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Gorkha

Geosciences Column: Extreme snowfall potentially worsened Nepal’s 2015 earthquake-triggered avalanche

Geosciences Column: Extreme snowfall potentially worsened Nepal’s 2015 earthquake-triggered avalanche

Three years ago, an earthquake-induced avalanche and rockfalls buried an entire Nepalese village in ice, stone, and snow. Researchers now think the region’s heavy snowfall from the preceding winter may have intensified the avalanche’s disastrous effect.

The Langtang village, just 70 kilometres from Nepal’s capital Kathmandu, is nestled within a valley under the shadow of the Himalayas. The town was popular amongst trekking tourists, as the surrounding mountains offer breathtaking hiking opportunities.

But in April 2015, a 7.8-magnitude earthquake, also known as the Gorkha earthquake, triggered a massive avalanche and landslides, engulfing the village in debris.

Scientists estimate that the force of the avalanche was half as powerful the Hiroshima atomic bomb. The blast of air generated from the avalanche rushed through the site at more than 300 kilometres per hour, blowing down buildings and uprooting forests.

By the time the debris and wind had settled, only one village structure was left standing. The disaster claimed the lives of 350 people, with more than 100 bodies never located.

Before-and-after photographs of Nepal’s Langtang Valley showing the near-complete destruction of Langtang village. Photos from 2012 (pre-quake) and 2015 (post-quake) by David Breashears/GlacierWorks. Distributed via NASA Goddard on Flickr.

Since then, scientists have been trying to reconstruct the disaster’s timeline and determine what factors contributed to the village’s tragic demise.

Recently, researchers discovered that the region’s unusually heavy winter snowfall could have amplified the avalanche’s devastation. The research team, made up of scientists from Japan, Nepal, the Netherlands, Canada and the US, published their findings last year in the EGU’s open access journal Natural Hazards and Earth System Sciences.

To reach their conclusions, the team drew from various observational sources. For example, the researchers created three-dimensional models and orthomosaic maps, showing the region both before it was hit by the coseismic events and afterwards. The models and maps were pieced together using data collected before the earthquake and aerial images of the affected area taken by helicopter and drones in the months following the avalanche.

They also interviewed 20 villagers local to the Langtang valley, questioning each person on where he or she was during the earthquake and how much time had passed between the earthquake and the first avalanche event. In addition, the researchers asked the village residents to describe the ice, snow and rock that blanketed Langtang, including details on the colour, wetness, and surface condition of the debris.  

Based on their own visual ice cliff observations by the Langtang river and the villager interviews, the scientists believe that the earthquake-triggered avalanche hit Langtang first, followed then by multiple rockfalls, which were possibly triggered by the earthquake’s aftershocks.

A three-dimensional view of the Langtang mountain and village surveyed in this study. Image: K. Fujita et al.

According to the researchers’ models, the primary avalanche event unleashed 6,810,000 cubic metres of ice and snow onto the village and the surrounding area, a frozen flood about two and a half times greater in volume than the Egyptian Great Pyramid of Giza. The following rockfalls then contributed 840,000 cubic metres of debris.  

The researchers discovered that the avalanche was made up mostly of snow, and furthermore realized that there was an unusually large amount of snow. They estimated that the average snow depth of the avalanche’s mountainous source was about 1.82 metres, which was similar to snow depth found on a neighboring glacier (1.28-1.52 metres).

A deeper analysis of the area’s long-term meteorological data revealed that the winter snowfall preceding the avalanche was an extreme event, likely only to occur once every 100 to 500 years. This uncommonly massive amount of snow accumulated from four major snowfall events in mid-October, mid-December, early January and early March.

From these lines of evidence, the team concluded that the region’s anomalous snowfall may have worsened the earthquake’s destructive impact on the village.

The researchers believe their results could help improve future avalanche dynamics models. According to the study, they also plan to provide the Langtang community with a avalanche hazard map based on their research findings.  

Further reading

Qiu, J. When mountains collapse… Geolog (2016).

Roberts Artal, L. Geosciences Column: An international effort to understand the hazard risk posed by Nepal’s 2015 Gorkha earthquake. Geolog (2016).

The day the Earth trembled: A first-hand account of the 25 April Nepal earthquake

The day the Earth trembled: A first-hand account of the 25 April Nepal earthquake

On the 25th April 2015, Viktor Bruckman, a researcher at the Austrian Academy of Sciences, and a team of his colleagues were a few hours into a hike between the settlements of Lamabagar, in a remote area of northeastern Nepal, and the Lapchi Monastery when a magnitude 7.8 earthquake struck Nepal. Their journey cut short by the trembling Earth, stranded in the heights of the Himalayas, this is their personal experience of the Gorkha earthquake, summarised by EGU Communications Officer Laura Roberts. 

