Browsing by Author "Poonam Chahal"

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Debris flow susceptibility assessment of Leh Valley, Ladakh, based on concepts of connectivity, propagation and evidence-based probability
(Springer Science and Business Media B.V., 2023) Choudhurimayum Pankaj Sharma; Anil Kumar; Poonam Chahal; Uma Kant Shukla; Pradeep Srivastava; Manoj K. Jaiswal
The Leh Valley which lies within the Trans Himalayan state of Ladakh, India, is known to be affected almost annually by debris flows ranging from minor to catastrophic scale events. The effect has been getting magnified due to increased urbanization and rapid growth in tourism industry. Though these flows are triggered by intense and abnormal rainfall events the conditioning factor has always been the topography and sediment availability. A lucid acknowledgement of the terrain condition and the degree of vulnerability of such events is required. For this a detail investigation of sediment availability, topographic conditions and their relation with known events becomes crucial. This study utilizes index of connectivity (IC) model to understand the sediment source-sink relationship and farther applied Flow-R model to simulate the probable scenario of events through predefined algorithms. We then use the Weights of evidence (WOE) method to compute the statistical probability of debris flow occurrence. This paper demonstrates the application of these three independent techniques and their implementation in a highly rugged terrain of Ladakh which is a region of frequent debris flows onslaught. The IC and Flow-R models are found to be counter supportive and effective in delineating areas which could be affected by flows that will solely originate in upstream areas where high angle channels directly connected to sediment sources are present. WOE-based model determines the probability of the rare and extensive flows that results from downward integration of other drainage networks in an open fan area. © 2022, The Author(s), under exclusive licence to Springer Nature B.V.
High-resolution climatic (monsoonal) variability reconstructed from a continuous ~2700-year sediment record from Northwest Himalaya (Ladakh)
(SAGE Publications Ltd, 2020) Choudhurimayum Pankaj Sharma; Suman Lata Rawat; Pradeep Srivastava; Narendra K Meena; Rajesh Agnihotri; Anil Kumar; Poonam Chahal; S.K.S. Gahlaud; U.K. Shukla
A chronologically well-constrained sedimentary archive from Upshi (Ladakh) was studied using a multi-proxy approach namely palynology, environmental magnetism, total organic carbon (TOC), total nitrogen (TN), stable isotopes of carbon and nitrogen providing a continuous vegetation, and paleoenvironmental history spanning the last ~2700 years with a temporal resolution of ~43 years. Pollen assemblage shows non-arboreal pollen (NAP) and non-pollen palynomorph (NPP) were dominant around the Upshi from ~2646 to 2431 cal. yr BP, indicating warmer conditions. Arboreal pollen (AP) and NAP gradually increased from 2431 to 1860 cal. yr BP in the study area, under warm and wet conditions, corresponding to the Roman Warm Period (RWP). This phase also witnessed enhanced sediment δ15N and χlf values. From ~1860 to ~1154 cal. yr BP increased Chenopodiaceae/Amaranthaceae and substantial spread of NPP suggest decreased temperature and prevalence of cold-dry climate. This period also records declining trends of χlf, δ15N, δ13Corg, TOC, and TN contents. From ~1154 to 293 cal. yr BP, the vegetation type reversed to mixed conifer and broad-leaved forest with significant increase in herbaceous taxa, rising δ15N, δ13Corg, TOC, and TN suggesting warm and wet conditions in the study area. This period broadly corresponds to the ‘Medieval Warm Period’ (MWP). Among all the proxies employed, depth profiles of TOC and TN (wt%) appear to respond best against external climate forcing showing remarkable correlation(s) with residual Δ14C in atmosphere, indicating dominance of intrinsic solar variability on regional climate/environment. The reconstructed recorded is well connected with established historical events and cultural activities of the Eurasian region. © The Author(s) 2019.
Late Pleistocene-Holocene flood history, flood-sediment provenance and human imprints from the upper Indus River catchment, Ladakh Himalaya
(Geological Society of America, 2022) Choudhurimayum Pankaj Sharma; Poonam Chahal; Anil Kumar; Saurabh Singhal; Y.P. Sundriyal; Alan D. Ziegler; Rajesh Agnihotri; Robert J Wasson; Uma Kant Shukla; Pradeep Srivastava
The Indus River, originating from Mana-sarovar Lake in Tibet, runs along the Indus Tsangpo suture zone in Ladakh which separates the Tethyan Himalaya in the south from the Karakoram zone to the north. Due to the barriers created by the Pir-Panjal ranges and the High Himalaya, Ladakh is located in a rain shadow zone of the Indian summer monsoon (ISM) making it a high-altitude desert. Occasional catastrophic hydrological events are known to endanger lives and properties of people residing there. Evidence of such events in the recent geologic past that are larger in magnitude than modern occurrences is preserved along the channels. Detailed investigation of these archives is imperative to expand our knowledge of extreme floods that rarely occur on the human timescale. Understanding the frequency, distribution, and forcing mechanisms of past extreme floods of this region is crucial to examine whether the causal agents are regional, global, or both on long timescales. We studied the Holocene extreme flood history of the Upper Indus catchment in Ladakh using slackwater deposits (SWDs) preserved along the Indus and Zanskar Rivers. SWDs here are composed of stacks of sand-silt couplets deposited rapidly during large flooding events in areas where a sharp reduction of flow velocity is caused by local geomorphic conditions. Each couplet represents a flood, the age of which is constrained using optically stimulated luminescence for sand and accelerator mass spectrometry and liquid scintillation counter 14C for charcoal specks from hearths. The study suggests occurrence of large floods during phases of strengthened ISM when the monsoon penetrated into arid Ladakh. Comparison with flood records of rivers draining other regions of the Himalaya and those influenced by the East Asian summer monsoon (EASM) indicates asynchronicity with the Western Himalaya that confirms the existing anti-phase relationship of the ISM-EASM that occurred in the Holocene. Detrital zircon provenance analysis indicates that sediment transportation along the Zanskar River is more efficient than the main Indus channel during extreme floods. Post-Last Glacial Maximum human migration, during warm and wet climatic conditions, into the arid upper Indus catchment is revealed from hearths found within the SWDs. © 2022. All Rights Reserved.