Shangguan Donghui

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.

Monitoring the glacier changes in the Muztag Ata and Konggur mountains, east Pamirs, based on Chinese Glacier Inventory and recent satellite imagery

Abstract Glaciers in the Muztag Ata and Konggur mountains of the eastern Pamir plateau, northwestern China, have been monitored by applying aerial photo stereo models (1962/66) and Landsat TM (1990) and ETM+ (1999) images, all of which have been compared in order to detect areal and frontal changes through the past four decades. The mean frontal retreat of glaciers in the Muztag Ata and Konggur mountains increased from 6.0 ma−1 between 1962/66 and 1990 to 11.2ma−1 between 1990 and 1999, with an overall glacier length reduction of 9.9% for the whole study period. The glacier area has decreased by 7.9%, mainly due to changes observed in the most recent period (1990–99), when the annual area loss almost tripled to 1.01 km2 a−1. Based on meteorological data from Taxkogan station since 1957, we conclude that climate change, particularly the rise in summer temperature after 1994, is the main forcing factor in glacier shrinkage.Glaciers in the Muztag Ata and Konggur mountains of the eastern Pamir plateau, northwestern China, have been monitored by applying aerial photo stereo models (1962/66) and Landsat TM (1990) and ETM+ (1999) images, all of which have been compared in order to detect areal and frontal changes through the past four decades. The mean frontal retreat of glaciers in the Muztag Ata and Konggur mountains increased from 6.0 m a -1 between 1962/66 and 1990 to 11.2 m a -1 between 1990 and 1999, with an overall glacier length reduction of 9.9% for the whole study period. The glacier area has decreased by 7.9%, mainly due to changes observed in the most recent period (1990-99), when the annual area loss almost tripled to 1.01 km 2 a -1 . Based on meteorological data from Taxkogan station since 1957, we conclude that climate change, particularly the rise in summer temperature after 1994, is the main forcing factor in glacier shrinkage.

Changes in the elevation and extent of two glaciers along the Yanglonghe river, Qilian Shan, China

We use topographic maps, historical data, multispectral satellite data and real-time kinematic GPS data to analyze glacier area, length and ice-elevation changes of two glaciers in the central Qilian Shan, China, between 1956 and 2007. We find that the fronts of Yanglonghe glacier No. 1 (5Y432A1) and Yanglonghe glacier No. 5 (5Y432A5) have retreated by 266.5 � 37.1 m (5.2 � 0.73 m a -1 ) and 181.4 � 37.1 m (3.6 � 0.73 m a -1 ) respectively, and that this retreat accelerated after 1999. During the study period, the glacier areas decreased by � 4.1% and 15.9% respectively. In addition, spatially non-uniform thinning, which averaged 20.2 � 11 m (0.4 � 0.22 m a -1 ) and 16.9 � 11 m (0.33 � 0.22 m a -1 ) in the ablation areas of 5Y432A1 and 5Y432A5 respectively, is observed using digital elevation models constructed using data from 1956, 1977 and 2007. The ice-volume depletion from 5Y432A1 (2.91 � 10 7 m 3 ) was 2.7 times greater than from the smaller 5Y432A5 (1.08 � 10 7 m 3 ). Based on records from nearby Tuole weather station, increasing annual temperatures are principally responsible for the observed glacier thinning and retreat.

Glacier changes in the Koshi River basin, central Himalaya, from 1976 to 2009, derived from remote-sensing imagery

Abstract We use remote-sensing and GIS technologies to monitor glacier changes in the Koshi River basin, central Himalaya. The results indicate that in 2009 there were 2061 glaciers in this region, with a total area of 3225 ±90.3 km2. This glacier population is divided into 1290 glaciers, with a total area of 1961 ±54.9 km2, on the north side of the Himalaya (NSH), and 771 glaciers, with a total area of 1264 ± 35.4 km2, on the south side of the Himalaya (SSH). From 1976 to 2009, glacier area in the basin decreased by about 19±5.6% (0.59±0.17%a–1). Glacier reduction was slightly faster on SSH (20.3 ±5.6%) than on NSH (18.8±5.6%). The maximum contribution to glacier area loss came from glaciers within the 1-5 km2 area interval, which accounted for 32% of total area loss between 1976 and 2009. The number of glaciers in the Koshi River catchment decreased by 145 between 1976 and 2009. Glacier area on SSH decreased at a rate of 6.2 ±3.2% (0.68 ±0.36% a–1), faster than on NSH, where the rate was 2.5 ±3.2% (0.27±0.36% a–1) during 2000-09. Based on records from Tingri weather station, we infer that temperature increase and precipitation decrease were the main causes of glacier thinning and retreat during the 1976-2000 period. Glacier retreat during the 2000-09 period appears to be controlled by temperature increase, since precipitation increase over this period did not offset ice losses to surface melting.

