---
title: "Magma versus lava"
subject: "Engineering Geology I"
chapter: 4
key: "semester_3/engineering_geology_i:magma-versus-lava"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/magma-versus-lava
site: BCT Engineering
---

# Magma versus lava

Engineering Geology I · Chapter 4: Petrology

- Asked in: 2066 Bhadra (old course), 2 marks
- Video: [What is magma and how is magma formed? | The difference between magma and lava](https://www.youtube.com/watch?v=-0Dq2ZYjZVo) — Maria Baias
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/magma-versus-lava
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-4

## Question

Differentiate between magma and lava.

## Short answer

Magma is molten rock with dissolved gases beneath the Earth's surface, solidifying into intrusive rocks like granite. Lava is magma that has erupted onto the surface, lost most gases, and cools to form extrusive rocks like basalt.

## Answer

| Point | Magma | Lava |
|---|---|---|
| Definition | Molten rock material with dissolved gases below the earth's surface | Molten rock that has erupted onto the surface, having lost most of its gases |
| Location | Underground (magma chamber) | On the earth's surface |
| Gas content | High | Low (gases escaped) |
| Temperature | Higher (700 - 1300 °C) | Slightly lower, cools quickly |
| Solidifies to | Intrusive (plutonic) rocks like granite | Extrusive (volcanic) rocks like basalt |

## Check yourself

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

1. Magma is molten rock where?
   A. Below the earth's surface with dissolved gases
   B. Erupted on the surface
   C. In the atmosphere
   D. In ocean water
   Answer: A. Lava is the erupted form. (Key point: Magma definition)

2. Which has higher gas content?
   A. Lava
   B. Magma
   C. Equal
   D. Neither has gas
   Answer: B. Lava has lost most gases. (Key point: Gas content)

3. Lava solidifies to what?
   A. Plutonic rocks like granite
   B. Sedimentary rocks
   C. Extrusive rocks like basalt
   D. Metamorphic rocks
   Answer: C. Magma gives intrusive rocks. (Key point: Product)

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