How extreme events impact Earth’s surface: reports from the 6th EGU Galileo conference

How extreme events impact Earth’s surface: reports from the 6th EGU Galileo conference

Throughout the year, EGU hosts a number of meetings, workshops, and conferences for the geoscience community. While the EGU’s annual General Assembly brings more than 15,000 scientists together under one roof, the EGU Galileo Conferences allows a smaller number of scientists to discuss and debate issues at the forefront of their discipline. In this blog post, the organisers of the 6th Galileo Conference “Perturbations of earth surface dynamics caused by extreme events” reflect on a week of insightful presentations and discussions on rare and catastrophic events.

“How do extreme events perturb Earth surface dynamics?” This question kept us busy during the entire week of the 6th EGU Galileo Conference “Perturbations of earth surface dynamics caused by extreme events”, which took place in Nepal from 13-19 October 2019. As organisers, we had aimed for a slightly unusual conference venue. We kept the nice hotels to a minimum of two nights and took the participants out to the Bhote Kosi for some camping for the remainder of the week to foster discussions and idea exchange.

The Bhote Kosi valley, about four hours’ drive north east of Nepal’s capital city Kathmandu, was heavily impacted by the April 2015 Gorkha earthquake and a subsequent glacier lake outburst flood event in 2016. This valley still today carries the signs of these earlier events in the form of large landslides, unstable slopes, and reworked river beds. As such, the valley serves as an ideal natural laboratory to better understand and quantify how the Earth’s surface responds to such perturbations. The Bhote Kosi had been a basecamp for a number of us studying natural hazards during the multiple field campaigns organised after the Gorkha earthquake, and this conference was a great opportunity to share what we have learned over the past years while directly illustrating the conference topics.

This conference brought together scientists studying a range of rare/extreme events and their broader impacts on Earth surface processes, biogeochemical cycles and human systems. Credit: Monique Fort

What seemed easy in the early days of planning did not come without inevitable doubts as the conference came closer. How do we make sure we have enough tents for everyone, how do we deal with the frequent power cuts, how do we make sure to cater enough local beer to thirsty geoscientists, and what if everyone contracted food poisoning? Fortunately, 60 participants, including ten Nepali colleagues and many early career scientists, blindly followed us without much afterthought and we were off for a busy and promising week.

The talks and posters covered most extreme event triggers: from earthquakes to volcanic eruptions and from wildfires to storms and tsunamis. These presentations provided food for thought for the geomorphologist, the geochemist, and the seismologist alike. Nepal, with the aftermath of the Gorkha earthquake, was well represented in these presentations, but many other parts of the world were covered as well.

Overall, this conference demonstrated the role of extreme events as geomorphic actors, able to shape landscapes and affect biogeochemical cycles. This conference also highlighted the large range of possible geomorphic responses, both in terms of magnitude and spatial extent, suggesting that the question of how these extreme events should be defined (are they large or are they rare events?) should ultimately be left to the investigators. It is however clear that in terms of geomorphic impact, an extreme event should lead to an observable perturbation above a, to-be defined, background variability, and be followed by a recovery period that leads to an old or new steady-state. As such, extreme events are not created equal and future research is needed to understand why such a range of responses are encountered.

Conference attendees had the opportunity to discuss questions and topics at the forefront of their field, from ethics in science to international cooperation. (Credit: Monique Fort) 

Time for discussion also allowed us to debate on the morality of post-disaster scientific work. We concluded that basic research questions related to these events need to be pursued and frequently require immediate mobilisation of scientific equipment and personal. However, this discussion also highlighted the need for clear and transparent international coordination so as to not interfere with relief efforts and avoid being perceived as greedy ambulance-chasing scientists. This important discussion was backed by input from a large Nepali delegation, providing an insight into how they had perceived these questions directly after the recent earthquake. Further discussions focused on the commonalities of different extreme events and the possibility to define a common framework that would allow us to compare the geomorphic impact of an earthquake to that of a storm or a wildfire.

Finally, this conference allowed us to lay the foundation blocks for future international coordination efforts. While the exact contours remain to be defined, all participants emphasised the need to prioritise research questions and resources in the case of rapid response efforts. These efforts require clear coordination with affected countries and funding bodies, but for instance also encourage scientific actors to agree on common publication strategies upfront.

Conference participants tour the Bhote Kosi valley to learn more about how extreme events can shape landscapes. (Credit: Monique Fort) 

In the middle of this busy schedule, a day of field excursion provided a welcome change. From small to large, the Bhote Kosi has it all: boulders, landslides, debris flows etc… Driving up the valley all the way to the Nepal-China border provides a humbling experience of how these idyllic landscapes can be turned into deadly traps in the blink of an eye. With closer scrutiny it becomes obvious that the whole landscape has been shaped by a myriad of these catastrophic events, directly questioning the notion of extremes.

After six days of presentations, posters, and late night discussions, it was time to close this intense, yet educational week. In the end there weren’t too many power cuts, no one got sick, most of us managed to shower with hot water and only a few reported spiders in their tents. In line with the local Nepali customs, the end of the conference was celebrated by inspired dancing until late at night when the first shuttles back to the airport started to take people back to Kathmandu.

By Maarten Lupker, ETH Zürich, Switzerland

60 scientists from all over the world came together for the opportunity to debate and discuss issues related to rare/extreme events and how they impact Earth system dynamics. Credit: Monique Fort


This conference was jointly organised with the Nepal Geological Society (NGS), without which this week would have never existed. While many people were involved, we would like to extend special thanks to Basanta Raj Adhikari and Ananta Prasad Gajurel from Tribhuvan University as well as the former president of NGS, Kabi Raj Paudyal and the present one Ram Prasad Ghimire. Bhairab Sitaula also provided invaluable help in all logistical aspects of this conference.

The conference was also co-sponsored by the US National Science Foundation, which provided overseas travel grants. Support from DiGOS & GFZ Potsdam were also greatly appreciated.

The organiser team: Christoff Andermann, Kristen Cook, Sean Gallen, Maarten Lupker, Christian Mohr, Ananta P. Gajurel, Katherine Schide, Lena Märki

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 (, 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.

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