Umesh K. Haritashya

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.

Modelling and Estimation of Different Components of Streamflow for Gangotri Glacier Basin, Himalayas

Abstract The understanding of the runoff generation processes is reviewed and simulation of daily streamflow is reported for the Gangotri Glacier basin (Central Himalayas) with area of ∼556 km2, of which ∼286 km2 is occupied by the glaciers, and altitude of 4000 to 7000 m.a.s.l. A hydro-meteorological database was established by collecting meteorological and hydrological data near the snout of the glacier for four melt seasons (2000–2003) covering the period from May to October every year. Flow was simulated using a snowmelt model (SNOWMOD) based on the temperature index approach. Two years (2000 and 2001) of the four-year data set were used to calibrate the model, and the remaining two years (2002 and 2003) were used for verification. The study was carried out during the ablation period, as the availability of data was restricted to that period, responsible for a major part of the runoff. The model performed well for both calibration and verification periods. The overall efficiency of the model, R 2, was 0.96 and the difference in volume of computed and observed streamflow was −2.5%, indicating a good model performance. Simulation of different components of streamflow clearly indicates that almost all the high peaks are attributed to melt. The model was also used to estimate the respective contributions by melt and rainfall to the total seasonal flow: for summer runoff, these were estimated to be about 97% and 3%. Such studies are very useful for the planning and management of water resources in high-altitude areas and for designing hydropower projects.

Himalayan glaciers: The big picture is a montage

Unusual miscarriages of science (1, 2) recently rocked climate change science and glaciology. An infamous paragraph, uncharacteristic of the rest of the contribution of Working Group II to the Intergovernmental Panel on Climate Change Fourth Assessment, claimed that Himalayan glaciers would disappear by 2035 (1). In such a monumental report, errors can be expected. However, this error, explicated in ref. 3, shredded the reputation of a large and usually rigorous international virtual institution. The gaffe by the Intergovernmental Panel on Climate Change helped to trigger a global political retreat from climate change negotiations, and it may prove to have been one of the more consequential scientific missteps in human history. An equally incorrect claim, on a different timescale, was that large Himalayan glaciers may be responding today to climate shifts 6,000–15,000 y ago (2). However, both mistakes (1, 2) and some solid scientific reporting on Himalayan glacier dynamics (4–10) highlight large gaps in the observational record. In PNAS, Fujita and Nuimura (11) competently reduced the knowledge gap.

ASSESSMENT OF THE EVOLUTION IN VELOCITY OF TWO DEBRIS-COVERED VALLEY GLACIERS IN NEPAL AND NEW ZEALAND

Abstract Feature tracking of orthorectified pairs of Advanced Spaceborne Thermal Emission and Reflection Radiometer satellite images is used to calculate velocities for the Tasman Glacier, New Zealand (2002–2014) and the Khumbu Glacier, Nepal (2001–2008). Velocities in the middle and upper ablation zones of both glaciers show a long‐term decrease of ∼10–20%, while the terminus of Khumbu Glacier has remained near stagnation throughout the study period. In contrast, there has been a recent acceleration of the lower terminus of Tasman Glacier, from ∼5 m a–1 in 2002 to 40 m a–1 in 2014. Both of these glaciers have an extensive supraglacial debris cover across their lower ablation regions, with the Khumbu Glacier terminating on land and the Tasman Glacier terminating in a proglacial lake. The rapid recent increase in velocity of the terminus of Tasman Glacier is closely correlated with the increase in size of its proglacial lake. These results indicate the complex dynamic changes that mountain valley glaciers may undergo in response to long‐term negative mass balance.

Remote Sensing of Glaciers in Afghanistan and Pakistan

Glaciers in Afghanistan and Pakistan are parts of an Asian “critical region” having significant roles in rising sea level, local and regional water resources, natural hazards, and geopolitical stability. The two countries lack fundamental and reliable quantitative information regarding glacier fluctuations. As part of the Global Land Ice Measurements from Space (GLIMS) project, we used satellite imagery and field observations to assess a relatively large number of glaciers in both countries. In Afghanistan, many glaciers have systematically been observed to be retreating and downwasting. Many glaciers have lost significant ice mass and have evolved into numerous smaller individual ice masses. Furthermore, the glaciers around the Kohi Bandakha massif in southern Badakshan Province are significantly more debris covered than other regions in Afghanistan. In Pakistan, the situation is more complex, as many glacier termini are variably stationary, advancing, or retreating. There appears to be a spatial trend with more retreating glaciers in the western Hindu Kush. To the east we observe more advancing glaciers and surging glaciers associated with an increase in precipitation. These observations suggest that glacier response to climate forcing is very different in Pakistan compared with conditions in the central and eastern Himalaya.

