Impact of a retrogressive thaw slump on surrounding vegetation communities in the Fenghuoshan mountains,Qinghai-Tibet Plateau

Under global warming,permafrost around the world is experiencing degradation which is especially so on the Third Pole,the Qinghai-Tibet Plateau(QTP),China.Retrogressive thaw slump(RTS)is one of the thermokarst features caused by rapid degradation of ice rich permafrost,which transforms landforms and threatens infrastructures,and even affects the terrestrial carbon cycle.In this work,vegetation communities surrounding a RTS in the Fenghuoshan Mountains of the interior portion of the Qinghai-Tibet Plateau have been investigated to examine the impact from RTS.This investigation indicates that the occurrence of RTS influences the vegetation community by altering their habitats,especially the soil water content,which forces the vegetation community to evolve in order to adapt to the alterations.In the interior part of RTS where it has been disturbed tremendously,alterations have produced a wider niche and richer plant species.This favors species of a wet environment in a habitat where it was a relatively dry environment of alpine steppe prior to the occurrence of RTS.This study adds to limited observations regarding the impact of RTS to vegetation community on the QTP and helps us to reach a broader understanding of the effects of permafrost degradation as well as global warming.

High-resolution assessment of retrogressive thaw slump susceptibility in the Qinghai-Tibet Engineering Corridor

Under the rapidly warming climate in the Arctic and high mountain areas,permafrost is thawing,leading to various hazards at a global scale.One common permafrost hazard termed retrogressive thaw slump(RTS)occurs extensively in ice-rich permafrost areas.Understanding the spatial and temporal distributive features of RTSs in a changing climate is crucial to assessing the damage to infrastructure and decision-making.To this end,we used a machine learning-based model to investigate the environmental factors that could lead to RTS occurrence and create a susceptibility map for RTS along the Qinghai-Tibet Engineering Corridor(QTEC)at a local scale.The results indicate that extreme summer climate events(e.g.,maximum air temperature and rainfall)contributes the most to the RTS occurrence over the flat areas with fine-grained soils.The model predicts that 13%(ca.22,948 km^(2))of the QTEC falls into high to very high susceptibility categories under the current climate over the permafrost areas with mean annual ground temperature at 10 m depth ranging from-3 to-1℃.This study provides insights into the impacts of permafrost thaw on the stability of landscape,carbon stock,and infrastructure,and the results are of value for engineering planning and maintenance.

Machine learning-based predictions of current and future susceptibility to retrogressive thaw slumps across the Northern Hemisphere

Retrogressive thaw slumps(RTSs)caused by the thawing of ground ice on permafrost slopes have dramatically increased and become a common permafrost hazard across the Northern Hemisphere during previous decades.However,a gap remains in our comprehensive understanding of the spatial controlling factors,including the climate and terrain,that are conducive to these RTSs at a global scale.Using machine learning methodologies,we mapped the current and future RTSs susceptibility distributions by incorporating a range of environmental factors and RTSs inventories.We identified freezing-degree days and maximum summer rainfall as the primary environmental factors affecting RTSs susceptibility.The final ensemble susceptibility map suggests that regions with high to very high susceptibility could constitute(11.6±0.78)%of the Northern Hemisphere's permafrost region.When juxtaposed with the current(2000-2020)RTSs susceptibility map,the total area with high to very high susceptibility could witness an increase ranging from(31.7±0.65)%(SSP585)to(51.9±0.73)%(SSP126)by the 2041-2060.The insights gleaned from this study not only offer valuable implications for engineering applications across the Northern Hemisphere,but also provide a long-term insight into the potential change of RTSs in permafrost regions in response to climate change.

Three‑Dimensional Numerical Modeling of Ground Ice Ablation in a Retrogressive Thaw Slump and Its Hydrological Ecosystem Response on the Qinghai‑Tibet Plateau,China

Retrogressive thaw slumps(RTSs),which frequently occur in permafrost regions of the Qinghai-Tibet Plateau(QTP),China,can cause signifcant damage to the local surface,resulting in material losses and posing a threat to infrastructure and ecosystems in the region.However,quantitative assessment of ground ice ablation and hydrological ecosystem response was limited due to a lack of understanding of the complex hydro-thermal process during RTS development.In this study,we developed a three-dimensional hydro-thermal coupled numerical model of a RTS in the permafrost terrain at the Beilu River Basin of the QTP,including ice–water phase transitions,heat exchange,mass transport,and the parameterized exchange of heat between the active layer and air.Based on the calibrated hydro-thermal model and combined with the electrical resistivity tomography survey and sample analysis results,a method for estimating the melting of ground ice was proposed.Simulation results indicate that the model efectively refects the factual hydro-thermal regime of the RTS and can evaluate the ground ice ablation and total suspended sediment variation,represented by turbidity.Between 2011 and 2021,the maximum simulated ground ice ablation was in 2016 within the slump region,amounting to a total of 492 m^(3),and it induced the reciprocal evolution,especially in the headwall of the RTS.High ponding depression water turbidity values of 28 and 49 occurred in the thawing season in 2021.The simulated ground ice ablation and turbidity events were highly correlated with climatic warming and wetting.The results ofer a valuable approach to assessing the efects of RTS on infrastructure and the environment,especially in the context of a changing climate.

