---
title: "GLOF: occurrence, causes and effects"
subject: "Engineering Geology II"
chapter: 5
key: "semester_4/engineering_geology_ii:glof-occurrence-effects"
source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/glof-occurrence-effects
site: BCT Engineering
---

# GLOF: occurrence, causes and effects

Engineering Geology II · Chapter 5: Geological Hazards

- Asked in: 2078 Chaitra, 2 marks; 2075 Bhadra, 2 marks; 2074 Bhadra, 2 marks; 2079 Chaitra, 1 marks; 2075 Baisakh, 2 marks; 2073 Magh, 4 marks; 2072 Magh, 5 marks; 2070 Bhadra, 2 marks; 2068 Magh, 1 marks (asked 9 times)
- Video: [Glacial Lake Outburst Flood (GLOF) | UGC NET GEOGRAPHY](https://www.youtube.com/watch?v=rg6wF9zsnzk) — Learn with Vijay 
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/glof-occurrence-effects
- Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-5

## Question

What is GLOF? How does it occur? Describe its causes and consequences (effects) as a geological hazard in Nepal.

## Short answer

GLOF is sudden outburst from a moraine-damed glacial lake. It occurs when a trigger (ice/rock avalanche, ice-core melt, earthquake) breaches the dam. Causes include glacier retreat, avalanches, piping, heavy rain. Consequences in Nepal: loss of life, destruction of hydropower (Dig Tsho 1985 destroyed Namche plant), bridges, and far-range sedimentation.

## Answer

A **Glacial Lake Outburst Flood (GLOF)** is the sudden release of a large volume of water from a glacial lake, usually dammed by a moraine or ice, which produces a destructive flood and debris flow downstream.

#### How it occurs
1. Glaciers retreat due to climate warming, leaving meltwater in depressions behind end or lateral moraines.
2. The lake grows (e.g. Imja, Tsho Rolpa) and is held back by an unconsolidated moraine dam.
3. A trigger acts and the dam breaches by overtopping, piping or collapse.
4. A flood wave with high discharge, carrying rock and ice debris, rushes down the valley.

```text
 glacier --> [ lake ] |moraine dam|
                      v breach
             ======> flood + debris ===>
```

#### Causes
- Climate change and glacier melt, giving rapid lake growth.
- An ice or rock avalanche or a landslide entering the lake, producing waves that overtop the dam.
- Melting of the ice core in the moraine; piping and seepage.
- Earthquake shaking.
- Heavy rainfall or snow melt raising the lake level.
- A weak, steep, unconsolidated moraine dam.
- Failure of a lake upstream (cascade).

#### Consequences in Nepal
- Loss of life and livestock; the 1985 Dig Tsho GLOF destroyed the nearly completed Namche hydropower project, bridges and farmland.
- Damage to hydropower plants, roads, trails, bridges and settlements; the 1998 Tam Pokhari GLOF and the 2016 Bhote Koshi GLOF (from a lake in Tibet) caused heavy damage.
- Heavy erosion and sedimentation, change of river course, and damage to farmland far downstream, sometimes more than 100 km away.
- Trans-boundary effects (Tibet to Nepal to India).
- Mitigation: monitoring, early warning, artificial lowering of the lake level (Tsho Rolpa), spillways and land-use planning.

## Check yourself

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

1. What is a GLOF?
   A. Overflow of a concrete dam
   B. Sudden release of water from a glacial lake dammed by moraine or ice
   C. Flooding from monsoon rain on plains
   D. Failure of a landslide dam
   Answer: B. GLOF is an outburst from a glacial lake that gives a destructive flood and debris flow. (Key point: GLOF definition)

2. Which is a typical trigger of a GLOF?
   A. Planting vegetation on the moraine
   B. A dry spell
   C. Ice or rock avalanche entering the lake and overtopping the dam
   D. Lowering of the lake by a spillway
   Answer: C. Avalanche waves, ice-core melt, piping and earthquakes breach the moraine dam. (Key point: GLOF cause)

3. Which event destroyed the Namche hydropower project in Nepal?
   A. 2015 Gorkha earthquake
   B. 2014 Jure landslide
   C. Tsho Rolpa lowering
   D. 1985 Dig Tsho GLOF
   Answer: D. The 1985 Dig Tsho GLOF destroyed the Namche project, bridges and farmland. (Key point: Nepal example)

4. Which measure mitigates GLOF risk?
   A. Artificial lowering of lake level and early warning
   B. Increasing glacier melt
   C. Building houses downstream
   D. Removing spillways
   Answer: A. Monitoring, early warning, lake lowering (Tsho Rolpa) and spillways reduce the hazard. (Key point: Mitigation)

## Related in Engineering Geology II

- [Effects of earthquake in Nepal](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Aearthquake-effects-nepal) — Engineering Geology II, chapter 5
- [Factors causing hazards in Nepal Himalaya](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Anepal-himalaya-hazard-factors) — Engineering Geology II, chapter 5

## Related in other subjects

- [Earthquake occurrence, terminology, causes, effects](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aearthquake-occurrence-terminology-causes-effects) — Engineering Geology I, chapter 2
- [Deforestation: causes and consequences](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Adeforestation-consequences) — Technology, Environment and Society, chapter 6, asked 2×
- [Global warming: meaning, causes, consequences](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aglobal-warming-causes-consequences) — Engineering Chemistry, chapter 3
- [Global environmental issues: causes and consequences](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Aglobal-env-issues-causes) — Technology, Environment and Society, chapter 4