northeast of Tokyo Bay in Chiba Prefecture, as well as at Oarai in Ibaraki Prefecture, Japan. On both locations, seawall has been installed as countermeasures against beach erosion, where wave sheltering effect of the main breakwater and beach changes in front of the seawall has also been observed. With this expansion, the present model can be applied to predict the three-dimensional beach changes on a coast with seawall on a pocket beach.     

Crystallization of microlites and degassing during magma ascent: Constraints on the fluid mechanical behavior of magma during the Tenjo Eruption on Kozu Island, Japan

Bubble and crystal textures provide information with regard to the kinetics of the vesiculation and crystallization processes. They also provide insights into the fluid mechanical behavior of magma in a conduit. We performed textural (bubble and crystal) and compositional analyses of pyroclasts that were obtained from the Tenjo pyroclastic flow, which resulted on account of the eruption in 838 A.D. on Kozu Island, about 200 km south of Tokyo, Japan. Pyroclasts in one flow unit (300∼2,060 kg/m³; average density 1330 kg/m³) can be classified into three types on the basis of vesicle textures. Type I pyroclasts have small isolated spherical bubbles with higher vesicularities (67–77 vol.%) and number density (10.8–11.7 log m⁻³). Type II pyroclasts have vesicularities similar to type I (61–69 vol.%), but most bubbles exhibit evidences of bubble coalescence, and lower number densities than type I (8.9–9.5 log m⁻³). Type III pyroclasts contain highly deformed bubbles with lower vesicularities (16–34 vol.%) and number densities (8.2–9.0 log m⁻³). The microlite volume fraction (DRE converted) also changes consistently across type I, type II, and type III as 0.06, 0.08, and 0.10–0.15, respectively. However, the number density of the microlites remains nearly invariant in all the pyroclast types. These facts indicate that the variation in the microlite volume fraction is controlled not by the number density (i.e., nucleation process), but by the size (i.e., growth process); the growth history of each type of microlite was different. Water content determinations show that the three types of pumices have similar H₂O contents (2.6±0.2 wt%). This fact implies that all three types were quenched at nearly the same depth (35±5 MPa, assuming that the magma was water-saturated) in the conduit. If the crystal sizes are limited only by growth time, a variation in this parameter can be related to the residence time, which is attributed to the flow heterogeneity in the conduit. By assuming a laminar Poiseuille-type flow, these textural observations can be explained by the difference in ascent velocity and shearing motion across the conduit, which in turn results in the differences in growth times of crystals, degrees of deformation, and bubble coalescence. Consequently, for crystals in the inner part of the conduit, the crystal growth time from nucleation to quenching is shorter than that near the conduit wall. The vesicle texture variation of bubbles in types I, II, and III results from the difference in the deformation history, implying that the effect of degassing occurred primarily towards the conduit wall.     

Measurement of debris mass changes and assessment of the dam-break flood potential of earthquake-triggered Hattian landslide dam

The Hattian landslide, which was triggered by the 2005 Kashmir earthquake, formed one of largest landslide dams in the world and it has posed a serious threat of flooding to people living in the lower reach of the Jhelum River. In order to understand deformation occurring in the body of the dam, physical measurements using a Differential Global Positioning System (DGPS) were conducted. Gradual deformation and slowly developing backward erosion initially were observed, leading eventually to a sudden creation of a deep hollow on the downstream slope of the landslide dam. The dimensions of this eroded gully were determined by laser scanning, and the results showed a significant loss of soil volume and a large change in the body of the dam. A breach formation model was used to predict the outflow hydrograph generated by constant downcutting of dam during a breaching event. A run-off analysis of the outflow hydrograph was conducted to evaluate inundation levels of flood waves in case the dam is breached. Hazardous downstream locations were identified near the junction of the Karli and Jhelum Rivers, suggesting a need for early warning system in order to avoid loss of lives.     

SHRIMP U-Pb Zircon Age of the Inishi Migmatite around the Kamioka Mining Area, Hida Metamorphic Complex, Central Japan

Abstract. SHRIMP U-Pb ages were determined on single zircons separated from the Inishi migmatite in the Kamioka mining area, Hida metamorphic complex, central Japan. Twenty one determinations were distributed within the age of 234.2±1.8 Ma, excluding one inner core of a grain. As the analyzed crystals were mostly euhedral igneous zircons, the age indicates the crystallization of zircons from granitic melt during the formation of Inishi migmatite. The age of ca. 234 Ma corresponded to the later stage of the major regional metamorphic event in the Hida complex, while the age of ca. 265 Ma determined in a grain suggested the inherited age of the earlier phase of the metamorphism.     

Accuracy assessment of QuickBird stereo imagery

The Geographical Survey Institute of Japan has recently carried out an evaluation of the metric performance of QuickBird stereo satellite imagery. This paper describes the accuracy assessment of the sensor orientation and geopositioning phases of the study, the aim of which was twofold. First, it was desired to confirm the metric potential of QuickBird imagery for 1:25 000 scale topographic mapping. Second, a determination was to be made of the accuracy attainable from the Basic image product. The techniques of rational functions and affine bundle adjustment were employed, the former with bias compensation. The results obtained both reassert the high precision of the rational functions approach and cast doubt upon the applicability of the 3D affine model for accurate geopositioning from QuickBird imagery.     

