Masahiro Tamai

The authors showed that cold nocturnal darainage flows break out in the northern part of Osaka Plain, can lower temperature of the part by 2℃ and have velocity profiles similar to those of gravity density currents on inclined plains. In the present study, numerical simulation using the WRF was conducted to examine structures and generation mechanisms of the flows. The accuracy of the calculation was checked by comparison with some existing meteorological data. The simulation results showed that the drainage flow which the authors have been studying is generated by outflow of cold air mass which accumulates in the Tada basin into Osaka Plain and there are other nocturnal drainages which flow on flood plains of the Akutagawa and Aigawa Rivers in the part.

A new method by the concept of entropy has been used to classify sediment color distribution. We objectively characterized the distribution profile and clarified the relationship between the geology and sediment characteristics. Sediment colors were defined by L*a*b* instead of RGB, and of the following four indexes, lightness, hue, saturation and chromaticity, lightness was the optimal index. In order to determine the optimal number of groups, a C-H criterion, Rs statistic and the skewness of the third moment on sediment color distribution were used. The sediment colors could be divided into 7 groups. Kagoshima Pref. has geology of the Shirasu plateaus, but the sediment color could be grouped by white minerals such as quartz and feldspar contained in granite and pyrophorite and colored minerals such magnetite contained in mafic volcanic rock, and therefore, they can be related to geology. In addition, it could be possible to make sediment transport path clear by focusing on a specific mineral such as olives.

Purposes of the present study are to obtain quantitatively color characteristics of sands which were collected in the mainland beaches in Kagoshima Pref., Japan and to examine relationships between the color characteristics and geological features of the surrounding area of the beaches. Some relationships between the two are clarified, such as that a lot of the beaches have sand colors of medium dark brown under the influence of late Pleistocene non-alkaline pyroclastic flow volcanic rocks, Holocene non-alkaline pyroclastic flow volcanic rocks and non-alkaline pyroclastic mafic volcanic rocks make beach sand color dark gray, and dark blown sands of some east coasts in Osumi Peninsula originate in middle Miocene to late Miocene granodiorite.