Speaker A
I can see the window. It looks like... well, rocks and debris are on one side, making access impossible, so we are currently approaching from the other side. That one. Three weeks after the Nepal floods.
Detailed analysis of Nepal's 2023 mega flood caused by a massive rock and glacier collapse at 5,200m, revealing unprecedented disaster scale and climate links.
Key Takeaways
- The Nepal flood was triggered by a massive rock and glacier collapse at high altitude, causing a debris flow equivalent to a magnitude 5.2 earthquake.
- Climate change-driven glacier retreat exposes unstable bedrock, increasing the risk of large-scale avalanches and floods in the Himalayas.
- Satellite imagery and seismic data are critical tools for analyzing and understanding such disasters but need to be integrated into predictive warning systems.
- Local communities suffer severe impacts, with homes destroyed and villages isolated, highlighting the need for better disaster response infrastructure.
- The event signals a growing trend of climate-related disasters in mountain regions with significant implications for regional safety and environmental management.
What the video covers
- The video investigates the cause of the devastating Nepal floods on August 26, 2023, focusing on a massive rock and glacier collapse on the northern slope of Langtang Lirung at 5,200m elevation.
- Survivors recount the sudden flood that swept through villages along the Trishuli River, destroying homes and isolating communities.
- Satellite imagery and seismic data confirm a collapse equivalent to a magnitude 5.2 earthquake, involving approximately 82 million cubic meters of debris.
- The collapse triggered a rock and ice avalanche that rapidly transformed into a massive debris flow and flood, engulfing the valley and causing unprecedented damage.
- The glacier retreat and exposure of unstable bedrock due to climate change have increased the risk and scale of such collapses in the Himalayas.
- Local experts link the accelerated disappearance of Himalayan glaciers since the 2000s to expanding unstable bedrock zones prone to collapse.
- The flood's impact was compounded by blocked river channels and glacial lakes formed by moraines, which released large volumes of water and debris.
- The video highlights the urgent need for improved monitoring, early warning systems, and disaster preparedness in high-altitude regions vulnerable to climate-driven hazards.
- Comparisons are drawn to previous glacier collapse floods in the region, emphasizing the growing frequency and severity of such events.
- The broader implications of Himalayan disasters on the Asian region are discussed, underscoring the importance of climate adaptation strategies.
Chapters
- 00:00Introduction and Survivor Accounts
- 05:16Personal Stories of Survival and Damage
- 10:28Geological Analysis of the Collapse
- 18:13Rock and Ice Avalanche Mechanism
- 21:18Glacial Lakes and Flood Dynamics
- 24:46Comparative Analysis with Past Glacier Floods
- 30:30Climate Change Effects on Glacier Stability
- 36:57Call for Improved Monitoring and Preparedness
Full Transcript — Download SRT & Markdown
Speaker A
The reporting team met a survivor who lived by the Trishuli River in Kathmandu. I know it must be very difficult for you, but could you tell us what happened on that day, August 26th? Save the children. A three-year-old son and a seven-year-old
Speaker A
The reporting team met a survivor who lived by the Trishuli River in Kathmandu. I know it must be very difficult for you, but could you tell us what happened on that day, August 26th? Save the Children. A three-year-old son and a seven-year-old
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daughter ready for school, then I saw my phone. My father-in-law called and said, "Save yourselves, run, don't stay there!" We didn't even think about our belongings, we just ran because the house was right by the river. That spot
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daughter. At the time, she was getting the children ready for the morning. The disaster that began on the mountain was charging toward the village. Instead of an evacuation siren, it was a phone call that rang out. I was getting my
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Yes. Muddy water that had gathered force while flowing down the valley poured into the Trishuli River. The swollen river breached its banks, turned into a massive flood, and swallowed her home. When I saw the water coming, we started to run. I held
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daughter ready for school, then I saw my phone. My father-in-law called and said, "Save yourselves, run, don't stay there!" We didn't even think about our belongings, we just ran because the house was right by the river. That spot
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Once. Tears. My hair was long, and because of it, I couldn't get up in the mud. There was nowhere to hold onto, so the rescuers had to cut my hair to save me. The eardrum is damaged, but they
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right there. That spot. Oh, this is the house. This is where the house was, right by the river. It swallowed everything in 20 minutes.
