Mapping of moraine dammed glacial lakes and assessment of their areal changes in the central and eastern Himalayas using satellite data

The relatively rapid recession of glaciers in the Himalayas and formation of moraine dammed glacial lakes(MDGLs) in the recent past have increased the risk of glacier lake outburst floods(GLOF) in the countries of Nepal and Bhutan and in the mountainous territory of Sikkim in India. As a product of climate change and global warming, such a risk has not only raised the level of threats to the habitation and infrastructure of the region, but has also contributed to the worsening of the balance of the unique ecosystem that exists in this domain that sustains several of the highest mountain peaks of the world. This study attempts to present an up to date mapping of the MDGLs in the central and eastern Himalayan regions using remote sensing data, with an objective to analyse their surface area variations with time from 1990 through 2015, disaggregated over six episodes. The study also includes the evaluation for susceptibility of MDGLs to GLOF with the least criteria decision analysis(LCDA). Forty two major MDGLs, each having a lake surface area greater than 0.2 km2, that were identified in the Himalayan ranges of Nepal, Bhutan, and Sikkim, have been categorized according to their surface area expansion rates in space and time. The lakes have been identified as located within the elevation range of 3800 m and6800 m above mean sea level(a msl). With a total surface area of 37.9 km2, these MDGLs as a whole were observed to have expanded by an astonishing 43.6% in area over the 25 year period of this study. A factor is introduced to numerically sort the lakes in terms of their relative yearly expansion rates, based on their interpretation of their surface area extents from satellite imageries. Verification of predicted GLOF events in the past using this factor with the limited field data as reported in literature indicates that the present analysis may be considered a sufficiently reliable and rapid technique for assessing the potential bursting susceptibility of the MDGLs. The analysis also indicates that, as of now, there are eight MDGLs in the region which appear to be in highly vulnerable states and have high chances in causing potential GLOF events anytime in the recent future.

Compression Characteristic and Creep Behavior of Moraine Soil at Xingkang Bridge,West Sichuan,China

The compression and creep characteristics of moraine soil are important mechanical properties of geomaterials to be analyzed during the construction process of engineering projects.However,related references about these characteristics through large-size in-situ tests have rarely been reported.In this study,in-situ tests of particle size distribution,compression deformation,and compression creep were conducted at the Xingkang Bridge,West Sichuan,China.The results show that the uniformity coefficient of moraine soil ranges from 12.1 to 183.3,and gradation coefficient ranges from 0.4 to 2.8.The total compression deformations of moraine samples during the conventional compression deformation test are 4.70,4.07,and 0.47 mm,and their residual deformations are 2.81,2.45,and 0.22 mm,respectively.The deformation modulus ranges from 127.3 to 676.4 MPa,and elastic modulus ranges from 316.3 to 765.7 MPa.During compression creep tests,moraine soil enters the steady creep stage after 3.8 h of loading pressure at 445 k Pa,and it keeps steady after 14 h of loading pressure at 900 k Pa.The Burgers model and generalized Kelvin model predict the deformation well in transient,deceleration and steady creep stages.Results provide a valuable reference for the analysis of the compression deformation and creep behavior of moraine soil during engineering construction and management.

Characteristics of mountain glacier surge hazard: learning from a surge event in NE Pamir, China

Abnormal glacier movement is likely to result in canyon-type hazards chain,such as the barrier lake of Yarlung Zangbo Grand Canyon formed by glacier debris flow in October 2018 in China.Glacier hazard usually evolves from the glacier surge and may occur in a regular cycle.Understanding the characteristics and process of glacier surge is important for early hazard recognition and hazard assessment.Based on field investigations,remote sensing interpretations and SAR offset-tracking surveys,this study confirms a typical glacier surge in the northeast Pamir,and presents its characteristics and processes."Black ice"mixed moraines choking uplift and overflowing lateral marine are the most important scenic characteristics,which were formed under the conditions of stagnant glacier downstream and abundant super-glacial moraine.Glacier movement event can be divided into a five-period cycle including quiescent,inoculation,initiation,fracture and decline.This surge event lasted for about 300 days,initiated in February 2015 developed extensive fracturing zone in spring and early summer at maximum velocity of 10±0.95 m/day,declined after August 2015 and recovered to quiescent status in October 2015 for the next inoculation.The average height of glacier"receiving"area increased by 20-40 m with 2.7-3.6×10^8 m^3 ice transferred from glacier"reservoir",and this volume accumulation again require 50-100 years for glacier mass balance which gives approximately 100 years frequency of the glacier surge.Nevertheless,long-period increase of precipitation and temperature were favorable for the occurrence,hydrological instability is the direct triggering mechanism,and while the Glacier Lake Outburst Flood(GLOF)hazards are unlikely to occur with this surge.

