Search

Kathmandu Valley, which is a rapidly growing place in Nepal, was largely damaged by the earthquakes of April 25 (Mw 7.8) and May 12 (Mw 7.3). For taking measures against future large earthquakes, knowledge of the long-term earthquake history is crucial for future disaster prevention or disaster reduction. Twelve seismites thicker than 0.2 m were identified from the Tokha Formation, the major part of which was deposited at about 20 – 17 ka (calibrated 14C ages). Some seismites show evidence of sliding occurred on the delta plain. The reconstructed earthquake recurrence period is ca. 0.25 ka or shorter. Six of the seismites show evidence of sliding when deformation structures were formed. This was probably due to the tilting of the surface in the studied site, where a buried flexure was discovered nearby. The discovery of the seismites with sliding in the delta plain deposit suggests the possibility of sliding by future large earthquakes and requirement of risk management for the plain area of the Kathmandu Valley.

Sediments indicating a rapid fall in lake level have been discovered in the late Pleistocene Gokarna Formation, Kathmandu Valley, Nepal. The indicators are observed along a widely traceable erosional surface in this formation, and is characterized by (1) gently inclined (ca. 10°) tabular cross-stratified sand beds of delta front deposits consisting of coarser material and showing gradual decrease in elevation of its top to the progradation direction, (2) an antidune cross-laminated sand bed that interfingers with the delta front deposit, and (3) an approximately 5m-deep erosional depression filled with convolute laminated sand beds and recognized at a location distal to that where deposits (1) and (2) were found.The early phase of rapid lake level fall caused minor erosion of the delta plain deposits by fluvial processes, introducing a higher rate of progradation of the delta front and resulting in the accumulation of deposit (1). The delta emerged as dry land due to further lowering of the lake level. The antidune cross-laminated sand bed shows evidence of having accumulated from a high-velocity stream that may have formed as the lake water drained from the delta front during the lowering of lake level. When the lake level fell below the level of the topographic high created by delta accumulation prior to the fall, incised valleys may have formed and part of them may have been filled with sediment at that time.The rapid fall in lake level is interpreted to have been the result of lake-wall failure, which would have occurred at the gorge outlet as the only discharge path for the basin. The initial rise of lake level causing accumulation of terrace sediments may have been due to the formation of a plug at this outlet, attributable to mass movement along the gorge.

History of Vegetation and Climate in the Kathmandu Valley

Vegetation and Climatic Changes in Nepal HimalayasII: A Preliminary Study of the Holocene Vegetational History in the Lake Rara National Park Area, West Nepal

We have successfully grown 〈1 1 1〉 oriented (La,Sr)(Al,Ta)O3 (LSAT) mixed-perovskite single crystals by the Czochralski method. Compositional uniformity and coloring phenomena are discussed in relation to the growth conditions. Since LSAT single crystals have excellent lattice matching with GaN, they are promising as new substrates for the growth of high-quality GaN epitaxial layers.

The chemiluminescence of the Cypridina luciferin analog, 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroirnidazo[1,2-a]pyrazin-3-one (MCLA), with O2 (1Δg) generated by the retro-Diels-Alder reaction of 3-(4′-methyI-l'-naphthyl)-propionic acid endoperoxide was studied in an aqueous solution with pH 7.12 at 37°C. The retro-Diels-Alder reaction occurs with a first-order rate constant of (4.16 ± 0.13) × 10−4/s to quantitatively yield O2 (1Δg) and 3-(4′-methyl-l'-naphthyl (-propionic acid. MCLA consumed equimolar amounts of O2 (1Δg) with a second-order rate constant (6.96 ± 0.27) × 108/M/s to emit light in an aqueous solution with pH 7.12 at 37°C. The chemiluminescence spectrum was identified as the fluorescence spectrum of 2-acetylamino-5-(p-methoxyphenyl)pyrazine (OMCLA), a major chemiluminescence reaction. Chemiluminescence spectra and product yields for MCLA reactions with O21Δg, with O2 (3Σ−g) and with superoxide anion radicals are identical, suggesting that all of these reactions occur via a common MCLA-2-hydrope-roxide intermediate formed by a combination of MCLA radicals and superoxide anion radicals. We have established practical use of NEPO as an O2 (1Δg) source and MCLA as a biological probe for detecting O2 (1Δg).

