The Sanjiangyuan region, known as the Chinese Water Tower, serves as a crucial ecological zone that is highly sensitive to climate change. In recent years, rising temperatures and increased precipitation have led to permafrost melt and frequent occurrences of thermokarst landslides, exacerbating soil erosion issues. Although studies have explored the impact of freeze-thaw action (FTA) on soil properties, research on this phenomenon within the unique geomorphological unit of thermokarst landslides, formed from degrading permafrost, remains sparse. This study, set against the backdrop of temperature-induced soil landslides, combines field investigations and controlled laboratory experiments on typical thermokarst landslide bodies within the permafrost region of Sanjiangyuan to systematically investigate the effects of FTA on the properties of soils within thermokarst landslides. Furthermore, this study employs the EPIC model to establish an empirical formula for the soil erodibility (SE) factor before and after freeze-thaw cycles (FTCs). The results indicate that: (1) FTCs significantly alter soil particle composition, reducing the content of clay particles in the surface soil while increasing the content of sand particles and the median particle size, thus compromising soil structure and enhancing erodibility. (2) FTA initially significantly increases soil organic matter content (OMC); however, as the number of FTCs increases, the magnitude of these changes diminishes. The initial moisture content of the soil significantly influences the effects of FTA, with more pronounced changes in particle composition and OMC in soils with higher moisture content. (3) With an increasing number of FTCs, the SE K-value first significantly increases and then tends to stabilize, showing significant differences across the cycles (1 to 15) (p < 0.05). This study reveals that FTCs, by altering the physicochemical properties of the soil, significantly increase SE, providing a scientific basis for soil erosion control and ecological environmental protection in the Sanjiangyuan area.

Hydrologically-induced landslides are ubiquitous natural hazards in the Himalayas, posing severe threat to human life and infrastructure. Yet, landslide assessment in the Himalayas is extremely challenging partly due to complex and drastically changing climate conditions. Here we establish a mechanistic hydromechanical landslide modeling framework that incorporates the impacts of key water fluxes and stocks on landslide triggering and risk evolution in mountain systems, accounting for potential climate change conditions for the period 1991-2100. In the drainage basin of the largest river in the northern Himalayas- the Yarlung Zangbo River Basin (YZRB), we estimate that rainfall, glacier/snow melt and permafrost thaw contribute similar to 38.4%, 28.8%, and 32.8% to landslides, respectively, for the period 1991-2019. Future climate change will likely exacerbate landslide triggering primarily due to increasing rainfall, whereas the contribution of glacier/snow melt decreases owing to deglaciation and snow cover loss. The total Gross Domestic Productivity risk is projected to increase continuously throughout the 21st century, while the risk to population shows a general declining trend. The results yield novel insights into the climatic controls on landslide evolution and provide useful guidance for disaster risk management and resilience building under future climate change in the Himalayas.

Thermokarst landslide (TL) activity in the Qinghai-Tibet Plateau (QTP) is intensifying due to climate warminginduced permafrost degradation. However, the mechanisms driving landslide formation and evolution remain poorly understood. This study investigates the spatial distribution, annual frequency, and monthly dynamics of TLs along the Qinghai-Tibet engineering corridor (QTEC), in conjunction with in-situ temperature and rainfall observations, to elucidate the interplay between warming, permafrost degradation, and landslide activity. Through the analysis of high-resolution satellite imagery and field surveys, we identified 1298 landslides along the QTEC between 2016 and 2022, with an additional 386 landslides recorded in a typical landslide-prone subarea. In 2016, 621 new active-layer detachments (ALDs) were identified, 1.3 times the total historical record. This surge aligned with unprecedented mean annual and August temperatures. The ALDs emerged primarily between late August and early September, coinciding with maximum thaw depth. From 2016 to 2022, 97.8 % of these ALDs evolved into retrogressive thaw slumps (RTSs), identified as active landslides. Landslides typically occur in alpine meadows at moderate altitudes and on gentle northward slopes. The thick ice layer near the permafrost table serves as the material basis for ALD occurrence. Abnormally high temperature significantly increased the active layer thickness (ALT), resulting in melting of the ice layer and formation of a thawed interlayer, which was the direct causing factor for ALD. By altering the local material, micro-topography, and thermal conditions, ALD activity significantly increases RTS susceptibility. Understanding the mechanisms of ALD formation and evolution into RTS provides a theoretical foundation for infrastructure development and disaster mitigation in extreme environments.

