What Caused the Himalayan Glacier Collapse That Triggered Central Nepal Flash Floods?

The large-scale breakage of a glacier in the Himalayas, which is situated close to the borders of the Tibet and Nepal, led to the occurrence of a series of catastrophic events in the central part of Nepal, resulting in the formation of a huge flood wave comprising water, ice, mud, and rocks.

At first, there were speculations that an earthquake of magnitude 4.4 had caused this tragedy. However, later researches showed that the tragedy was caused by a large scale of breakage of glaciers and rocks at a considerable height.

As stated by data from the US Geological Survey (USGS), about 0.2 sq. km. of glacial ice and bedrock was broken off at the height of about 5,200 m.

What Took Place at the Glacier Collapse in the Himalayas?

The disaster started with the separation of one piece of the glacier from the main glacier located at high altitude in the Himalayas. According to satellite images provided by Planet Labs, the terminus of a glacier near Langtang Lirung became detached and fell to the valley about 1.2 kilometres lower.

Besides being just a fall of ice mass, it caused the movement of rock and other debris down the valley rapidly changing the local conditions and causing tremendous amounts of water and sediments to move down the valley.

The debris flow into the valley created a surge which had the potential to act like a flood containing significant amount of debris rather than being a regular overflow of a river.

What Made the Glacier Collapse so Deadly?

Such an event becomes especially powerful due to extreme altitude and steep nature of the Himalayan mountains. The detachment of a large mass from the glacier located on high altitude leads to the massive release of gravitational energy within a very short time period.

The rock debris created a temporary obstacle to the flow of water creating a barrier lake behind it. This type of natural phenomenon can become quite dangerous because water keeps accumulating during existence of the unstable debris barrier.

The breaking of such a barrier causes rapid release of water and all accumulated sediments resulting in a torrent carrying mud, rocks and other debris.

Did the Earthquake Cause the Glacier Collapse?

At first glance, an earthquake could have been one of the contributing factors that caused this disaster. At the very beginning, this event was described in connection with a 4.4 magnitude earthquake.

However, in the later stages of the geological and satellite investigation, the magnitude of the ice and rock collapse became clear. According to the information from the USGS, the seismic activity caused by the mass collapse was equivalent to a much larger 5.2 magnitude earthquake.

This is important to note since a high altitude disaster could have several factors that contribute to the occurrence of such a disaster. In addition to the earthquake, there could be an unstable rock, weak structure of glaciers, meltwater, etc.

Thus, the glacier collapse cannot be described with one particular factor in isolation.

How Was the Flood Able to Reach Communities Downstream?

In the case of this disaster, the topography helped the flood reach communities downstream very quickly as the water was funneled through narrow valleys formed in the mountains rather than spread out on a flat plain.

This greatly increased the velocity of the water and the damage it could do.

When the barrier broke down, the water, mud, stones and other glacial materials continued traveling downstream. The structures close to the river channels did not have much time to react to this rapidly developing situation.

The infrastructure in the area of the Nepal-Tibet border, such as the Gyirong Port border crossing, suffered damage from this disaster, it is claimed.

Why Are Himalayan Glaciers at Risk?

The region of the Himalayas is highly sensitive to variations in climate, temperature and precipitation. In essence, glaciers are not inert blocks of ice; instead, they are constantly reacting to environmental changes.

Increased temperature can cause faster melt of the glaciers, changing the stability of the ice, snow and rocks at the high altitudes. On the other hand, melting ice contributes to the creation or enlargement of glacial lakes.

If the unstable ice or rock breaks off and falls into the lake, this can result in displacement of the water and trigger the development of either the glacial lake outburst floods (GLOFs) or some other type of high-altitude floods.

In the steep valleys of the Himalayas, the debris and water can cover quite large distances in a relatively short amount of time.

The Broader Connection with Climate Change

The incident in Nepal also points out to a wider problem of the Hindu Kush-Himalayan region. Increased temperatures can affect glaciers, permafrost and mountain slopes and increase the risk of compound hazards.

At the same time, it should be understood that there is a difference between the immediate trigger of a collapse and the long-term processes that could make the mountains unstable. Not every glacier collapse can be automatically attributed to climate change.

Instead, the climate-induced glacier retreat, changes in meltwater regimes, mountain slope instability and extreme weather conditions can create conditions in which natural events will have more serious consequences.