Samjwal Ratna Bajracharya

The State and Fate of Himalayan Glaciers

Going More Slowly Himalayan glaciers sometimes are called the “Third Pole” because of the amount of snow and ice they contain. Despite their importance as a global water reservoir and their essential role in Asian hydrology, how their mass is changing in response to global warming is not well known. Bolch et al. (p. 310) review the contemporary evolution of glaciers in the Himalayan region, including those of the less well sampled region of the Karakoram to the Northwest, in order to provide a current, comprehensive picture of how they are changing. Most Himalayan glaciers are retreating at rates comparable to glaciers elsewhere in the world. In the Karakorum, on the other hand, advancing glaciers are more common. Himalayan glaciers are a focus of public and scientific debate. Prevailing uncertainties are of major concern because some projections of their future have serious implications for water resources. Most Himalayan glaciers are losing mass at rates similar to glaciers elsewhere, except for emerging indications of stability or mass gain in the Karakoram. A poor understanding of the processes affecting them, combined with the diversity of climatic conditions and the extremes of topographical relief within the region, makes projections speculative. Nevertheless, it is unlikely that dramatic changes in total runoff will occur soon, although continuing shrinkage outside the Karakoram will increase the seasonality of runoff, affect irrigation and hydropower, and alter hazards.

Glaciers, glacial lakes and glacial lake outburst floods in the Mount Everest region, Nepal.

Abstract Recent climate changes have had a significant impact on the high-mountain glacial environment. Rapid melting of glaciers has resulted in the formation and expansion of moraine-dammed lakes, creating a potential danger from glacial lake outburst floods (GLOFs). Most lakes have formed during the second half of the 20th century. Glaciers in the Mount Everest (Sagamartha) region, Nepal, are retreating at an average rate of 10–59 ma–1. From 1976 to 2000, Lumding and Imja Glaciers retreated 42 and 34 ma–1, respectively, a rate that increased to 74 ma–1 for both glaciers from 2000 to 2007. During the past decade, Himalayan glaciers have generally been shrinking and retreating faster while moraine-dammed lakes have been proliferating. Although the number of lakes above 3500 m a.s.l. has decreased, the overall area of moraine-dammed lakes is increasing. Understanding the behaviour of glaciers and glacial lakes is a vital aspect of GLOF disaster management.

Geomorphic and geologic controls of geohazards induced by Nepal’s 2015 Gorkha earthquake