Changes in Glacier Volume in the North Bank of the Bangong Co Basin from 1968 to 2007 Based on Historical Topographic Maps, SRTM, and ASTER Stereo Images

Abstract Heterogeneous mass wastage has been found across the northwestern Tibet Plateau, and both slight positive and negative average mass budgets were observed using different data sets during the past decades. The north bank of the Bangong Co Basin partly covers the Western Kunlun Mountains and Karakoram Mountains. The assessment of glacier mass budget in this region over a long period is of particular interest to understanding the regional diversity of the mass changes of glaciers. Changes in glacier mass in the area of concern were assessed by differentiation of digital elevation models (DEMs) from the earliest available topographic maps, the Shuttle Radar Terrain Mission (SRTM), and the Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) stereo images. Results show that glaciers in this basin have in general experienced a decelerated mass loss but with regional differences. Glaciers were found to have lost a volume of 4.45 ± 0.63 km3 from 1968 to 2007, corresponding to -0.18 ± 0.03 m a-1 water equivalent (w.e.) in the north bank of the Bangong Co Basin. Loss of glacier mass in this region from 1999 to 2007 was 0.11 ± 0.12 m w.e. a-1, which was approximately half the loss that occurred from 1968 to 1999 (-0.20 ± 0.01 m w.e. a-1). From 1968 to 1999, higher mass losses were found in the north with smaller losses in the south, while from 1999 to 2007 there was more loss of mass in the southeast and a somewhat balanced mass budget in the northeast.

Quality in the GLIMS Glacier Database

Global Land Ice Measurements from Space (GLIMS) is an international initiative to map the world’s glaciers and to build a geospatial database of glacier vector outlines that is usable via the World Wide Web. The GLIMS initiative includes glaciologists at 82 institutions, organized into 27 Regional Centers (RCs), who analyze satellite imagery to map glaciers in their regions of expertise. The results are collected at the U.S. National Snow and Ice Data Center (NSIDC) and ingested into the GLIMS Glacier Database. A concern for users of the database is data quality. The process of classifying multispectral satellite data to extract vector outlines of glaciers has been automated to some degree, but there remain stages requiring human interpretation. To quantify the repeatability and precision of data provided by different RCs, we designed a method of comparative image analysis whereby analysts at the RCs and NSIDC could derive glacier outlines from the same set of images, chosen to contain a variety of glacier types. We carried out four such experiments. The results were compiled, compared, and analyzed to quantify inter-RC analysis consistency. These comparisons have improved RC ability to produce consistent data, and in addition show that in the lower reaches of a glacier, precision of glacier outlines is typically 3 to 4 pixels. Variability in the accumulation area and over parts of the glacier that are debris covered tends to be higher. The ingest process includes quality control steps that must be passed before data are accepted into the database. These steps ensure that ingested data are well georeferenced and internally consistent. The GLACE experiments and ingest time quality control steps have led to improved quality and consistency of GLIMS data. This chapter presents the GLACE experiments and the quality control steps incorporated in the data ingest process. More recent similar studies are referenced.

Glacier Changes in the Lancang River Basin, China, between 1968–1975 and 2005–2010

Abstract The Lancang River Basin (LRB) crosses from the higher inland Tibet Plateau to lower south Asia. Glaciers in upper reaches of the basin are significant reservoirs of freshwater and are considered to contribute substantially to the runoff of the Lancang River. In this study, we present the results of glacier inventories of the LRB and demonstrate its changes during the past 40 years, based on investigations conducted during two periods: the first (1968–1975) and the second (2005–2010) glacier inventory of China. Total area of the 423 measured glaciers in the LRB decreased by 98.50 ± 26.61 km2 from 328.16 ± 20.29 km2 in 1968–1975 to 229.66 ± 16.48 km2 in 2005–2010, indicating a loss in total glacier area of about 30% ± 8% during the past 40 years (at a mean area loss rate of 0.75% ± 0.2% a-1), which is comparable to glacier changes in other regions of high Asia. Southern glaciers in the LRB have experienced greater area loss than the northern inland Tibet regions, indicating more sensitivity of temperate glaciers to climate warming. The general warming trend but with less significant precipitation changes during the past 50 years (1960–2010), which has been confirmed by the observation of several meteorological stations across from the south to the north of the basin, could be one of the main causes accounting for the overall glacier recessions in the LRB.

Glaciers in China and Their Variations

This chapter summarizes recent glacier variations in China as investigated using remote-sensing methods. We find that glaciers in China have lost a tremendous amount of ice mass since the Little Ice Age maximum: area and ice volume have decreased by 26.7 and 24.5 % of the respective amounts of glaciers based on maps compiled during the late 1950s and 1980s. Chinese Glaciers have been in a general state of mass loss during recent decades as monitored by satellite remote-sensing methods over glaciers totaling one fifth of the glacier area in China. At present, the ability to monitor ice volume change and the surface velocity of glaciers by satellite is relatively new, but shows potential for glaciers having complex topographical conditions in the high mountains. This is an important research focus, in part because Chinese economic development is locally heavily impacted by changes in the glacier dynamical regime due to (1) glaciers’ role in supplying meltwater to most of the region and (2) potential for local glaciological hazards.