Vestiges of the Kerguelen Mantle Plume in Southern Tibet:Evidence from 123-117 Ma Magmatism in the Dingri Area of the Central Tethys Himalaya

The widely distributed Early Cretaceous magmatism in the Tethys Himalaya(TH)of southern Tibet is related to the Kerguelen mantle plume.Associated magmatic activity products are distributed in the eastern TH,where the active age is earlier than the peak ages of the Kerguelen mantle plume.This study investigated magmatic activity of the Dingri area in the central TH which was coeval with the Kerguelen mantle plume.The intrusion in the Dingri area contains diabases and monzonites.The zircon age of diabase is 123±1 Ma,and that of monzonite is 117±1 Ma.Geochemistry and Sr-Nd isotopic analyses show that the mafic-intermediate dikes were formed in an intraplate extensional environment.The diabase is derived from the enriched lithospheric mantle and monzonite is derived from partial melting of the lower crust,with both magmatic evolutions being contaminated by crustal materials.These characteristics are similar to those of the Rajmahal-Sylhet basalt,a typical Kerguelen mantle plume product.The discovery of the Dingri mafic-intermediate dikes of the central TH suggests that the TH and Rajmahal-Sylhet Traps formed a continuous mantle plume overflow magmatic belt which was a product of the continuous eruption of the Kerguelen mantle plume.

Characteristics of landslide in Koshi River Basin,Central Himalaya

Koshi River basin, which lies in the Central Himalayas with an area of 71,500 km2, is an important trans-boundary river basin shared by China, Nepal and India. Yet, landslide-prone areas are all located in China and Nepal, imposing alarming risks of widespread damages to property and loss of human life in both countries. Against this backdrop, this research, by utilizing remote sensing images and topographic maps, has identified a total number of 6877 landslides for the past 23 years and further examined their distribution, characteristics and causes. Analysis shows that the two-step topography in the Himalayan region has a considerable effect on the distribution of landslides in this area. Dense distribution of landslides falls into two regions: the Lesser Himalaya(mostly small and medium size landslides in east-west direction) and the TransitionBelt(mostly large and medium size landslides along the river in north-south direction). Landslides decrease against the elevation while the southern slopes of the Himalayas have more landslides than its northern side. Change analysis was carried out by comparing landslide distribution data of 1992, 2010 and 2015 in the Koshi River basin. The rainfallinduced landslides, usually small and shallow and occurring more frequently in regions with an elevation lower than 1000 m, are common in the south and south-east slopes due to heavy precipitation in the region, and are more prone to the slope gradient of 20°~30°. Most of them are distributed in Proterozoic stratum(Pt3ε, Pt3 and Pt2-3) and Quaternary stratum. While for earthquake-induced landslides, they are more prone to higher elevations(2000~3000 m) and steeper slopes(40°~50°).

Correlates of avifaunal diversity along the elevational gradient of Mardi Himal in Annapurna Conservation Area,Central Nepal

Background:Patterns of biological diversity and richness can vary along the elevational gradients among mountain systems making it difficult to conclude the general pattern.The drivers of such pattern are also poorly known in the southern flank of the Himalaya due to limited studies.Therefore,we assessed the species richness,seasonal patterns and drivers of avian diversity along an elevational gradient on Mardi Himal trekking trail,a newly open tourist route in Annapurna Conservation Area of the central Himalaya.Methods:Two surveys(winter and summer seasons of 2019)were conducted from the bank of Seti-Gandaki River confluence(1030 m above sea level,asl)up to the Low Camp(3050 m asl)of the Mardi Himal.The point count method was employed in every 100 m rise in the elevation.Diversity indices were calculated and bird abundance data on species,sites,seasons and environmental variables were analyzed.Generalized linear model,polynomial regression and ordinary least square regression were performed to examine the importance of environmental factors in shaping the avian richness pattern.Results:A total of 673 individuals of birds belonging to 112 species,of which 72 in winter and 80 in summer,were recorded.We observed a hump-shaped pattern of the overall species richness along the elevational gradient.The richness pattern remained consistent even when explored by season,for winter and summer separately.Diversity indices were found higher during the summer.Elevation and mean monthly temperature in both seasons showed non-linear relation with avian species richness.Precipitation exhibited positive association in summer whereas the same in winter was negatively correlated with avian species richness.Distance to the nearest water source and the nearest human settlement were negatively correlated with the richness of birds.Small-ranged and insectivorous birds were under the strong influence of gradients on climatic variables like temperature and precipitation.Conclusions:We conclude that the combined effects of multiple factors such as area,gradients of climate(i.e.temperature and precipitation),resource availability and disturbance play an important role in bird diversity and richness pattern along an elevational gradient of a montane environment in Mardi Himal.

