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5 July 2018

Cadia gold mine: Planet Labs imagery of the sequence of events of the tailings dam failure in March 2018

Cadia gold mine: Planet Labs imagery of the sequence of events of the tailings dam failure in March 2018

Back in March I blogged about the tailings dam failure at Cadia Gold Mine on Friday 9th March 2018.  This failure involved the collapse of a structure between two tailings ponds; fortunately on this occasion there was no release of tailings to the environment.  This is the best image of the failure site that I have seen, posted on the website of Mining Journal:

Cadia Gold Mine

The tailings dam failure at Cadia Gold Mine, courtesy of Mining Journal.

 

Prompted by a recent exchange about this event, I have been back to take a look at the Planet Labs archive of imagery of this event.  It’s quite interesting.  This is an image collected on 9th March (the day of the failure) at 01:14 UTC.  In this image the structure is intact:

Cadia gold mine

Planet Labs image of the site of the Cadia gold mine failure in March 2018. Image collected at 01:14 UTC on 9th March 2018. Image used with permission.

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This image was collected on the same day, but about 22 hours later at 23:32 UTC on 9th March.  The failure has now developed:

Cadia gold mine

Planet Labs image of the tailings dam failure at Cadia gold mine. Images collected at 23:32 UTC on 9th March 2018. Image used with permission

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An image collected on 11th March 2018 at 01:13 UTC shows no change, but one collected on the same day at 23:31 UTC shows that a secondary failure has developed:-

Cadia gold mine

Planet Labs image of the secondary failure of the tailings structure at Cadia gold mine. Image collected at 23:31 on 11th March 2018. Used with permission.

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The most recent images show little change bar the construction of a new haul road:-

Recent Planet Labs image of the site of the tailings dam failure at Cadia gold mine. Image dated 00:57 UTC on 26th June 2018. Used with permission.

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So, interestingly, this was a two phase failure event.  Newcrest, the mining company responsible, are now storing their tailings at another site in the old Cadia Hill open pit mine.

Reference

Planet Team (2017). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://api.planet.com

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3 July 2018

Shimian County: a freak rockfall accident in China

Shimian County: a freak rockfall accident in China

The Chengdu Business Daily has a report (in Chinese) of a freak rockfall accident that occurred in Shimian County in Sichuan Province, China on 30th June.  At the time a coach was driving on the S217 Provincial Road between Chengdu and Wuhu, carrying 38 people.  The coach was struck by a large boulder.  The image below, from the same source, shows the aftermath of the accident:-

Shimian County

The aftermath of the rockfall accident in Shimian County, Sichuan Province, on 30th June 2018. Image from the Chengdu Business Daily.

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It appears that the boulder penetrated, and became wedged through, the windscreen of the coach.  The driver, Zhao Jianguo, a 44 year old native of Chengdu, was pinned in his seat and was killed.  A further six people were injured.  Despite his fatal injuries the driver managed to steer the coach to a safe stop, saving the lives of the remaining passengers.  The coach left a ten metre long skid mark in the road prior to hitting the guard rail, which is being interpreted as an indication that the driver was applying the brakes prior to the impact with the crash barrier on the side of the road, despite his very serious injuries.

Rockfalls on highways in China are not unusual, and impacts between rocks and vehicles are common in mountain chains around the world.  I have not seen an example in which a boulder that must weigh several tonnes penetrates a vehicle in this way however.  It is a truly freak accident.

We are now well into the monsoon season across Asia, and reports of landslides are coming thick and fast, as expected.  Spectacular debris flow videos are emerging from the heavy rains in Vietnam for example, including this remarkable example (which occurs in two phases):-

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And this one on Liveleak, which I cannot embed (but is worth a look).

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2 July 2018

Guang’an: a dramatic retaining wall failure video

Guang’an: a dramatic retaining wall failure video

Youtube has a cool video showing the impact of a retaining wall failure in the city of Guang’an in Sichuan Province, China.  The event reportedly occurred early in the morning yesterday (6:50 am on 1st July 2018):

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The event reportedly involved the failure of a 50 m section of retaining wall during heavy rainfall.  Interestingly, Liveleak has a second video that shows a part of the failure of the wall from the foot of the slope.  This still is taken from that video:-

Guang'an

Retaining wall failure at Guang’an in Sichuan, China. Still from a video on Liveleak.

