Creating a rock glacier inventory of the northern Nyainqêntanglha range (Tibetan Plateau) based on InSAR time-series analysis

The northern Nyainq&#234;ntanglha range on the southern Tibetan Plateau reaches an elevation of 7150 m and is mainly characterized by a periglacial landscape. A monsoonal climate, with a wet period during the summers and arid conditions during the rest of the year governs the landscape processes. Large parts of the mountain range are considered permafrost due to the high altitude and the associated low air temperature. Rock glaciers, which are bodies of ice-rich debris, are a typical landform. The recently published IPCC report on the cryospheres of high mountain areas highlights the sensitivity of rock glaciers to climate warming and emphasizes the importance of their study.We study the distribution of rock glaciers of the northern Nyainq&#234;ntanglha range and our aim is to produce an inventory of active rock glaciers based on their surface motion characteristics. The lack of higher order vegetation and the relatively low winter precipitation enable us to employ Interferometric Synthetic Aperture Radar (InSAR) time-series techniques to study both seasonal and multi-annual surface displacement patterns. InSAR is a powerful microwave remote sensing technique, which makes it possible to study displacement from a few millimeters to centimeters and decimeters per year. It is thus suitable to detect sliding and creeping processes related to periglacial landscapes and permafrost conditions on the Earth&#8217;s surface. We use both Sentinel-1 (2015-2019) and TerraSAR-X ScanSAR data (2017-2019) for our analysis.In this study we differentiate rock glaciers from the surrounding seasonally sliding slopes by their significantly higher surface creeping rates with mean velocities of 5&#8211;20 cm yr-1. We also observe that the velocity of rock glaciers is less dependent on the summer monsoon, which allows us to further differentiate between rock glaciers and other landforms. This method could potentially be used to create rock glacier inventories in other remote regions, as long as the snow cover in winter is thin enough to allow continuous InSAR time-series analysis. These rock glacier inventories are necessary to assess the effects of climate change on vulnerable high mountain regions.

Download Full-text

InSAR time series analysis of seasonal surface displacement dynamics on the Tibetan Plateau

10.5194/tc-2019-262 ◽

2019 ◽

Cited By ~ 1

Author(s):

Eike Reinosch ◽

Johannes Buckel ◽

Jie Dong ◽

Markus Gerke ◽

Jussi Baade ◽

...

Keyword(s):

Time Series ◽

Tibetan Plateau ◽

Time Series Analysis ◽

Surface Displacement ◽

The Tibetan Plateau ◽

Permafrost Degradation ◽

Nam Co ◽

Freeze Thaw ◽

Series Analysis ◽

Spatial Coverage

Abstract. Climate change and the associated rise in air temperature have affected the Tibetan Plateau to a significantly stronger degree than the global average over the past decades. This has caused deglaciation, permafrost degradation and increased precipitation, heavily changing the water balance of this region. Surface displacement processes are likely to change as the ground continues to warm up and as such it is vital to understand both seasonal and interannual processes dynamics. The Nam Co area is well suited to studying these processes via Interferometric Synthetic Aperture Radar (InSAR) time series analysis, due to its lack of higher vegetation and relatively thin snow cover. The short revisit time of the Sentinel-1 system further reduces the risk of temporal decorrelation, making it possible to produce surface displacement models with good spatial coverage. We created three different surface displacement models to study freeze-thaw processes, seasonal sliding and linear creep. Most slopes of the area are unstable, with velocities of 8 to 17 mm yr−1, and some landforms reach velocities of up to 18 cm yr−1. The monsoonal climate accelerates those movements during the summer months through high temperatures and heavy rainfall. The fastest moving landforms, some of which have been identified as rock glaciers, do not follow this seasonal pattern of accelerated velocity in summer, instead they follow a linear sliding pattern. It is unclear if this linearity is connected to the ice content in those landforms. Flat regions at Nam Co are mostly stable on a multiannual scale but some experience subsidence, which could be caused by permafrost degradation. We observe a very clear seasonal freeze-thaw cycle in the valleys, where thawing and subsequent freezing of the active layer cause a vertical oscillation of the ground of up to a few centimeters, especially near streams and other water bodies.

Download Full-text

Inventory of active rock glaciers in the western Nyainqêntanglha Range, Tibetan Plateau

10.5194/egusphere-egu21-2461 ◽

2021 ◽

Author(s):

Eike Reinosch ◽

Markus Gerke ◽

Björn Riedel ◽

Antje Schwalb ◽

Qinghua Ye ◽

...