Researching land use in Nepal

Bruckman is part of an international team of researchers, from Austria, Nepal and China, studying the land use and forest resource management in the densely wooded and remote Gaurishankar Conservation Area, in eastern Nepal. Bruckman and his team want to better understand how the local communities are linked to the resources in the area and how their daily life has been affected since the introduction of the Conservation Area. Their research project also aims to explore how the ongoing building of the largest hydropower plant in Nepal: the Upper Tamakoshi Hydropower Project (UTHP) might disrupt the local populations.

The team conducted a set of semi-structured interviews in order to assess land management practices and the impact of new management policies since the Gaurishankar Conservation Area was set up in 2010 (by Dr. Viktor Bruckman).

The team conducted a set of semi-structured interviews to assess land management practices and the impact of new management policies since the Gaurishankar Conservation Area was set up in 2010 (Credit: Dr. Viktor Bruckman).

To answer these questions, Bruckman and his colleagues travelled to Nepal in April to participate in workshops with government and institutional bodies based in Kathmandu, as well as visiting local communities deep within the Gaurishankar Conservation Area to conduct face-to-face interviews.

Beyond the hydropower construction site there are no roads, meaning the team had to hike across the rugged Himalayas to reach the residents of the most remote settlements and the target location for setting up monitoring plots. Their planned route would take them 25 km from Lamabagar, at 2000 m above sea level, reaching Lapchi Monastery, close to the Tibetan border, two days later having climbed to an altitude of 3800 m.

The hike

On the morning of the 25th April, a team composed of Bruckman, his Nepalese colleague Prof. Devkota, Devkota’s student Puskar and Prof. Katzensteiner from the University of Natural Resources and Life Sciences Vienna (BOKU), set off on the trek to Lapchi. They were accompanied, albeit a little later following breakfast, by three porters who carried the bulk of their scientific equipment, some food and other ‘home comforts’ such as sleeping bags and mattresses. Given the physical effort the trek would involve, many of the food supplies were delivered to Lapchi via helicopter, a few days in advance – local porters would meet the team at settlements downstream of the monastery and deliver the provisions over the course of the next few days.

Despite the constant drizzle and strains of the climb, the entire team was stuck by the beauty of the surroundings: steep cliffs of metamorphosed sedimentary series (Tethys Himalaya within the Central Himalayan Domain), diverse mix deciduous forests and glistening streams.

The moment everything changed

At 12:05, not long after having traversed the most challenging section of the hike thus far, walking along the Lapchi River Valley, the ground under the team’s feet started to quiver. The quiver quickly grew to a strong shake dislodging football sized rocks from the surrounding slopes. The realisation hit the researchers that they were experiencing an earthquake and their primary concern was to seek shelter from the ongoing rock fall triggered by the ground shaking.

“Large rocks, with size equal to small houses, smashed into the river breaking into smaller pieces which where flung in all directions”, describes Bruckman, who by now had found protection, alongside Prof. Devkota, behind a large tree.

A few moments later, the earthquake ended and both emerged from behind the tree unharmed.

Left: Rockfall from the opposite cliffs made our location a highly dangerous place. Right: Seconds after the main tremor was over, everything was changed. The river color turned brown, dust and Sulphur smell was in the air and the path was destroyed by small landslides or rocks (Credit: Prof. Dr. Klaus Katzensteiner).

Left: Rockfall from the opposite cliffs made the researchers’ location a highly dangerous place. Right: Seconds after the main tremor was over, everything was changed. The river color turned brown, dust and Sulphur smell was in the air and the path was destroyed by small landslides or rocks (Credit: Prof. Dr. Klaus Katzensteiner).

They found Prof. Katzensteiner sheltering under a large rock overhang, but there was no sign of Puskar. The three men eyed up a large boulder which had come to rest on the path and feared the worst. Some minutes later, Puskar appeared, unharmed, along the path accompanied by a lama – a Buddhist monk – who’d encouraged the student to run up hill away from the projectiles from the river.

“The lama saved our student’s life; he was almost hit by a large rock which destroyed the water bottle attached to his backpack,” says Bruckman.

A stroke of luck

With their porters some hours trek behind them, almost no food supplies and no other equipment, and worried about potential flash floods as a result of landslides upstream, the group decided to make their way out of the valley and head back towards Lamabagar, only to find that the trail had been wiped out by a massive landslide.

The lama’s knowledge of the local terrain was invaluable as he guided the scientists to a meditation centre, where a group of about 20 lamas kindly took them in, sharing their food, offering tea and a place to sleep.

