The Tone River which has the largest river basin in Japan rises in Mt. Oominakamiyama in the northern part of Gunma Prefecture. It runs down south to Maebashi City, and changes course to the east, then discharges into the Kashimanada Sea at Choshi City in Chiba Prefecture. It, however, used to flow south near Kurihashi Town in Saitama Prefecture, which lies mid-way between Maebashi and Chosi, and flowed in to Tokyo Bay. This rerouting was achieved by the work of the Tokugawa Bakufu in 1654. Before rerouting, the estuary had been in the northern part of the present Sumida Ward, the eastern part of Tokyo. In the estuary area, which corresponds to the Kohtoh region, consisting of Sumida and Koto Wards and the eastern part of Edogawa Ward at present, the sea was shallow and a lot of sand bars scattered over. The Kohtoh region naturally had favorable conditions for reclamation. When Ieyasu Tokugawa entered Edo Castle in 1590, the environs of the castle were limited, because the east side of the castle faced to an inlet called Hibiya Irie, and the other sides were surrounded by rough plateaus. Topographically the site was good for a fortress but too small to make a town and farming estate. Soon after his settlement, Hibiya Irie was reclaimed to build a town for warriors and citizens, and the Onagi cannel was excavated in the shallow sea which spread on the east of the Edo City for transporting food and salt. The soil dredged from the Onagi channel was used for filling the northern part of the channel. It was the first reclamation work in the Koto sea region. Since then reclaiming works have continued in the Koto sea region, which used to be the estuary of the Tone River. A lot of land has been reclaimed due to garbage disposal in the city since 1655. In the Tokyo Bay area, about 2, 700 ha was had reclaimed during the Edo era period over 270 years, and about 6, 000 ha from Meiji Era to the present over about 140 years. As a result of those reclamation works, the sea area of the Koto region has been replaced by man-made lands, with the exception of some ship routes.
The so-called heat island phenomena found over large urban areas are thought to arise due to many causes; one of the major causes of the phenomena is direct heating of the lower atmospheric boundary layer by anthropogenic heat emissions. However, no quantitative assessment of this cause has been reported. Recently developed numerical regional meteorological modeling techniques enable us to estimate the temperature rise resulting from anthropogenic heat emissions into the atmosphere. However, it remains difficult both to perform more than a single-year integration with these numerical meteorological models and to evaluate the annual mean temperature rise resulting from anthropogenic heat. Using a simplified analytical atmospheric dispersion model we estimated the annual mean air temperature rise in the surface layer due to direct heating by anthropogenic heat emissions in to the urban atmosphere over the Tokyo metropolitan area. The validity of this model was verified by applying it to the dispersion of nitrogen oxides over the same area. The temperature rise at the center of Tokyo resulting from anthropogenic heat emissions was estimated to be about 0.7 to 1.1°C. On the other hand, observations from our densely distributed, long-term monitoring network in this area showed that the annual mean temperature at the center of Tokyo was about 2.6 °C higher than the surrounding rural areas. We conclude that direct heating by anthropogenic heat sources accounts for 27% to 42% of the annual average observed heat-island intensity in the Tokyo metropolitan area.
