---
title: "Geological agents; geological cycle"
subject: "Engineering Geology I"
chapter: 6
key: "semester_3/engineering_geology_i:geological-agents-geological-cycle"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/geological-agents-geological-cycle
site: BCT Engineering
---

# Geological agents; geological cycle

Engineering Geology I · Chapter 6: Physical Geology

- Asked in: 2068 Chaitra, 4 marks
- Video: [What is Geological cycle: Geologic Cycle](https://www.youtube.com/watch?v=2Mjo8MT4whk) — Geotourism and Modern Geotechniques
- 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-agents-geological-cycle
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-6

## Question

Mention different geological agents and explain the geological cycle.

## Short answer

Geological agents include running water, groundwater, glaciers, wind, waves and gravity. The geological cycle is the continuous cyclic transformation of rocks: magma cools to igneous rock, weathering and erosion produce sediments that turn into sedimentary rock, heat and pressure form metamorphic rock, and melting returns them to magma.

## Answer

Geological agents are natural forces that wear down, move and rebuild the earth's surface. They are:

1. **Running water (rivers)**, the most important agent.
2. **Groundwater**, working below the surface.
3. **Glaciers (ice)**.
4. **Wind**.
5. **Sea waves, tides and currents**.
6. **Gravity** (mass movement), **volcanism** and **organisms** (including humans).

Each agent does three kinds of work: **erosion** (wearing away), **transportation** (carrying) and **deposition** (laying down), which together shape landforms.

#### Geological cycle
The **geological cycle** is the continuous, slow, cyclic process by which the rocks of the earth's crust are formed, destroyed and re-formed into other kinds of rock. It has no start or end. It links the rock cycle, the hydrological cycle and plate tectonics.

```text
                 cooling
    Magma --------------------> Igneous rock
      ^                          |        |
      |              weathering, |        | heat,
      |                 erosion  |        | pressure
      | melting                  v        |
      |                     Sediments     |
      |          compaction,     |        |
      |          cementation     v        v
      |                   Sedimentary --> Metamorphic
      |                      rock   heat,    rock
      |                           pressure    |
      +---------------------------------------+
```

- Magma cools to **igneous rock**.
- Weathering, erosion, transport and deposition give **sediments**, which become **sedimentary rock** by lithification (compaction and cementation).
- Heat and pressure change any rock (igneous or sedimentary, or older metamorphic rock) into **metamorphic rock**.
- Deep burial and melting return the rock to **magma**.

Uplift brings deep rocks back to the surface, where weathering starts the cycle again. Engineers use this idea to understand why different rock types occur at a site.

## Check yourself

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

1. Which is the most important geological agent?
   A. Running water
   B. Wind
   C. Glaciers
   D. Organisms
   Answer: A. Rivers do the most landscape change. (Key point: Most important)

2. Which three kinds of work does each agent do?
   A. Folding, faulting, uplift
   B. Erosion, transportation, deposition
   C. Melting, cooling, burial
   D. Solution, fusion, fission
   Answer: B. Together they make a landform. (Key point: Three works)

3. What does the geological cycle link?
   A. Only the rock cycle
   B. Only plate tectonics
   C. Rock cycle, hydrological cycle and plate tectonics
   D. Only weather
   Answer: C. It has no start or end. (Key point: Cycle)

4. Magma cooling gives:
   A. Sedimentary rock
   B. Metamorphic rock
   C. Sediments
   D. Igneous rock
   Answer: D. Weathering of it gives sediments. (Key point: Igneous)

## Related in Engineering Geology I

- [Geological agents and their geological work](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ageological-agents-and-their-geological) — Engineering Geology I, chapter 6, asked 7×
- [Geological cycle](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ageological-cycle) — Engineering Geology I, chapter 6, asked 2×