Mega retrogressive thaw slumps (MRTS, >10(6) m(3)) are a major threat to Arctic infrastructure, alter regional biogeochemistry, and impact Arctic carbon budgets. However, processes initiating and reactivating MRTS are insufficiently understood. We hypothesize that MRTS preferentially develop a polycyclic behavior because the material is thermally and mechanically prepared for subsequent generation failure. In contrast to remote sensing, geophysical reconnaissance reveals the inner structure and relative thermal state of MRTS decameters beneath slump surfaces, potentially controlling polycyclicity. Based on their life cycle development, five (M)RTS were studied on Herschel Island, an MRTS hotspot on the Canadian Beaufort coast. We combine >2 km of electrical resistivity tomography (ERT), 500 m of ground-penetrating radar (GPR) and annual monitoring of headwall retreat from 2004 to 2013 to reveal the thermal state, internal structure, and volume loss of slumps. ERT data were calibrated with unfrozen-frozen transitions from frost probing of active layer thickness and shallow boreholes. In initial stage MRTS, ERT displays surficial thermal perturbations a few meters deep, coincident with recent mud pool and mud flow development. In early stage polycyclic MRTS, ERT shows decameter deep-reaching thermal perturbations persisting even 300 years after the last activation. In peak-stage polycyclic MRTS, 3D-ERT highlights actively extending deep-reaching thermal perturbations caused by gully incisions, mud slides and mud flows. GPR and headwall monitoring reveal structural disturbance by historical mud flows, ice-rich permafrost, and a decadal quantification of headwall retreat and slump floor erosion. We show that geophysical signatures identify long-lasting thermal and mechanical disturbances in MRTS predefining their susceptibility to polycyclic reactivation.

We investigate the Gisla perched talus slope (Trollaskagi peninsula, northern Iceland), from which a landslide (more specifically a debris avalanche) occurred in October 2020. Although this talus slope is located outside of the permafrost climatic boundaries, geomorphological evidence (i.e., molards in the landslide deposits) suggest that degradation of azonal permafrost could be among the destabilising factors of the landslide. The thermal dynamics of talus slopes is currently poorly understood, as air convection ( the 'chimney effect') can play a role in the persistence of permafrost at the base of talus slopes. We use the software FEFLOW to run physical-based simulations of heat transfer within a cross- of the Gisla talus slope, from -20,000 years to present. We explore the sensitivity of our model to document the initial porosity/ ice content of the talus slope (0.3, 0.5 and 0.8), and the thermal conductivity (TC) of the rock phase (0.75, 1.1 and 1.75 W.m(-1).K-1). Analysis of air temperature data show that the region has been undergoing a general temperature increase for the last similar to 40 years, supporting the possibility that permafrost degradation is among the destabilising factors of the landslide. Our temperature measurements show that a chimney effect indeed occurs at the Gisla talus slope. Although our modelling approach does not simulate air convection itself, permafrost persists at the base of the talus slope in all model scenarios. Increasing the initial porosity/ice content and decreasing the TC of the rock phase enhances persistence of permafrost in the Gisla talus slope. Our approach is unconventional as we initially know that ground ice was present in the Gisla talus slope at the time of the landslide; it attests that the permafrost dynamics in the talus slope is best represented by our most ice-conservative scenario - i.e., with a TC of 0.75 W.m(-1).K-1.

The increase in temperatures and changing precipitation patterns resulting from climate change are accelerating the occurrence and development of landslides in cold regions, especially in permafrost environments. Although the boundary regions between permafrost and seasonally frozen ground are very sensitive to climate warming, slope failures and their kinematics remain barely characterized or understood in these regions. Here, we apply multisource remote sensing and field investigation to study the activity and kinematics of two adjacent landslides (hereafter referred to as twin landslides) along the Datong River in the Qilian Mountains of the Qinghai-Tibet Plateau. After failure, there is no obvious change in the area corresponding to the twin landslides. Based on InSAR measurements derived from ALOS PALSAR-1 and -2, we observe significant downslope movements of up to 15 mm/day within the twin landslides and up to 5 mm/day in their surrounding slopes. We show that the downslope movements exhibit distinct seasonality; during the late thaw and early freeze season, a mean velocity of about 4 mm/day is observed, while during the late freeze and early thaw season the downslope velocity is nearly inactive. The pronounced seasonality of downslope movements during both pre- and post-failure stages suggest that the occurrence and development of the twin landslide are strongly influenced by freeze-thaw processes. Based on meteorological data, we infer that the occurrence of twin landslides are related to extensive precipitation and warm winters. Based on risk assessment, InSAR measurements, and field investigation, we infer that new slope failure or collapse may occur in the near future, which will probably block the Datong River and cause catastrophic disasters. Our study provides new insight into the failure mechanisms of slopes at the boundaries of permafrost and seasonally frozen ground.

