---
title: "Plate tectonics and plate boundaries"
subject: "Engineering Geology I"
chapter: 2
key: "semester_3/engineering_geology_i:plate-tectonics-and-plate-boundaries"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/plate-tectonics-and-plate-boundaries
site: BCT Engineering
---

# Plate tectonics and plate boundaries

Engineering Geology I · Chapter 2: Basic Reviews of the Earth

- Asked in: 2081 Bhadra, 0.5+1.5 marks; 2081 Kartik (new course), 0.5+1.5 marks; 2076 Chaitra, 2 marks; 2074 Chaitra, 2 marks; 2068 Baisakh, 1 marks; 2066 Bhadra (old course), 2 marks; 2065 Shrawan (old course), 2 marks; 2063 Baisakh (old course), 2 marks (asked 8 times)
- Video: [The 4 Tectonic Plate Boundaries and the Hazards they Create](https://www.youtube.com/watch?v=oCPjgv2Pccc) — Simple Geography
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/plate-tectonics-and-plate-boundaries
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-2

## Question

What is plate tectonics? Describe the different types of plate boundaries (margins).

## Short answer

Plate tectonics is the theory that Earth's lithosphere is divided into moving plates, causing earthquakes and volcanoes at their boundaries. Divergent boundaries create new crust as plates move apart; convergent boundaries destroy crust through subduction or collision, forming trenches and mountains; transform boundaries involve horizontal sliding, causing strike-slip faults.

## Answer

**Plate tectonics** is the theory that the Earth's rigid outer shell, the lithosphere, is broken into a number of large and small plates that float on the plastic asthenosphere and move relative to each other at a few centimetres per year. Most earthquakes, volcanoes and mountain building occur along plate edges.

#### Types of plate boundaries
**1. Divergent (constructive) boundary**
- Plates move apart; magma rises and forms new crust.
- Examples: Mid-Atlantic Ridge, East African Rift.
- Features: mid-ocean ridges, rift valleys, shallow earthquakes, basaltic volcanism.

**2. Convergent (destructive) boundary**
- Plates move towards each other; one may sink (subduct) under the other.
- Types:
  - Ocean-ocean: island arcs and trenches (Japan, Mariana).
  - Ocean-continent: trench and volcanic mountain chain (Andes).
  - Continent-continent: collision and folded mountains (Himalaya, Alps).
- Features: shallow to deep earthquakes, volcanoes (not at continent-continent collisions), trenches, fold mountains.

**3. Transform (conservative) boundary**
- Plates slide horizontally past each other; crust is neither created nor destroyed.
- Example: San Andreas Fault.
- Features: strike-slip faults, shallow strong earthquakes.

```text
 Divergent      Convergent       Transform
 <-- | -->      --> | <--       ^  |
   ridge          trench         | v
```

## Check yourself

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

1. Lithospheric plates float on the:
   A. Outer core
   B. Moho
   C. Crust
   D. Asthenosphere
   Answer: D. The plastic asthenosphere lies below the lithosphere. (Key point: Plate tectonics)

2. At a divergent boundary:
   A. Plates move apart and new crust forms
   B. Plates collide
   C. Plates slide past
   D. Crust is destroyed
   Answer: A. Rising magma creates new crust. (Key point: Divergent)

3. Which is a transform boundary example?
   A. Mid-Atlantic Ridge
   B. San Andreas Fault
   C. Himalaya
   D. Andes
   Answer: B. Plates slide horizontally there. (Key point: Transform)

## Related in Engineering Geology I

- [Evidences of plate tectonics](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aevidences-of-plate-tectonics) — Engineering Geology I, chapter 2
- [Himalaya formation and plate tectonic evidence](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ahimalaya-formation-and-plate-tectonic) — Engineering Geology I, chapter 2
- [Convergent versus divergent plate boundary](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aconvergent-versus-divergent-plate-boundary) — Engineering Geology I, chapter 2, asked 3×
- [Plate boundary and mountain formation](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aplate-boundary-and-mountain-formation) — Engineering Geology I, chapter 2