Fission–track Ages and Magnetic Susceptibility of Cretaceous to Paleogene Volcanic Rocks in Southeastern Sikhote Alin, Far East Russia

Abstract: Seven zircon fission-track ages and 30 magnetic susceptibilities were measured on welded pyroclastic rocks from the Bogopol and Sijanov Groups of the Cretaceous to Paleogene volcanic rocks in the southeastern part of the eastern Sikhote Alin volcano-plutonic belt, Far East Russia. The fission-track ages range from 42. 7 Ma to 64. O Ma which indicate that both the groups are of Early Paleogene time. Two thirds of the samples from the Bogopol Group have high magnetic susceptibility values, more than 3 A- 10^-3 SI unit, which imply that they are of the magnetite–series, whereas the samples from the Sijanov Group show 3 A- 10^-3 to 8 A- 10^-5 SI unit which suggest this group of probably the ilmenite-series.
The Paleogene age and high magnetic susceptibility of the Bogopol Group are quite similar to the Paleogene igneous rocks of the San'in belt, Southwest Japan. This suggests, taking accounts of the opening of the Japan Sea, that the eastern Sikhote Alin volcano-plutonic belt continued to the San'in Belt, and that the Paleogene igneous rocks along the Japan Sea coast of Northeast Japan were situated along the volcanic front of the eastern Sikhote Alin volcano-plutonic belt.     

Kizawa tunnel cracked on 23 October 2004 Mid-Niigata earthquake: An example of earthquake-induced damage to tunnels in active-folding zones

Earthquakes in active-folding zones often trigger long-lasting landform changes. Since an underground structure closely follows the motion of its surrounding soils and rocks even after it was damaged in an intense earthquake, experts in charge of reconstruction have to wait until they are convinced that the soils and rocks have been stabilized. Kizawa tunnel was seriously cracked during the 23 October 2004 Mid-Niigata Earthquake. The upper half of the tunnel's cross-section near the north mouth shifted about 0.5 m sideways. Since a ring-shaped cross-section of a tunnel sustains the surrounding soil pressure, this crack pattern seemed to be serious. The authors collaborated with the Nagaoka Regional Development Bureau, Niigata Prefectural Government, in investigating the causes of the damage and in conducting long-term observation of the soils and rocks. This paper summarizes some findings for rational rehabilitations through the investigations.     

Study by MOA of extrasolar planets in gravitational microlensing events of high magnification

A search for extrasolar planets was carried out in three gravitational microlensing events of high magnification, MACHO  98–BLG–35  , MACHO  99–LMC–2  and OGLE  00–BUL–12  . Photometry was derived from observational images by the MOA and OGLE groups using an image subtraction technique. For MACHO  98–BLG–35  , additional photometry derived from the MPS and PLANET groups was included. Planetary modelling of the three events was carried out in a supercluster computing environment. The estimated probability for explaining the data on MACHO  98–BLG–35  without a planet is <1 per cent. The best planetary model has a planet of mass ∼(0.4–1.5)× M _Earth at a projected radius of either ∼1.5 or ∼2.3 au. We show how multiplanet models can be applied to the data. We calculate exclusion regions for the three events and find that Jupiter-mass planets can be excluded with projected radii from as wide as about 30 au to as close as around 0.5 au for MACHO  98–BLG–35  and OGLE  00–BUL–12  . For MACHO  99–LMC–2  , the exclusion region extends out to around 10 au and constitutes the first limit placed on a planetary companion to an extragalactic star. We derive a particularly high peak magnification of ∼160 for OGLE  00–BUL–12  . We discuss the detectability of planets with masses as low as Mercury in this and similar events.     

A new variant of saponite‐rich micrometeorites recovered from recent Antarctic snowfall

Abstract– Eight saponite‐rich micrometeorites with very similar mineralogy were found from the recent surface snow in Antarctica. They might have come to Earth as a larger meteoroid and broke up into pieces on Earth, because they were recovered from the same layer and the same location of the snow. Synchrotron X‐ray diffraction (XRD) analysis indicates that saponite, Mg‐Fe carbonate, and pyrrhotite are major phases and serpentine, magnetite, and pentlandite are minor phases. Anhydrous silicates are entirely absent from all micrometeorites, suggesting that their parental object has undergone heavy aqueous alteration. Saponite/serpentine ratios are higher than in the Orgueil CI chondrite and are similar to the Tagish Lake carbonaceous chondrite. Transmission electron microscope (TEM) observation indicates that serpentine occupies core regions of fine‐grained saponite, pyrrhotite has a low‐Ni concentration, and Mg‐Fe carbonate shows unique concentric ring structures and has a mean molar Mg/(Mg + Fe) ratio of 0.7. Comparison of the mineralogy to hydrated chondrites and interplanetary dust particles (IDPs) suggests that the micrometeorites are most similar to the carbonate‐poor lithology of the Tagish Lake carbonaceous chondrite and some hydrous IDPs, but they show a carbonate mineralogy dissimilar to any primitive chondritic materials. Therefore, they are a new variant of saponite‐rich micrometeorite extracted from a primitive hydrous asteroid and recently accreted to Antarctica.