---
title: "Landslide versus debris flow"
subject: "Engineering Geology I"
chapter: 6
key: "semester_3/engineering_geology_i:landslide-versus-debris-flow"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/landslide-versus-debris-flow
site: BCT Engineering
---

# Landslide versus debris flow

Engineering Geology I · Chapter 6: Physical Geology

- Asked in: 2066 Bhadra (old course), 2 marks
- Video: [Every Landslide Type Explained in 9 Minutes](https://www.youtube.com/watch?v=xy6nU7nfFUM) — Explaini Mate
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/landslide-versus-debris-flow
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-6

## Question

Differentiate between landslide and debris flow.

## Short answer

A landslide slides as a coherent mass along a distinct slip surface with low to moderate water content. A debris flow moves like a viscous fluid with very high water content, no distinct slip surface, and deposits as a lobate fan.

## Answer

| Point | Landslide (slide) | Debris flow |
|---|---|---|
| Movement | Sliding as a mass along a slip surface | Flows like a viscous fluid |
| Material | Rock, soil or debris | Saturated mixture of water, soil, gravel and boulders |
| Water content | Low to moderate | Very high (above liquid limit) |
| Speed | Slow to rapid | Rapid to very rapid |
| Slope | Moderate to steep | Steep channels, deposit on the gentle fan |
| Slip surface | Distinct | No distinct surface; the whole mass deforms |
| Trigger | Rain, earthquake, cutting | Intense rainfall, flash floods, landslide dam |
| Deposit | Hummocky body | Lobate fan and levees |

## Check yourself

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

1. How does a debris flow move compared with a landslide?
   A. A debris flow slides on a distinct surface; a landslide flows
   B. Both flow like water
   C. Neither moves under gravity
   D. A debris flow flows like a viscous fluid; a landslide slides along a slip surface
   Answer: D. Debris flow has no distinct slip surface; the whole mass deforms. (Key point: Movement)

2. Water content of a debris flow is:
   A. Very high, above the liquid limit
   B. Very low, as in dry rock
   C. Zero
   D. Same as a dry rock fall
   Answer: A. A landslide has low to moderate water content. (Key point: Water content)

3. The typical deposit of a debris flow is:
   A. Hummocky body at the slope
   B. Lobate fan with levees
   C. A flat delta in the sea
   D. Layered marine sediment
   Answer: B. A hummocky body is typical of a landslide. (Key point: Deposit)

4. Debris flows are mainly triggered by:
   A. Only slow weathering
   B. Only cooling of magma
   C. Intense rainfall, flash floods or landslide dam release
   D. Only wind
   Answer: C. Landslides can also be triggered by earthquake and cutting. (Key point: Trigger)

## Related in Engineering Geology I

- [Short note: Debris flow](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ashort-note-debris-flow) — Engineering Geology I, chapter 6
- [Landslide versus slope failure](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Alandslide-versus-slope-failure) — Engineering Geology I, chapter 6

## Related in other subjects

- [Landslide versus debris flow](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Alandslide-vs-debris-flow) — Engineering Geology II, chapter 5, asked 2×