25 Remote sensing and GIS for alpine glacier change detection in the Himalaya

Abstract Concerns over greenhouse-gas forcing and warmer temperatures have initiated research into understanding climate forcing and associated Earth-system responses. Alpine glacier fluctuations are directly and indirectly related to climate change. Consequently, it is essential to be able to assess glacier fluctuations from space and determine the causal mechanisms responsible for change. Although satellite imagery and topographic information can be used for alpine glacier mapping, interpreting causal mechanisms for changing glacial boundary conditions and climate is difficult, as there is a significant disconnect between information on boundary conditions and process mechanics. Therefore, information integration and computer-assisted approaches to glacier mapping, parameter estimation, and numerical modeling are required to produce reliable results that go beyond traditional image interpretation and mapping. Only in this way can a multitude of forcing factors and interrelated processes be evaluated in an objective way to quantitatively ascertain the role of climate on glacier fluctuations in the Himalaya.

New Zealand’s Glaciers

New Zealand’s mountains support 3,153 inventoried glaciers, 99.4 % of this number (_99.9 % by volume) on South Island, and the remaining few on Mt. Ruapehu, a North Island volcano. Here we (1) provide a historical, geological, and climatic context for New Zealand’s glaciers; (2) review published knowledge of their current state and recent dynamics; (3) present a synoptic overview from ASTER imaging of the glaciers of Mt. Ruapehu (North Island), including relations to volcanic activity; use ASTER to examine changes affecting glaciers of Mt. Aoraki (Mt. Cook, South Island) and selected areas southward to Milford Sound; and (4) review limnological, climatic, and debris load controls on New Zealand’s glacier fluctuations. Half or more of New Zealand’s ice mass has disappeared since the Little Ice Age (LIA). New Zealand has some of the world’s highest ice mass accumulation rates, shortest glacier response times, and greatest concentrations of glacier debris discharge. For the smaller glaciers on steep slopes, especially those in high-precipitation zones and descending into warm climatic zones where ablation is rapid and response times are short, these small glaciers are not responding to the end of the LIA, but rather their observed fluctuations are a response to decadal climate oscillations and centennial-scale trends (including atmospheric warming). Decadalscale climate changes driving short-term glacier fluctuations of fast-response glaciers in New Zealand correlate, foremost, to the Antarctic Oscillation (AAO) and the Southern Oscillation Index (SOI), and, second, to the El Nino Southern Oscillation (ENSO). In contrast, the largest low-sloping valley glaciers have long response times due to their great thicknesses and insulating debris loads, and their lengths exhibit no discernible influence from decadal climate oscillations; consequently they are far out of equilibrium with the long-term warming and short-term fluctuating climate. Many glacier attributes are interrelated in a web of positive and negative dynamical feedbacks. For example, high ice discharge (which by itself is associated with short glacier response times) can remove surficial debris and allow rapid ablation, thereby further shortening response times. Large glacial lakes are characterized by a separate range of dynamic behavior. Lake formation and growth are promoted on slowresponse low-gradient glaciers with thick debris cover, and overdeepened valleys, as well as by climatic warming. Once the lakes enlarge, coalesce, and expand past a critical point, rapid calving and a host of other ablation processes accelerate, commonly beyond control by further climate change. New Zealand’s Southern Alps climate has a strong east–west gradient affecting all its climate parameters. However, thus far the dynamical responses of glaciers of comparable geomorphic types are very similar on the east and west sides of the Main Divide of the Southern Alps. Although we observe substantial climatic and climate change differences across the Alps, thus far glacier responses appear to be uniform across the entire mountain range.

