Experts have analyzed that the devastating flood in Risuwa’s Lhende River last Wednesday was caused by an avalanche from an altitude exceeding 5,000 meters. According to Dr. Sudip Thakuri, the energy and temperature generated by the rapid fall of a massive ice mass transformed the flowing water into a sediment-laden flood. He noted that the nature of the floods in Risuwagadhi and Chamoli are similar, with glacier lakes and avalanches both posing significant risks. Dr. Thakuri recommended measures such as risk zone mapping, early warning systems, and effective land-use policies to mitigate damage.
Experts are analyzing the recent flood using various data and statistics. They identify a large glacier collapse in the northern part of Langtang as the main cause of the catastrophic flood. However, the exact nature of the so-called ‘glacial tsunami’ remains unclear among researchers. Dr. Thakuri, Associate Professor at Tribhuvan University, explained that the flood resulted from a large volume of snow falling from Nepal’s higher elevations.
In an edited interview with Krishna Gyawali, Dr. Thakuri discussed the causes of the Risuwa flood. What could have triggered the swift and massive flood in the Lhende River? Understanding where the flood originated is crucial. Data suggests the event began above 5,000 meters. The glacier in the northern slope of Langtang was approximately at that height, above a river valley at about 3,000 meters.
Therefore, a large ice mass likely fell nearly 2,000 meters downward. Gravity’s pull and the size of the ice mass contributed to its speed. The steepness of the area further accelerated the flow. The flood reached Risuwagadhi rapidly, initially traveling over 120 km/h, maintaining this speed downstream. The velocity is estimated to have decreased only upon reaching Chitwan.
Why did the flood containing the glacier ice gained such unnaturally high speed after falling from roughly 5,000 meters? Experts haven’t reached a clear consensus. Reports indicate a large ice block fell from above with massive energy release. The relatively high temperature at that elevation caused the fast-moving ice fragments to melt and turn into a slurry almost instantly.
Current hypotheses suggest that the landslide area may have contained accumulated snow or water, and the glacier might have altered its path previously. There is a possibility that rocks and debris covering an inner melting zone collided with the landslide, acting as a lubricant for the glacier to slide down. These combined factors might have created a large debris flow.
The flood carried not just water but rocks, soil, debris, and trees at high speed, causing wide-scale destruction downstream. Are there precedents for such a large and catastrophic Himalayan disaster? Rarely have such losses to human life and infrastructure been recorded in Nepal in the past 200 years. Similar events include floods in Sikkim (India), the Chamoli flood caused by the Nanda Devi landslide, last year’s Risuwagadhi flood, and floods in Thame and Seti.
Compared to these, the Risuwagadhi flood stands out as the most massive and destructive. Which past events resemble the Risuwagadhi flood? It was caused by an avalanche and shares many characteristics with the Chamoli flood in India, though damages there were comparatively less. Other floods, like Kedarnath, stemmed from cloudburst-induced heavy rains, and the Sikkim event resulted from citizen landslide.
It is essential to distinguish flood causes; Risuwagadhi and Chamoli floods share a similar nature. Currently, the risk of glacier lake outburst disasters and avalanches is rising. Dr. Thakuri conducted studies a few years ago, noting avalanches are not new — about 400 people have died in avalanches since 1920. However, an event of this scale is unprecedented. Nepal hosts roughly 1,500 glaciers, with small ones continually forming; about 200 glaciers are considered at risk. Previously, only large glacier lakes were considered hazardous, but now even smaller ones pose threats.
What might cause the massive ice block to fall? Geological factors, temperature increases, or other reasons? Snow and ice falling from Himalayan glaciers is a natural process. However, rising temperatures may have disrupted the relationship between the ground and ice. Crevices and infiltrating water can weaken rocks. Increased precipitation in the Himalayas has allowed water to seep into cracks, facilitating ice mass movements. Warmer temperatures cause surface ice to melt, weakening glaciers.
The rapidly falling ice block generated considerable energy and heat, contributing to the formation of the sediment-laden flood. Permafrost is typical in the Himalayas; rising temperatures cause this frozen soil to thaw, increasing avalanche risks. While avalanches occur regularly, understanding such massive events demands further research. Identifying hazardous glaciers was once simpler, but unpredictable avalanches like this have increased danger levels.
Glaciers and avalanches pose substantial risks in watershed areas, as many rivers originate from these glaciers. New incidents can be far beyond prior forecasts. Upper Khumbu region hosts glaciers that could affect downstream regions anytime. Many parts of Nepal from east to west remain risk-prone. Identifying and mapping these zones and securing communities are essential. There were signs of glacier lake outburst in Chamoli and Risuwagadhi floods, but glacier collapses were later confirmed.
Should avalanche research be prioritized? Yes, avalanche and rockfall incidents require urgent focus. Any material falling from high Himalayan regions constitutes an avalanche. These risks persist strongly. Snow accumulates in the mountains forming glaciers that flow downward. Uncontrolled glaciers can accumulate ice that later causes avalanches. Over years, snow compacts into ice and slowly descends steep slopes, known as glaciers. Rising temperatures accelerate melting.
Paying close attention to glacier movement is critical. Avalanches differ from normal glacier movement; they involve sudden large ice or rockfalls, separate from normal glacier flow. Scientists attribute increasing Himalayan disasters mainly to rising temperatures. Nepal’s greenhouse gas emissions are about 0.5 percent globally, negligible in climate change impact. External factors primarily drive temperature rises, with developing and developed nations bearing responsibility. However, temperature increases in high Himalayan zones exceed the global average, fueling ongoing debate about its contributory roles.
Events from Risuwagadhi to Malekhu cause risk and damage. How can communities be better protected? Emphasis must be placed on preparedness and early warning systems. Policies must be enacted to relocate settlements and infrastructure away from high-risk zones. When removal is impossible, early warning and mapping become critical. Residents of affected areas told us they had lived there long-term but worried such high-impact damages were new.
How can we even imagine such disaster damages? Compared to Earth’s long-term history, human lifespans are short. Lack of disasters in recent decades or generations doesn’t guarantee safety. At Thame in Solukhumbu, houses were built near a river, indicating the area wasn’t free of risk despite ancestral efforts. Human activities have amplified these risks.
You have mentioned early warning systems could reduce damage. What should such a system look like? Currently, sensors measure water levels on some rivers, and sensors with sirens are installed on several glaciers. Yet, these efforts are insufficient. Many risk zones require integrated early warning systems, even in small areas. In major disasters, minutes of warning can save lives. Appropriate sensors and alert systems in the Risuwagadhi region could have saved many.
We must be more vigilant after such events. Regarding climate justice, what action should Nepal take with the international community? International cooperation is essential for technology and knowledge sharing. Preparedness depends on accurate data collection. Nepal can demand financial compensation and work through UN representation of developing countries to mobilize resources. When claiming compensation, effective advocacy and access in UN platforms are critical.