Heterogeneity of Surface Heat Exchange of Slopes and Potential Drivers of the Initiation of Thaw Slump,Qinghai‑Tibet Plateau

In the mountainous permafrost area,most thaw slumps are distributed in north or northeast-facing shady slope areas.It is commonly known that there is a heterogeneity in permafrost between diferent slope aspects,but there has been a lack of detailed measured data to quantitatively evaluate their relationships,and in-depth understandings on how the slope aspects are linked to the distribution of thaw slumps.This study examined the heterogenous thermal regime,soil moisture content,and surface radiation at two slope sites with opposing aspects in a warming permafrost region on the Qinghai-Tibet Plateau(QTP).The results indicate that similar air temperatures(T_(a))were monitored on the two slopes,but there were signifcant diferences in ground temperature and moisture content in the active layer from 2016 to 2021.The sunny slope exhibited a higher mean annual ground surface temperature(T_(s)),and over the fve years the mean annual temperature at the top of permafrost was 1.3–1.4℃warmer on the sunny slope than the shady slope.On the contrary,the near-surface soil moisture content was about 10–13%lower on the sunny slope(~22–27%)than the shady slope(~35–38%)during the thawing season(June–September).Radiation data indicate that signifcantly higher shortwave downward radiation(DR)appeared at the sunny slope site.However,due to the greater surface albedo,the net radiation(Rn)was lower on the sunny slope.Slope aspect also afects the ground ice content due to its infuence on ground temperature,freeze-thaw cycles,and soil moisture.Shady slopes have a shallower burial of ice-rich permafrost compared to sunny slopes.The results highlight greatly diferent near-surface ground thermal conditions at the two slope sites with diferent aspects in a mountainous permafrost region.This helps identify the slope-related causes of increasing thaw slumps and provides a basis for predicting their future development.

Automatic Identifcation of Thaw Slumps Based on Neural Network Methods and Thaw Slumping Susceptibility

Thaw slumping is a periglacial process that occurs on slopes in cold environments,where the ground becomes unstable and the surface slides downhill due to saturation with water during thawing.In this study,GaoFen-1 remote sensing and fused multi-source feature data were used to automatically map thaw slumping landforms in the Beilu River Basin of the Qinghai–Tibet Plateau.The bi-directional cascade network structure was used to extract edges at diferent scales,where an individual layer was supervised by labeled edges at its specifc scale,rather than directly applying the same supervision to all convolutional neural network outputs.Additionally,we conducted a 5-year multi-scale feature analysis of small baseline subset interferometric synthetic aperture radar deformation,normalized diference vegetation index,and slope,among other features.Our study analyzed the performance and accuracy of three methods based on edge object supervised learning and three preconfgured neural networks,ResNet101,VGG16,and ResNet152.Through verifcation using site surveys and multi-data fusion results,we obtained the best ResNet101 model score of intersection over union of 0.85(overall accuracy of 84.59%).The value of intersection over union of the VGG and ResNet152 are 0.569 and 0.773,respectively.This work provides a new insight for the potential feasibility of applying the designed edge detection method to map diverse thaw slumping landforms in larger areas with high-resolution images.

Potential of Multi‑temporal InSAR for Detecting Retrogressive Thaw Slumps: A Case of the Beiluhe Region of the Tibetan Plateau

Permafrost degradation due to climate warming is severely reducing slope stability by increasing soil pore water pressure and decreasing shear strength.Retrogressive thaw slumps(RTSs)are among the most dynamic landforms in permafrost areas,which can result in the instability of landscape and ecosystem.However,the spatiotemporal characteristics of surface deformation of RTSs are still unclear,and the potentials of deformation properties in mapping large-scale RTSs need to be further assessed.In this study,we applied a multi-temporal Interferometric Synthetic Aperture Radar(MT-InSAR)method to map the spatiotemporal variations in surface deformation of RTSs in the Beiluhe region of the Tibetan Plateau by using 112 scenes of Sentinel-1 SAR data acquired from 2017 to 2021.The deformation rates of RTSs ranged from−35 to 20 mm/year,and three typical motion stages were inferred by analyzing the deformation variation trend of the headwall of RTSs:stable,abrupt thaw,and linear subsidence.A total of 375 RTSs were identifed in the Mati Hill region by combining InSAR-based deformation results with visual interpretation of optical remote sensing images.Among them,76 RTSs were newly developed,and 26%more than the inventory derived from the optical images alone.This study demonstrated that the combination of InSAR-derived deformation with optical images has signifcant potential for detecting RTSs with high accuracy and efciency at the regional scale.