Small-amplitude lake-level fluctuations have been recognized from the aggrading delta-plain deposits in the lower parts of the Thimi and Gokarna formations, Kathmandu Valley, Nepal. The delta-plain deposits consist or gravelly sand beds of fluvial channel origin (coarse-sediment interval) and alternation of' fine to very line sand and sandy silt beds (line-sediment interval). Wave generated structures occur in the sand beds or the fine sediment intervals. The vertical and lateral facies changes suggest that the deposition or a set of coarse- and fine-sediment intervals associated with prograding delta front deposits was controlled by a lake-level rise and fall sequence superimposed on a long-term lake­ level rise trend. The aggradation of fluvial sediments occurred during a lake-level rise period with sufficient sediment supply to fill a newly created accommodation space on the delta plain. The observation or wave-generated structures in an overlying fine-sediment interval suggests that the delta plain was subsequently inundated due to further lake-level rise, exceeding the sedimentation rate. Subsequent delta progradation occurred during a lake-level stabilized phase after a lake­ level fall. The small-amplitude lake-level changes are thought to be attribute able to seasonal wet and dry cycles, as inferred based on the presence of peculiar aggrading delta successions, implying that lake-level fluctuations may have occurred over short time scales, and on the results of a previous palaeopalynological study in which a moist palacoclimate was inferred in the lower part of the Gokarna Formation in particular.

Himalayan corridors Kitamura (1955) postulated that the temperate zone of the southern side of the Great Himalayas represented a corridor through which Sino-Japanese plants migrated westwards, and named it the Himalayan corridor. However, he did not pay much attention to the eastward distribution of Mediterranean elements through the corridor and extended the Sino-Japanese region up to Afghanistan by drawing the Himalayan corridor (Kitamura, 1957). The southern slopes in the Himalayas are generally drier than the northern slopes. In the case of the Great Himalayas, however, the south-facing slope is moister than the north facing one. Therefore, there are two corridors along the Outer and Lesser Himalayas respectively, on the south facing slopes and on the north facing slopes, and the Great Himalayas provide a corridor on its southern slope. The northern side of the Great Himalayas can not act as a corridor due to its dryness. The eastern elements extended their distribution range westwards through the moister corridor and the western elements migrated eastwards through the drier corridor. However, for example, wet sal (Shorea robusta) forest occurring on the south-facing slopes of the Siwalik range in Central Nepal can not survive on the south facing slopes in the western Siwaliks. It moves to the north-facing slope and it is replaced by the dry hill sal forest in the west Siwalik range. The dry hill sal forest gives place to the subtropical decidous hill forest dominated by Anogeissus latifolia in the west Siwalik. The deciduous hill forest dominated by Anogeissus latifolia is replaced by the subtropical scrub composed of Olea cuspidata, Dodonea viscosa etc. in the further west. On the north-facing slope, the wet Sal forest replaces Castanopsis indicaSchima wallichiana forest in the west Siwalik where the dryness caused by the increase of mediterraneity of climate is prevailing. The Siwalik range provides corridors on the south and north sides of the range for the eastward migration of western elements and westward distribution of eastern elements. In the Lesser Himalayas, Quercus lanuginosa-Q. incana forest is replaced by Q. incana forest in West Nepal, and Q. incana forest occurs on the all exposures in West Nepal and Kumaon region in India and then it is confined to the northern side of the Lesser Himalayas westwards. Cedrus deodara forest replaces Q. incana forest on the southern slopes of the western Lesser Himalayas where Q. incana forest move to the northern side. The Himalayan corridors are twisted in this way.

DOI = 10.3126/hjs.v5i7.1314 Himalayan Journal of Sciences Vol.5(7) (Special Issue) 2008 p.129