Relevance: GS I (Physical Geography) & GS III (Disaster Management) | Source: The Hindu 

1. What is the News?

• Scientists from ISRO recently studied a deadly flash flood that hit Dharali village (Uttarakhand) in August 2025.
• The Discovery: Most people think Himalayan floods only happen when a “Glacial Lake” bursts. However, this study found a new danger: the sudden collapse of isolated ice patches hidden on mountain slopes.

2. The Concept of ‘Nivation’

To understand why these ice patches collapse, we need to know a simple geography process called Nivation:

• The “Hollow” Formation: In very cold areas, snow collects in small dips on the mountainside.
• Freeze and Melt: During the day, some snow melts into water and seeps into the ground. At night, it freezes and expands, cracking the rocks.
• The Result: This “freeze-thaw” cycle creates a bowl-shaped hole called a Nivation Hollow, where a thick patch of ice sits for years.

3. Why did the flood happen?

• Loss of the “Blanket”: Usually, these ice patches are covered by a thick layer of fresh snow that acts like an insulating blanket, keeping the ice frozen and stable.
• The Trigger: Because of global warming, this “blanket” of snow has disappeared. The ice patch became exposed to direct heat and heavy rain.
• The Collapse: On a hot, rainy day, the exposed ice patch suddenly shattered and slid down the mountain, carrying rocks and mud, causing a flash flood in the valley below.

The “UPSC Trap”

• The “Only Lake” Trap: UPSC might give a statement saying, “All Himalayan flash floods are caused by Glacial Lake Outbursts (GLOFs).” This is incorrect. ISRO has proved that “Ice Patch Collapses” are a separate and major threat.
• The “Nivation” Trap: Do not confuse Nivation with wind erosion. It is strictly a water-based process (freezing and melting).

UPSC Value Box

With reference to Himalayan geography and disaster management, consider the following statements:

1. ‘Nivation’ is a process where the ground is eroded due to the repeated freezing and thawing of water under a snow bank.
2. Recent findings by ISRO suggests that the collapse of isolated ice patches can trigger flash floods, even in the absence of a glacial lake.
3. Glacial Lake Outburst Floods (GLOFs) are the only recognized reason for the high-intensity floods in the Uttarakhand Himalayas.

Which of the statements given above is/are correct?

(a) 1 and 2 only

(b) 2 and 3 only

(c) 1 only

(d) 1, 2 and 3

Correct Answer: (a)