北麓河青藏公路沿线多年冻土区热融滑塌型边坡植被防护力学效应研究

为评价青藏公路沿线多年冻土区高寒草甸和人工种植植物固土护坡力学贡献,本研究选取位于青藏公路沿线北麓河地区一处热融滑塌灾害作为研究区。以原生草甸(主要植物种为嵩草(Carex myosuroides Vill.)和藏嵩草(Kobresia tibetica Maxim.))和人工种植垂穗披碱草(Elymus nutans Griseb.)、星星草(Puccinellia tenuiflora(Griseb.)Scribn.&Merr.)、冰草(Agropyron cristatum(L.)Gaertn.)、早熟禾(Poa annua L.)、碱茅(Puccinellia distans(L.)Parl.)和中华羊茅(Festuca sinensis Keng ex S.L.Lu)等6种生长期为1 a草本为研究对象,通过开展室内原状根-土复合体剪切试验,探讨了草本根系增强热融滑塌型边坡体抗剪强度作用贡献,并采用静力平衡法对该热融滑塌型边坡稳定性进行了评价。主要得到如下结果:通过室内洗根试验得到根-土复合体试样平均含根量由高至低依次为原生草甸(33.33 mg·cm^(-3))、垂穗披碱草(16.95 mg·cm^(-3))、早熟禾(13.12 mg·cm^(-3))、中华羊茅(5.80 mg·cm^(-3))、冰草(3.89 mg·cm^(-3))、星星草(3.15 mg·cm^(-3))、碱茅(2.86 mg·cm^(-3));平均株高由高至低依次为垂穗披碱草(10.93 cm)、原生草甸(9.64 cm)、冰草(6.88 cm)、早熟禾(5.22 cm)、中华羊茅(3.90 cm)、碱茅(3.86 cm)、星星草(2.90 cm);区内原生草甸和6种人工种植草本根-土复合体抗剪强度均显著高于不含根系素土,其中原生草甸和人工种植垂穗披碱草根系增强土体抗剪强度作用增幅相对较大,分别为42.17%和30.96%;由静力平衡法计算得到含根系边坡安全系数均高于不含根系素土边坡,边坡安全系数由大至小依次为原生草甸(1.47)、垂穗披碱草(1.39)、早熟禾(1.38)、冰草(1.37)、碱茅(1.36)、星星草(1.32)、中华羊茅(1.32)、素土(0.96)。该研究结果对于有效防治青藏公路沿线北麓河地区热融滑塌灾害,同时为进一步有效防治青藏公路沿线热融滑塌灾害引发的水土流失、草地退化等灾害提供理论依据和实际指导。

青藏公路五道梁-沱沱河段高寒草甸根系力学效应研究

本项研究以青藏公路五道梁-沱沱河段一处发育的高寒草甸热融滑塌灾害作为研究对象,采用野外原位测量与室内单根、群根抗拉试验以及草甸层原位拉裂试验,研究了区内草本植物单根和群根力学性能及其特征,进一步评价了植物根系增强高寒环境热融滑塌区土体抗拉强度和提高边坡浅层稳定性贡献。结果表明:草本单根抗拉力及单根抗拉强度与根径间均呈幂函数关系;草本植物根数与群根抗拉力及群根抗拉强度之间均符合线性函数关系;草甸层原位抗拉试验值总体小于理论计算值。区内草本根系显著增强土体抗拉强度,且其增强土体强度贡献与根径、含根量和土壤密实度之间表现出显著相关性。本研究结果为有效防治青藏公路沿线高寒草甸热融滑塌、水土流失等地质灾害,起到提供理论支撑和实际指导作用。