Landslides induced by freeze-thaw processes on grasslands are one of the major geohazards, and their scale and frequency are increasing as the global warms. Freeze-thaw induced landslides degrade surface vegetation and soil properties, reduce biodiversity, intensify landscape fragmentation, and lead to losses in economy, human and animal lives. Despite substantial progress in research on landslides, there has been little study focused on how ground freeze-thaw events affect landslides. By critically analyzing previous studies, this paper proposes a conceptual framework for the forms and types, development, dominant factors, monitoring techniques, and impact mechanisms of freeze-thaw induced landslides. Landslides are controlled by soil characteristics and topographic slope, which are major intrinsic determinants. Increased rainfall, rising temperatures, and thickening active layer due to climate change are all direct drivers of freeze-thaw induced landslides. Vegetation conditions, animal behavior interference, and wind erosion all affect the occurrence and development process of landslides by modifying vegetation cover, soil physical and chemical properties, and structure. Currently, landslide monitoring techniques have evolved rapidly with improved efficiency and accuracy, but with only few applications for freeze-thaw induced landslides. There are a variety of prediction models for landslides, but few consider freeze-thaw effects and lack field validation. The new perspective on the occurring types and dominant factors enhances theoretical understanding of the formation mechanisms, which helps further monitor and analysis of freeze-thaw induced landslides. Future studies should concentrate on the coupling mechanism of multiple factors and the development of an accurate prediction system, which will greatly benefit the understanding and early detection of freeze-thaw induced landslides.

The role of snow is underrated in the dendrogeomorphic research in terms of the interpretation of the climate factors responsible for the geomorphic activity. We analysed snow parameters and the combined effect of spring and summer climate variables to interpret their role in debris flow/flood and flow-like landslide initiation in two Central European mid-mountain regions. We revisited the tree-ring based chronologies based on a total of 1043 trees for four debris flow/flood catchments and four flow-like landslide bodies. Three approaches were used to determine the event year, including a floating event-response index and different weighted index thresholds. In addition, data from precipitation and streamflow gauges were used to identify the best indicators of rapid snow melting and find the best explanatory climate factors during event years using logistic regression. We identified 24-40 event years with hydrogeomorphic activity and 10-29 years with flow-like landslide reactivations during 1961-2017. The amount of melted snowpack and rain-on-snow during spring were considered the best rapid snowmelt parameters obtained from the precipitation gauges due to highest correlations with the stream gauge data (R = 0.69-0.70). We identified very likely rapid snowmelt in seven debris flow/flood event years and six landslide event years since 1981. Furthermore, high maximum snowpack in spring combined with extreme oneday rainfall in summer were the best explanatory factors for hydrogeomorphic activity, but probably not during the high-magnitude debris flows, which were more dependent on the extreme summer rainfall alone. Landslide reactivations were most likely to occur during years with extreme one-day rainfall events in May to September preceded by a wet period since the last day of continuous snow cover. This study defines a step-by-step procedure to reveal the role of snowmelt and antecedent precipitation in dendrogeomorphic research and shows likely scenarios of geomorphic activity typical of the study area.

Thermokarst landslides (TL) caused by the thaw of ground ice in permafrost slopes are increasing on the Qinghai-Tibet Plateau (QTP), but the understanding of the spatially suitable environmental conditions including terrains and climate for them has not been fully established. Here, we applied multiple machine learning models and their ensemble to explore factors controlling the TL and map its susceptibility at a fine resolution. The models were calibrated and validated using a split-sample approach based on an inventory of TLs from the remote sensing data. The models indicated that summer air temperature and rainfall were the most two important factors controlling the occurrence and distribution of TLs, provided that other geomorphic conditions (i.e., slope, solar radiation, and fine soil) were suitable. The final ensemble susceptibility map based on downscaled climate data and terrain data suggested that ca. 1.4% of the QTP land was classified in high- to very high-susceptibility zone, which is likely to increase in response to future climate change. This study integrated local topography and climate in susceptibility modeling and provided new insights into the geomorphic sensitivity to climate change but also the engineering support over the QTP.

Climate change results in physical changes in permafrost soils: active layer thickness, temperature, soil hydrology and abrupt thaw features in ice-rich soils. Abrupt thaw features create new landforms such as ponds, lakes and erosion phenomena. In this chapter, current observations of physical changes in permafrost soils are discussed, including their effect on the soil carbon cycle. For the carbon cycle changes, the results of observations and experimental studies are emphasized. First, the effects of soil warming without further geomorphological change is considered. The potential effect of self-amplifying soil warming by heat production from bacterial production is discussed. Next, the changes in geomorphological processes expressed by formation of thaw ponds, lakes and erosion features are considered. These contribute to an increase of CO2 and non-CO2 greenhouse gas emissions. Hydrological changes include the effects of permafrost thaw on the water cycle via groundwater flow and directly climate-driven changes in precipitation and evapotranspiration. These result in river discharge changes with effects on floodplains, and influence transport of carbon from permafrost regions to the Arctic Ocean. Soil hydrology changes - wetting or drying - induce changes in the pattern of greenhouse gas emissions of permafrost soils.