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With global warming and increasing engineering activities, one effective approach to mitigating frost hazards in warm permafrost regions is proactive cooling of foundations soils. Thermosyphons are important proactive cooling engineering measures. Evaluating the effectiveness of thermosyphons is necessary for engineering design and stability analysis of tower foundations. Based on field monitoring data, the current paper presents the analysis on the evaporator temperatures, the effectiveness of thermosyphons, and the characteristics in changing hydrothermal regimes of foundation soils along the Qinghai–Tibet Power Transmission Line (QTPTL) from Golmud, Qinghai Province to Lhasa, Tibet Autonomous Region, China. The results showed that thermosyphons effectively cooled the surrounding soils from early October to early May of the next year. In cold seasons (from October to the next May when thermosyphons were working), the evaporator temperatures changed synchronously with air temperature, and the temperature differences along the evaporator were relatively small (less than 3 °C). At the monitoring site, with the help of thermosyphons, the backfilled soils around the tower foundation re-froze completely and the thermal disturbance caused by the construction activities disappeared after the first cold period from mid-November 2010, when the foundation was constructed, to early May 2011. Due to the functioning thermosyphons, the cooling effect of the thermosyphons on foundation soils in cold seasons not only offset the warming effect of the building and operating of tower footings, but also progressively cooled the foundation soils during the first four operating years from 2011 to 2014. The more remarkable heat release was mainly because the cooling process in every year began much earlier. This resulted in the extension of the cooling period and the shortening of the warming period, resulting in an ongoing cooling of the foundation soils. As a result, the bearing capacity of the foundation soils was improved and sustained. Numerical simulations may be conducted in future to evaluate the necessary quantity and design layout of the thermosyphons around a tower foundation. [ABSTRACT FROM AUTHOR]

In permafrost regions along the Qinghai–Tibet Power Transmission Line (QTPTL) from Golmud, Qinghai Province to Lhasa, Tibet Autonomous Region, China, 130 tower foundations were selected for foundation displacement observations. Based on observations, displacement characteristics and mechanisms of tower foundations in plateau permafrost soils were analyzed. The results showed that vertical displacement of the footings (VDF) was the dominant displacement type of tower foundations, while changes in footing span (horizontal distance between two tower footings) (CFS) and differences in vertical displacement (DVD) between two adjacent footings of each tower were relatively small. The VDF of most tower foundations (about a quarter of the 130 observed foundations) performed as settlement rather than frost jacking. Due to the effective cooling of thermosyphons, frost jacking of tower foundations mainly occurred in cold seasons (from October to the next May); and because of the hysteresis of heat transfer process in foundation soils, settlement happened in cold seasons, too. Combining with the analysis of the thermal regimes of foundation soils, it was found that the ground temperature under the foundation was the most important factor influencing the VDF of tower foundations. In addition, the creep of the underlying warm and high ice-content permafrost was inferred as the main cause for the foundation settlement. The relatively slight frost jacking of tower foundations mainly resulted from frost heaving in situ of foundation soils and heaving possibly due to considerable water migration within the foundation pit. On slope terrains, the downslope movement (creep) of active layer soils resulted in considerable CFS of tower foundations. DVD between two adjacent tower footings might be derived from jacking of tower foundations with thermosyphons and the artesian sub-permafrost water migration. The effect of the latter was stronger, especially when the artesian water resulted in the development of ground icing. These results and conclusions may provide valuable references for the design and maintain of similar structures in permafrost regions. [ABSTRACT FROM AUTHOR]

Glaciers and glacial lakes in the Bosula Mountain Range need special attention, because their instability may cause disastrous consequences to the downstream settlements and the Sichuan-Tibet Road. The latter is a pivotal traffic line in the Southeast Tibetan Plateau. In order to investigate the state of glaciers and glacial lakes in the Bosula Mountain Range, we estimated the changes in glacier/glacial lake boundaries, glacier surface elevation, and glacier flow velocity between 2000 and 2021 based on multisource remote sensing data. Our results showed that, from the period 2000–2013 to the period 2013–2021, the average shrinking rate of glacier area increased from 0.99 km2/a to 1.74 km2/a, and the average expanding rate of glacial lake area increased from 0.04 km2/a to 0.06 km2/a. From the period 1990–2011 to the period 2015–2019, the average thinning rate of glaciers increased from 0.83 m/a to 1.58 m/a. These results indicate the Bosula Mountain Range is one of the fastest melting glacierized regions in the High Mountain Asia, and the factors that account for this may include quick temperature rise, abundant summer rainfall, and thin debris cover. In spite of strong ice melting, the observed changes in glacier boundaries, surface elevation, and flow velocity show no sign of surge activity, and the frequency of glacier lake outburst has not increased since 1989. Currently, three proglacial lakes that expanded quickly during 2000–2021 are now prominent hazards. They are directly threatened by accidental ice calving and ice avalanche, and their outburst could cause considerable damage to the downstream settlements and the Sichuan-Tibet Road. [ABSTRACT FROM AUTHOR]

