Causes of large-scale landslides in the Lesser Himalaya of central Nepal

Geologically and tectonically active Himalayan Range is characterized by highly elevated mountains and deep river valleys. Because of steep mountain slopes, and dynamic geological conditions, large-scale landslides are very common in Lesser and Higher Himalayan zones of Nepal Himalaya. Slopes along the major highways of central Nepal namely Prithvi Highway, Narayangadh-Mugling Road and Tribhuvan Highway are considered in this study of large-scale landslides. Geologically, the highways in consideration pass through crushed and jointed Kathmandu Nappe affected by numerous faults and folds. The relict large-scale landslides have been contributing to debris flows and slides along the highways. Most of the slope failures are mainly bechanced in geological formations consisting phyllite, schist and gneiss. Laboratory test on the soil samples collected from the failure zones and field investigation suggested significant hydrothermal alteration in the area. The substantial hydrothermal alteration in the Lesser Himalaya during advancement of the Main Central Thrust (MCT) and thereby clay mineralization in sliding zones of large-scale landslide are the main causes of large-scale landslides in the highways of central Nepal. This research also suggests that large-scale landslides are the major cause of slope failure during monsoon in the Lesser Himalaya of Nepal. Similarly, hydrothermal alteration is also significant in failure zone of the large-scale landslides. For the sustainable road maintenance in Nepal, it is of utmost importance to study the nature of sliding zones of large-scale landslides along the highways and their role to cause debris flows and slides during monsoon period.     

Hydrogen, Oxygen and Sulfur Isotope Studies of Seafloor Hydrothermal System at the Desmos Caldera, Manus Back-arc Basin, Papua New Guinea: An Analogue of Terrestrial Acid Hot Crater-lake

Abstract. The Onsen site is an active submarine hydrothermal system hosted by the Desmos caldera in the Eastern Manus Basin, Papua New Guinea. The hydrothermal fluid is very acidic (pH=1.5) and abundant native sulfur is deposited around the vent. The δ³⁴S values of native sulfur range from -6.5 to -9.3 %o. δ³⁴S values of H₂S and SO₄ in the hydrothermal fluid are -4.3 to -9.9 %o and +18.6 to +20.0 %o, respectively. These δ³⁴S values are significantly lower than those of the other hydrothermal systems so far reported. These low δ³⁴S values and the acidic nature of the vent fluids suggest that volcanic SO₂ gas plays an important role on the sulfur isotope systematic of the Onsen hydrothermal system. Relationship among the δ³⁴S values of S-bearing species can be successively explained by the model based on the disproportionation reaction starting from the volcanic SO₂ gas. The predicted δ³⁴S values of SO₂ agree with the measured whole rock δ³⁴S values. δD and δ¹⁸O values of clay minerals separated from the altered rock samples also suggest the contribution of the magmatic fluid to the hydrothermal system. Present stable isotopic study strongly suggests that the Onsen hydrothermal site in the Desmos caldera is a magmatic submarine hydrothermal system.     

GEOGRAPHICAL LITERATURE IN JAPAN

This is the third in a series of reports on Japanese geographic research prepared in cooperation with the Association of Japanese Geographers (AJG). Like the two previous reports, which appeared in the August and November issues, it has been modified for the English-speaking readership of THE PROFESSIONAL GEOGRAPHER. However, unlike the previous articles, each of which aimed at providing data regarding Japanese research on specific geographic topics, this paper is intended to supply the reader with an inventory of those materials that will be needed for the conduct of research in Japan. —H. Jesse Walker, Member, U.S. National Committee, IGU.     

Star formation associated with high-velocity mass outflows (invited review)

Energetic mass outflows have been detected in molecular line observations towards young stellar objects. In this review we take the Orion-KL as an example to discuss the overall structure of a high-velocity outflow and its environment. The kinematics of the high-velocity molecular emission show clear evidence of a bipolar jet which originates in the vicinity of IRc2, a massive protostar. Towards the ends of the jet, 0.05 pc away from the origin of the flow, the interaction between the high-velocity flow and the ambient molecular gas excites shocks. The protostar is encircled by a disc of dense molecular gas, the inner 0.04 pc of which is expanding while the outer part shows signs of rotation and contraction. A comparison between the dynamical timescales of the disk and the bipolar jet may suggest that the disk itself, or some mechanism of disk formation, is also responsible for the bipolar nature of the high-velocity flow.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.NRO, a branch of the Tokyo Astronomical observatory, is a cosmic-radio observing facility open to outside users.     

Electrodynamical synchronization of AM Herculis-type stars

A new mechanism is proposed for the explanation of synchronous rotations in AM Herculis-type binaries. In contrast to the resistive mechanism of Josset al. (1979), our model predicts that an asynchronous rotation, if it is present, damps exponentially and the damping time is inversely proportional to the electrical conductivity. It is shown by using the parameters which fit for AM Herculis that a typical damping time is very short compared with the lifetime of the system.Paper presented at the I.A.U. Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

海洋天然气水合物的地球物理研究(Ⅰ)：岩石物性

本文综述了含水合物沉积物的岩石物性模型，讨论水合物饱和度与岩石物性的关系，关于纵波速度与水合物饱和度的关系，有一些简单模型，如孔隙度降低模型，时间平均方程、时间平均－Wood加权方程，也有复杂模型，如根据弹性模量计算的模型、根据等效介质中地震波传播理论的模型，本文还介绍了含水合物沉积物的电阻率、电导率模型与含注重气沉积物的岩石物性。     

Remote sensing parameterization of the processes of energy and water cycle over desertification areas

In order to understand the processes of land surface-atmosphere interaction over de-sertification area, it is indispensable to utilize of satellite remote sensing. Two scenes of LandsatTM were used to produce a set of maps of surface reflectance, MSAVI, vegetation coverage, sur-face temperature, net radiation, soil heat flux, sensible heat flux and latent heat flux. Statisticalanalysis based on these maps revealed some quantitative significant land surface characteristics.Future developments of the method are also discussed.     

Possible manifestations of slab window magmatisms in Cretaceous southwest Japan

The slab window system related to ridge subduction is studied to explain the conspicuous activity and the along-arc migration of the magmatisms in the eastern margin of Eurasian continent in the late Mesozoic. The trend of the granite ages is scrutinized with systems approach and analyzed by the statistical method in Cretaceous southwest Japan, a reference field of the Eurasian eastern margin. The magmatic distribution of simultaneous activity was determined to be the V-shape of the slab window, excluding dating errors from the located age data. The slab window magmatism has the most dominant zone of the acidic rocks at or near the centerline of the window (the spreading center of two plates), and also has the subdominant zone of the acidic to intermediate rocks on either side of the window.As the slab window opens due to the plate motions, the upwelling current is adiabatically induced in the asthenosphere to fill the window gap. The partial melt is generated in the upwelling flux and transports heat to the lower crust to make greater granitic magma chambers by heat conduction to, and assimilation with, the crustal matter. The younger and hotter slabs outside the window also play a role in partial slab melting and/or dehydration to the asthenosphere and generate the subdominant granodioritic and adakitic and/or high-magnesian andesitic magmatisms as the pre- and post-activities of the main granite genesis.The slab window formed by the subducted ridge between the Kula and Pacific plates was the strong heat source of the active magmatisms and migrated at the rate of 2.8 cm/year from southwest to northeast about 8000 km along the continental margin. The growth of the continent associated with the active acidic to intermediate magmatisms including the adakitic and/or high-magnesian andesitic activities is modeled by the slab window system.