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Everything she loved in this world. The downstream village swept away by the flood. The flood swept through it. The bridge was cut off, leaving the village on the other side of the river isolated . The residents hung two steel cables
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Yes. Muddy water that had gathered force while flowing down the valley poured into the Trishuli River. The swollen river breached its banks, turned into a massive flood, and swallowed her home. When I saw the water coming, we started to run. I held
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It is still buried in mud. Water. Everyone was shouting, "Come here, come here!" They were all screaming at me to run, and in that split second, I looked back and...I don't even know what happened. They said a landslide had
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my little son, and my daughter ran ahead. My mother-in-law and husband were following behind. The waves pushed me up higher. It took my son and my daughter, and the force of the water threw me further up. Now, her hair...
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riverbed now. Our grandparents never imagined such a huge flood could come from the Trishuli River. They say this is the biggest flood in nearly 40 years of history. An unprecedented disaster, different in both nature and scale. It began with a massive collapse on the
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Once. Tears. My hair was long, and because of it, I couldn't get up in the mud. There was nowhere to hold onto, so the rescuers had to cut my hair to save me. The eardrum is damaged, but they
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The traces of the collapse remain clearly visible in satellite imagery. Incident occurred. This The collapsed area is visible through the satellite footage that we viewed from above.
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said medication or surgery might fix it. She was the only one in her family who was rescued. Right.
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The scale of the collapsed rock mass is enormous, equivalent to covering the entire area of Yeouido with six-story apartment buildings. This At the moment of this massive collapse, seismic waves equivalent to a magnitude 5.2 earthquake were recorded. The debris,
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Everything she loved in this world. The downstream village swept away by the flood. The flood swept through it. The bridge was cut off, leaving the village on the other side of the river isolated. The residents hung two steel cables
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/h. The debris flow continued to grow in size. By the time it reached the Yala Peak main camp, where Koreans are presumed to have gone missing, it had grown large enough to engulf the entire valley. As the debris flow left
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between both sides to create a temporary path. They cling to these ropes to cross the river, barely managing to continue their daily lives.
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collapse in the mountains grow into a flood that covers the river? The rock slope became unstable, and the rock and glacier fell together, spreading rapidly through the valley to cause damage, but the specific processes have not yet been fully uncovered. Following
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It is still buried in mud. Water. Everyone was shouting, "Come here, come here!" They were all screaming at me to run, and in that split second, I looked back and... I don't even know what happened. They said a landslide had
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entered the Langtang mountain range, the valley swept by the flood appeared in the distance. And soon, the magnificent snowy mountain came into view. The slope is visible. Since the rock and glacier-collapsed slope is inaccessible to us, we are now
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occurred, but a moment later, a massive flood struck the village. House-sized boulders that fell from the mountain rolled in front of the house along with the muddy water. Now. For a moment, we didn't know what was happening... we just... Let's go. It looks like a
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The geological conditions are not much different from the collapsed slope, and it has been under the same climatic influence at a similar altitude. Can we identify the cause of the disaster here , in an environment similar to the time
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riverbed now. Our grandparents never imagined such a huge flood could come from the Trishuli River. They say this is the biggest flood in nearly 40 years of history. An unprecedented disaster, different in both nature and scale. It began with a massive collapse on the
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is pouring down from the distant glacier slopes. Now. Where the glacier has melted away, bedrock is exposed. It's the bedrock that had been frozen solid for a long time. Once the ice cover disappears, the bedrock is directly exposed to
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northern slope of Langtang Lirung in the Himalayas. That day, the entire slope where bedrock and glaciers met gave way at once. A so-called rock and ice avalanche. This single moment triggered the unprecedented disaster.
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through cracks and weak spots in the bedrock, it can weaken the bedrock itself. The rate at which Himalayan glaciers are disappearing has doubled since the 2000s. This. Local experts say this is why the range of unstable bedrock zones is also expanding. The
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The traces of the collapse remain clearly visible in satellite imagery. Incident occurred. The collapsed area is visible through the satellite footage that we viewed from above.
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the glacier has retreated about 500 m. So it was under a thick glacial sheet, the rock and the slope were under a thick sheet, so you have an open rock surface that didn't face anything. The extent and stability of bedrock zones
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Yes. We confirmed it, and to estimate its volume, we set a plane that best fits the area and then calculated the amount of the portion that rose above that plane. Our initial calculation was approximately 82 million cubic meters.
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the thing that we are noting about. They. The reporting team followed the valley upward until they encountered the glacier. You have to come slowly.