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I am not quite sure what to make of the images from the videos of the state of the materials behind the unfailed sections of the wall after the failure:-

Guang'an

The aftermath of the retaining wall failure in Guang’an, Sichuan Province, China on 1st July 2018. Still from a video on Liveleak.

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The resultant landslide was a classic slump, with the roadway moving downwards and outwards as the support at the toe of the slope failed. The Chengdu Economic Daily has an article about the landslide (in Mandarin).  This article indicates that cracks had started to appear in the fill behind the wall on 22nd June, and that the authorities had been aware of the problem.  These cracks enlarged rapidly on the day of the failure, such that local people were able to provide warnings that a failure night occur.  The landslide occurred in several phases, starting at 6:50 am, and there was a significant failure at about 11 am too. In total about 50 households have now been evacuated.  The slope was reportedly about 30 m in tall. Interestingly there is quite a large section of this wall that remains standing, as the still below shows:

 

Guang'an

The aftermath of the retaining wall failure at Guang’an in Sichuan, China. Still from a video on Youtube.

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Managing the remaing sections of that wall will be challenge in the forthcoming rainy season.

 

 

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29 June 2018

Lai Chau: multiple landslides in Vietnam in recent days

Lai Chau: multiple landslides in Vietnam in recent days

In the last few days heavy rainfall in Lai Chau in the north of Vietnam has triggered multiple landslidesThe most impressive of these was captured on a video:-

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The video shows that when the landslide occurred there were excavators working on the slope, one of which can be seen in the still below:-

Lai Chau

One of the landslides in Lai Chai, Vietnam, highlighting one of the two excavators that was caught up in the slide. Still from a Youtube video.

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This article in Tuoi Tre News, which also has a video of the landslide from a different article, indicates that the driver of one of the excavators managed to escape his vehicle before the landslide, whilst the other went over the cliff with his machine.  Remarkably he survived and was rescued:

Pham Van Sang and his colleague were using separate excavators to clear mud and rocks left from a recent landslide on a section of National Highway 12 in Sin Ho District, Lai Chau on Tuesday evening when a new mudslide sent a fresh wave of debris tumbling down a mountain flanking the road.  While his colleague managed to evacuate his machine in time, Sang was still inside his excavator when it was pushed off a 50-meter-high cliff.  After the fall, Sang managed to climb about three meters back up the cliff before passing out from fatigue. 

He was later brought to the Lai Chau Province Hospital for emergency treatment. The victim suffered three broken ribs, injuries to two vertebrae and his cheekbone, and pulmonary effusion, doctors said, adding that they performed an emergency surgery to remove fluid from his lungs.

Others have been less fortunate.  Reports suggest that these landslides and floods have killed at least 23 people.  One of the most significant events occurred at Nam Ha in Sin Ho district, where a landslide swept through the village on 24th June.  The image below shows the landslide; at least four people were killed:-

Lai Chau

Ther landslide at Nam Ha in Lai Chau, Vietnam, which killed at least four people. Image from Voice of Vietnam.

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Landslides are a growing menace in Vietnam in both mountainous areas and along rivers.

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26 June 2018

Waioeka Gorge: a new landslide video from New Zealand

Waioeka Gorge: a new landslide video from New Zealand

On Sunday, a landslide occurred at Waioeka Gorge on State Highway 2, the main road between Gisborne and Rotorua in New Zealand.  The landslide was captured on video by a motorist, Michael Tabudravu, who stopped when he saw debris on the road ahead of the main event.  Stuff has a nice article about the event, in which they provide his description of the landslide:

About three other cars coming from the other direction had stopped to see what was going on, too. Some tried to manoeuvre around the debris and keep driving.  The cliff face where the rock had come from was clearly unstable, Tabudravu said on Monday. 

“I could see it started cracking underneath – this big crack…Then the whole thing just came down.” 

By then most other drivers had left, heading back the same way they came. But Tabudravu whipped out his phone in time to record the face collapse into a wave of rubble. 

“It’s not something you see every day…It was a bit of an adrenalin rush to be honest.”

This is video of the event:-

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The landslide appears to be a wedge failure (note the very clear rock mass discontinuity that defines the detachment zone on the opposite wall), with the rock mass showing rapid disintegration to flow down the gully:-

Waioeka Gorge

The rockslide at Waioeka Gorge in New Zealand. Still from a Youtube video shot by Michael Tabudravu.