Integrated approach for understanding spatio-temporal changes in forest resource distribution in the central Himalaya

Intense anthropogenic exploitation has altered distribution of forest resources. This change was analyzed using visual interpretation of satellite data of 1979, 1999 and 2009. Field and interactive social surveys were conducted to identify spatial trends in forest degradation and data were mapped on forest cover and land use maps. Perceptions of villagers were compiled in a pictorial representation to understand changes in forest resource distribution in central Himalaya from 1970 to 2010. For- ested areas were subject to degradation and isolation due to loss of con- necting forest stands. Species like Lantana camara and Eupatorium adenophorum invaded forest landscapes. Intensity of human pressure differed by forest type and elevation. An integrated approach is needed to monitor forest resource distribution and disturbance.

Assessing resource vulnerability quadrants under changing precipitation trends in Uttarakhand,Central Himalayan region

The Central Himalayan region is vulnerable to the adverse effects of climate change and characterized by regional climatic conditions.The livelihood of the mountain communities across the Himalaya is at risk owing to the consequences of variable precipitation patterns.There exists limited empirical research on precipitation variability due to inadequate hydro-meteorological stations at highaltitude regions.The study uses a novel methodology which integrates precipitation variability with resource sensitivity over the three verticals of Central Himalaya:Himadri,Himachal and Shivaliks and across four major river basins:Yamuna,Upper Ganga,Ghaghar and Ramganga.The magnitude of the significant precipitation trends was estimated through time series analysis at a 95%confidence interval.To assess the sensitivity of natural resources(forest,water and land)and human resources,fourteen mountain-specific indicators were identified which captured resource index using data standardization and principal component analysis.Sen’s slope and Resource index were plotted in a 2D Cartesian coordinate to draw precipitation-resource quadrants with their effective coverage area:High Precipitation and Scarce Resources(35.92%);Low Precipitation and Abundant Resources(30.10%);Low Precipitation and Scarce Resources(22.33%)and High Precipitation and Abundant Resources(11.65%).This helped in developing quadrant-specific adaptation strategies under regional variability of precipitation.The methodology and the research findings will certainly assist water experts,resource managers and policy makers to strengthen adaptive capacity and improve the resilience of vulnerable communities across Himalaya.

Mass balance and morphological evolution of the Dokriani Glacier,central Himalaya,India during 1999–2014

Glaciological mass balance(MB)is considered the most direct,undelayed and unfiltered response of the glaciers to climatic perturbations.However,it may inherit errors associated with stake underrepresentation,averaging over the entire glacier and human bias.Therefore,proper validation of glaciological MB with geodetic MB is highly recommended by the World Glacier Monitoring Service(WGMS).The present study focuses on the Dokriani Glacier,central Himalaya which is one of the bench-mark glaciers in the region and has glaciological MB records from 1993 to 2013 with intermittent gaps.In the present study,firstly the glaciological MB series is extended to 2014 i.e.,field-based MB for one more year is computed and,to compare with it,the geodetic MB is computed for the 1999–2014 period using high resolution Cartosat-1 digital elevation model(DEM)and SRTM DEM.Finally,the study assesses the regional representation of the Dokriani Glacier in terms of MB and evaluates the influence of the MB regime on its morphological evolution.Results show that the average glaciological MB(-0.34±0.2 m water equivalent(w.e.)y-1)is more negative than the geodetic MB(-0.23±0.1 m w.e.y-1)for the 1999–2014 period.This is likely because of the partial representation of glacier margins in the glaciological MB,where melting is strikingly low owing to thick debris cover(>30 cm).In contrast,geodetic MB considers all marginal pixels leading to a comparatively low MB.A comparative assessment shows that the MB of Dokriani Glacier is less negative(possibly due to its huge accumulation area)than most other glacier-specific and regional MBs,restricting it to be a representative glacier in the region.Moreover,continuous negative MB has brought a peculiar change in the epiglacial morphology in the lower tongue of the glacier as differential debris thickness-induced differential melting has turned the glacier surface into a concave one.This concavity has led to development of a large(10–20 m deep)supraglacial channel which is expanding incessantly.The supraglacial channel is also connected with the snout wall and accelerates terminus disintegration.Given the total thickness of about 30–50 m in the lower glacier tongue,downwasting at its current pace,deepening/widening of supraglacial channel coupled with rapid terminus retreat may lead to the complete vanishing of the lower one km glacier tongue.

