Consider the following features related to a glacial lake outburst flood (GLOF): a. Involves sudden release of meltwater b. Failure of moraine and ice dam c. Large downstream discharge causing floods d. Rapid event casting for few seconds Select the correct answer from the options given below:
(a), (b) and (c) are correct
Understanding Glacial Lake Outburst Floods (GLOFs)
A Glacial Lake Outburst Flood (GLOF) is a type of flood that occurs when a dam containing a glacial lake fails. Glacial lakes form when glaciers melt, and the meltwater is held back by a natural dam, often made of ice or moraine (loose rock and sediment deposited by a glacier). The sudden failure of this dam releases a large volume of water rapidly, causing significant flooding downstream.
Analyzing the Features of a Glacial Lake Outburst Flood
Let's examine each feature listed in the question to determine if it accurately describes a GLOF:
- a. Involves sudden release of meltwater: This is a defining characteristic of a GLOF. The failure of the natural dam leads to the rapid discharge of water accumulated in the glacial lake.
- b. Failure of moraine and ice dam: Glacial lakes are commonly dammed by moraine deposits left by retreating glaciers or by ice itself. The failure of these natural dams is the primary trigger for a GLOF.
- c. Large downstream discharge causing floods: The sudden release of a massive volume of water results in a surge of water flowing downstream. This large discharge overwhelms river channels and causes significant flooding in areas below the glacial lake.
- d. Rapid event casting for few seconds: While a GLOF is a rapid event compared to regular river flow, the flood wave propagates downstream and the event typically lasts longer than just a few seconds. The dam failure might be sudden, but the resulting flood can impact areas for minutes, hours, or even longer, depending on the distance and topography. Therefore, describing the event casting as lasting "for few seconds" is inaccurate.
Identifying Correct Glacial Lake Outburst Flood Characteristics
Based on the analysis of each feature:
- Feature (a) - Sudden release of meltwater - is correct.
- Feature (b) - Failure of moraine and ice dam - is correct.
- Feature (c) - Large downstream discharge causing floods - is correct.
- Feature (d) - Rapid event casting for few seconds - is incorrect.
Thus, the correct features related to a Glacial Lake Outburst Flood (GLOF) from the given list are (a), (b), and (c).
| Feature | Description | Correctness for GLOF |
|---|---|---|
| a. Sudden release of meltwater | Core process of a GLOF | Correct |
| b. Failure of moraine and ice dam | Common cause of dam failure | Correct |
| c. Large downstream discharge causing floods | Major consequence of GLOF | Correct |
| d. Rapid event casting for few seconds | Duration of flood wave propagation/impact | Incorrect |
Revision Table: Glacial Lake Outburst Flood Features
| Key Aspect | GLOF Characteristic |
|---|---|
| Mechanism | Sudden release of water from a glacial lake |
| Cause | Failure of the lake's dam (moraine, ice, bedrock) |
| Outcome | Large, rapid downstream flood discharge |
| Duration | Rapid onset, but downstream impact lasts longer than seconds |
Additional Information on Glacial Lake Outburst Floods
Glacial Lake Outburst Floods (GLOFs) are serious natural hazards, particularly in mountainous regions experiencing glacier retreat due to climate change. Several factors can trigger the failure of a glacial lake dam:
- Increased water pressure in the lake
- Melting of an ice dam
- Overtopping and erosion of a moraine dam
- Seismic activity (earthquakes)
- Avalanches or rockfalls into the lake creating waves that overtop the dam
The impacts of GLOFs can be devastating, including loss of life, destruction of infrastructure (roads, bridges, buildings, power plants), and damage to agricultural land. Early warning systems and risk assessments are crucial for mitigating the effects of GLOFs.
Important Questions from Hazards and Disasters
Which one of the following is a meteorological hazard?
Match the List - I with List - II and select the correct answer from the code given below :
List-I
(Emitter)
List-II
(Emitted Products)
A. Decaying plants
1. Carbon monoxide
B. Volcanoes
2. Salt spray
C. Ocean
3. Hydrogen sulphide
D. Forest fires
4. Sulfur oxides
Who is the Executive Head of the National Disaster Management Authority (NDMA)?
Which of the following is perceived relatively a low-risk problem in the context of human welfare?
To characterize hazardous waste following characteristics are taken into account :
(A) Conductivity
(B) Ignitability
(C) Corrosivity
(D) Magnetic succeptibility
(E) Reactivity
Choose the correct answer from the options given below :