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There is also an interesting video on Youtube, posted by CCTV, showing a building collapse in Guangxi Zhuang Autonomous Region in China.  The report suggests that this landslide occurred in Weijiagou Village, resulting in the collapse of over 20 houses and the evacuation of nearly 380 people:-

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The video includes other landslides triggered by the heavy rainfall, including one that killed six people.

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22 June 2018

A remarkable debris flow video from Ladakh

A remarkable debris flow video from Ladakh

A video has been posted on to Youtube in the last week that shows a remarkable debris flow from Ladakh in northern India.  According to the text the video was taken at Nubra Ladakh.  It seems that that Nubra is, in the words of Wikipedia:

“a tri-armed valley located to the north east of Ladakh valley. Diskit the capital of Nubra is about 150 km north from Leh town, the capital of Ladakh district, India. Local scholars say that its original name was Ldumra (the valley of flowers). The Shyok River meets the Nubra or Siachan River to form a large valley that separates the Ladakh and Karakoram Ranges. The Shyok river is a tributary of the Indus river. The average altitude of the valley is about 10,000 ft. i.e. 3048 metres above the sea level.”

This is the video:-

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The debris flow is clearly very high energy and high velocity:-

Ladakh

The debris flow at Nubra in northern India. Still from a Youtube video.

 

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The exact location of this event is not clear, but the of the debris flow origin appears to be one of the glaciated valleys:-

Ladakh

Google Earth image of the Nubra Valley in Ladakh, northern India.

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The weather does not seem to indicate heavy rainfall, but this area is a high altitude desert in which rainfall is rare.  The debris flow may be associated with a glacial event, such as a GLOF, or perhaps a localised cloudburst.

Back in 2010 the Ladakh region was hit by a very serious debris flow disaster, which killed at least 234 people, with up to a further 800 people reported to have been lost.    There was a further significant event in this region is 2010, which caused substantial damage but claimed only two lives.  In both cases the volume of rainfall was not large in global terms, but was exceptional for this region.

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21 June 2018

Hidroituango: Renewed movement suggests a landslide of up to 200,000 cubic metres may occur soon

Hidroituango: Renewed movement suggests a landslide of up to 200,000 cubic metres may occur soon

News reports suggest that there is an increase in movement on the slopes above the lake at Hidroituango.  This is being interpreted by those responsible for monitoring at the site as indicating that a landslide in the range of 100,000 to 200,000 m³ may occur in the next few days.   RCN Radio reported last night that workers have now been evacuated from the site in anticipation of the slip.  However, there has not been a need to trigger new evacuations of the communities downstream over and above the 2,500 families that remain in emergency shelters.

A landslide of up to 200,000 m³, whilst large, is not being considered as being sufficient to endanger the integrity of the dam, and nor is it expected to generate a wave of sufficient magnitude to trigger an overtopping event.  In the last two weeks the level of the lake has dropped by seven metres as drier conditions affect the catchment.  The reduced head of water has led to a decrease in the flow through the dam itself.

The image below shows a Planet Labs image collected yesterday (20th June 2018) of the Hidroituango dam site.  The location of the anticipated landslide is not clear, but the reduced level of the lake is apparent:-

Hidroituango

Planet Labs image of the Hidroituango dam site. Image collected on 20th June 2018, used with permission.

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EPM now expects to bring the situation under control by October, allowing restoration works to begin to bring the site back to a state that provides complete control of the lake level, and ultimately that provides the capability to generate power.  However, that is likely to require considerable work given the level of damage and the effects of the emergency works.

Reference

Planet Team (2017). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://api.planet.com

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19 June 2018

Mars: a landslide triggered by a small meteoroid impact

Mars: a landslide triggered by a small meteoroid impact

The University of Arizona has released a really interesting image of the aftermath of a meteoroid impact on Mars that triggered a comparatively long run out landslide:-

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HiRISE image of a meteoroid impact crater on Mars, with its associated landslide deposit. Image via the University of Arizona.

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The imagery was captured by the HiRISE instrument.  The impact event is thought to have occurred about a decade ago. The meteoroid has created a crater with a diameter of about 5 m, and a more substantial impact debris field.  The landslide appears to have initiated very close to the crater, but the crater itself remains intact:-

Mars

HiRISE image of the debris and landforms from the Mars impact event, and the associated landslide source. Image via the University of Arizona.

