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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).

When mountains collapse…

When mountains collapse…

Jane Qiu, a grantee of the Pulitzer Center on Crisis Reporting, took to quake-stricken Nepal last month — venturing into landslide-riddled terrains and shadowing scientists studying what makes slopes more susceptible to failure after an earthquake. The journey proved to be more perilous than she had expected.

What would it be like to lose all your family overnight? And how would you cope? It’s with these questions in mind that I trekked with a heavy heart along the Langtang Valley, a popular touristic destination in northern Nepal.

Exactly a year ago this week, this remote Himalayan watershed witnessed the single most horrific canastrophy of the Gorkha Earthquake: a massive avalanche engulfed Langtang and nearby villages, leaving nearly 400 people killed or missing.

The quake shook up ice and snow at five locations along a 3-kilometre ridge between 6,800-7,200 metres above sea level. They went into motion and swept huge amounts of loose debris and fractured rocks along their way — before crashing several kilometres down to the valley floor.

The avalanche generated 15 million tonnes of ice and rock, and sent powerful wind blasting down the valley, flattening houses and forests. Wind speeds exceeded 322 kilometres per hour and the impact released half as much energy as the Hiroshima nuclear bomb. Nothing in its path could have survived.

A pile of commemorating stones on the debris that buried Langtang and nearby villages last April, killing and leaving missing nearly 400 people. (Credit: Jane Qiu)

A pile of commemorating stones on the debris that buried Langtang and nearby villages last April, killing and leaving missing nearly 400 people. (Credit: Jane Qiu)

Where the villages used to stand is now a gigantic pile of debris, up to 60 metres deep. It’s effectively a mass grave where people pile up stones and put up prayer flags to mark where their loved ones used to live.

It’s hard to come to terms with the scale of the devastation. Everybody in the valley has lost somebody to the monstrous landslide. About two dozen children from 16 families, who were in schools in Kathmandu during the earthquake, lost all their family in the matter of a few minutes.

It’s a sombre reminder of how dangerous it can be in the Himalayas — where people live so close to ice and where population growth and the search for livelihood often push them to build in hazardous areas.

The only building in the village of Langtang that survived the avalanche. The rocky enclave protected it from the crushing debris and the powerful blast. (Credit: Jane Qiu)

The only building in the village of Langtang that survived the avalanche. The rocky enclave protected it from the crushing debris and the powerful blast. (Credit: Jane Qiu)

Under-appreciated danger

The Langtang tragedy also reminds us how deadly landslides can be during an earthquake — a danger that is often under-appreciated. While earthquakes and landslides are like conjoined twins that go hand in hand, most of the resources go into building houses that can sustain strong shaking, and far too little into mitigating landslide risks.

In both the 2005 magnitude-7.6 Kashmir Earthquake in Pakistan and the 2008 magnitude-7.8 Wenchuan Earthquake in China — which killed approximately 26,000 and 90,000 people, respectively — a third of the fatalities were caused by landslides. While it’s certainly important to build earthquake-proof houses, it’s equally important to build them at safe locations.

In addition to the killer avalanche in Langtang, the Gorkha Earthquake unleashed over 10,000 landslides across Nepal, which blocked rivers and damaged houses, roads, and hydropower stations. Many valleys are totally shattered — with landslide scars running down from the ridge top like gigantic waterfalls, and numerous small failures marring the landscape like fireworks shooting across the sky.

Driving along the Aniko Highway that connects Nepal with Tibet, it’s not difficult to see that many houses had survived the shaking only to be crushed by debris flows and rock falls. The border remains closed because of continuing landslide hazards. The highway, which used to have some of the worst traffic jams in Nepal, is totally deserted.

A building in Kodari — which used to be a bustling trade town at the Nepal-Tibet border — was unscathed during the earthquake only to be damaged by large rock falls. (Credit: Jane Qiu)

A building in Kodari — which used to be a bustling trade town at the Nepal-Tibet border — was unscathed during the earthquake only to be damaged by large rock falls. (Credit: Jane Qiu)

Enduring legacy

A major concern is that Nepal will suffer from more severe landslides than usual for a long time. During the last monsoon, the landslide rate was about ten times greater than an average year. And my trek along the Langtang Valley was accompanied by frequent sound tracks of falling rocks and shifting slopes. A number of times, I had to run from boulders crushing down onto the trail — a clear sign that there are lots of instability in the system.

The instability could go on for years or even decades and will be exacerbated by rainfall and aftershocks. This enduring legacy is often not fully taken on board in quake recovery — with devastating consequences. Eight years after the Wenchuan Earthquake, for instance, settlements built after the disaster continue to be inflicted by a heightened level of landslides, which cause floods and destroy infrastructures.

This points to the importance of rigorous risk assessment before reconstruction and close monitoring afterwards. There is also an urgent need to better understand what makes mountainsides more susceptible to landslides after an earthquake and how they recover over time.

To achieve that end, several research groups went into landslide-ridden areas in Gorkha’s immediate aftermath. They wanted to capture what happened to the landscape immediately after the quake, so they could track the changes in the coming years.

Early warning

Last month, I joined one such team — consisting of Christoff Andermann, Kristen Cook and Camilla Brunello, of the German Research Centre for Geosciences (GFZ) in Potsdam, Germany, and their Nepalese coordinator Bhairab Sitaula — on a field trip along the Arniko Highway.

