Evaluation of potential landslide damming: Case study of Urni landslide,Kinnaur, Satluj valley,India

This work aims to understand the process of potential landslide damming using slope failure mechanism,dam dimension and dam stability evaluation. The Urni landslide, situated on the right bank of the Satluj River, Himachal Pradesh(India) is taken as the case study. The Urni landslide has evolved into a complex landslide in the last two decade(2000-2016) and has dammed the Satluj River partially since year 2013,damaging ～200 m stretch of the National Highway(NH-05). The crown of the landslide exists at an altitude of ～2180-2190 m above msl, close to the Urni village that has a human population of about 500.The high resolution imagery shows ～50 m long landslide scarp and ～100 m long transverse cracks in the detached mass that implies potential for further slope failure movement. Further analysis shows that the landslide has attained an areal increase of 103,900 ± 1142 m^2 during year 2004-2016. About 86% of this areal increase occurred since year 2013. Abrupt increase in the annual mean rainfall is also observed since the year 2013. The extreme rainfall in the June, 2013; 11 June(～100 mm) and 16 June(～115 mm),are considered to be responsible for the slope failure in the Urni landslide that has partially dammed the river. The finite element modelling(FEM) based slope stability analysis revealed the shear strain in the order of 0.0-0.16 with 0.0-0.6 m total displacement in the detachment zone. Further, kinematic analysis indicated planar and wedge failure condition in the jointed rockmass. The debris flow runout simulation of the detached mass in the landslide showed a velocity of ～25 m/s with a flow height of ～15 m while it(debris flow) reaches the valley floor. Finally, it is also estimated that further slope failure may detach as much as 0.80 ±0.32 million m^3 mass that will completely dam the river to a height of 76±30 m above the river bed.     

First results of convectively generated long-period Kelvin waves in the low-latitude mesosphere during Indian summer monsoon

Spectral analysis of Tirunelveli (8.7°N, 77.8°E) MF radar winds for the year 2007 indicate the presence of long-period Kelvin waves with periods ～23 and ～16 days in the low-latitude mesosphere during Indian summer monsoon months. The dominant presence of these slow-phase speed waves at mesospheric altitudes motivated us to investigate their origin and vertical propagation characteristics. Space-time Fourier analysis of NCEP winds and OLR show the presence of these periodicities with zonal wavenumber 1 indicating that tropical convection is the potential source for these waves and westward phase of stratospheric QBO winds might have favoured these waves to reach the mesosphere.     

Cosmic ray effects induced in a rock exposed on the moon or in free space: contrast in patterns for ‘tracks’ and ‘isotopes’

Analytical studies are reported here for two cosmogenic effects due to low energy particles in extraterrestrial samples:

1. Formation of latent chemically etchable tracks in crystalline materials due to solid state damage as a result of ionisation losses suffered by multicharged cosmic ray nuclei, and
2. Production of low threshold isotopes due to nuclear interactions of solar cosmic ray particles.

The present analytical treatment is different from those previously reported and is more directly applicable to recent studies of low energy cosmogenic effects in meteorites and in lunar samples. We consider irradiation of ellipsoidal rocks in space and on the Moon. In the latter case, different irradiation geometries corresponding to different burials in the regolith are also considered. It is shown that results of irradiation of an object on the surface of a parent body differ from that of an object in free space in more complex manner than a uniform reduction by a factor of two due to the change over from 2π to 4π irradiation. Isocontours for ‘tracks’ or ‘isotopes’ are found to be markedly different in the two cases. Thus, the irradiation geometry must be explicitly taken into account in interpreting low-energy cosmogenic effects in lunar rocks. Simultaneous analyses of tracks and radioisotopes of different half-lives should allow one to establish principal irradiation geometries both for meteorites and lunar samples.     

Eigenfrequencies of rotationally and tidally distorted white dwarf models of stars

In the present paper we have studied the eigenfrequencies of small adiabatic barotropic pseudo-radial and nonradial modes of oscillations of the white dwarf models of rotating stars in binary systems. In this work the methodology of Mohan and Saxena (in Astrophys. Space Sci. 113:155, 1985) has been used that utilizes the averaging technique of Kippenhahn and Thomas (in Proc. IAU Colloq., vol. 4, p. 20, 1970) and certain results on Roche equipotential as that given by Kopal (in Advances in Astronomy and Astrophysics, Academic Press, 1972). The objective of this study is to investigate the effects of rotation and/or tidal distortion on the periods of oscillations of rotationally and/or tidally distorted white dwarf models of stars assuming it to be the primary component of the binary system and rotating uniformly. The results of present study show that the eigenfrequencies (both radial and nonradial modes) of the rotationally distorted and rotationally and tidally distorted white dwarf model of stars in binary systems tend to decrease under the influence of rotational distortions and rotational and tidal distortions, respectively. However, results are contrary for tidally distorted white dwarf model of stars.