Two boring cores obtained by boring surveys conducted at Akatsuka Park of Itabashi Ward and at Haginaka Park of Ota Ward in the eastern part of the Musashino Uplands, Tokyo metropolitan area, were reexamined. Shapes, refractive indices, and chemical composition of volcanic glass shards, mineral composition, and refractive indices of heavy minerals of several tephra layers from these cores were determined. As a result, it was revealed that 6 tephras correlate with the tephras in the Kazusa Group of the Boso Peninsula, where magnetostratigraphy, biostratigraphy, and tephrostratigraphy had been well established. A-22, A-16, and A-10 tephras collected from Akatsuka Core are identified as U8 tephra (0.85-0.95 Ma) in the lower part of the Umegase Formation, O18 tephra (1.07-1.16 Ma) in the middle part of the Otadai Formation, and Kd5A tephra (1.21-1.27 Ma) in the upper part of the Kiwada Formation, respectively. H-27, H-7, and 11-2 tephras collected from Haginaka Core are identified as Kd21 (>1.45 Ma), Kd24, and Kd25 (1.60-1.65 Ma) tephras positioned in the middle part of the Kiwada Formation, respectively. Thus, these correlations indicate that the sediments (mostly of marine origin on the continental shelf) approximately-50 m and -170 m depth in the northern part of Central Tokyo correlate with the lower part of Umegase Formation to the upper part of the Kiwada Formation, and the sediments (showing oceanic and bathyal environment) -50 m t -100 m depth in the southern part of Central Tokyo correlate with the middle part of the Kiwada Formation. Comparing sedimentary facies and thickness between central Tokyo and the Boso Peninsula, it is suggested that the Kazusa Group in the Boso Peninsula is composed of semi-pelagic sediments accumulated in a subsiding forearc basin called the Kazusa Trough, and that the sediment environment in central Tokyo had changed from semi-pelagic in the Kazusa Trough to shallow marine on continental shelf around 1.3 Ma.
The authors re-examine conventionally used terms for hills on the basis of a morphometric study of landforms in Japan. Relative relief and drainage density are calculated for every 250 m grid on topographic maps. Figure 2 shows relative relief on the vertical axis and drainage density on the horizontal axis. Hills are clearly delineated from mountains by these parameters. The relative relief for hills is smaller than 110 m120 m, and the drainage density is greater than 4050 streams/km2. The Shiranuka Hills in Hokkaido should more appropriately be called the Shiranuka Mountains, because of their high mean relative relief (134.3 m) and lower drainage density. Figure 2 also indicates a possible subdivision of hills into 2 types, or 'flat topped hills' with a relative relief of less than 60 m, and 'ridge hills' with a relative relief of 60 m 120 m. The standard deviation of relief energy can also be taken as a criterion to distinguish the 2 types of hill, namely, the flat topped hills have a standard deviation of 8.120.6, in contrast to the ridge hills, which have a standard deviation of 21.029.8. The drainage density generally increases corresponding to the length of time through which terraces are transformed into hills and the amount of uplift. Therefore, hills have greater drainage density than terraces. But, it is worthy of note that the drainage density is never greater than 7080 streams/km2. The greatest density is found in the Oku-Noto Hills, one of the ridge hills 480, 000780, 000 years old. Indications are that the development of a drainage system culminates at some stage between flat-topped hills and ridge hills, and then valleys are gradually unified, resulting in a lower drainage density. Both flat-topped hills and ridge hills may be derived from various origins such as terraces, depositional surfaces of pyroclastic flows, dissected Tertiary or early Quaternary soft rocks, or degradation of mountains with medium relief. But, the formation of ridge hills requires a greater speed of uplift, and rocks that are hard enough to sustain steep slopes with a relative relief of 80 m120 m. The conditions being the same, ridge hills are older than flat-topped hills.
The surface faults of the Mid Niigata prefecture Earthquake in 2004 appeared along preexisting active fault traces (lines) of the Obirou fault, as well as the northern part of the western marginal fault of the Muikamachi basin. The vertical displacement of surface faults are within 30 cm, and the three areas with distinct faults can be summarized as follows. At Obirou, in Hirokami village (Uonuma city), the road surface is vertically displaced by approximately 30 cm just along the active fault line, and the waterways located on the fault line are compressed and broken. At Shitakura, in the Horinouchi town (Uonuma city), the surfaces of both the highway and the old road are cracked and vertically displaced by approximately 20 cm. At Aoshima, in Koide town (Uonuma city), the surface faults clearly extend over 500 m in length. Paddy fields, gardens, waterways, roads, and houses are vertically displaced by approximately 20 cm. The facts mentioned above indicate that the Mid Niigata prefecture Earthquake in 2004 (probably the main shock) was caused by the rejuvenation of these active faults.