Nepals quake-driven landslide hazards Large earthquakes can trigger dangerous landslides across a wide geographic region. The 2015 Mw 7.8 Gorhka earthquake near Kathmandu, Nepal, was no exception. Kargal et al. used remote observations to compile a massive catalog of triggered debris flows. The satellite-based observations came from a rapid response team assisting the disaster relief effort. Schwanghart et al. show that Kathmandu escaped the historically catastrophic landslides associated with earthquakes in 1100, 1255, and 1344 C.E. near Nepals second largest city, Pokhara. These two studies underscore the importance of determining slope stability in mountainous, earthquake-prone regions. Science, this issue p. 10.1126/science.aac8353; see also p. 147 Satellite imaging isolated hazard potential for earthquake-triggered landslides after the 2015 Gorkha earthquake in Nepal. INTRODUCTION On 25 April 2015, the Gorkha earthquake [magnitude (M) 7.8] struck Nepal, followed by five aftershocks of ≥M 6.0 until 10 June 2015. The earthquakes killed ~9000 people and severely damaged a 550 by 200 km region in Nepal and neighboring countries. Some mountain villages were completely destroyed, and the remote locations, blocked roads, and landslide-dammed rivers prevented ground access to many areas. RATIONALE Our “Volunteer Group” of scientists from nine nations, motivated by humanitarian needs, focused on satellite-based systematic mapping and analysis of earthquake-induced geohazards. We provided information to relief and recovery officials as emergency operations were occurring, while supported by one of the largest-ever NASA-led campaigns of responsive satellite data acquisitions over a vast disaster zone. Our analysis of geohazards distribution allowed evaluation of geomorphic, tectonic, and lithologic controls on earthquake-induced landsliding, process mechanisms, and hazard process chains, particularly where they affected local populations. RESULTS We mapped 4312 coseismic and postseismic landslides. Their distribution shows positive associations with slope and shaking intensity. The highest areal densities of landslides are developed on the downdropped northern tectonic block, which is likely explained by momentary reduction of the normal stress along planes of weakness during downward acceleration. The two largest shocks bracket the high-density landslide distribution, the largest magnitudes of the surface displacement field, and highest peak ground accelerations (PGAs). Landslides are heavily concentrated where PGA was >0.6g and slope is >30°. Additional controls on landslide occurrence are indicated by their clustering near earthquake epicenters and within specific lithologic units. The product of PGA and the sine of surface slope (defined as the landslide susceptibility index) is a good indicator of where most landslides occurred. A tail of the statistical distributions of landslides extends to low values of the landslide susceptibility index. Slight earthquake shaking affected vulnerable materials hanging on steep slopes—such as ice, snow, and glacial debris—and moderate to strong shaking affected poorly consolidated sediments deposited in low-sloping river valleys, which were already poised near a failure threshold. In the remote Langtang Valley, some of the most concentrated destruction and losses of life outside the Kathmandu Valley were directly due to earthquake-induced landslides and air blasts. Complex seismic wave interactions and wave focusing may have caused ridgetop shattering and landslides near Langtang but reduced direct shaking damage on valley floors and at glacial lakes. CONCLUSION The Gorkha earthquake took a tremendous, tragic toll on human lives and culture. However, fortunately no damaging earthquake-caused glacier lake outburst floods were observed by our satellite analysis. The total number of landslides was far fewer than those generated by comparable earthquakes elsewhere, probably because of a lack of surface ruptures, the concentration of deformation along the subsurface thrust fault at 10 to 15 km depth, and the regional dominance of competent high-grade metamorphic and intrusive igneous rock types. Landslide distribution and effects of a huge landslide. (A) Landslides (purple dots) are concentrated mostly north of the tectonic hinge-line. Also shown are the epicenters of the main shock and largest aftershock. Displacements are from the JAXA ALOS-2 ScanSAR interferogram (21 Feb and 2 May 2015 acquisitions). (B and C) Before-and-after photographs obtained by D. Breashears in Langtang Valley showing complete destruction of a large part of Langtang village by a huge landslide. The Gorkha earthquake (magnitude 7.8) on 25 April 2015 and later aftershocks struck South Asia, killing ~9000 people and damaging a large region. Supported by a large campaign of responsive satellite data acquisitions over the earthquake disaster zone, our team undertook a satellite image survey of the earthquakes’ induced geohazards in Nepal and China and an assessment of the geomorphic, tectonic, and lithologic controls on quake-induced landslides. Timely analysis and communication aided response and recovery and informed decision-makers. We mapped 4312 coseismic and postseismic landslides. We also surveyed 491 glacier lakes for earthquake damage but found only nine landslide-impacted lakes and no visible satellite evidence of outbursts. Landslide densities correlate with slope, peak ground acceleration, surface downdrop, and specific metamorphic lithologies and large plutonic intrusions.

The status and decadal change of glaciers in Bhutan from the 1980s to 2010 based on satellite data

Abstract In order to monitor changes in the glaciers in the Bhutan Himalaya, a repeat decadal glacier inventory was carried out from Landsat images of 1977/78 (~1980), 1990, 2000 and 2010. The base map of glaciers was obtained by the object-based image classification method using the multispectral Landsat images of 2010. This method is used separately to delineate clean-ice and debris-covered glaciers with some manual editing. Glacier polygons of 2000,1990 and ~1980 were obtained by manual editing on 2010 by separately overlaying respective years. The 2010 inventory shows 885 glaciers with a total area of ~642 ± 16.1 km2. The glacier area is 1.6% of the total land cover in Bhutan. The result of a repeat inventory shows 23.3 ± 0.9% glacial area loss between ~1980 and 2010, with the highest loss (11.6 ±1.2%) between ~1980 and 1990 and the lowest (6.7 ±0.1%) between 2000 and 2010. The trend of glacier area change from the 1980s to 2010 is -6.4 ± 1.6%. Loss of glacier area was mostly observed below 5600 m a.s.l. and was greater for clean-ice glaciers. The equilibrium-line altitude has shifted upward from 5170 ± 110 m a.s.l. to 5350 ± 150 m a.s.l. in the years ~1980-2010.

The glaciers of the Hindu Kush Himalayas: current status and observed changes from the 1980s to 2010

The fate of the Hindu Kush Himalayan glaciers has been a topic of heated debate due to their rapid melting and retreat. The underlying reason for the debate is the lack of systematic large-scale observations of the extent of glaciers in the region owing to the high altitude, remoteness of the terrain, and extreme climatic conditions. Here we present a remote sensing–based comprehensive assessment of the current status and observed changes in the glacier extent of the Hindu Kush Himalayas. It reveals highly heterogeneous, yet undeniable impacts of climate change.

