---
title: "Siwalik zone in detail"
subject: "Engineering Geology I"
chapter: 7
key: "semester_3/engineering_geology_i:siwalik-zone-in-detail"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/siwalik-zone-in-detail
site: BCT Engineering
---

# Siwalik zone in detail

Engineering Geology I · Chapter 7: Geology of Nepal

- Asked in: 2078 Bhadra, 2 marks; 2078 Kartik, 2 marks (asked 2 times)
- Video: [The Shivalik Range: Altitude, Geology & Doon Valley Explained | Geography for UPSC](https://www.youtube.com/watch?v=au9W0GgBnyY) — UPSC EduRev
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/siwalik-zone-in-detail
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-7

## Question

Describe the Siwalik zone in detail (lithology and structure).

## Short answer

The Siwalik zone consists of Lower (sandstone-mudstone alternations), Middle (massive salt-and-pepper sandstone), and Upper (boulder conglomerate) molasse of Miocene-Pleistocene age. Strata are folded into anticlines and synclines striking WNW-ESE, often steeply dipping near the MBT, and cut by thrust faults.

## Answer

**Siwalik (Churiya) zone.** The southernmost hill belt of Nepal, 10-50 km wide, altitude about 300-1500 m (up to 2000 m), lying between the MFT and MBT. Rocks are Miocene to Pleistocene molasse sediments, eroded from the rising Himalaya, mostly weak and poorly consolidated.

**Lithology (three divisions)**
- **Lower Siwalik:** alternation of fine-grained sandstone, mudstone and siltstone; red, purple and grey colours (Miocene).
- **Middle Siwalik:** thick, massive, coarse "salt and pepper" sandstone with some mudstone and conglomerate lenses (Mio-Pliocene).
- **Upper Siwalik:** poorly cemented boulder-pebble conglomerate with sandstone and clay (Plio-Pleistocene).

**Structure:** the strata are folded into anticlines and synclines with strike roughly parallel to the Himalaya (WNW-ESE), often steeply dipping or overturned in the north near the MBT, and cut by thrust faults such as the MBT and MFT.

**Engineering problems:** soft, erodible rocks, landslides, gullying, debris flow and flash floods. The sandstones are mostly too weak for good aggregate; the boulders and gravels of the Upper Siwalik conglomerate and of the river beds are the usual aggregate sources.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. The Siwalik zone lies between:
   A. MBT and MCT
   B. MCT and STDS
   C. The Terai and sea
   D. MFT and MBT
   Answer: D. It is the southernmost hill belt. (Key point: Boundaries)

2. The Middle Siwalik is mainly:
   A. Thick massive coarse 'salt and pepper' sandstone
   B. Boulder conglomerate
   C. Red mudstone and siltstone
   D. Marble
   Answer: A. Upper is conglomerate; Lower is fine sandstone and mudstone. (Key point: Middle Siwalik)

3. The Upper Siwalik consists of:
   A. Massive coarse sandstone
   B. Poorly cemented boulder-pebble conglomerate with sandstone and clay
   C. Fine mudstone only
   D. Schist
   Answer: B. It is Plio-Pleistocene. (Key point: Upper Siwalik)

4. The Siwalik sandstones are useful as:
   A. Hard bedrock for deep dams only
   B. Source of arsenic
   C. Good aggregate, though the zone has soft erodible rocks
   D. Poor material for any use
   Answer: C. Landslides and gullying are still problems. (Key point: Engineering)

## Related in Engineering Geology I

- [Lesser Himalaya zone in detail](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Alesser-himalaya-zone-in-detail) — Engineering Geology I, chapter 7
- [Lithology of Lesser and Tethys Himalaya; Siwalik difference](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Alithology-of-lesser-and-tethys) — Engineering Geology I, chapter 7
- [Discontinuities; Siwalik and Higher Himalaya lithology](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Adiscontinuities-siwalik-and-higher-himalaya) — Engineering Geology I, chapter 7
- [Geological division of Terai and Siwalik zone](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ageological-division-of-terai-and) — Engineering Geology I, chapter 7
- [Lithology of Higher Himalaya and Tethys zone](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Alithology-of-higher-himalaya-and) — Engineering Geology I, chapter 7, asked 3×
- [Geology of the Terai zone](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ageology-of-the-terai-zone) — Engineering Geology I, chapter 7, asked 2×

## Related in other subjects

- [Engineering geological problems of Siwalik zone](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asiwalik-problems) — Engineering Geology II, chapter 2, asked 4×
- [Three phase system and transition zone](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Athree-phase-transition-zone) — Concrete Technology and Masonry Structure, chapter 2, asked 8×
- [Solid phases in hcp; transition zone](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Ahcp-solids-transition-zone) — Concrete Technology and Masonry Structure, chapter 2