Keyword(s):

Tibetan Plateau ◽

High Reliability ◽

Surface Velocity ◽

Windward Side ◽

Mountain Range ◽

The Tibetan Plateau ◽

Automated Classification ◽

Rock Glacier ◽

North West ◽

Rock Glaciers

The western Nyainq&#234;ntanglha Range on the Tibetan Plateau (TP) reaches an elevation of 7162 m and is characterized by an extensive periglacial environment. Here, we present the first rock glacier inventory of the central TP containing 1433 rock glaciers over an area of 4622 km&#178;. The rock glaciers are identified based on their surface velocity. The surface velocity is derived from Sentinel-1 satellite data of 2016 to 2019 via InSAR time series analysis. 16.4 % of the inventoried rock glaciers are classified as active with a surface velocity above 10 cmyr-1 and 80.0 % are classified as transitional with 1 to 10 cmyr-1. The western Nyainq&#234;ntanglha Range forms a climate divide between the dry continental climate brought by the Westerlies from the north-west and the Indian Summer Monsoon to the south. 89.7 % of all active rock glaciers and 74 % of the free ice glacial area are located on the southern side. The higher moisture availability on the southern (windward) side of the mountain range is likely the cause of a higher rock glacier occurrence and the greater activity.Manually identifying and outlining rock glaciers is time consuming and subjective. To ensure a high reliability and comparability of our inventory, we therefore combined a manual approach with an automated classification. Three analysts worked in tandem to generate the manual outlines according to the guidelines of the IPA action group on &#8216;Rock glacier inventories and kinematics&#8217;. A subset of these outlines acted as training areas for a pixel-based maximum likelihood classification. Both the manual and the automated classification were performed based on DEM parameters (elevation, slope etc.), optical datasets (Sentinel-2 and NDVI) and surface velocity (generated with InSAR). 87.8 % of all manually outlined rock glaciers were identified successfully at a true positive rate of 69.5 %. 18 additional rock glaciers were added to the inventory based on the automated classification. This combined approach is therefore beneficial to generate a complete inventory. The automated classification can, however, not replace the expertise of an analyst as it greatly overestimates the actual rock glacier area.

Download Full-text

Dynamic Changes of NDVI in the Growing Season of the Tibetan Plateau During the Past 17 Years and Its Response to Climate Change

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph16183452 ◽

2019 ◽

Vol 16 (18) ◽

pp. 3452 ◽

Cited By ~ 6

Author(s):

Xianglin Huang ◽

Tingbin Zhang ◽

Guihua Yi ◽

Dong He ◽

Xiaobing Zhou ◽

...

Keyword(s):

Climate Change ◽

Time Series ◽

Tibetan Plateau ◽

Time Series Analysis ◽

Environmental Changes ◽

Climatic Factors ◽

Growing Season ◽

Lag Time ◽

The Tibetan Plateau ◽

Series Analysis

The fragile alpine vegetation in the Tibetan Plateau (TP) is very sensitive to environmental changes, making TP one of the hotspots for studying the response of vegetation to climate change. Existing studies lack detailed description of the response of vegetation to different climatic factors using the method of multiple nested time series analysis and the method of grey correlation analysis. In this paper, based on the Normalized Difference Vegetation Index (NDVI) of TP in the growing season calculated from the MOD09A1 data product of Moderate-resolution Imaging Spectroradiometer (MODIS), the method of multiple nested time series analysis is adopted to study the variation trends of NDVI in recent 17 years, and the lag time of NDVI to climate change is analyzed using the method of Grey Relational Analysis (GRA). Finally, the characteristics of temporal and spatial differences of NDVI to different climate factors are summarized. The results indicate that: (1) the spatial distribution of NDVI values in the growing season shows a trend of decreasing from east to west, and from north to south, with a change rate of −0.13/10° E and −0.30/10° N, respectively. (2) From 2001 to 2017, the NDVI in the TP shows a slight trend of increase, with a growth rate of 0.01/10a. (3) The lag time of NDVI to air temperature is not obvious, while the NDVI response lags behind cumulative precipitation by zero to one month, relative humidity by two months, and sunshine duration by three months. (4) The effects of different climatic factors on NDVI are significantly different with the increase of the study period.

Download Full-text

Pushing the limits of electrical resistivity tomography measurements on a rock glacier at 5500 m a.s.l. on the Tibetan Plateau: Successes and Challenges

10.5194/egusphere-egu2020-8159 ◽

2020 ◽

Author(s):

Nora Krebs ◽

Anne Voigtländer ◽

Matthias Bücker ◽

Andreas Hördt ◽

Ruben Schroeckh ◽

...

