- Various theories explain Nepal floods, including glacial collapse and debris flow
- Earthquake-triggered avalanches and landslides are also considered causes
- Global warming causes rain at 4,000 metres, melting glaciers and destabilising debris
Various theories have emerged regarding the catastrophic floods in Nepal. One prevailing view attributes the disaster to a glacial collapse and the subsequent flow of thousands of tonnes of debris. According to the US Geological Survey (USGS), a sudden collapse of ice and rock in the upper Himalayas sent a massive volume of water and debris rushing downwards, causing widespread destruction.
A second theory suggests that the situation was triggered by avalanches and landslides caused by an earthquake.
A third theory points to the bursting of a glacial lake as the cause of these conditions. One emerging theory suggests that due to global warming and climate change, precipitation at altitudes of 4,000 metres is occurring as rain rather than snow.
To understand the devastating deluge in Nepal, one must examine the causes of the disaster that struck Dharali in Uttarakhand's Uttarkashi district in August 2025; the Nepal flood was essentially a larger-scale version of the Dharali event. The destructive surge in Dharali also originated from the base of Shrikhand mountain at an altitude of approximately 4,000 metres.
At the time, various theories circulated regarding the cause - ranging from the presence of a glacial lake to heavy rainfall - but scientists from the Wadia Institute provided a specific explanation in their report.
They attributed the event to rapid climate change and shifts in weather cycles driven by global warming. The impact of global warming has become so severe that areas at 4,000 metres, which once received snowfall, now experience rain. This rainfall is extremely hazardous because rising temperatures - a consequence of climate change - are causing glaciers to retreat rapidly. As glaciers recede, they leave behind thousands of tonnes of debris, including massive boulders, stones, sand and soil.
Continuous rainfall causes water to accumulate within this debris. When triggered by events like landslides or earthquakes, this mass suddenly destabilises and rushes down steep slopes, unleashing a destructive deluge upon the low-lying areas.
In his report on the Dharali incident, Wadia Institute of Himalayan Geology scientist Manish Mehta concluded that the disaster was caused neither by a cloudburst nor a glacial lake outburst. Instead, it was triggered by accumulation of water beneath a massive deposit of moraine or loose debris left by glaciers on Mount Shrikanth.
Global warming and rising temperatures caused rapid snowmelt, leading to water pooling in that area. The report indicates that the unique geomorphology of Mount Shrikanth, combined with continuous rainfall, destabilised the steep slopes, resulting in devastation across Harsil and Dharali.
Furthermore, the floods that struck Raini in Chamoli district in February 2021 bear a striking resemblance to the disaster in Nepal. In both instances, a torrent surged from the high Himalayas, destroying the NTPC hydroelectric project in the lower reaches. The flood in the Rishi Ganga (Raini area) was caused by a massive landslide in the upper reaches that broke a glacier, triggering a destructive surge from the lake formed below, a scenario remarkably similar to the catastrophic floods in Nepal.
Similarly, a devastating flood occurred in the Tamak Nala of Chamoli's Niti Valley in August 2026. The nature of this event also closely mirrored the disaster in Nepal. Factors such as global warming and rainfall occurring at altitudes as high as 4,000 metres are cited as the underlying causes. The flood in the Tamak Nala - fueled by water, debris and massive boulders - swept away a large iron bridge as if it were a mere straw. A glacier base is situated at an altitude of 4,000 metres, where vast quantities of moraine have accumulated over time.
This material comprising stones, soil and debris mixes with water and rushes downstream at high speed, transforming into a destructive torrent. Mount Hathi (Hathi Parvat) looms above the Tamak Nala, serving as the source of five major glaciers. The Tamak Nala lies to its south and the base of the mountain holds massive deposits of moraine.
Similarly, the 2013 floods triggered by the bursting of the Chorabari Glacier lake near Kedarnath had claimed thousands of lives and caused extensive infrastructure damage. That catastrophe was caused by a massive avalanche or glacial rupture at Gandhi Sarovar located within the Chorabari Glacier above Kedarnath. The resulting floods were so devastating that it wreaked havoc as far downstream as Rishikesh.
So, the catastrophic floods in Nepal mirrors the Kedarnath tragedy. There too, a glacial lake had burst following a glacial rupture and had swept massive amounts of moraine along with rushing water.
Mehta, the scientist at Wadia Institute of Himalayan Geology, told NDTV in an exclusive interview that a massive landslide did occur at the site of the flood in Nepal. The landslide likely caused a glacier to break off and crash into a lake situated below it; the resulting breach of the lake unleashed floods downstream.
Mehta said a vast amount of glacial debris accumulated over a large area was swept down, causing immense destruction as videos from the site clearly indicated thousands of tonnes of debris were carried into the plains by the force of the rushing water.
He told NDTV that glaciers worldwide are rapidly retreating due to global warming and rainfall is now being observed at altitudes of 4,000 metre - areas where snow should typically be present.
Mehta said there's an urgent need for further study to fully understand the underlying causes of the catastrophic floods in Nepal but current evidence strongly suggests that a massive landslide triggered the collapse of the glacier and the lake situated in front of it, propelling the mass downwards.