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There is a good write-up of this in Universe Today:

In that time, the MRO has acted as a relay for other missions to send information back to Earth and provided a wealth of information of its own on the Red Planet. Most recently, it captured an image of an impact crater that caused a landslide, which left a long, dark streak along the crater wall. Such streaks are created when dry dust collapses down the edge of a Martian hill, leaving behind dark swaths.

In this respect, these avalanches are not unlike Recurring Slope Lineae (RSL), where seasonal dark streaks appear along slopes during warmer days on Mars. These are believed to be caused by either salt water flows or dry dust grains falling naturally. In this case, however, the dry dust on the slope was destabilized by the meteor’s impact, which exposed darker material beneath.

The impact that created the crater is believed to have happened about ten years ago. And while the crater itself (shown above) is only 5 meters (16.4 feet) across, the streak it resulted in is 1 kilometer (0.62 mi) long! The image also captured the faded scar of an old avalanche, which is visible to the side of the new dark streak.

In terms of morphology, this landslide is reminiscent of the rock avalanches flowing across ice, such as this example from Alaska:

Mars

The Lamplugh Glacier rock avalanche via Paul Swanstrom.

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It even has the distinctive digitate lobe structure seen at the toe of the landslide.  The wonderful Mount Dixon rock avalanche video suggested that this structure can be formed by slow creep at the end of the main movement period.

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18 June 2018

Hidroituango: a substantial step towards reducing the immediate risk

Hidroituango: a substantial step towards reducing the immediate risk

On Sunday a significant milestone was reached in the ongoing efforts to reduce the risks at the Hidroituango dam site in Colombia.  Efforts have been ongoing to raise the crest of the dam, reducing the likelihood of it being overtopped by a wave triggered by the failure of the slopes around the lake.  The first target was to reach 410 m, at which point the spillway became operational (should it be required).  Yesterday the crest of the dam reached 415 m, providing considerable additional security.

The next target is 418 metres; the ultimate aim is to reach 435 metres.

The consequence of these improvements to the structure is that the level of warning has been reduced for a substantial part of the population living downstream from the dam.  This improved dam safety, plus the decease of inflows as the mountains upstream from the dam move out of the rainy season, has allowed 11,000 people to move back.  However, 4,000 people remain evacuated.

Hidroituango

A recent image of the dam site at Hidroituango. Image from Caracol.com.co.

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The image above shows he current state of the dam at Hidroituango.  Note the very large volume of material tipped on the upstream face of the dam.  This appears to be the material that is being used to try to reduce the leaks in the structure.

 

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15 June 2018

Kilauea volcano: large-scale slumping on the rim of Halema‘uma‘u crater

Kilauea volcano: large-scale slumping on the rim of Halema‘uma‘u crater

The ongoing major eruptive event at Kilauea volcano in Hawaii has generated a wide range of spectacular videos and extensive news coverage.  At the summit of Kilauea is the large Halema‘uma‘u crater, which has been undergoing major morphological changes in response to recent events.  Most importantly, a little more than a month ago the lava lake that had occupied this space drained down.  In response, the walls of the crater have undergone large-scale slumping.  Volcanic landslides are well-documented, but rarely in this level of detail.

The USGS has a page that provides their latest photographs and videos of the Kilauea eruptive event, which includes remarkable imagery of these slumps.  For example, this image shows the sequential curved tension cracks that mark the back of a series of large slumped blocks:-

Kīlauea

Cracking and slumping of the Halema‘uma‘u crater walls are clearly evident in this aerial view captured during HVO’s overflight of Kīlauea’s summit on 9th June 2018. Image from the USGS.

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Whilst the image below gives a wider perspective view of this slumping process.  In some cases the slumped blocks have deformed by over 100 metres:-

Kilauea

Slumped blocks at the Halema‘uma‘u crater. Image via the USGS, collected on 12th June 2018.

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There is a wonderful drone video, collected this week, that provides a panoramic overview of the deformation.

This is a textbook case of slumping in response to changes in the local stress state.  We see successive slump blocks like this in conventional landslides too, though rarely with such clarity.  A very interesting element of this is the lack of rotation in the blocks, none of which appear to be backtilted.  I wonder if this is because of the circular planform of the blocks (whereas in non-volcanic landslides they tend to have a more linear planform).  Presumably this circular shape inhibits the development of rotation.

The USGS have been monitoring the development of these slumps at Kilauea,  so in due course there should be some fantastic data on the ways in which these landslides evolve.

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