The major ion and trace element chemistry of water samples, including springs, rivers and irrigation ditches, collected during a survey on August 2016 in the Upper Mustang region of the Mustang District of Dhawalagiri Zone (Nepal) has been investigated. The Upper Mustang region, a cold desert, represents a hot-spot for climate change: indeed, violent hailstorms and rainstorms have been recently observed, consequently exposing land to erosion. Results of this study indicate that waters in the region belong to the Caâ\u80\u93HCO3, Caâ\u80\u93Mgâ\u80\u93Clâ\u80\u93SO4and Naâ\u80\u93Kâ\u80\u93Cl-types, reflecting different hydrochemical regimes. Uranium is widespread in waters, with concentrations up to 19 µg/L recorded in a potable water supply. Locally, anoxic conditions affect uranium mobility due to the low solubility of U(IV) minerals. Highly toxic thallium was detected in a thermal spring at an elevated concentration (45 µg/L Tl). The association of thallium with high concentrations of iron suggests that these elements are derived from pyrite oxidation. Detectable levels of thallium were also measured in the water of an irrigation ditch. Lithium concentrations ranged from 7 µg/L to 12 mg/L in the thermal water and showed a strong association with chloride ions. Arsenic concentrations up to 4.7 µg/L were measured in tributaries of the Kali Gandaki river. The data provide evidence that solutes in water have originated from an array of input sources, including carbonate dissolution, the dissolution of soluble salts, silicate weathering and localized sulfide oxidation. In particular, chemical weathering of granitic rocks is likely the primary source for metals and metalloids in waters. Since the erosion rate is a factor affecting lithological weathering, high-intensity rainfalls due to climate change are expected to influence the release and fate of potentially harmful elements in the in the Upper Mustang Valley
The geology of the Himalayas is intricated and intriguing. It features numerous tectonic bodies and structures too complex to interpret. Along with such mysteries it has too many common geohazards, such as landslides. In this study, a detailed geological investigation is carried out to overcome the discrepancies in structural interpretation, the nature of two crystalline bodies, and non-uniformity in geological mapping in the central Himalayan arc, in the Jajarkot district of Nepal. Along with the geological exploration and landslide characterization of the area, consequent landslide susceptibility mapping is performed considering 13 causative factors related to geology, topography, land use, hydrology, and the anthropogenic factor, using two bivariate statistical models. This study concludes that the two metamorphic crystalline bodies in the study area are most probably the klippen, due to the absence or erosion of the root zone. The field study revealed that haphazard road excavation without the consideration of geological and geotechnical features has caused shallow landslides. The results obtained from the susceptibility maps, with a varying range of susceptibility zones, are in good agreement with the spatial distribution of pre-historic landslides. The results of the susceptibility modeling are validated by calculating landslide density and plotting area under curves (AUC). The AUC value for the WOE, and the FR method, revealed an overall success rate of 79.42% and 77.62%, respectively.
The Lesser Himalaya is a fold-thrust belt in the Himalaya. In the Nepal Himalaya, several active faults, among which the Badi Gad Fault is one of them, are identified and mapped by many researchers in the past, However, very less study has been carried out on the existence of this fault and its extension. In the present study, an attempt was made to assess the fault and to map its extension in the region based on the geological as well as geomorphological criteria. For this purpose, a detailed geological map was prepared from Ridi to the Shantipur area in 1:25,000 scales. During the field work, several geological as well as geomorphic evidences of the existence of active fault were found, and some of them are also found under the aerial photo observation. These evidences include the presence of shear zones, clustering of large and several landslides along a confined linear zone, river course diversion, terrace tilting, fault scarps etc. In the present work, the Badi Gad Fault is traced out continuously from the Ridi to the Shantipur area and even extended far to the NW direction under aerial photo. The fault follows the moderate hills of the left bank of the present course of the Badi Gad River. Major shear zones found in the region are the Tal Khola, Aslewa, Eksingaun, Juhan, Gultung, and the Rupakot shear zones. These shear zones are represented by the wide zone of fault gauge, fault breccias, silickensides, striations and large landslides. Besides, other geomorphic evidences traced out are location of spring lines, tilted river terraces in Pul Camp and Wamitaksar area, river course diversion of the Lumdi Khola and fault scarp at Bhanjyangaun of Aslewa. Such types of fault-controlled geomorphic features are also found from the Rudrabeni-Wamitaksar areas under the aerial photos. Based on the fault controlled geomorphological study in the field and aerial photos interpretation, an attempt was made to map the Badi Gad Fault, an active strike slip fault in the region.
This paper explores openly available geo-spatial and earth observatory data to understand landslide risk in data scarce rural areas of Nepal. It attempts to explore the application of open-source data and analytical models to inform future landslide research. The first step of this procedure starts from the review of global open datasets, literatures and case studies relevant to landslide research. The second step is followed by the case study in one of the mountainous municipalities of Nepal where we tested the identified open-source data and models to produce landslide susceptibility maps. Past studies and experiences show that the major potential sites of landslide in Nepal are highly concentrated in a geologically weak area such as the active fault regions, shear zones, axis of folds and unfavorable setting of lithology. Triggering factors like concentrated precipitation, frequent earthquake phenomenon and haphazard infrastructural development activities in the marginally stable mountain slopes have posed serious issues of landslides mostly through the geologically weak regions. In this context, openly available geo-spatial datasets can provide baseline information for exploring the landslide hazard scenario in the data scarce areas of Nepal. This research has used the available open-source data to produce a landslide susceptibility map of the Bithadchir Rural Municipality in Bajhang District and Budiganga Municipality in Bajura District of the Sudurpaschim Province of Nepal. We used qualitative analysis to evaluate the parameters and assess the susceptibility of landslide; the result was classified into five susceptibility zones: Very High, High, Moderate, Low, and Very Low. Slope and Aspect were identified to be the major determinants for the assessment. This approach is applicable, specifically, for the preliminary investigation in the data scarce region using open data sources. Furthermore, the result can be used to plan and prioritize effective disaster risk reduction strategies.
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