Interactions among late Cenozoic global cooling, tectonic activity and regional climate evolution of the northeastern Tibetan Plateau remain elusive. To further understand the relative contributions of global climate change and tectonism, we conducted a comprehensive study of heavy minerals, rock magnetism, and branched glycerol dialkyl glycerol tetraethers (brGDGTs) in late Cenozoic sediments of the Laojunmiao section (ca. 12.7 Ma to 5 Ma) in the Jiuxi Basin. Our results reveal a notable increase in magnetic susceptibility (χ) and saturation isothermal remanent magnetization (SIRM) at 8.5 Ma, aligning with an accelerated decrease in temperature captured by brGDGTs. Combined with heavy mineral analysis, we propose that the profound changes in magnetic parameters and temperature are closely linked to the intensive uplift of the northern Qilian Shan since 8.5 Ma. Furthermore, this ongoing uplift has occurred simultaneously with persistent aridification in the Jiuxi Basin and its adjacent regions. The Qilian Shan might have reached a threshold elevation and began to act as a moisture barrier to northwestward moisture since 8.5 Ma. By synthesizing hydroclimate evolution records from the northeastern Tibetan Plateau, we deduce that changing topography resulting from tectonic uplift may have exerted a significant influence on regulating the moisture distribution in this region during the mid- to late Miocene. • Temperature reconstructed using brGDGTs declined at an accelerated rate at 8.5 Ma • Magnetic enhancement of lacustrine-delta fan sediments occurred at 8.5 Ma. • The northern Qilian Shan was uplifted at 8.5 Ma, simultaneous with regional drying. • Tectonic uplift was the primary driver of this climate transition at 8.5 Ma. [ABSTRACT FROM AUTHOR]

The TanDEM-X DEM is a valuable data source for estimating glacier mass balance. However, the accuracy of TanDEM-X elevation over glaciers can be affected by microwave penetration and phase decorrelation. To investigate the bias of TanDEM-X DEMs of glaciers on the Tibetan Plateau, these DEMs were subtracted from SPOT-6 DEMs obtained around the same time at two study sites. The average bias over the studied glacier areas in West Kunlun (175.0 km2) was 2.106 ± 0.012 m in April 2014, and it was 1.523 ± 0.011 m in Geladandong (228.8 km2) in October 2013. By combining backscatter coefficients and interferometric coherence maps, we found surface decorrelation and baseline decorrelation can cause obvious bias in addition to microwave penetration. If the optical/laser data and winter TanDEM-X data were used as new and historic elevation sources for mass-balance measurements over an arbitrary observation period of 10 years, the glacier mass loss rates in West Kunlun and Geladandong would be potentially underestimated by 0.218 ± 0.016 and 0.158 ± 0.011 m w.e. a−1, respectively. The impact is therefore significant, and users should carefully treat the bias of TanDEM-X DEMs when retrieving a geodetic glacier mass balance. [ABSTRACT FROM AUTHOR]

Many of the unprotected tower footings along the Qinghai–Tibet Power Transmission Line (QTPTL) were buried by open excavation in thaw-unstable permafrost. Their thermal stability was of concern due to climate warming and human-induced thermal disturbances. On the basis of ground temperature measurements during the last three years, the tower foundation soils were stable during the studied period from 2011 to 2013 in spite of appreciable impacts of engineering construction of tower footings on the thermal regimes of the surrounding and underlying permafrost. The thaw front near a typical concrete footing was 0.67 m to 1.74 m deeper than that at adjacent natural, undisturbed sites in summer, and ground temperatures near such footings were lower than those at nearby natural sites in winter. This thermal enhancement (TE) effect of concrete footings lengthened the duration of freezing and thawing of the surrounding soils, deepened the permafrost table near the tower foundations, and subsequently adversely affected the thermal stability of the tower foundation soils. Numerical modeling was used for simulating the long-term thermal stability of the foundations soils and impacts of the TE effect, ice contents, mean annual ground temperature (MAGT), embedding depths of tower footings, and climate warming on ground thermal regime. Under the scenario of climate warming by 2.6 °C within the next 50 years, the active layer thickens and permafrost temperatures at depths rise progressively with time. The ice contents and MAGT of permafrost remarkably would affect the degradation rate of permafrost around the footings. The TE effect of the footings thickened the active layer by at least 1 m relative to natural sites 20-m away from the footings. The thaw settlement of tower foundation soils could present higher risk for the unprotected footings with a shallow (< 5.8 m) embedment in warm and ice-rich permafrost soils under a warming climate. In the end, some recommendations and suggestions were made. [ABSTRACT FROM AUTHOR]

