Himalayan Alluvial Fan Danger: Dharali Tragedy: Alluvial Fans & Unseen Dangers in Himalayan Settlements
Himalayan Alluvial Fan Danger: Dehradun, August 17, 2025: The devastation in Dharali was as much a natural calamity as it was a consequence of human oversight. This is why everything in Dharali, nestled within a unique geological formation, was buried under debris in an instant. Scientists call this specific structure an Alluvial Fan. Soil carried by rivers deposits on the flat part of an alluvial fan, and this mineral-rich soil is incredibly fertile. Soil that nourishes the apple orchards and crops like potatoes and peas in Dharali and Harsil. The most terrifying aspect of this formation is its potential for sudden flash floods, and what’s alarming is that many villages, towns, and cities in Uttarakhand, and across the Himalayan states, are situated in similar locations.
Let’s first understand what an Alluvial Fan is. It’s called an alluvial fan because its shape resembles a fan. A river, typically flowing through very steep and narrow mountain slopes like a drain, enters a flat area. The narrow, upper end of the river is called the Apex, and the flat, wider section is known as the Apron. In these steep, narrow slopes, the water’s velocity is like a bullet, but it slows down significantly upon reaching the apron. It’s in this apron that sand, silt, and soil accumulate. Naturally, if there’s a settlement in or around the apron, disaster is inevitable.
Dr. Manish Mehta, a senior scientist at the Wadia Institute of Himalayan Geology in Dehradun, who has been studying glaciers for a long time, explains that alluvial fan-like structures are extremely vulnerable to floods. He points out that towns like Agastyamuni, Tilwara, and Phata in the Mandakini Valley, and Gangotri in the Ganga Valley, are all situated on similar formations.
Clearly, all these locations are precariously perched on the edge of danger. Thus, there’s an urgent need for awareness and vigilance. It’s the government’s responsibility to identify and mark cities, towns, and villages located on alluvial fans, and to commission scientific studies of these areas. Based on these study reports, comprehensive safety measures should be implemented for such towns. While humans cannot control nature, alertness can, to some extent, mitigate the impact of its destructive force.