Having found a place of shelter, Bruckman and his colleagues, knowing how worried their families would be, were desperate to contact them. But amongst the high peaks of the Himalayas, in one of the most remote parts of Nepal, mobile phone signal is hard to come by. Only once, on the morning of the 26th of April, were the group successful in reaching loved ones, but it was enough: they were able to communicate they had survived, but were now trapped in the Lapchi River Valley.

The retreat where lamas provided the scientists with food and shelter (Credit: Prof. Dr. Klaus Katzensteiner).

The retreat where lamas provided the scientists with food and shelter (Credit: Prof. Dr. Klaus Katzensteiner).

Back home, a rescue mission started: The scientists’ families, the officials of their institutions, their countries Foreign Ministries’, Embassies and the local military all rallied to locate and bring home the researchers. Five days after first arriving at the Buddhist meditation centre, the group was rescued by a helicopter, which took them to the safety of military camp Charikot.

Retracing their steps, this time in a helicopter, Bruckman and his colleagues realised the scale of the devastation caused by the earthquake. The first village they’d intended to reach on their hike, Lumnang, was completely destroyed. 80% of the building structures in the valley had disappeared. Landslides has wiped out large sections of the trail, meaning returning to Lamabagar would have been out of the question.

Tragedy

The team’s porters, travelling behind the researchers when the earthquake hit, were far less fortunate. Tragically, one of the team’s porters was killed by a landslide triggered by the earthquake, whilst another was seriously injured. Only one returned safely to Lamabagar. Whilst hiking, the scientists overtook several groups of people also headed towards Lapchi and a team of hydropower experts – they are all reported missing.

The region, already damaged by the April 25th earthquake, was further rocked by a powerful, magnitude 7.3, aftershock. Since then, Bruckman and his colleagues have been unable to reach their contacts in Lamabagar. Reports indicate that hardly any structures were left standing in the village.

A view of Lamabagar prior to the earthquakes. At 2000m a.s.l., the village lies on the flat riverbed of the Upper Tamakoshi River, which developed as a consequence of a massive landslide (probably earthquake-induced) in the past (by Dr. Viktor Bruckman).

A view of Lamabagar prior to the earthquakes. At 2000m a.s.l., the village lies on the flat riverbed of the Upper Tamakoshi River, which developed as a consequence of a massive landslide (probably earthquake-induced) in the past (Credit: Dr. Viktor Bruckman).

The future

Following the earthquake, the scientists realise that the original research aims are no longer valid and “we would probably not meet the communities’ needs if we stick to the original ideas”, explains Bruckman.

Therefore, the plan is to carefully assess the regions current situation and develop a new research proposal which will focus on supporting the remote villages on a long-term and sustainable basis. In the event of any future field work in the region, the scientist will ensure they carry, at the very least, an Emergency Position Indicating Radio Beacon (EPIRB), if not a satellite phone.

Science aside, their experience in the Nepal means the scientists were deeply touched by the kindness extended to them by the lamas and now seek to support the communities affected by the earthquakes. In particular they want to raise funds for the families of the porters who passed away and were injured while transporting their supplies.

 By Laura Roberts, EGU Communications Officer

A message from Bruckman and his colleagues

Please help us support the affected families.

For the purpose of collecting donations, we opened an account at the University of Natural Resources and Life Sciences Vienna (BOKU). Funds will be collected in a transparent manner and directly used for supporting the porter’s families and the villagers of Lumnang, who have lost everything and they will most likely not receive help from other sources soon. We will facilitate support through the trustworthy Nepalese project partners (including full documentation) and the Lamas of Lapchi monastery and from the retreat where we were able to stay. Please help us to support this remote region; even a small contribution is very much appreciated. Our direct contacts ensure that 100% of the donations reach the target group.

Here are the account details for wire transfer:

Recipient: Universität für Bodenkultur Wien, Spenden IBAN: AT48 3200 0018 0050 0512 BIC: RLNWATWWXXX Payment reference: 7912000003

Payments via Credit Card are also possible (Master Card and Visa). Should you wish to pay per credit card, please send an e-mail containing your name, address, card number, expiry date and security code (3-digits) to c.hofer@boku.ac.at.

We thank you very much for your contribution!

The team after their ordeal. They extend their deepest condolences to the family of the porter that lost his life during our the Prof. Dr. Klaus Katzensteiner).

The team after their ordeal. They extend their deepest condolences to the family of the porter who lost his life during the expedition. (Credit: Prof. Dr. Klaus Katzensteiner).

 

This blog post is a summary of: How a geophysical extreme event dramatically changed fieldwork plans – a personal account of the Gorkha Earthquake, originally posted on the EGU’s Energy, Resources and the Environment Division Blog.

For more information about the 2015 April and May earthquakes, please see the links provided in the original blog post. You can also access more information via this information briefing issued by the EGU.