--- title: "Geology of Nepal; significance of HFT, MBT, MCT" subject: "Engineering Geology I" chapter: 7 key: "semester_3/engineering_geology_i:geology-of-nepal-significance-of" source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/geology-of-nepal-significance-of site: BCT Engineering --- # Geology of Nepal; significance of HFT, MBT, MCT Engineering Geology I · Chapter 7: Geology of Nepal - Asked in: 2059 Chaitra (old course), 3+2+3 marks - Video: [Himalaya's Fold mountains and Thrust boundaries explained with animation (part 2/3) | UPSC](https://www.youtube.com/watch?v=mF58L2J0FK4) — Zeta Axis (UPSC-SSC) - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/geology-of-nepal-significance-of - Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-7 ## Question Describe the geology of Nepal with a neat sketch and mention the engineering significance of the HFT, MBT and MCT. ## Short answer Nepal's geology consists of five zones separated by thrusts: Terai, Siwalik, Lesser Himalaya, Higher Himalaya, and Tethys. MFT/HFT is active, causing earthquakes and surface rupture. MBT is a crushed zone causing landslides. MCT is a thick shear zone with rockfalls and landslides, all avoided for structures. ## Answer From south to north, Nepal is divided into five **tectonic zones**, separated by major thrusts and faults (discontinuities): ```text S N Terai | Sub-Him | Lesser Him | Higher Him | Tethys |(Siwalik)| | | MFT/HFT MBT MCT STDS ``` 1. **Terai (Gangetic plain):** Quaternary alluvium. 2. **Sub-Himalaya (Siwalik zone):** Miocene to Pleistocene molasse sediments. 3. **Lesser Himalaya:** Precambrian to Palaeozoic low-grade metamorphic rocks and sediments. 4. **Higher Himalaya (Great Himalaya):** high-grade metamorphic rocks and granites. 5. **Tibetan-Tethys Himalaya:** Palaeozoic to Cretaceous fossiliferous marine sediments. **Boundaries (major discontinuities)** - **Main Frontal Thrust (MFT) / Himalayan Frontal Thrust (HFT):** between the Terai and Siwalik. - **Main Boundary Thrust (MBT):** between the Siwalik and Lesser Himalaya. - **Main Central Thrust (MCT):** between the Lesser and Higher Himalaya. - **South Tibetan Detachment System (STDS):** between the Higher Himalaya and the Tethys zone. #### Geological sketch (simplified north-south section) ```text Terai |Siwalik| Lesser Him. | Higher Him. | Tethys alluv.|sandst.| phyllite, | gneiss, | limest., gravel|mudst. | quartzite, | schist, | shale | | limestone | granite | MFT MBT MCT STDS ``` #### Engineering significance of HFT (MFT), MBT and MCT - **HFT (MFT):** the youngest thrust and still active; it can cause earthquakes and surface rupture. It controls the Terai margin, flooding and changes in groundwater, and gives poor ground for structures. - **MBT:** a wide zone of crushed and sheared rock between the Siwalik and the Lesser Himalaya; a major cause of landslides, and difficult ground for tunnels and roads. - **MCT:** a thick shear zone of highly deformed schist and gneiss, with hot springs; it is partly active, has frequent rockfalls and landslides, and is a risk for hydropower projects. Hence these zones are avoided for dams, tunnels and bridges unless special design is done. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. From south to north, which is the correct order of the tectonic zones of Nepal? A. Terai, Lesser Himalaya, Sub-Himalaya, Higher Himalaya, Tethys B. Terai, Sub-Himalaya (Siwalik), Lesser Himalaya, Higher Himalaya, Tethys C. Sub-Himalaya, Terai, Lesser Himalaya, Tethys, Higher Himalaya D. Terai, Sub-Himalaya, Higher Himalaya, Lesser Himalaya, Tethys Answer: B. Nepal's five zones from south to north are Terai, Sub-Himalaya (Siwalik), Lesser Himalaya, Higher Himalaya and Tethys. (Key point: Order of tectonic zones) 2. Which thrust separates the Lesser Himalaya from the Higher Himalaya? A. MBT B. MFT C. MCT D. STDS Answer: C. The Main Central Thrust (MCT) lies between the Lesser and Higher Himalaya; the MBT is south of the Lesser Himalaya and STDS is north of the Higher Himalaya. (Key point: Boundary thrusts) 3. Why is the HFT (MFT) important in engineering? A. It is the oldest, inactive thrust and so gives stable ground B. It is the youngest, active thrust causing surface rupture, earthquakes and flooding or groundwater changes at the Terai margin C. It only separates Tethys sediments and has no hazard D. It is a hot-spring zone of schist and gneiss Answer: B. The HFT is the youngest, still active thrust, so rupture, earthquakes and Terai margin flooding and groundwater changes make it poor ground. (Key point: Significance of HFT) 4. Which statement correctly describes the MBT zone for engineering? A. A thick zone of deformed schist and gneiss with hot springs B. A wide zone of crushed and sheared rock, a major cause of landslides, difficult for tunnels and roads C. A flat alluvial zone with a high water table D. A glacier zone with GLOF hazard only Answer: B. The MBT is a wide crushed, sheared zone causing landslides and tunnel and road difficulty; the schist, gneiss and hot springs description fits the MCT. (Key point: Significance of MBT and MCT) ## Related in Engineering Geology I - [Define engineering geology; scope and importance](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Adefine-engineering-geology-scope-and) — Engineering Geology I, chapter 1, asked 24× - [Discontinuities and engineering problems in Nepal Himalaya](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Adiscontinuities-and-engineering-problems-in) — Engineering Geology I, chapter 7 - [Scope and importance of geology in civil engineering](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ascope-and-importance-of-geology) — Engineering Geology I, chapter 1, asked 24× - [Engineering significance of fault](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aengineering-significance-of-fault) — Engineering Geology I, chapter 5, asked 6× - [Engineering significance of three rock types](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aengineering-significance-of-three-rock) — Engineering Geology I, chapter 4, asked 5× - [Types of river channel and engineering significance](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Atypes-of-river-channel-and) — Engineering Geology I, chapter 6, asked 5× ## Related in other subjects - [Scope of engineering geology in civil engineering](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Ascope-engineering-geology) — Engineering Geology II, chapter 1 - [PPP model and its significance in Nepal](https://www.bctengineer.com/question.md?key=semester_8%2Fengineering_professional_practice%3Appp-development-nepal) — Engineering Professional Practice, chapter 6, asked 2× - [Control system and its significance in engineering](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Awhat-is-cs-significance) — Control Systems, chapter 1 - [Scope and jurisdiction of Nepal Engineering Council](https://www.bctengineer.com/question.md?key=semester_8%2Fengineering_professional_practice%3Anec-scope-jurisdiction) — Engineering Professional Practice, chapter 3, asked 4×