Frequency and size change of ice–snow avalanches in the central Himalaya:A case from the Annapurna II glacier

Glaciers have retreated and shrunk in High Mountain Asia since the mid-20th century because of global warming,leading to glacier instability and hazardous iceesnow avalanches.However,the complex relationship between iceesnow avalanches and factors such as climate and potential triggers are difficult to understand because of the lack of observational data.Here,we addressed iceesnow avalanches on the Annapurna II glacier in Nepal,Central Himalaya.We constructed an iceesnow avalanche history using long-term multi-source remote sensing images(1988-2021)and mapped the velocity fields of glaciers using cross-correlation analysis on SAR and optical images.Then,we investigated the impact of climate change and earthquakes on the frequency and size of iceesnow avalanches.The results demonstrate that the frequency of iceesnow avalanches has increased from 10 in 1988 to 27 in 2020,but the average area of iceesnow avalanche deposits has decreased by approximately 70%,from 3.4×10^(5) m^(2) in 1988 to 1.2×10^(5) m^(2) in 2020.The evolutionary characteristic of ice avalanches is linked to the impact of glacier retreat(reduction in ice material supply)and increased activity under climate change.The glacier movement velocity controls the size of iceesnow avalanches and can be set as an indicator for iceesnow avalanche warnings.On the Annapurna Ⅱ glacier,an iceesnow avalanche occurred when the glacier velocities were greater than 1.5 m d^(-1).These results offer insights into iceesnow avalanche risk assessment and prediction in high-mountain areas,particularly in regions characterised by dense glacier distribution.

On the spatio-temporal variation in b-value after 25 April 2015 Gorkha,Nepal earthquake

In the present study,the spatial-temporal distribution of b-value along the five faults area(the Judi fault,Thaple fault,Kathmandu fault,Motihari-Gauri Shanker fault,and Motihari-Everest fault)was investigated after the Gorkha earthquake(M7.8).The earthquake catalog of 10,500 events was prepared by compiling the published catalogs.The study area is bounded in the central Himalaya from 26.5°to 29°in latitude direction and 84°to 87°in longitude direction.The frequency magnitude distribution shows the variation of the b-value along with fault areas from 0.45 to 0.69,indicating a common characteristic of aftershock sequences.In particular,the Judi fault area,Thaple fault area,and Motihari-Everest fault area are characterized by the low b-values of 0.45±0.02,0.48±0.02,and 0.55±0.04,respectively.These regions could be the source region for future earthquakes.The low b-value observed for fault areas are also consistent with the thrust faulting pattern in the region as indicated by the focal mechanism of mainshock and major aftershocks.The temporal variation of b-value shows inevitable fluctuations during25 April to 12 May 2015.Among the area selected,the Motihari-Everest fault area is in critical strain(mechanically locked)conditions,as indicated by the stepwise energy release pattern.

Gorkha earthquake (MW7.8) and aftershock sequence: A fractal approach

On April 25, 2015, Nepal was struck by the MW7.8 Gorkha earthquake followed by an intense aftershock sequence. It was one of the most destructive earthquakes in the Himalayan arc, causing more than 8900 fatalities. In this study, we analyzed the dataset (429 events, magnitude of completeness (Mc) ≥ 4.2 local magnitude) of the first 45 days after the Gorkha earthquake to estimate the seismicity parameters b-value, D-value, and p-value. We used the maximum likelihood method to estimate the b-value and Omori-Utsu parameters, whereas the correlation integral method was applied to estimate the fractal dimension (D-value). The analysis was carried out using running and sliding window techniques. The lowest b-value (0.57 ± 0.04) and the highest D-value (1.65 ± 0.02) were computed at the time of the Gorkha earthquake, after which the b-value significantly increased to a maximum of 1.57. It again dropped to 0.93 at the time of the major aftershock on May 12, 2015. The D-value showed an initial quick drop and then decreased in a wavy pattern until the end of the study period, indicating the clustering and scattering of earthquakes in a fault region. The b-value contour map identified the eastern part of the study area as a high stress region (b = ~0.8), implying that the stress shifted to that region. The D-value contour map reveals that the seismogenic structure shifted from linear to planar in the region. The rate of aftershock decay (p = 0.86 ± 0.04) for a short period reflects that the level of stress decreased rapidly. This study helps to understand the level of stress and seismicity pattern of a region, which could be useful for aftershock studies.

