Model Answer
0 min readIntroduction
The Siwalik Range, also known as the Outer Himalayas, forms the southernmost and youngest fold of the Himalayan mountain system. Extending for over 2,400 km from the Indus River in the northwest to the Brahmaputra River in the east, it spans across parts of India, Nepal, Bhutan, and Pakistan. These ranges are primarily composed of unconsolidated sediments deposited by rivers originating from the Himalayas, representing the foreland basin formed due to the collision of the Indian and Eurasian plates. Understanding the Siwaliks is crucial as they influence the climate, drainage, and resource availability of the Indo-Gangetic Plain.
Topographical Characteristics
The Siwalik Range exhibits distinct topographical features:
- Elevation and Extent: The elevation generally ranges from 600 to 1200 meters, increasing towards the east. The range is not continuous; it’s broken into several sub-ranges, often referred to as ‘duns’ (longitudinal valleys) like the Dehradun and Paonta Valley.
- Drainage: The range is dissected by numerous seasonal streams known as ‘khads’. These khads originate in the higher Himalayas and carry substantial sediment load, contributing to the alluvial fans and plains below. Major rivers like the Indus, Ganga, and Brahmaputra have their headwaters in or near the Siwaliks.
- Alluvial Fans and Plains: The southern slopes of the Siwaliks are characterized by the deposition of alluvial fans formed by the debris carried down by the rivers. These fans gradually merge into the vast Indo-Gangetic Plain.
- Forest Cover: The Siwalik hills are covered by dense forests, primarily deciduous and subtropical, providing habitat for diverse flora and fauna.
Structural Characteristics
The structural characteristics of the Siwalik Range are closely linked to its geological formation:
- Geological Composition: The Siwaliks are primarily composed of unconsolidated sediments – gravel, sand, silt, and clay – deposited over millions of years. These sediments are derived from the erosion of the higher Himalayas.
- Folding and Faulting: The range exhibits characteristic anticlines and synclines, indicating the folding of sedimentary layers due to compressional forces. Faulting is also prevalent, resulting in the formation of valleys and terraces. The Main Boundary Thrust (MBT) and Main Central Thrust (MCT) are major geological features associated with the Siwalik’s structure.
- Thrust Faults: The Siwaliks are formed by the thrusting of younger sedimentary rocks over older ones. This process is a direct result of the ongoing collision between the Indian and Eurasian plates.
- Youngest Formation: Geologically, the Siwaliks are the youngest part of the Himalayan system, formed during the Pleistocene and Holocene epochs.
The Siwalik sediments are categorized into three main formations: Lower Siwaliks, Middle Siwaliks, and Upper Siwaliks, each representing different stages of deposition and geological activity.
| Formation | Characteristics | Age |
|---|---|---|
| Lower Siwaliks | Coarse conglomerate, sandstone; rich in fossils of mammals. | Miocene (23-5.3 million years ago) |
| Middle Siwaliks | Alternating sandstone and shale; less fossiliferous. | Pliocene (5.3-2.6 million years ago) |
| Upper Siwaliks | Unconsolidated gravel, sand, silt, and clay; abundant fossils. | Pleistocene-Holocene (2.6 million years ago – present) |
Conclusion
In conclusion, the Siwalik Range is a geologically young and structurally complex mountain system characterized by its low elevation, dissected topography, and unconsolidated sedimentary composition. Its formation is directly linked to the ongoing tectonic activity of the Himalayas, and it plays a vital role in shaping the landscape and influencing the environment of the Indo-Gangetic Plain. Understanding its characteristics is crucial for hazard assessment, resource management, and sustainable development in the region.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.