The changes of Lop Nur Lake and the disappearance of Loulan

The causes of the disappearance of the ancient town of Loulan in Xinjiang, China have been generally agreed to derive from two factors: human activities and natural factors (environmental variations). In this paper, the Muzart Glacier was selected as an example, and found that the length of the glacier has been gradually decreasing and the snow line has been retreating to a higher altitude, both results contributing to a decrease in river flow below the Muzart Glacier. From the distribution of moraines in the Tianshan Mountains and adjacent areas in different periods, the paper speculates that there have been four minor glacial periods since the Quaternary. Although the durations and scales of the four minor glacial periods were different, they all indirectly influenced the formation and disappearance of the Lop Nur Lake. The events of the fourth minor glacial period are the important impact factors in the existence and disappearance of Loulan. Whether the disappearance of Loulan can be related to the events of the three previous minor glacial periods needs further investigation.

Marine Oxygen Isotope Stage(MIS)-6 Glacial Advances on the Tibetan Plateau More Extensive than during MIS-2 due to More Abundant Precipitation

Numerous studies dated glacial deposits within the Himalayan-Tibetan orogen.While most focus on young deposits,i.e.,younger than the Last Glacial Maximum(LGM or Marine oxygen Isotope Stage(MIS)-2,~20 ka),older moraines such as those from MIS-6(~130–191 ka)are much harder to date and interpret due to the less well-preserved nature of their surfaces and boulders,as well as their scattered and continuous age distribution due to long-lived erosion since deposition.Here,we dated with~(10)Be,two imbricated moraines near Yadong in southern Tibet,as MIS-2 and 6,showing that the most extensive,smooth surfaces were abandoned during MIS-6.Compiling published data from 54 MIS-6 moraines on the Tibetan Plateau reveals that they exist in most regions,dry or humid.They are particularly well-preserved(sharp crests)in eastern and northern Tibet,while in southern and central Tibet,their crests are rounded to sub-rounded.Because both MIS-2 and 6 were equally cold,and because MIS-6 moraines are much more extensive than those from the LGM,we conclude that MIS-6 glacial advances were controlled by more abundant precipitation than during MIS-2.This would be consistent with the peak in Asian monsoon during MIS-6,revealed by sediments from the South China Sea.

Loess-paleosol sequence on Loess Plateau and uplift of the Qinghai-Xizang Plateau

Correlation of the loess-paleosol sequence on Loess Plateau and the tectonodimatic cycle it reflects with the moraine-paleosol sequence on Qingbai-Xizang Plateau and the uplift process it reflects, indicates that both sequences are synchronous to each other on phase variation with a quasi-period of 0.4 Ma, i.e. the eccentricity variation period. The response of the variation of the Asian paleomonsoon and the paleoclimatic change to the uplift stages and altitudes and the underlying surfaces is studied.

The Quaternary fault in Jiamu area,the Xinjiang Uygur Autonomous Region

The Quaternary Tailan River fault has been found in the Tianshan foothills area, the Xinjiang Uygur Autonomous Region. It is the recent boundary fault of the Tarim Basin coupling with the West Tianshan Mountains. In the light of measurement data of the slip which cuts the Quaternary deposits of different ages, the Quaternary kinematic figures of the Tailan River fault are estimated as follows: crustal shortening 3.7 km and shortening rate 1.59 mm/a, uplift of Tianshan Mountains 1.34 km and uplift rate 0.56 mm/a, and additional relief of 900 m. Considering the contribution of the Gumubiezi anticline close to the south of the Tailan River fault, the Quaternary crustal shortening and shortening rate of the Jiamu area are 4.8 km and 2 mm/a respectively. The above-mentioned data coincide with the crustal shortening rate calculated from the growth strata in the Kuqa area, as well as the GPS measurements in the Lake Issyk area and the Korla-Urumqi area, reflecting the fast thrusting period within the