Glacier-Glacial Lake Interactions and Glacial Lake Development in the Central Himalaya,India(1994–2017)

Despite several regional glacier and glacier lake inventories, the relationship between receding glacier, glacial lake evolution(glacial-lake interactions) and their sensitivity to different forcing factors have not been properly understood yet. To better understand these processes, we used satellite images collected in 1994, 2015 and 2017 to monitor the spatially-explicit evolution of glacial lakes and glacier changes. The results show a total of 1 353 glacial lakes covering an area of 7.96 km;in the year 2015. Out of these, a total of 137 glacial lakes having an area of >0.01 km;and located within 2 km periphery of mother glacier have been selected for the monitoring of spatial development between 1994 and 2017. We found an increase in the total lake area from ~4.9 to ~7.73 km;between 1994 and 2017,corresponding to an overall expansion of ~57%. The total area covered by the glaciers associated with these lakes reduced from ~365 km;in 1994 to ~358 km^(2) in 2017, accounting for a glacier loss of ~7 km^(2) and corresponding to ~1.92% reduction. Our study results are in agreement with global glacier behavior, revealing a rapid glacier recession and accelerated glacial lake expansion under an unprecedented climate change scenario. In addition, the results suggest a significant reduction in the glacier area and a close relationship between the glacier melting and lake changes.

喜马拉雅山脉中段土地覆被的垂直分异特征

Characterized by obvious altitudinal variation,habitat complexity,and diversity in land cover,the Mt.Qomolangma region within the central Himalayas is one of the most sensitive areas to climate change in the world.At the same time,because the Mt.Qomolangma region possesses the most complete natural vertical spectrum in the world,it is also an ideal place to study the vertical structure of alpine land cover.In this study,land cover data for 2010 along with digital elevation model data were used to define three methods for dividing the northern and southern slopes in the Mt.Qomolangma region,i.e.,the ridgeline method,the sample transect method,and the sector method.The altitudinal distributions of different land cover types were then investigated for both the northern and southern slopes of the Mt.Qomolangma region by using the above three division methods along with ArcGIS and MATLAB tools.The results indicate that the land cover in the study region was characterized by obviously vertical zonation with the south-six and north-four pattern of vertical spectrum that reflected both the natural vertical structure of vegetation and the effects of human activities.From low to high elevation,the main land cover types were forests,grasslands,sparse vegetation,bare land,and glacler/snow cover.The compositions and distributions of land cover types differed significantly between the northern and southern slopes;the southern slope exhibited more complex land cover distributions with wider elevation ranges than the northern slope.The area proportion of each land cover type also varied with elevation.Accordingly,the vertical distribution patterns of different land cover types on the southern and northern slopes could be divided into four categories,with glaciers/snow cover,sparse vegetation,and grasslands conforming to unimodal distributions.The distribution of bare land followed a unimodal pattern on the southern slope but a bimodal pattern on the northern slope.Finally,the use of different slope division methods produced similar vertical belt structures on the southern slope but different ones on the northern slope.Among the three division methods,the sector method was better to reflect the natural distribution pattern of land cover.

1990-2015年喜马拉雅山脉中段柯西河流域土地覆被垂直带变化

The study of mountain vertical natural belts is an important component in the study of regional differentiation.These areas are especially sensitive to climate change and have indicative function,which is the core of three-dimensional zonality research.Thus,based on high precision land cover and digital elevation model(DEM)data,and supported by MATLAB and ArcGIS analyses,this paper aimed to study the present situation and changes of the land cover vertical belts between 1990 and 2015 on the northern and southern slopes of the Koshi River Basin(KRB).Results showed that the vertical belts on both slopes were markedly different from one another.The vertical belts on the southern slope were mainly dominated by cropland,forest,bare land,and glacier and snow cover.In contrast,grassland,bare land,sparse vegetation,glacier and snow cover dominated the northern slope.Study found that the main vertical belts across the KRB within this region have not changed substantially over the past 25 years.In contrast,on the southern slope,the upper limits of cropland and bare land have moved to higher elevation,while the lower limits of forest and glacier and snow cover have moved to higher elevation.The upper limit of alpine grassland on the northern slope retreated and moved to higher elevation,while the lower limits of glacier and snow cover and vegetation moved northward to higher elevations.Changes in the vertical belt were influenced by climate change and human activities over time.Cropland was mainly controlled by human activities and climate warming,and the reduced precipitation also led to the abandonment of cropland,at least to a certain extent.Changes in grassland and forest ecosystems were predominantly influenced by both human activities and climate change.At the same time,glacier and snow cover far away from human activities was also mainly influenced by climate warming.