---
title: "Define fold with neat sketch"
subject: "Engineering Geology I"
chapter: 5
key: "semester_3/engineering_geology_i:define-fold-with-neat-sketch"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/define-fold-with-neat-sketch
site: BCT Engineering
---

# Define fold with neat sketch

Engineering Geology I · Chapter 5: Structural Geology

- Asked in: 2081 Chaitra (new course), 2 marks; 2066 Bhadra (old course), 1 marks (asked 2 times)
- Video: [Folds - an introduction](https://www.youtube.com/watch?v=fQKx89OXI1s) — Geology in a Jiffy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/define-fold-with-neat-sketch
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-5

## Question

Define fold with a neat sketch.

## Short answer

A fold is a bend in originally flat rock layers due to compression, forming an anticline (upfold) or syncline (downfold). Parts include limbs, hinge, and axial plane.

## Answer

A **fold** is a bend or wavy curvature of originally flat rock layers (beds), produced by compressive stress acting on plastic rocks over a long time.

```text
            Axial plane
                |
                |        (crest)
          ___   |   ___
        /     \ | /     \
   ____/       \|/       \____
    limb      hinge      limb
```

Parts: **limbs** (sides), **hinge** (line of maximum curvature), **axial plane** (plane dividing the fold symmetrically), **crest** (top) and **trough** (bottom). An upfold is an **anticline** and a downfold is a **syncline**.

## Check yourself

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

1. Fold is?
   A. Fracture with movement
   B. Fracture without movement
   C. Bend of originally flat beds from compression of plastic rocks
   D. Erosion surface
   Answer: C. Wavy layers. (Key point: Fold)

2. Hinge?
   A. Side
   B. Plane dividing fold
   C. Top
   D. Line of maximum curvature
   Answer: D. Limbs are sides. (Key point: Hinge)

3. Axial plane?
   A. Divides fold symmetrically
   B. Joins limbs
   C. Horizontal
   D. Top surface
   Answer: A. Contains hinge lines. (Key point: Axial plane)

4. Upfold?
   A. Syncline
   B. Anticline
   C. Monocline
   D. Fault
   Answer: B. Downfold is syncline. (Key point: Anticline)