Glaciers Shrinking in Nepal Himalaya

Glaciers are repositories of information for climate change studies, as they are sensitive to global temperature and precipitation changes. Due to global warming the impact was directly influencing in the melting of the glaciers and enhancing in recent decades. The rapid melting of glaciers reduce the glacier area by which the glaciers are fragmented with increase in glacier number (Bajracharya et al., 2006a,b, 2007a,b, 2008, 2009a). The history of glacier study in Nepal is not old, it was just started by Fritz Műller in 1956; who visit Nepal as a participant in the Swiss Everest Expedition. During following years, the number of scientific expeditions has gradually increased. However, Nepal has no glaciers under longterm observation, though a number of fragmented and short studies have been made on the AX010 Glacier, Mera Glacier, Yala Glacier and Rikha Samba Glacier. The AX010 has the densest observations in terms of Glacier extent, mass balance, and ice flow (Fujita et al., 2001). The systematic investigation of glaciers in Nepal was first organized by Nagoya and Kyoto Universities of Japan. The Glaciological Expedition of Nepal (GEN), led by Higuchi (1976, 1977, 1978, 1980), carried out a series of field studies in coordination with Department of Hydrology and Meteorology (DHM) Nepal. The first detailed study of AX010 glacier was conducted in 1978/1979 (Ageta et al., 1980, 1992; Kadota et al., 1997), Yala Glacier was studied since the 1980s, and Rikha Samba Glacier has been surveyed intermittently since 1974 (Nakawo et al., 1976; Fugii et al., 1996; Fugita et al., 1997). The glaciers of Nepal was first mapped by ICIMOD in 2001 from the Indian Survey topographic maps published from 1963 to 1982. The maps were prepared from the aerial photographs of 1957 to 1959 with extensive field work (Mool et al.; 2001, 2005). The study revealed 3,252 glaciers with 5,323km2 glacier area, which is almost 3.6% of the total land cover of Nepal. The second generation of glacier mapping of Nepal (Bajracharya et al., 2011 unpub.) was based on the satellite images of 2008/2009, which shows that the number of glacier has apparently increased but the total area has decreased drastically. The total number of glaciers in this survey shows 3808 glaciers with 4212km2 glacier area and 346km3 estimated ice reserves. The glacier area loss is about 20% in last 40 years. The glacier cover of Nepal reduces to 2.9% of total land cover in Nepal. The subsidence of glacier surface by 0.40m per year in Dudh Koshi basin is also reported since late 1960s due to the melting of the glaciers (Bolch, 2008). Bajracharya et al., 2008 has also reported the glacier retreat rate of 10 to 60m per year in Dudh Koshi basin. GEN, 2006 has studied many glaciers and reported the glacier retreat

Lemthang Tsho glacial Lake outburst flood (GLOF) in Bhutan: cause and impact

BackgroundThe Hindu Kush Himalayan (HKH) region being seismically active and sensitive to climate change is prone to glacial lake outburst flood (GLOF). The Lemthang Tsho GLOF breached in the evening of 28 July 2015 innorth-western Bhutan is reminds of the looming threat, and stresses the need to have good risk management plan. The need to understand the physical processes in generating GLOF to is therefore imperative in order to effectively manage the associated risk. The paper therefore assesses the cause and impact of the Lemthang Tsho GLOF event using field and remote sensing data.ResultsThe collapse of near vertical wall of supraglacial lake triggered by 2 days of incessant rainfall, opened up the englacial conduit resulting in emptying of interconnected supraglacial lakes into Lemthang Tsho. The5.1 magnitude earthquake epicentered 187 km to southeast in the Indian state of Assam in the morning (7:10 am Bhutan Standard Time) of the same day is unlikely to have played any role in triggering the event. The estimated volume of water unleased is 0.37 million m3, with peak discharge estimated to be ranging from 1253 to 1562 m3/s, and velocity of 7.14–7.57 m/s. The impact was minimal and confined up to 30 km downstream from the lake. The flood took lives of 4 horses, washed away 4 timber cantilever bridges, 148 pieces of timber, damaged 1 acre of land, and washed away 1 km of trail. The team also monitored 3 out of 25 identified critical glacial lakes and downgraded the risk of all 3 critical glacial lakes based on the finding. This brings the number of critical glacial lakes in Bhutan to 22.ConclusionThe threat of GLOF still looms large in the Himalaya, particularly in view of impact of climate change and frequent seismic activities. There is a need for good risk management practices which starts fromidentification of critical glacial lakes, to prioritize in-depth investigation. As the present list of critical glacial lakes are largely based on inventory done over a decade based on topographic maps some of which datedback to 1960s, we need to revisit the critical glacial lakes and assess the risk considering recent changes. The new assessment needs to consider supraglacial lakes as one of the criteria in evaluating the GLOF risk, as highlighted by the Lemthang Tsho GLOF.

