The Sivalik Hills or Range -- also spelled Shiwalik, Shivalik or Siwalik and sometimes called Churia or Chure Hills or Outer Himalaya -- are the southernmost and geologically youngest east-west mountain chain of the Himalayan System. The Sivaliks crest at 600 to 1,200 meters and have many sub-ranges. They extend 1,600 km from the Teesta River in Sikkim, westward through Nepal and Uttarakhand, continuing into Kashmir and Northern Pakistan. They are cut through at wide intervals by large rivers flowing south from the Himalaya. Smaller rivers without sources in the high Himalaya are more likely to detour around sub-ranges. Southern slopes have networks of small rills and channels, giving rise to ephemeral streams during the the monsoon and into the post-monsoon season until groundwater supplies are depleted.
The Sivalik Hills are chiefly composed of sandstone and conglomerate rock formations which are the solidified detritus of the great range in their rear, but often poorly consolidated. They are bounded on the south by a fault system called the Main Frontal Thrust, with steeper slopes on that side. Below this, the coarse alluvial Bhabhar zone makes the transition to the nearly level plains. Rainfall, especially during the summer monsoon, percolates into the bhabar, then is forced to the surface by finer alluvial layers below it in a zone of springs and marshes along the northern edge of the Terai or plains. This wet zone was heavily malarial before DDT was used to suppress mosquitoes. It was left forested by official decree by Nepal's Rana rulers as a defensive perimeter called Char Kose Jhadi (four kos forest, one kos equalling about three km or two miles). Upslope, the permeable geology together with temperatures routinely exceeding 40 celsius throughout April and May only supports a low, sparse, drought-tolerant scrub forest.
Sivapithecus (a kind of ape, formerly known as Ramapithecus) is among many fossil finds in the Sivalik region.
North of the Sivalik belt a higher range, the 1,500-3,000 meter Mahabharat Lekh (Range) also known as the Lesser Himalaya rises steeply along fault lines. In many places the two ranges are adjacent but in other places structural valleys 10-20 km wide separate them. These valleys are called Duns or Doons in India (as in the Doon Valley) which includes Dehradun, as also Patli Dun and Kothri Dun, both in Corbett National Park in Uttarakhand, and also Pinjore Dun in Himachal Pradesh). In Nepal, these valleys are called Inner Terai and include Chitwan, Dang-Deukhuri and Surkhet.
Low population densities in the Sivaliks and along the steep southern slopes of the Mahabharat Range, plus virulent malaria in the damp forests on their fringes create a cultural, linguistic and political buffer zone between dense populations on plains to the south and in "hills" beyond the Mahabharat escarpment, isolating the two populations from each other and enabling different evolutionary paths with respect to language, race and culture.
In a few places local tribes such as Van Gujjars, or Gujjars have developed quasi-pastoral livestock-dependent or shifting agriculture strategies that support some population buildup, with significant environmental costs from deforestation and denudation.
See also
References
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Wikisource has the text of the 1911 Encyclopædia Britannica article Siwalik Hills. |
- This article incorporates text from the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.
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