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.

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 High Mountain Asia contains the largest volume of glacier ice outside the polar regions, and contain the headwaters of some of the largest rivers in central Asia. These glaciers are losing mass at a mean rate of between –0.18 and –0.5 m water equivalent per year. While glaciers in the Himalaya are generally shrinking, those in the Karakoram have experienced a slight mass gain. Both changes have occurred in response to rising air temperatures due to Northern Hemisphere climate change. In the westerly influenced Indus catchment, glacier meltwater makes up a large proportion of the hydrological budget, and loss of glacier mass will ultimately lead to a decrease in water supplies. In the monsoon-influenced Ganges and Brahmaputra catchments, the contribution of glacial meltwater is relatively small compared to the Indus, and the decrease in annual water supplies will be less dramatic. Therefore, enhanced glacier melt will increase river flows until the middle of the twenty-first century, but in the longer term, into the latter part of this century, river flows will decline as glaciers shrink. Declining meltwater supplies may be compensated by increases in precipitation, but this could exacerbate the risk of flooding.

Abstract: In this paper we illustrate the geochemical diversity of the basalts of Panjal ( c. 289 Ma), Rajmahal ( c. 117 Ma) and Deccan ( c. 65 Ma) continental large igneous provinces (continental LIPs) from India as controlled by multiple mantle sources. The Panjal primitive basalts are formed by 5–20%, Rajmahal basalts by 10–20% and Deccan picritic basalts by 1–20% melting of the mantle. The depth of melting beneath Deccan is greater than beneath Rajmahal, which greater than beneath Panjal. We have categorized the Panjal, Rajmahal and Deccan basalts into Type I and Type II. The Type I basalts with lower La/Nb, Th/Nb and Th/Yb ratios and higher ε Nd i values ( ε Nd i = −3 to +8) are derived from the sublithospheric sources; some of the Type I basalts represent lithosphere-contaminated melts. The Type II basalts with higher La/Nb, Th/Nb and Th/Yb ratios and lower ε Nd i values ( ε Nd i = −20 to −3) are produced from the subcontinental lithosphere. We estimate that lithosphere and sublithosphere (plume and/or E-MORB patches within asthenosphere) have contributed, respectively, approximately 67 and 33% to the Panjal, 52 and 48% to Rajmahal, and 28 and 72% to Deccan LIPs. Fertility of the Indian subcontinental lithosphere may have increased with decreasing age related to the break-up of Gondwana. Supplementary material: References for the geochemical data, extracted from the GEOROC database, on the basaltic rocks from Panjal, Rajmahal and Deccan Large Igneous Provinces are available at: https://doi.org/10.6084/m9.figshare.c.3821881

Abstract: The Cambrian Nongpoh granitoids, intrusive into the Precambrian gneissic complex and metasediments of the Shillong Group, represent a major phase of granitic magmatism in the Shillong Plateau. The Nongpoh granitoids comprise diorite, granodiorite, porphyritic and grey granites. Porphyritic granite is the dominant lithology exposed in the Nongpoh granitoids, and contains three types of enclaves, viz. xenoliths of gneissic rocks, dark grey porphyry and biotite-rich microgranular enclaves. The mafic magmatic enclaves (MMEs) of various dimensions and shapes, including rounded, ellipsoidal, rectangular, angular to subangular, and stretched bodies, were produced by evolving nature and contrasting kinematics of interacting felsic and mafic magmas. The biotite-rich enclaves are due to the injection of syn-magmatic mafic dykes in felsic magma. The various textural assemblages and sub-linear variations between silica and major oxides, chemical mixing and element diffusion suggest that multistage magma hybridization was the key process during the evolution of the Nongpoh granitoids. The 501 Ma age obtained by chemical (U–Th–Pb) dating of monazite in MME ascertained the age of the magma hybridization event in the Nongpoh granitoids, which is equivalent to the igneous activity at 500 Ma during the amalgamation of Eastern Gondwana.