Himalayan Glaciers (India, Bhutan, Nepal): Satellite Observations of Thinning and Retreat

This chapter summarizes the current state of remote sensing of glaciers in the India, Nepal, and Bhutan regions of the Himalaya, and focuses on new methods for assessing glacier change. Glaciers in these Himalaya regions exhibit complex patterns of changes due to the unique and variable climatic, topographic, and glaciological parameters present in this region. The theoretical understanding of glaciers in the Himalaya is limited by lack of sufficient observations due to terrain breadth and complexity, severe weather conditions, logistic difficulties, and geopolitics. Mapping and assessing these glaciers with satellite imagery is also challenging due to inherent sensor limitations and information extraction issues. Thus, we still lack a complete understanding of the magnitude of feedbacks, and in some places even their sign, between climate changes and glacier response in this region. In this chapter we present the current status of glaciers in various climatic regimes of the Himalaya, ranging from the monsoon-influenced regions of the central-eastern Himalaya (Nepal, Garhwal, Sikkim, and Bhutan) through the monsoon transition zone of Himachal Pradesh (India), to the dry areas of Ladakh (western Himalaya). The case studies presented here illustrate the use of remote sensing and elevation data coupled with glaciermapping techniques for glacier area and elevation change detection and ice flow modeling in the context of the Himalaya.

Remote sensing based glacial lake inventory in the Hindu Kush-Himalaya region

Glacial lake inventory is the main method to investigate the glacial lakes in remote area and provides required information for glacier risk management and climate change research. A glacial lake inventory based on Landsat TM/ETM+ images has been carried in Hindu-Kush Himalaya regions, and 20204 glacial lakes with total area of 1955.75 km2 are documented by this inventory. This paper introduced the method and material and discussed the merits and demerits of the method. Landsat based glacial lake inventory is effective method for large scale area, but more detail inventory with high resolution satellite images is necessary for glacier risk management and glacial lake change detection. The distribution characteristics is also analyzed by this paper, obvious regional difference was found by this inventory, the formation and distribution of glacial lake are controlled by terrain, glaciation and conditions. The selection of assessment method and criteria need to consider the regional feature of glacial lakes and their environment.

Decadal glacial lake changes in the Koshi basin, central Himalaya, from 1977 to 2010, derived from Landsat satellite images

Changes in glacial lakes and the consequences of these changes, particularly on the development of water resources and management of glacial lake outburst flood (GLOF) risk, has become one of the challenges in the sustainable development of high mountain areas in the context of global warming. This paper presents the findings of a study on the distribution of, and area changes in, glacial lakes in the Koshi basin in the central Himalayas. Data on the number of glacial lakes and their area was generated for the years 1977, 1990, 2000, and 2010 using Landsat satellite images. According to the glacial lake inventory in 2010, there were a total of 2168 glacial lakes with a total area of 127.61 km2 and average size of 0.06 km2 in the Koshi basin. Of these, 47% were moraine dammed lakes, 34.8% bedrock dammed lakes and 17.7% ice dammed lakes. The number of glacial lakes increased consistently over the study period from 1160 in 1977 to 2168 in 2010, an overall growth rate of 86.9%. The area of glacial lakes also increased from 94.44 km2 in 1977 to 127.61 km2 in 2010, a growth rate of 35.1%. A large number of glacial lakes in the inventory are small in size (≤ 0.1 km2). End moraine dammed lakes with area greater than 0.1 km2 were selected to analyze the change characteristics of glacial lakes in the basin. The results show that, in 2010, there were 129 lakes greater than 0.1 km2 in area; these lakes had a total area of 42.92 km2 in 1997, increasing to 63.28 km2 in 2010. The distribution of lakes on the north side of the Himalayas (in China) was three times higher than on the south side of the Himalayas (in Nepal). Comparing the mean growth rate in area for the 33 year study period (1977-2010), the growth rate on the north side was found to be a little slower than that on the south side. A total of 42 glacial lakes with an area greater than 0.2 km2 are rapidly growing between 1977 and 2010 in the Koshi basin, which need to be paid more attention to monitoring in the future and to identify how critical they are in terms of GLOF.