The Qinghai–Tibet Power Transmission Line (QTPTL), crossing about 550 km permafrost regions, was constructed between July 2010 and October 2011. Based on 4 years of field observations since the construction, thermal and displacement performances of tower foundations in permafrost regions along the QTPTL were analyzed. The observational results from 10 monitored towers showed that the re-freezing process of foundation soils of deeply embedded pile foundations largely took 2 to 3 months. While for shallowly-buried footings, it took one to two cold seasons due to the significant thermal impacts of the foundation construction. After the re-freezing, the thermal regimes of foundation soils mainly determined by the thermosyphon cooling and enhanced heat transfer process of the concrete foundation. With the thermosyphon cooling, foundation soils around and under tower foundations cooled significantly and cold bulbs developed under tower foundations. But for shallowly-buried footings without thermosyphon, the maximum thaw near the footings could be as much as 2.0 m greater than that in the natural ground due to enhanced heat transfer process of the concrete footings. Foundation displacement observations at 130 monitored towers showed that the majority of tower foundations suffered subsidence rather than heave during the observational period. The subsidence was considerable in warm, ice-rich permafrost regions. After the tower assembling and line hanging, the subsidence rate of most of tower foundations decreased substantially. Up to the present, all 130 monitored tower foundations had the accumulative subsidence within an allowable range. Experiences and lessons learned from the QTPTL will be of value for future similar constructions in permafrost regions. [ABSTRACT FROM AUTHOR]

The aridity history of monsoon-dominated areas has previously been traced by high-resolution studies of the well-known loess and red clay sequences on the Chinese Loess Plateau. However, the aridity process further west in China and the differences from the monsoon regime are unclear because no continuous aeolian sequences have been found in those areas. Here we describe and interpret an 88.4-m-thick Neogene aeolian sequence containing 40 visually-defined, brownish-red clay and gray caliche nodule layers in the eastern Xorhol Basin, northeast of the Tibetan Plateau. Magnetostratigraphic results show that the sequence was deposited between ~ 13 and 2.6 Ma. The sequence can be divided into two parts with different climate conditions according to magnetic susceptibility (MS): the lower part (13–11.5 Ma) indicates a more changeable climate with higher MS values (average 15 × 10 − 8 m 3 kg − 1 ) dominated by magnetite; the upper part (10.3–2.6 Ma) reflects a drier climate with lower, stable MS values (average 9.5 × 10 − 8 m 3 kg −1 ) mainly arising from hematite. Our results indicate that the intensified aridity of the Asian interior started between 11.5 Ma and 10.3 Ma, when MS decreased significantly due to outward growth of the Tibetan Plateau at around 12 Ma, together with ongoing global cooling and regression of the Neotethys Ocean during the Cenozoic. [ABSTRACT FROM AUTHOR]

Abstract: The changes in the thickness of permafrost and the distribution characteristics of ground ice are of great importance for engineering and environmental issue research in permafrost regions. This study was conducted in the permafrost observation field in Qumahe in the east of the Tibetan Plateau by using electrical resistivity tomography (ERT) for investigating the depth of permafrost base and the structure of permafrost. The results demonstrated that the ERT can detect the depth of permafrost base, identify the characteristics of ground ice and the variation of permafrost types in Qumahe. Also, the effects and accuracy of ERT were evaluated combining the information provided by borehole and ground temperature monitoring. The comprehensive analysis of the data shows that the distribution of permafrost and ground ice in this area is strongly influenced by geographical, topographical and other local factors. The depth of the permafrost base within the observation field differs by 30m. Aspect, surface water and vegetation conditions have the most significant influence on the thickness of permafrost. A seasonal stream in the low-lying area of the observation field also brings strong influence to permafrost thermal disturbance and thickness. Meanwhile, different geomorphic unit and surface conditions significantly influence the development of ground ice. To be specific, the massive ground ice is mainly developed in the flat swamping wetland, especially the low-lying wetland. In terms of depth, the massive ground ice is mainly developed within 5 to 10m below the permafrost table. [Copyright &y& Elsevier]