青藏高原中部可可西里热融滑塌发育特征及灾害效应

受青藏高原暖湿化气候的影响,高原中部的可可西里多年冻土呈现快速的退化状态,并由此诱发大量的热喀斯特地貌发育。热融滑塌作为多年冻土区最为典型的热喀斯特地貌,其快速发育是多年冻土响应气候及环境变化的指示器。考察发现热融滑塌的快速发育对区域环境及重大基础设施均具有显著的灾害效应,但由于缺乏高精度的空间数据,对这一区域热融滑塌的分布特征缺乏细致的研究。本研究基于高分系列卫星产品影像资料解译,并结合2021年野外调查验证,开展了可可西里地区热融滑塌分布特征及灾害效应研究。研究结果表明:全区共发育热融滑塌1734个,总面积约30.82 km^(2),主要分布在海拔4700~4800 m的丘陵山区缓坡地带,其中4°~6°的坡面热融滑塌分布最多,约占总数量的32%,总面积的38%。由于坡向对地表热量分布及地下冰赋存条件的影响,对热融滑塌分布影响较大,北坡(N)及东北坡(NE)分布较多,约占59%。广泛发育的热融滑塌不仅对寒区生态环境、水环境、气候环境有重要的影响,也对重大基础设施及藏区居民生命财产具有灾害效应。本研究对可可西里地区未来工程规划及国家公园建设具有重要的指导意义。

冻土区边坡热融滑塌的稳定性评价与治理

以青海省道312线玛多至色吾沟公路K315段边坡热融滑塌为研究对象,结合气象水文特征及工程地质条件,分析该处热融滑塌的原因。通过室内实验及指标反算确定了岩土体基本参数,采用GB50021—2001《岩土工程勘察规范》和基于有效应力原理的两种不同计算方法对热融滑塌斜坡的稳定性进行评价。根据评价结果,提出圆截面抗滑桩及回填反压两种手段对滑坡进行治理,综合考虑环境保护、工程经济性等因素,建议采取回填反压的处理方式。

冻土斜坡模型试验相似分析

南水北调工程、青藏铁路建设工程等一系列工程的实施,将进一步影响和加剧青藏高原多年冻土区斜坡稳定性问题,冻土区边坡开挖及斜坡稳定性是工程活动中必须解决的问题之一,冻土斜坡稳定性研究在国内尚属空白。通过相似模型试验对高原多年冻土区斜坡在自然和人类活动影响下的失稳机制和活动规律进行分析,是开展研究的重要手段。根据相似理论第一定律,对冻土斜坡模型试验进行了相似分析,应用积分类比法推导并建立了冻土斜坡模型试验的相似指标和相似判据,得出在用原状土作模型介质时,6个相似常数减少为2个相似常数,即cτ和cl。模型与原型的时间比例尺是由几何比例尺决定的,即cτ=c2l,仅有一个相似参数为自变量,另一个为因变量。据此对青藏高原多年冻土区青藏公路沿线K3035处冻土斜坡进行了相似模型设计和冻融模型试验。模型再现了K3035处7°斜坡在4个冻融循环条件下,坡体中部(水平、垂向)4#位移伸张计质点位移曲线随时间的变化特征。实验表明,斜坡土体中部在第一次冻融循环中已有滑动迹象,随着滑坎进一步后退和靠近观测基准点,必然出现一次较大的位移,直至周边土体出现滑塌为止。模型试验结果与现场观测资料相比较是令人满意的。

青藏工程走廊典型热融灾害现象及其热影响研究

在全球变暖及人类工程活动的影响下,青藏工程走廊内的热融灾害普遍发育。研究走廊内各类热融灾害的发育现状及其对多年冻土的热影响对今后的工程规划和冻土环境保护具有一定的指导意义。本文通过大量的野外调查工作,总结了走廊内热融灾害的类型及其发育现状,并选取3种典型热融灾害进行现场地温监测,分析其对多年冻土的热影响方式和程度。研究结果表明:3种热融灾害对其发育区域及附近的多年冻土都产生了巨大的热影响,热融滑塌和热融沟主要影响浅层的地温状况,而热融湖塘的影响范围更大,其发育甚至会导致湖塘下部形成多年融区。此外,侧向热流计算结果表明,3种热融灾害全年都在向其周边的多年冻土放热,通过对比发现热融湖塘的侧向热侵蚀能力最强,其次是热融沟,侧向热侵蚀最小的是热融滑塌。

青藏高原多年冻土区斜坡稳定性研究进展

青藏高原多年冻土区斜坡失稳是伴随着青藏公路建设和运营过程中出现的一种灾害性的地质现象,其中以热融滑塌最为显著。本文根据斜坡失稳时所处的环境以融滑塌为例,提出了冻融循环过程中流塑状粉土沿厚层地下冰面滑动的滞水润滑效应的形成机理;通过相似模拟试验,可以看出,垂直于坡面的变形主要表现为融沉变形和部分冻胀变形;建立了温度场、变形场的数值模拟模型,分析了坡体不同深度在冻融循环过程中的位移变化规律,得出冻土斜坡位移主要发生在浅部的结论。最后指出目前研究存在的主要问题及进一步的研究方向。

