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Gorkha earthquake

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.

Geosciences Column: An international effort to understand the hazard risk posed by Nepal’s 2015 Gorkha earthquake

Geosciences Column: An international effort to understand the hazard risk posed by Nepal’s 2015 Gorkha earthquake

Nine months ago the ground in Nepal shook, and it shook hard: on April 25th 2015 the M7.8 Gorkha earthquake struck and was followed by some 250 aftershocks, five of which were greater than M 6.0. The devastation left behind in the aftermath of such an event, and how to coordinate disaster-relief efforts in a vast, mountainous region, is difficult to imagine. Yet, this December at the 2015 AGU Fall Meeting, I came a little closer.

At the meeting I attended the press conference ‘Future Himalayan seismic hazards: Insights from earthquakes in Nepal’. It focused, mainly, on the outcomes of two research papers published in Science on the role that both past and the recent Gorkha earthquakes can play in triggering quake-induce landslides. The findings of the research were covered widely by the media.

I was struck, not only by those findings, but by the personal accounts of the scientists who’d seen the devastation left behind by the earthquake. But more still, what really caught my attention, was the multinational effort and collaboration that went into the research.

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

Before-and-after photographs of Nepal’s Langtang Valley showing the near-complete destruction of Langtang village due to a massive landslide caused by the 2015 Gorkha earthquake. Photos from 2012 (pre-quake) and 2015 (post-quake) by David Breashears/GlacierWorks. Distributed via
NASA Goddard on Flickr. Click to enlarge.

After the press conference I met with Dalia Kirschbaum of the NASA Goddard Space Flight Centre and Dan Shugar of the University of Washington Tacoma, two of the co-authors of the 2015 Gorkha earthquake paper, to discuss this aspect of the research in more detail.

Given the vast geographical area over which the Gorkha earthquake had caused damage, as well as the hard-to-access mountainous terrain, the team used satellite imagery to map earthquake-induced landslides. They also monitored the stability of the region’s moraine dammed glacial lakes, prone to outburst following earthquakes due to the failure of moraine damns.

When a large scale disaster occurs the International Charter on Space and Major Disasters allows for the dedicated collection of space data to contribute towards humanitarian and charitable efforts in areas affected by natural or man-made disasters. Following the Gorkha earthquake, Nepal called for the activation of the charter.

Following Nepal activating the Charter, satellite imagery was provided by NASA, the Japan Aerospace Exploration Agency, the China Space Agency, as well as private organisations such as DigitalGlobe, to name but a few.

This project was “different to what we had seen in the past in terms of international collaboration,” Dalia told me during our conversation.

A group of nine nations, coordinated by the Global Land Ice Measurements from Space, began assessing the imagery provided and mapping the earthquake-induced geohazards, including landslides. In the first instance the data was used to identify potentially hazardous situations where communities and infrastructure might be at risk. This was followed by an effort to build a landslide inventory, which could provide information about the distribution, character, geomorphological, lithological and tectonic controls which govern the occurrence of earthquake triggered landslides.

An international volunteer geohazards team mapped landslides triggered by the 2015 Nepal Gorkha earthquake and its aftershocks. The landslides were mapped using a range of different satellite products. Credit: Landslide mapping team/NASA-GSFC. Distributed via NASA Goddard on Flickr.

An international volunteer geohazards team mapped landslides triggered by the 2015 Nepal Gorkha earthquake and its aftershocks. The landslides were mapped using a range of different satellite products. Credit: Landslide mapping team/NASA-GSFC. Distributed via NASA Goddard on Flickr.

Simultaneously, scientists from the British Geological Survey and Durham University also began to build a database of known geohazards in the region. The data was shared between the two working groups.

“For no other major earthquakes have landslide inventories come from such a diverse range of datasets and organisations,” explained Dalia.

Neither had emergency remote sensing been undertaken so quickly.

I was interested in why the Nepal earthquakes in particular had inspired this, so far unique – but hopefully not the last – diverse international collaboration to better understand earthquake-induced geohazards.

Dan Shugar thinks it was because so many geoscientists have a deep personal connection with Nepal. Durham University scientists, for example, take geology students to the region on an annual field trip.

“Everybody loves Nepal! The nature of the country really lent itself to people wanting to help,” he added.

Field visit identifies light damage at Tsho (lake) Rolpa. Post-earthquake image of Tsho Rolpa appears identical to its appearance shortly before the earthquake. Two areas of fractures —believed formed by the May 12 2015 aftershock— were observed on the engineered part of the end moraine from a helicopter during an inspection undertaken by the U.S. Geological Survey at Tsho Rolpa. Photos from 27 May by Brian Collins/USGS, courtesy of USAID-OFDA (Office of Foreign Disaster Aid). Distributed via NASA Goddard on Flickr.

Field visit identifies light damage at Tsho (lake) Rolpa. Post-earthquake image of Tsho Rolpa appears identical to its appearance shortly before the earthquake. Two areas of fractures —believed formed by the May 12 2015 aftershock— were observed on the engineered part of the end moraine from a helicopter during an inspection undertaken by the U.S. Geological Survey at Tsho Rolpa. Photos from 27 May by Brian Collins/USGS, courtesy of USAID-OFDA (Office of Foreign Disaster Aid). Distributed via
NASA Goddard on Flickr.

For many, including Dan, it rose from a need to contribute to the humanitarian effort. Despite having trained as a geomorphologist and actively researching Alpine natural hazards, prior to the Gorkha earthquake he’d not had the opportunity to apply his knowledge and expertise to help others. It allowed him to offer help in the same way a medic might do by flying out to the scene of a disaster and offering medical expertise and treating the injured.

For Dalia, the positive impact made in the Nepal crisis by the international effort of quickly gathering, sharing and interpreting Earth observation data, was an important driver in keeping her linked to the project.

This effort is now seeing a life beyond the Nepal earthquakes. NASA satellites had previously been involved in the acquisition of data sets to aid in humanitarian crisis, such as in the aftermath of hurricanes. The successful approach taken during the Nepal earthquakes will now help coalesce NASA’s disaster programme and how NASA will respond to natural hazards in the future. It is leading to a more formalised disaster response programme.

The lessons learnt from the Nepal earthquake are ongoing, with much still being done in the scientific realms to better understand the hazards posed by the tectonics of the region, and associated geohazards triggered by the earthquakes. Many of the international collaborations fostered during the crisis are ongoing and will hopefully mean an improved response to future natural hazards in the region.

By Laura Roberts Artal, EGU Communications Officer. With many thanks to Dalia Kirschbaum and Dan Shugar.

References

Schwanghart, W., Bernhart, A., Stolle, A., et. al.,: Repeated catastrophic valley infill following medieval earthquakes in the Nepal Himalaya, Science, vol. 351, 6269, 147-150, doi: 10.1126/science.aac9865, 2016.

Kargel, J. S., Leonard, G. J., Shugar, D.H., et al.,: Geomorphic and geologic controls of geohazards induced by Nepal’s 2015 Gorkha earthquake, Science,vol. 351, 6269, 147-150, doi: 10.1126/science.aac8353, 2016.

Unfortunately, some of the publications referenced in this post are close access – but other links included in this post, as well as the post itself, hopefully convey the overall message of the research.