Abstract Reconstructing the stratigraphic architecture of deposits prior to Cenozoic Himalayan uplift is critical for unravelling the structural, metamorphic, depositional and erosional history of the orogen. The nature and distribution of Proterozoic and lower Paleozoic strata have helped elucidate the relationship between lithotectonic zones, as well as the geometries of major bounding faults. Stratigraphic and geochronological work has revealed a uniform and widespread pattern of Paleoproterozoic strata >1.6 Ga that are unconformably overlain by <1.1 Ga rocks. The overlying Neoproterozoic strata record marine sedimentation, including a Cryogenian diamictite, a well-developed carbonate platform succession and condensed fossiliferous Precambrian–Cambrian boundary strata. Palaeontological study of Cambrian units permits correlation from the Indian craton through three Himalayan lithotectonic zones to a precision of within a few million years. Detailed sedimentological and stratigraphic analysis shows the differentiation of a proximal realm of relatively condensed, nearshore, evaporite-rich units to the south and a distal realm of thick, deltaic deposits to the north. Thus, Neoproterozoic and Cambrian strata blanketed the northern Indian craton with an extensive, northward-deepening, succession. Today, these rocks are absent from parts of the inner Lesser Himalaya, and the uplift and erosion of these proximal facies explains a marked change in global seawater isotopic chemistry at 16 Ma.

Abstract This chapter examines the along-arc variation in the crustal structure of the Himalayan Mountain Range. Using results from published seismological studies, plus large teleseismic body-wave and surface-wave datasets which we analyse, we illustrate the along-arc variation by comparing the crustal properties beneath four representative areas of the Himalayan Mountain Range: the Western Syntaxis, the Garhwal–Kumaon, the Eastern Nepal–Sikkim, and the Bhutan–Northeastern India regions. The Western Syntaxis and the Bhutan–Northeastern India regions have a complicated structure extending far out in front of the main Range, whereas the Central Himalaya appear to have a much simpler structure. The deformation is more distributed beneath the western and eastern ends of the Range, but in general, the crust gradually thickens from c. 40 km on the southern side of the Foreland Basin to c. 80 km beneath the Tethys Himalaya. While the gross crustal structure of much of the Himalaya is becoming better known, our understanding of the internal structure of the Himalaya is still sketchy. The detailed geometry of the Main Himalayan Thrust and the role of the secondary structures on the underthrusting Indian Plate are yet to be characterized satisfactorily.

Abstract The subduction of Indian plate lithosphere during its collision with Asian plate in the Eocene resulted in a regional metamorphic belt along the strike of the Himalayan orogen. High-/ultrahigh-pressure (HP/UHP) metamorphic rocks (eclogites and host gneisses) confirm the metamorphic event in western Himalaya (Kaghan c. 46 Ma and Tso Morari at c. 47 Ma) at mantle depths (>90 km: coesite-stable). In contrast, HP/UHP rocks have not been reported from central and eastern Himalaya and only highly retrogressed eclogites and granulites ( c. 25 to 13 Ma) occur. The presence of UHP rocks in western Himalaya and highly retrogressed eclogites and granulites in central and eastern Himalaya was regarded as evidence for a diachronous India–Asia collision. Despite the along-strike regional homogeneity in major lithotectonic units of the Himalayan orogen, metamorphic diachroneity is enigmatic. It is unlikely to have a subduction-related prolonged progressive metamorphic event. In contrast, the age difference and preservation of UHP phases in the west and their transformation into granulites in central and eastern Himalaya could be associated with their prolonged residence times at crustal levels in the central and eastern Himalaya whereas the rocks exhumed rapidly in the west. The higher thermal events relating to melting of the subducting Indian lithosphere in central and eastern Himalaya evidenced from ultra-potasic volcanics in southern Tibet probably decompressed the early metabasites into granulitized eclogites, even resetting their geological clock, which is why eclogites and granulites in the east show younger ages compared with their UHP counterparts in the west.

Abstract Snow albedo is an important climate parameter as it governs the amount of solar energy absorbed by the snow and can be considered a major contributor to the surface radiation budget. The present study deals with the estimation of temporal variation of snow albedo at the upper elevation zone of glaciated Mago Basin of Arunachal Pradesh in eastern Himalaya. Moderate Resolution Imaging Spectroradiometer (MODIS) Daily Snow Products (MOD10A1 and MYD10A1) at 500 m spatial resolution were used. Both the MODIS data for ten years (2003–13) and the Advanced Spaceborne Thermal Emission and Reflection (ASTER) digital elevation model (DEM) of the study area were downloaded from NASA DAAC of NSIDC. The percentage area under different snow types (dry snow, wet snow, firn and ice) was determined by masking the upper elevation zone of the DEM into the albedo images. The average monthly slopes show a decreasing trend in area (%) of dry snow and wet snow and an increasing trend for firn and ice. Dry snow and wet snow cover percentages were observed to be decreasing, whereas firn and ice cover showed an increasing trend for most of the months. Firn dominated the type of snow, followed by ice then wet snow; the smallest area (%) was that of dry snow for the study period.

Abstract Successful sustainable development and geohazard mitigation in the Himalaya requires an understanding of the nature and dynamics of Earth surface processes and landscape evolution. In recent years, geoscience studies of Himalayan environments have been increasing due to better accessibility, modern technologies and the understanding that there is a necessity to determine the nature and predict likely environmental changes that are occurring due to natural and human influences. The Himalaya is one of the most dynamically active tectonic and geomorphic regions on our planet, and it is the most glaciated mountain area outside of the polar realms. The high mountains and deep valleys are a consequence of the continued collision of the Indian and Eurasian continental plates, rapid uplift and intense denudation by glacial, fluvial, landsliding, aeolian and weathering processes. These processes change over time, influenced by topographic development, climate change and humans. Defining the rates and magnitudes of these processes and their interactions is fundamental in developing a framework to quantify, model and predict future changes for geohazard mitigation and sustainable development.