Keyword(s):

Electrical Resistivity ◽

Tibetan Plateau ◽

Internal Structure ◽

Electrical Resistivity Tomography ◽

High Resistivity ◽

Mountain Range ◽

The Tibetan Plateau ◽

Rock Glacier ◽

Resistivity Tomography ◽

Rock Glaciers

Geophysical methods provide a powerful tool to understand the internal structure of active rock glaciers. We applied Electrical Resistivity Tomography (ERT) to a rock glacier at an elevation of 5500 m a.s.l. in the semi-arid Nyainq&#234;ntanglha mountain range on the Tibetan plateau, China. &#160;The investigations comprised three transects across the rock glacier and its catchment, each spanning over a distance of 296 m up to 396 m, equipped with 75 up to 100 electrodes respectively. Our measurements were successful in revealing internal structures of the rock glacier, but were also accompanied by challenges.We successfully detected first-order permafrost structures, such as a shallow about 4 m thick active layer of low electrical resistivity values that was underlain by potentially ice rich zones of high resistivity. Further high-resistivity zones were found and interpreted as dense bed rock of adjacent slopes that undergird the loose rock glacier debris.Challenges, we faced in the application of ERT, were mainly posed by the morphology and internal structure of the rock glacier itself. Coarse debris created a rough surface that prevented a uniform setup with accurate 4 m spacing. The presence of loosely nested blocks of pebble size up to boulders with large interspaces resulted in high contact resistances. The consequent low injection current densities and possible noisy voltage readings downgraded part of the data, causing low data density and resolution. Coupling was partly improved by attaching salt-watered sponges to the electrodes and adding more conductive fine-grained materials to the electrodes. The detected high resistivity ice layer impeded deep penetration of electrical currents, which caused that the lower limit of the permanently frozen zone could not be defined.Despite these challenges, the captured ERT profiles are an indispensable contribution to the sparse field data on the internal structure of rock glaciers on the Tibetan plateau. Our results contribute to a better understanding of the prospective evolution of rock glaciers in dry, high mountain ranges under a changing climate.

Download Full-text

Analysis of the hydrological and tectonic deformation in the eastern part of the Tibetan plateau, from FLATSIM automated time series analysis of Sentinel-1 InSAR

10.5194/egusphere-egu21-12866 ◽

2021 ◽

Author(s):

Laëtitia Lemrabet ◽

Marie-Pierre Doin ◽

Cécile Lasserre ◽

Anne Replumaz ◽

Marianne Métois ◽

...

Keyword(s):

Time Series ◽

Tibetan Plateau ◽

Time Series Analysis ◽

Surface Deformation ◽

Tectonic Deformation ◽

The Tibetan Plateau ◽

Continental Scale ◽

Series Analysis ◽

Fault Systems ◽

Seasonal Signal

The global and systematic coverage of Sentinel-1 radar images allows characterizing, by radar interferometry (InSAR), surface deformation on a continental scale.Our study focuses on the eastern part of the Tibetan plateau, where a combination of major strike-slip and thrust fault systems accommodates part of the deformation related to the collision between the Indian and Eurasian plates.We use an automated Sentinel-1 InSAR processing chain based on the NSBAS approach (Doin et al., 2011, Grandin, 2015) to measure the interseismic deformation across these fault systems. Processing is made on the CNES high-performance computer center in Toulouse in the FLATSIM project framework (ForM@Ter LArge-scale multi-Temporal Sentinel-1 Interferometric Measurement, Durand et al., 2019). We perform a time series analysis of the 2014-2020 Sentinel-1 InSAR data set, for 1200 km-long tracks (acquired along 7 ascending and 7 descending orbits), covering a 1&#160;700&#160;000 km2 area, with a 160 m spatial resolution. From about 130 acquisitions per track, we perform about 600 interferograms, with short, three months, and one-year temporal baselines. After inversion, we obtain time series of line-of-sight (LOS) delay maps, including residual atmospheric delay and network misclosure measurements. The time series are fitted by a seasonal signal plus a velocity trend. The velocity field on overlap areas agrees within less than 1~mm/yr.Finally, we decompose the LOS velocity maps into a vertical and a horizontal contribution.InSAR velocity maps highlight surface deformation patterns mostly localized on known major faults, short-wavelength patterns attributed to slope instabilities phenomena, and hydrological signals.The seasonal signal combines residual atmospheric phase delays and widespread hydrological phenomena in sedimentary basins, which we interpret in parallel with the regional geological map.&#160; Masking areas affected by dominant gravitational slope or hydrological deformation allows to better focus on tectonic deformation.We finally discuss slip partitioning on the various fault systems from the velocity maps and 2D profiles&#8217; analysis.

Download Full-text