---
title: "Geological division of Terai and Siwalik zone"
subject: "Engineering Geology I"
chapter: 7
key: "semester_3/engineering_geology_i:geological-division-of-terai-and"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/geological-division-of-terai-and
site: BCT Engineering
---

# Geological division of Terai and Siwalik zone

Engineering Geology I · Chapter 7: Geology of Nepal

- Asked in: 2072 Chaitra, 3 marks
- Video: [Structure and Physiography - Geological division of India | Class 11 Geography | Chapter 2 | NCERT](https://www.youtube.com/watch?v=9lPrmOG8WEw) — Smart Tute
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/geological-division-of-terai-and
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-7

## Question

Explain the geological division of the Terai and Siwalik zones.

## Short answer

Terai: Bhabar (coarse boulder/gravel belt) and Terai proper (sand, silt, clay with high water table). Siwalik: Lower (Miocene fine sandstone, mudstone), Middle (thick salt-and-pepper sandstone), Upper (boulder conglomerate) with Dun valleys filled with alluvium. Siwalik rocks thrust over Terai along MFT.

## Answer

#### Terai zone
A flat Quaternary alluvial plain (60-300 m), divided into:
- **Bhabar:** a coarse boulder and gravel belt at the foot of the Siwalik.
- **Terai proper:** sand, silt and clay with a high water table.

#### Siwalik zone
Hills of 300-1500 m (up to 2000 m) between the MFT and MBT, divided into:

| Division | Age | Lithology |
|---|---|---|
| Lower Siwalik | Miocene | Fine sandstone, mudstone, siltstone, variegated |
| Middle Siwalik | Mio-Pliocene | Thick, coarse salt-and-pepper sandstone with mudstone |
| Upper Siwalik | Plio-Pleistocene | Boulder conglomerate, sandstone and clay |

The Siwalik zone also has **Dun valleys** (e.g. Chitwan and Dang) filled with alluvium. The Terai deposits are the youngest; the older Siwalik rocks are thrust over the Terai along the MFT.

## Check yourself

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

1. What distinguishes the Bhabar from the Terai proper?
   A. Bhabar is coarse boulder and gravel at the Siwalik foot; Terai proper is sand, silt and clay with a high water table
   B. Bhabar is clay; Terai proper is gravel
   C. Both are bedrock
   D. Bhabar lies north of the Siwalik
   Answer: A. Bhabar is the coarse belt at the foot of the Siwalik; the Terai proper is finer with a high water table. (Key point: Bhabar and Terai proper)

2. Which Siwalik division is Mio-Pliocene sandstone?
   A. Lower
   B. Middle
   C. Upper
   D. Terai
   Answer: B. Middle Siwalik is Mio-Pliocene thick coarse sandstone; Lower is Miocene and Upper is Plio-Pleistocene. (Key point: Siwalik divisions and ages)

3. What is the age and structural relation of Terai and Siwalik?
   A. Terai is older and thrust over Siwalik
   B. Terai is the youngest, and the older Siwalik is thrust over it at the MFT
   C. Both are same age with no fault
   D. Siwalik is Quaternary alluvium
   Answer: B. The Terai is youngest; Siwalik is older and thrust over it along the MFT. (Key point: Relation of Terai and Siwalik)

## Related in Engineering Geology I

- [Siwalik zone in detail](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Asiwalik-zone-in-detail) — Engineering Geology I, chapter 7, asked 2×
- [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×
- [Physiographic division; Siwalik and Higher Himalaya](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aphysiographic-division-siwalik-and-higher) — 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
- [Soil and rock types of Himalayan zones](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Asoil-and-rock-types-of) — Engineering Geology I, chapter 7

## 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×
- [Problems of Siwalik and Higher Himalaya](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asiwalik-higher-himalaya-problems) — Engineering Geology II, chapter 2, asked 2×
- [Problems of Lesser Himalaya and Terai](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Alesser-himalaya-terai-problems) — Engineering Geology II, chapter 2, asked 5×
- [Oxidation pond for Terai town, 12,000](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Aoxidation-pond-terai-12000) — Sanitary Engineering, chapter 7