That was their fourth trip in Nepal since last June when they began to map the landslides and installed a dozen broadband seismometers, along with weather stations and river-flow sensors, over 50 square kilometres of badly shaken terrains.

The team often attracted a few curious onlookers when they worked away, but nothing provoked more excitement than the drone, says Cook. The crowd, especially kids, were thrilled to see the little robotic device buzzing around like a gigantic mosquito, she adds. A camera and sensors onboard can help them to locate the landslides and monitor debris movement, especially after rainstorms.

 

Christoff Andermann, Camilla Brunello and Bhairab Sitaula performing maintenance on a broadband seismometer and weather station near the village of Chaku on the Arniko Highway (Credit: Jane Qiu)

Christoff Andermann, Camilla Brunello and Bhairab Sitaula performing maintenance on a broadband seismometer and weather station near the village of Chaku on the Arniko Highway (Credit: Jane Qiu)

Another exciting aspect of their research is the use of seismology to probe geomorphic processes over a large area. Landslides are effectively earthquakes that occur near the surface, and produce signals that can be picked up by seismometers.

The team, led by Niels Hovius of GFZ, can detect precursory seismic signals days before a landslide happens. They also study ground properties by measuring how traffic vibrations travel through the ground.

Because seismic waves travel faster when subsurface materials are wet, the researchers are able to trace how rainfall penetrates into and through the ground. This determines the pressure of water in spaces between soil and rock particles, a key factor controlling slope stability.

Such studies will one day allow researchers to determine the rainfall thresholds that could precipitate a landslide and capture deformation precursors days in advance. This offers a real prospect of an effective early warning system, which is urgently needed in a country that is increasingly plagued by landslides.

By Jane Qiu, freelance science writer in Beijing

Further reading

Qiu, J. Listening for landslides, Nature 532, 428-431 (2016).

Jane Qiu, an awardee of the 2012 EGU Science Journalism Fellowship, is a Chinese freelance science writer in Beijing. She is passionate about the origin and evolution of the Tibetan Plateau and surrounding mountain ranges—a vast elevated land also known as the Third Pole because it boasts the largest stock of ice outside the Arctic and the Antarctic. 

Travelling extensively across the Third Pole, up to 6,700 meters above sea level (http://science.sciencemag.org/content/351/6272/436), Qiu has covered wide-ranging topics—from the meltdown of Himalayan glaciers, grassland degradation, the origin of woolly rhino, to the people of Tibet. Her work regularly appears in publications such as Nature, Science, The Economist, Scientific American, and SciDev.Net.

Qiu’s journey to the Third Pole began with Marine Biological Laboratory’s Logan Science Journalism Fellowship that allowed her to travel to the Arctic and the Antarctic and report climate change first hand. These experiences sowed the seeds for her later fascination with geoscience and environmental studies, and afforded her the insight to draw parallels between these geographically diverse regions.

Imaggeo on Mondays: Annapurna snow avalanche

Imaggeo on Mondays: Annapurna snow avalanche

The Annapurna massif is located in an imposing 55 km long collection of peaks in the Himalayas, which behave as a single structural block. Composed of one peak (Annapurna I Main) in excess of 8000 m, a further thirteen peaks over 7000 m and sixteen more of over 6000 m, the massif forms a striking structure within the Himalayas.

Annapurna I Main, the tenth highest peak in the world, is towering at an impressive 8,091 m. Renowned for its difficult climbing conditions, it holds one of the highest fatality rates of the 8000+ peaks. October 2014 marked a particular dark period in the mountain’s climbing history when 39 trekkers were killed during severe snowstorms and avalanches while completing a popular hike circling Annapurna I.

Martin Struck, a PhD student at the University of Wollongong, Australia, captured this extraordinary photograph of a surging avalanche early one morning in October 2012. Martin visited the Annapurna massif as part of his Diploma project at the University of Potsdam about suspended sediment fluxes in the Kali Gandaki River which cuts the world’s deepest gorge through the Himalayas between the Annapurna and Dhaulagiri massifs. The snow avalanche careered down the ~35° sloping northeast flank of Tilicho himal, a peak only 10 km away from the Annapurna I summit.

“The avalanche is one of five I spotted that morning in the area. The tracks and runout zones of previous snow and/or dry snow avalanches are clearly visible in the image,” describes Martin.

He explains that rising morning temperatures triggered the avalanches, causing the failure of stable snow which had fallen on the night before.

The area is close to Tilicho Lake, located at about 4900 m above sea level, and one of many Himalayan glacial lakes which play a crucial role in the supply of water to the inhabitants of Nepal.

“Snow and glacial melt contribute approximately 10% to the annual discharge of the main Nepalese rivers, but are of significant important outside the monsoon season,” explains Martin.

Earlier on this year, a study published in the open access journal, The Cryosphere, found that if greenhouse-gas emissions continue to rise, glaciers in the Everest region of the Himalayas could experience dramatic change in the decades to come. The glacier model used in the paper shows that glacier volume could be reduced between 70% and 99% by 2100. The findings have important implications for the future availability of water in the region: a significant decrease in glacial volume would have consequences for agriculture and hydropower generation. You can learn more about this research and it’s consequences in this Press Release: Glacier changes at the top of the world – Over 70% of glacier volume in Everest region could be lost by 2100.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

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.