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The scale of the collapsed rock mass is enormous, equivalent to covering the entire area of Yeouido with six-story apartment buildings. At the moment of this massive collapse, seismic waves equivalent to a magnitude 5.2 earthquake were recorded. The debris,
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It's a glacial lake. So. The reason the lake formed here is that moraine was blocking the front, and a small channel eventually opened up. If a lake like that gets too much water.
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mixed with meltwater, swept through the valley, scraping up soil and rocks from the ground. In just seven minutes, it struck the Nepal-China border trade zone, located about 20 kilometers from the collapse site. At this time, the speed of the debris flow reached 180 km
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had been observed recently along the path of this disaster. Yet, the debris flow that gathered water from somewhere eventually led to a major flood. Even if all the ice that collapsed from the slope has melted. The amount of water
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/h. The debris flow continued to grow in size. By the time it reached the Yala Peak main camp, where Koreans are presumed to have gone missing, it had grown large enough to engulf the entire valley. As the debris flow left
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In that case, at least millions of tons . Where did all that extra water come from? The valley leading to the glacier was strewn with rocks of all sizes in their natural state. After walking for over four hours, climbing over piles of
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the valley and poured into the Trishuli River, the disaster changed its form once again. It had turned into a massive flood. Anyway, this is the total. However, more than a month after the accident, some questions remain unanswered. How could a rock and ice
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But looking closely, it is melting in places with water dripping, And a thick stream of water flows below. Let's clear away the rocks and soil from the surface. Only then is the ice revealed.
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collapse in the mountains grow into a flood that covers the river? The rock slope became unstable, and the rock and glacier fell together, spreading rapidly through the valley to cause damage, but the specific processes have not yet been fully uncovered. Following
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hundreds of meters. It is covered by an average of about 1 meter of rock debris , and research shows that a glacier 40 to 100 meters thick is connected underneath. Local experts suggest that the glacier hidden under the debris may
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the valley, the Current Affairs Planning team headed to the Himalayan site with an expert from the Korea Polar Research Institute who has studied glaciers and climate environments. All
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reached 0.92 square kilometers. The argument is that the initial massive ice-rock mass that collapsed struck this hidden glacier. It is one hypothesis as to where the millions of tons of additional water came from. The main cause was the huge amount of ice
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We tracked the causes to find out how that day's disaster began. As we
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identified two risk factors. Unstable bedrock exposed where the glacier melted. And the glacier hidden under the rock debris. These are quiet changes that were not considered relevant to disasters and thus received no attention. When you talk about rock
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entered the Langtang mountain range, the valley swept by the flood appeared in the distance. And soon, the magnificent snowy mountain came into view. The slope is visible. Since the rock and glacier-collapsed slope is inaccessible to us, we are now
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people live now. The Bhotekoshi River basin, where a flood occurred due to a glacier collapse 10 years ago. Like the Trishuli basin that suffered from this massive flood, it is a river originating from the Himalayas.
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approaching from the opposite slope. The team arrived on the opposite side of the Langtang Lirung collapse site.
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hydroelectric plant is being built in a similar way to the Ut-1 site, where nine Koreans went missing in the recent series of flood disasters. Our reporting team traveled upstream to see a hydroelectric plant that has already been completed and is in operation.
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The geological conditions are not much different from the collapsed slope, and it has been under the same climatic influence at a similar altitude. Can we identify the cause of the disaster here, in an environment similar to the time
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A truck was blocking the road with its wheels stuck. 15 minutes by car. Ah.
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of the rock and ice collapse? This is meltwater from the glacier. It's incredibly cold. Wow, this is glacial meltwater. The water contains information resulting from its reactions with the rocks, soil, or vegetation it encountered while flowing down. Upstream of the waterway. Water
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Built in 2001, this plant was heavily damaged by floods ten years ago. the stock and all the water went down to the power plant and everything was destroyed. The plant management spent 80 billion won in our currency at the
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is pouring down from the distant glacier slopes. Now. Where the glacier has melted away, bedrock is exposed. It's the bedrock that had been frozen solid for a long time. Once the ice cover disappears, the bedrock is directly exposed to
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completely rebuilt to withstand much higher water pressure. No matter how much you expand facilities, disasters beyond prediction can happen at any time, so they also invested effort into an early warning system. Like in case of flood, we have this early warning
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temperature changes and water. This can make the mountain slopes much more unstable. Ultimately, as ice turns into liquid water, slope instability increases. Since that water has to drain somewhere, if it passes between the ice and the underlying bedrock, or
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for unprecedented disasters is difficult, finding ways to minimize damage remains a task we must keep thinking about. You can't fight them.
