Flash Floods in Uttarkashi District

• 06 Aug 2025

Why in News? 

Flash floods, triggered by heavy rainfall, have caused widespread devastation along the Kheer Ganga river in Uttarkashi district, Uttarakhand.  

• The floods, which hit the town of Dharali, a popular tourist spot situated 8,600 feet above sea level, have resulted in significant loss of life, with many others feared missing. 

Key Points 

• Reasons for Flash Floods: 
  • Experts suggest that a glacier collapse or a glacial lake outburst (GLOF) upstream, rather than a cloudburst, likely triggered the flash flood in Dharali village. 
  • The Indian Meteorological Department (IMD) recorded minimal rainfall during the disaster, well below the typical levels that cause cloudburst-induced flooding, leading experts to suggest the possibility of a glacier burst or GLOF, supported by satellite images showing significant glaciers and glacial lakes above Dharali. 
• Disaster Risk: 
  • According to the Wadia Institute of Himalayan Geology, Uttarakhand is home to 1,266 glacial lakes, ranging from small to large bodies of water, some of which pose significant downstream threats. 
  • The National Disaster Management Authority (NDMA) has identified 13 glacial lakes as high-risk, with five classified as extremely dangerous. 
  • Such disasters occur when water accumulates at high elevations and is suddenly released—heavy rainfall alone cannot trigger such catastrophic events. 

Flash Flood 

• Definition: Flash floods are sudden increases in water levels during or immediately after intense rainfall. They are highly localized and short-lived events, typically occurring within 6 hours of rainfall.  
• Causes:  
  • Flash floods are primarily caused by intense rainfall that overwhelms the soil’s absorption capacity and drainage systems.   
  • Apart from heavy rain, flash floods can also result from rapid snowmelt due to sudden temperature rise, dam or levee breaches, ice or debris jams, and sudden glacial lake outbursts.  
  • Additionally, urbanisation with impervious surfaces like roads and buildings increases runoff, reducing water absorption and intensifying flood risks.  

Glacial Lake Outburst (GLOF) 

• About: A GLOF is a type of catastrophic flood that occurs when the dam containing a glacial lake fails, releasing a large volume of water. 
  • This type of flood is typically caused by the rapid melting of glaciers or the buildup of water in the lake due to heavy precipitation or the inflow of meltwater. 
  • In February 2021, Chamoli district in Uttarakhand witnessed flash floods which are suspected to have been caused by GLOFs. 
• Causes: 
  • These floods can be triggered by a number of factors, including changes in the volume of the glacier, changes in the water level of the lake, and earthquakes. 
  • According to the NDMA (National Disaster Management Authority), glacial retreat due to climate change occurring in most parts of the Hindu Kush Himalayas has given rise to the formation of numerous new glacial lakes, which are the major cause of GLOFs.