---
title: "Weathering and erosion; volcanism"
subject: "Engineering Geology I"
chapter: 6
key: "semester_3/engineering_geology_i:weathering-and-erosion-volcanism"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/weathering-and-erosion-volcanism
site: BCT Engineering
---

# Weathering and erosion; volcanism

Engineering Geology I · Chapter 6: Physical Geology

- Asked in: 2068 Chaitra, 4 marks
- Video: [What Are Volcanoes and How Are They Formed?](https://www.youtube.com/watch?v=R_pDKyg5YKY) — ClickView
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/weathering-and-erosion-volcanism
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-6

## Question

Define weathering and erosion. Write short notes on volcanism.

## Short answer

Weathering is the in-place breakdown of rocks; erosion is the removal and transport of weathered material by agents like water and wind. Volcanism is the process of magma, gases and pyroclasts erupting from the interior, building landforms such as cones and plateaus, with hazards including ashfall, lava flows and lahars.

## Answer

#### Weathering
The in-place breakdown of rocks by physical, chemical and biological processes.

#### Erosion
The removal and transport of weathered material by agents such as water, wind and ice. Weathering prepares the rock; erosion carries it away.

#### Volcanism
**Volcanism** is the process by which molten rock (magma), gases and rock fragments rise from the interior and erupt on the earth's surface (or are intruded into the crust).

- **Causes:** pressure release or fault openings at plate margins (subduction zones, mid-ocean ridges) and hot spots.
- **Products:** lava, gases, pyroclasts (ash, lapilli, bombs).
- **Types of eruption:** central (through a single vent, often explosive) and fissure (usually quiet, along long cracks).
- **Landforms:** cones, calderas, lava plateaus (e.g. the Deccan).
- **Hazards:** ash fall, lava flows, mud flows (lahars), poisonous gases.

## Check yourself

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

1. Erosion is:
   A. Removal and transport of weathered material
   B. Breaking in place
   C. Melting
   D. Compaction
   Answer: A. Weathering prepares; erosion carries. (Key point: Erosion)

2. What is volcanism?
   A. Wind erosion
   B. Process by which magma, gases and fragments rise and erupt at the surface or intrude the crust
   C. Sedimentation
   D. Glacier flow
   Answer: B. It includes eruptions through vents and fissures. (Key point: Volcanism)

3. Where does volcanism occur?
   A. Only in deserts
   B. Only on coasts
   C. Plate margins (subduction, mid-ocean ridges) and hot spots
   D. Only in glaciers
   Answer: C. Pressure release or faults open paths. (Key point: Causes)

4. Which is a volcanic hazard?
   A. Frost wedging
   B. Karst collapse
   C. Deflation
   D. Lahars (mud flows), ash fall, lava flows, gases
   Answer: D. Products include lava, gases, pyroclasts. (Key point: Hazards)

## Related in Engineering Geology I

- [Volcanism; chemical weathering](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Avolcanism-chemical-weathering) — Engineering Geology I, chapter 6
- [Weathering versus erosion](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aweathering-versus-erosion) — Engineering Geology I, chapter 6, asked 5×