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through cracks and weak spots in the bedrock, it can weaken the bedrock itself. The rate at which Himalayan glaciers are disappearing has doubled since the 2000s. This. Local experts say this is why the range of unstable bedrock zones is also expanding. The
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The Sisa Planning Chang reporting team, along with experts, looked into whether signs of cascading disasters can be detected in advance, and whether a surveillance system can be established to translate this into actual response.
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same phenomenon was observed on the northern slope of Langli, where a rockfall occurred. The one thing is very clear to us. This area was a glacier for a long time, and checking the data from 1990 to this 36 years,
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floods, and glacial collapses just like the ones that occurred this time. However, in the case of this specific incident, under the changing environment of the high-altitude region , the landslide and the collapse of glaciers and rocks dragged in
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the glacier has retreated about 500 m. So it was under a thick glacial sheet, the rock and the slope were under a thick sheet, so you have an open rock surface that didn't face anything. The extent and stability of bedrock zones
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next, and I think we can refer to this as a chain of disasters. If you look at the footage of the initial event, it appears as a line.
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exposed after glaciers melt have not yet been properly studied, so this is a matter of what exactly is happening below the crust, which is one thing that we have to explore very precisely, so that is my understanding and that is
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At first, they weren't bonded, but then they collapsed. The height of the fall exceeds 1,000 meters. Because it fell from such a great height, it shattered into pieces.
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the thing that we are noting about. They. The reporting team followed the valley upward until they encountered the glacier. You have to come slowly.
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Should we call that the height of the fall? What is it estimated to be?
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While following a steep cliff, they discovered a lake. Glacial meltwater had pooled at the edge of the valley.
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When we convert the destructive force of that ice and rock impact, it comes to about 675,000 tons of TNT. To give you an idea of how much energy 675,000 tons of TNT is, it's equivalent to 45 times the destructive power of the
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It's a glacial lake. So. The reason the lake formed here is that moraine was blocking the front, and a small channel eventually opened up. If a lake like that gets too much water,
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Yes. And the phenomenon known as entrainment erosion is something that generally occurs in areas where debris flows take place. However, the landslide in Nepal, in the Himalayas, involved entrainment erosion on a scale we can't even imagine, so I think it's
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Then it can overflow or breach the barrier, potentially causing a sudden flood. If debris from a landslide or similar event hits a glacial lak...
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Do we have systems to monitor each of these—glacial retreat, ice collapse, impact melting, entrainment erosion, and flash floods? While technologies for assessing risks and monitoring each individual disaster have advanced, monitoring systems or research regarding these chain disasters, where
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events occur sequentially or simultaneously, have not been established. To respond to such disasters, we need research on this entire sequence of processes.
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You are also conducting ex-post analysis of satellite imagery, right? Don't you think there's a lack of effort, or perhaps a greater need, to utilize that as predictive data for medium-to long-term disaster events?
Speaker A
Yes. You've hit the nail on the head. From a research perspective, we usually look at the big picture of how glacier fluctuations in these regions will ultimately affect our climate environment in the future. As a result, the areas we focus our primary
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monitoring, analysis, and constant observation efforts on have been largely centered on large-scale glacier regions. In the case of the glaciers in this specific area, the scale of the glaciers themselves is not that large.
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That’s why it’s a region we haven’t been paying close attention to, but retrospective analysis of the slope stability shows that this area was actually in a more dangerous state than the larger glaciers we thought would have a greater impact on the
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climate environment. Now, when looking at the case of Nepal, it still feels a bit like a story from another country.
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Are disasters in our country also shifting toward a character of sequential and complex disasters? In our country's topographical conditions, which are highly mountainous, while we may not see the same large-scale landslides as those in Nepal, we do see
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quite a lot of cases where landslides occur, grow in size as they travel down valleys through erosion, and cause significant damage to the areas below.
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With over 900mm of rain falling since yesterday, the mountain behind the village collapsed from the top, instantly engulfing the village below. Due to this torrential downpour, ten people have died and four are missing in Sancheong alone. We need to build a
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system to prepare for these types of disasters, but first, are there any limitations to the existing models used to predict such disasters?
