Scientists and students from the Wadia Institute of Himalayan Geology (WIHG), an autonomous institute under the Department of Science & Technology, Government of India, have embarked on an important study in the Zanskar catchment area. The purpose of this comprehensive study is to better understand the landform evolution in transitional climatic zones. This was achieved using a combination of morphostratigraphy, Optically Stimulated Luminescence (OSL) dating, and provenance analysis of landforms like valley fill terraces and alluvial fans.
About Zanskar River
Zanskar River, one of the largest tributaries of the upper Indus catchment, drains transversely northward from the Higher Himalaya. The river flows through the arid, highly folded, and thrusted Zanskar ranges in Ladakh, a region dominated by the Indian summer monsoon. Two notable streams, the Doda and the Tsarap Lingti Chu, converge at Padam to form the Zanskar, which in turn joins the Indus at Nimu.
Importance of Landforms in the Study
The fill terrace landform, created when a stream or river starts to incise into the material it deposited in the valley, played an instrumental role in the study. Additionally, alluvial fans – triangle-shaped deposits of gravel, sand, and smaller sediment particles – were also examined as part of the research effort.
The Methodologies Employed for Study
The investigation utilized Morphostratigraphy, which is the organization of rock or sediment strata into units based on their surface morphology. It also employed Optically-Stimulated Luminescence, a late Quaternary dating technique used to date the last time a quartz sediment was exposed to light. Provenance Analysis, the determination of the source region (provenance) of a sediment sample, was also a key component in understanding the time of deposition of the sand and climatic conditions during the formation of the sediments.
Key Findings of the Study
Upon conclusion of the study, it was revealed that the wide valley of Padam in the upper Zanskar is a hotspot of sediment buffering, having stored a substantial amount of sediments. More significantly, these sediments heavily contributed to erosion, primarily from the Higher Himalayan crystalline that lies in the headwater region of Zanskar. The primary factor for this erosion was identified as deglaciation and Indian Summer Monsoon derived precipitation in the headwaters.
The Significance of the Study
The comprehensive study led by the WIHG not only provided insights into river-borne erosion and sedimentation but also helped understand the evolution of large riverine plains, terraces, and deltas. Furthermore, it laid bare a 35 thousand-year history of river erosion and identified hotspots of erosion and wide valleys that act as buffer zones. The study also revealed how rivers in the drier Ladakh Himalaya operated on longer time scales and responded to varying climates.
Understanding Water and Sediment Routing
The high altitude desert of Ladakh Himalaya, sandwiched between Greater Himalayan ranges and Karakoram Ranges, is traversed by the Indus and its tributaries. The understanding of water and sediment routing became crucial during infrastructure development and other works in the river catchment area. The study’s findings will help to ensure that future development takes into account the area’s unique geography.
Source: PIB