Digital Terrain Modeling and Glacier Topographic Characterization

The Earth’s topography results from dynamic interactions involving climate, tectonics, and surface processes. In this chapter our main interest is in describing and illustrating how satellite-derived DEMs (and other DEMs) can be used to derive information about glacier dynamical changes. Along with other data that document changes in glacier area, these approaches can provide useful measurements of, or constraints on glacier volume balance and—with a little more uncertainty related to the density of lost or gained volume—mass balance. Topics covered include: basics on DEM generation using stereo image data (whether airborne or spaceborne), the use of ground control points and available software packages, postprocessing, and DEM dataset fusion; DEM uncertainties and errors, including random errors and biases; various glacier applications including derivation of relevant geomorphometric parameters and modeling of topographic controls on radiation fields; and the important matters of glacier mapping, elevation change, and mass balance assessment. Altimetric data are increasingly important in glacier studies, yet challenges remain with availability of high-quality data, the current lack of standardization for methods for requiring, processing, and representing digital elevation data, and the identification and quantification of DEM error and uncertainty.

Theoretical Foundations of Remote Sensing for Glacier Assessment and Mapping

The international scientific community is actively engaged in assessing ice sheet and alpine glacier fluctuations at a variety of scales. The availability of stereoscopic, multitemporal, and multispectral satellite imagery from the optical wavelength regions of the electromagnetic spectrum has greatly increased our ability to assess glaciological conditions and map the cryosphere. There are, however, important issues and limitations associated with accurate satellite information extraction and mapping, as well as new opportunities for assessment and mapping that are all rooted in understanding the fundamentals of the radiation transfer cascade. We address the primary radiation transfer components, relate them to glacier dynamics and mapping, and summarize the analytical approaches that permit transformation of spectral variation into thematic and quantitative parameters. We also discuss the integration of satellite-derived information into numerical modeling approaches to facilitate understandings of glacier dynamics and causal mechanisms.

Integration of classification tree analyses and spatial metrics to assess changes in supraglacial lakes in the Karakoram Himalaya

Alpine glacier responses to climate change reveal increases in significant retreat with corresponding increases in the production of glacier meltwater and development of supraglacial lakes. The rate of occurrence and spatial extent of lakes in the Himalaya are difficult to determine because current spectral-based image analyses of glacier surfaces are limited through anisotropic reflectance and lack of high-quality digital elevation models (DEMs). Additionally, the limitations of multivariate classification algorithms to classify glacier features in satellite imagery have led to an increased interest in non-parametric methods, such as classification and regression trees. This article demonstrates the utility of a semi-automated approach that integrates classification tree-based image segmentation and spatial metrics in an object-oriented analysis to differentiate supraglacial lakes from glacier debris, ice, ice-cliffs, and lateral and medial moraines. We used 2000 and 2004 Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) visible and near-infrared (VNIR) and shortwave infrared (SWIR) imagery to characterize and assess supraglacial conditions on the Baltoro Glacier in the Karakoram Himalaya. Input variables for the image segmentation include ASTER VNIR and SWIR spectral bands, indices (e.g. normalized difference water index (NDWI), normalized difference vegetation index (NDVI), and normalized difference snow index (NDSI)), image band ratios (e.g. NIR/red, middle infrared (MIR)/green, and MIR/red), and DEM derivatives. Classification tree analysis was used to generate initial image segments and it was particularly effective in differentiating water from ice and other glacier surface features. The object-oriented analysis included the use of Boolean logic and squared pixel (SqP) spatial metric to refine the classification tree output. The results of classification tree-based image segmentation show that NDWI is the most important single variable for characterizing glacier surface features followed by NDVI, NIR/red ratio, and green and red spectral bands. Lake features extracted from both images show that there were 131 lakes in 2000 as compared to 157 lakes in 2004. In general, there was a significant increase in the planimetric area of these lakes from 2000 to 2004, and we documented the formation of 26 new lakes. It appears that lake-size increments occur mostly in the lower part of the ablation zone, whereas most of the new lakes are formed in the upper part of the ablation zone. The classification tree outputs are intuitive and the data-derived thresholds eliminate commonly subjective visual determination of such threshold values used in image segmentation. The results of this study show that glacier lakes in high-mountain environments can be characterized without topographic information, which is difficult to obtain from a DEM. Also, the semi-automated method described in this article can potentially eliminate the often laborious visual multitemporal analysis of glacier lake surface change, thereby producing consistent and replicable results needed to assess the trends of alpine glacier response to climate change in the Himalaya.