GeoLog

Geomorphology

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: recreating geological processes in the lab

Imaggeo on Mondays: recreating geological processes in the lab

Many of the processes which take place on Earth happen over very long time scales, certainly when compared to the life span of a person. The same is true for geographical scale. Many of the processes which dominate how our planet behaves are difficult to visualise given the vast distances (and depths) over which they occur.

To overcome this difficulty, scientists have developed and resorted to a number of tools; from geological mapping right through to generating computer models. One such tool dates back some two centuries: analogue experiments. Initially they started off as roughly scaled experiments to test a range of hypothesis. Famously, James Hutton used analogue models to prove that the folding of originally horizontal strata is the result of lateral compression. With time they have become increasingly sophisticated, allowing researchers to replicate a vast range of conditions and environments which lead to a better understanding of how our planet works.

Today’s Imaggeo on Monday’s image, by Stephane Dominguez, a researcher Chargé de Recherche CNRS, in Montpellier, shows the final evolution stage of an analog experiment dedicated to the study of Relief Dynamics – how surface topography comes to be – and what role tectonics, erosion and sedimentation play in the formation of landscapes. In such experiments, typical scaling is 1cm = a few hundred meters and 1s = a few tens of years.

In this particular experiment “we used a specific granular material mixture (made of water saturated silica, microbeads, PVC and graphite powders, to simulate a portion of the upper terrestrial crust submitted to tectonic extension (where the crust is being stretched, such as at, but not limited to, continental rifts and divergent plate boundries),”explains Stephane.

At the same time, the research team used a rainfall system to project micro water droplets on the model surface. This causes water runoff to initiate and starts the growing reliefs to be eroded.

“We obtain a very realistic morphology that continuously evolves in response to complex interactions between surface deformation (induced by normal fault activity – caused by the stretching of the crust) and surface processes (erosion, sediment transport and deposition).”

 

References

Ranalli, G.: Experimental tectonics: from Sir James Hall to the present, Journal of Geodynamics, 32, 65-76.

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/.

Imaggeo on Mondays: Through the hole

Imaggeo on Mondays: Through the hole

The Gunung Mulu National Park is an area so geologically remarkable and home to such incredibly diverse fauna and flora it has been declared a World Heritage Area.  Located on the island of Borneo, the park is famous for its over 100 different palm species and 3500 other plant types. Geologically speaking, a trip though the varied landscapes will be rewarded with views of deep gorges and hidden valleys, as well as towering limestone and sandstone pinnacles. The predominantly calcareous landscape means most make the journey to remote area to catch a glimpse of the world’s second largest cave chamber. With dimensions of 600 m by 415 m and 80 m high, Sarawak Chamber is a natural wonder worthy of making the journey to Borneo for!

“The picture was taken in February 2014 while I was on a two month trip to Indonesia and Malaysia after graduating from my Master studies. Eventually I found one of the most beautiful places on the island of Borneo: the Gunung Mulu National Park,” explains Juliane Krenz, a PhD candidate at the Department of Environmental Science of the University of Basel.

Aside from the staggering Sarawak Chamber, the national park is crisscrossed by at least 295 km of explored caves.  Made up of the Mulu Sandstone Formation, overlain by the Melinau Formation – which formed in coral rich lagoons some 20 million years ago – the caves are home to a host of species, from bats to swiftlets.

“After spending a few days exploring one of the largest cave systems in the world, I wanted to get deeper into the rainforest and climb Mount Api to see the so-called “pinnacles” – an incredible limestone karst formation everybody was talking about,” Juliane says.

The journey to reach the “pinnacles” involved an hour’s boat ride and three hours walk through the rainforest, eventually reaching a small base camp impressive for its setting: three houses next to a crystal clear stream surrounded by mountains covered in dense forest.

The hike to the sandstone spires began in earnest the next morning. To reach the impressive formations Juliane had to climb an endless number of natural steps made of slippery roots and stones of varying heights from a comfortable 20cm up to 1m, with a total elevation increase of 1200 m in little over 2km – turning the hike into an adventurous climbing trip.

“After 3 hours hiking mostly vertically we reached the top and looked down on an innumerable amount of silver-greyish rock pinnacles spiking out between the dense bright green forest, some of them being up to 40m tall. None of us would have guessed that there were so many,” describes Juliane.

Capturing the beauty of the setting was no easy task.

“I had seen many impressive photographs of the spikes but I was looking for the special focus. Eventually I chose the hole as a frame making the largest pinnacles look like they are part of a miniature world – like me wandering through the rain forest.”

By Laura Roberts Artal , EGU Communications Officer and Juliane Krenz, a PhD candidate at the Department of Environmental Science of the University of Basel.

For more information on the Gunung National Park:

In 1977-78 there was a large expedition (followed by many others known as the Mulu Cave project) founded by the Royal Geograpical Society to explore the dimensions of the cave system. The “pinnacles” at Mount Api are part of the limestone ridge between North Thailand and New Guinea.  The area is full of limestone spikes of various sizes (from few centimeters up to several meters) that are formed through weathering and dissolution over centuries. Nowadays, most research is focused on the ecology and biodiversity in the caves and the surrounding areas.

An earlier version of this post stated Sarawak Chamber was the largest cave chamber in the world. That accolade goes to Hang Sơn Đoòng in Vietnam. With thanks to @TerjeSolbakk for helping us improve this post. 

 

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/.

Imaggeo on Mondays: Dune ridge perspective

Imaggeo on Mondays: Dune ridge perspective

Imagine taking a hike over soft, ever shifting sands. This is exactly what Martina Klose, a researcher at USDA, did when she captured this beautiful photograph. While most of us will likely think of deserts as inhospitable and static landscapes, they can tell us much about dune forming processes, as Martina explains in today’s blog post.

The photograph shows the view down from the crest of a megadune in the Badain Jaran Desert in China. It was taken during a two-day field trip in the course of the International Conference on Aeolian Research (ICAR) VIII, which took place in Lanzhou, China, in 2014.

Aeolian processes are wind-generated processes, such as the emission, transport, and deposition of sediment

The Badain Jaran desert is located north of the Hexi Corridor in western Inner Mongolia and is one of the largest areas of shifting sands in China. With maximum dune heights of a few hundred meters, the Badain Jaran Sand Sea hosts some of the largest megadunes in the world. The sand sea is not only dry, however – amongst the dunes are a number of lakes of various sizes, creating a picturesque environment. You can see what it looks like from space by following the link to this NASA satellite image!

In general, wind is the driving force for dune formation. In the case of the Badain Jaran Sand Sea, the local topography and the subsurface water source are likely additional factors contributing to the development and evolution of the dune fields.

After a long bus drive on the way to the sand sea, climbing one of the giant dunes was a welcoming exercise for most of the conference participants – rewarded with a stunning view from the dune crest and optionally a fun slide down the dune slope.

 By Martina Klose, USDA-ARS Jornada Experimental Range

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/.

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