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Yes. In fact, most existing disaster prediction models generally work by understanding the relationship between past conditions and disasters, then making predictions based on the premise that a disaster will occur under identical conditions.
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As you mentioned, models for single disasters are mostly statistical because they are built using historical data. Because of this, they are unable to reflect the actual impacts of the extreme rainfall or anomalous climate conditions we are experiencing today.
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Then, it seems necessary for the current statistical models based on past data to shift into a different type of predictive model.
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That's correct. Since current models are fundamentally based on past events, we need to shift our thinking to break free from that and move toward predicting even unprecedented disasters .
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Large-scale disasters that we truly couldn't have imagined might happen again. As you know, the climate crisis is causing various extreme conditions like intense rainfall and snowfall, so we need to develop predictive models to respond when these events are forecast;
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I see this as an urgent issue. Just this summer, we saw how heavy rain fell in a short time, leading to unexpected landslides and floods, which resulted in massive damage. So, could such predictions or warning systems that weren't possible before become feasible
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through these new models in the future? Actually, I think there are about two things that need to be considered for future predictive models. First, it is important to develop models that incorporate changing environmental factors due to climate change, allowing
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us to simulate unprecedented disasters and extreme phenomena. Second, it's not just the natural environment changing; we also need to look at the spaces where people live. Areas like mountain valleys or coastlines weren't really used in the past, but now that people
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are utilizing deeper and more remote areas, the scale of disasters increases when extreme phenomena occur. Our role as scientists isn't to say, "Don't live here." However, we should develop predictive models that can at least show people what kind of risks they
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have to accept if they stay in those areas. From the perspective that one disaster can trigger another, if we were to go back and build a predictive system, what should we consider? The truth is, no matter how much technology
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advances, it is extremely difficult to predict exactly what day, month, and time a glacier will collapse. However, as you just mentioned, since we know these disasters can occur sequentially, the most important thing that needs to happen at the very beginning is this. I
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think the first and most important step is to identify high-risk areas through long-term monitoring and determine which regions require constant surveillance. Next, we need to identify the dangerous early warning signs that could trigger a chain reaction in those
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areas through study and analysis, and then build a system that constantly monitors those signs and connects them directly to alert and preparedness systems. We shouldn't just think about the long-term impacts of climate change-related disasters, but also mid- to short-term impacts—after all,
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that's preparation for things that could happen in our lifetime. I felt that such a perspective is necessary; what do you think?
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Yes. From a disaster perspective, it is clear. Just as we understand this event as a chain reaction, I think we need to make an effort to understand the gap between very long-term climate disasters and large-scale, short-term local disasters. In the case of the
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Nepal disaster, a new keyword called " cascading disaster," which we hadn't dealt with before, has emerged. Because of that, I think we need further research on new concepts and new response strategies for these cascading disasters. From this point of view, I
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believe that if we approach and conduct research on various disasters expected to occur in our country in the future using this concept of cascading disasters, we will be able to reduce damage and build a safer society. For the people of Nepal, water is both the
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foundation of life and an object of faith. The Himalayas, where that water begins, are quietly changing. As glaciers gradually disappear, the Himalayan highlands are being shaken.
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These changes, which no one was looking at, linked one disaster to the next. The Himalayan region is called the water tower of Asia, and these mountain glaciers serve as the headwaters for ten major Asian rivers flowing downstream. Although these changes are
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happening in the Himalayas of Nepal, we must always keep in mind that they could eventually have a huge impact on the entire Asian region. The impacts of climate change are being experienced not only in the Himalayas but also in
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our country through various phenomena. Unexpectedly heavy rainfall in the summer is, in fact, one of the climate crises caused by melting glaciers. So, these series of disasters caused by melting glaciers in the Himalayas can be seen, from a global perspective, as
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an impact that is, to some extent, approaching us as well. Experiencing this disaster in Nepal, many are calling it an unprecedented catastrophe. With our country's climate also changing rapidly, and all kinds of disasters, such as heavy rain and
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various others, occurring in unprecedented ways, it is time that we stop just analyzing such major disasters after they happen, and instead, think very seriously about how to respond in advance and prepare for them.
Topics:Nepal flood 2023Langtang Lirung collapseHimalayan glacier retreatrock and ice avalanchedebris flow disasterclimate change impactsatellite imagery analysisearly warning systemsmountain flood disasterTrishuli River flood
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