小样本条件下多年冻土地区斜坡稳定性的可靠性分析方法

青藏铁路和青藏公路沿线的斜坡稳定对交通线路的安全运营十分重要,与其稳定性评价有关的土的参数指标样本很少,且离散性很大,很难得到较为准确的统计特性,针对此问题,该文基于区间理论,提出了一种小样本条件下多年冻土地区斜坡稳定问题的可靠性分析方法。主要考虑斜坡的热融滑塌,采用无限边坡稳定分析理论,给出了功能函数表达式,将不确定变量视为边界变化的区间变量,区间的下界和上界分别为采样数据的最小值和最大值,用功能函数的中值与离差之比η来估计斜坡稳定的可靠性,η将随样本数量发生变化。为了估计η和概率可靠指标β的关系,将不确定变量视为随机变量,给出了β和η比值的区间估计表达式,并采用上述方法分析了青藏铁路K3035处冻土斜坡稳定的可靠性。

多年冻土热融滑塌的地温变化及滑坡过程分析

随着青藏高原工程强度的提高,冻土区斜坡稳定性成为工程建设必须面对和解决的问题,其中最为严重也是较难防治的斜坡失稳是热融滑塌.针对典型热融滑塌进行的温度监测资料表明,在滑塌的影响下,其下多年冻土地温年变化幅度趋小而年平均地温升高,导致产生这一现象的原因在于每年进入多年冻土的冷能有所降低.滑坡溯源侵蚀范围监测资料表明,滑塌范围的扩展随地温的周期变化波动进行,并主要集中在7～9月,最大扩展范围出现在沿坡体倾向方向.热融滑塌的产生与多年冻土条件和外因力的诱发关系密切,工程治理要考虑引起滑坡消亡的基本条件.

青藏高原多年冻土区热融滑塌变形现场监测分析

为了了解青藏高原多年冻土区K3035里程热融滑塌体的变形特征,分别在未滑动土体、近滑塌前缘滑体中布设了2个变形监测孔,利用Geokon-603型测斜仪实施了近1 a的变形监测。结果表明,发育在平缓斜坡上的热融滑塌具有明显的变形特征,其位移主要发生在土层浅部,越往深部,位移越小,这一监测结果通过室内数值模拟得到了验证。将阳坡的K3035热融滑塌与阴坡的K3057热融滑塌体的变形做了对比监测,无论是滑塌体后缘还是前缘,前者的滑动变形均显著大于后者。而无热融滑塌发育的斜坡(青藏铁路DK1139)土体变形量极小,这种差异一方面说明了开挖是导致热融滑塌发生的直接因素,另一方面,由于热融滑塌的影响,其后缘相对稳定的原斜坡土体也处于相对较大的蠕变变形之中。

冻土区典型热融滑塌地温变化及防治效果模拟

冻土地区斜坡的稳定性很大程度上取决于坡体内温度场的分布状况.在野外观测数据无法完整的反映出热融滑塌发展过程中斜坡温度场分布的情况下,结合青藏公路K3035热融滑塌的气候及工程地质条件,应用有限元方法进行了滑塌过程温度场分布的数值模拟,并与实际观测资料进行了对比,进一步讨论了在滑坎位置填埋碎石的工程防治措施的效果.结果表明滑坎位置下多年冻土不稳定,容易导致斜坡的进一步滑塌,而防治措施能有效遏制滑塌趋势.

青藏工程走廊热融滑塌灾害勘设要点与工程处治措施研究

热融滑塌是多年冻土地区广泛发育的低角度热融灾害,对青藏高速公路的选线、勘察、设计、施工和运营均有较大的影响。基于青藏工程走廊热融滑塌灾害的地调数据,该文开展了青藏高速公路沿线典型热融滑塌灾害勘设要点与工程处治措施的研究。结果表明:基于运动方式可以将热融滑塌划分为坍塌沉陷式和牵引滑动式两类,其形成过程归结于质点迁移效应和滞水润滑效应;严禁对热融滑塌区域进行扰动,可以结合遥感、无人机以及地球物理技术进行综合勘查。与此同时,在设计阶段应根据热融滑塌的类型开展相应的绕避、架空以及排水等工程措施研究;对热融滑塌的处治宜采用综合防治体系,并加强对灾害的监测与预报。

青藏公路风火山地区的热融滑塌

提要 风火山地区热融滑塌按其运动方式可归纳为坍塌沉陷式和牵引滑动式两类,各类按其表面形状的差异又可分出不同的形态。修筑各种挡墙和土埝,可以控制热融滑塌的发展。