11 July 2013
Over the last few days Central China has been experiencing exceptionally heavy monsoon rainfall, causing very high levels of damage. The TRMM data for landslide potential for the last seven days of rainfall highlights the areas considered likely to be affected by landslides (and note that there are also substantial parts of N. India and Nepal that are experiencing problems:
Unfortunately, the worst of the rainfall appears to have affected the areas struck by the 2008 Wenchuan earthquake in Sichuan Province. This is a zone that remains very vulnerable to landslides because of the legacy of the seismic even, compounded by inappropriate development in the rush to rebuild after the earthquake. The effects have been disastrous. The largest impact to date is the landslide at Sanxi in the area administered by Dujiangyan City, which is reported to have killed 12 people whilst a further 11 are missing, with very limited chances of survival. The landslide is reportedly very large, with a travel distance of 2 km and a volume of 1.5 million cubic metres.
Elsewhere in this region landslides are causing substantial issues, and it is surprising that there have not been more fatalities. For example, the earthquake-devastated town of Beichuan was reportedly flooded once again. Xinhua has a set of images of landslide damage elsewhere across the Beichuan and Wenchuan regions, including these:
In some cases the damage from these events looks to be very serious, causing long term disruption. Unfortunately, with the rainy season only just starting, there may be more to come. Finally, Typhoon Soulik is likely to make landfall over SW China in the next 48 hours, bringing exceptional levels of rainfall to areas within a few hundreds of kilometres of the coast:
Whilst it is unlikely that the rainfall from this event will affect Sichuan, it is likely to cause serious damage and disruption to this other part of China.
10 July 2013
It is now over three weeks since the landslide disaster in Uttarakhand. An unusual aspect of this disaster is the degree of uncertainty of the magnitude of the losses, with estimates from politicians for example ranging from 1,000 to 10,000 people. Finally though, it does seem that some element of clarity is emerging. Thus, the NGO Actionaid is reported to have determined the toll to be over 5,000 people. On the other hand, the Vice-Chairman of the National Disaster Management Agency reportedly said yesterday that their estimate is over 4,000 people, but that as many as 11,600 may be missing according to the UN. It does now seem likely that the toll will be at least 3,975 as these named people will be officially declared dead tomorrow.
Meanwhile, the difficulties of arranging the relief efforts continue. Incredibly, some of the stranded pilgrims are only just being rescued – for example, a group of 52 people were rescued today from Gunji, and there are reports that as many as 500 people remain stranded. The major issue continues to be that of landslides, which have both blocked and undermined roads. There is a nice report here about the effects of these landslides, which are proving very hard to manage. Indeed, a 74 member rescue team sent to Kedarnath became stranded, running out of food and succumbing to illness before being rescued yesterday.
The NRSC has produced a map of landslides in the Kedarnath area, which is a very interesting tool. I have shown the landslides at Kedarnath itself previously, but here they are highlighted properly on Bhuvan:
However, it is not just this valley that has been so seriously affected. This is one further to the east, which also suffered a very large scale landslide event:
6 July 2013
Videos of Kedarnath on the day of the disaster, and in the aftermath, including a video of the disaster as it happened
On Youtube an individual named Raghubeer Bisth has posted a series of videos of Kedarnath (see previous posts on Kedarnath here, here, here, here, here, and here) on the days of the disaster, and in the immediate aftermath. I’ll post these in what I think may be approximate chronological order. The most important is the third one, although the fourth gives a fantastic insight into what happened.
Kedarnath Bridge on 16/06/2013 at 6:30 pm:
Disaster on 16-06-2013 , evening at 19.06 pm
Disaster in kedarnath 2013 (helipad)
Kedarnath on 19-06-2013
4 July 2013
The satellite images of Kedarnath give us a good idea of what caused the disaster almost three weeks ago. Given the amount of eye-witness reports, it is possible to come up with a chronology of events:
The disaster was triggered by very intense monsoon rainfall in the period 15th to 17th June. Unfortunately there is no rain gauge data for this area, and rainfall patterns are notoriously variable in high mountain areas, but an automatic weather station operated by the Wadia Institute of Himalayan Geology near to the Chorabari glacier recorded 315 mm on 15th and 16th June. This level of rainfall is not unprecedented, but usually occurs at the peak of the monsoon in July or August. The important factor here is that the rainfall fell at a time when there was still snow on the ground – and any high mountain landslide expert will tell you that the combination of heavy rainfall on melting snow is the tailor-made for landslides.
The effect of the heavy rainfall and rapid snow melt was to generate huge amounts of water in the landscape. The media images of the area clearly show the impacts, with multiple shallow failures on steep slopes. This image, from the Indian Express, shows just a few of these landslides on the slopes adjacent to the town:
The landslides shown in the image above were not a major problem,but combined with the large volumes of water in the rivers, were causing problems downstream of Kedarnath, especially at the village of Rambara. A pilgrim, Ghanshyam Sharm, trekking down from Kedarnath by mule reported that the village was already becoming washed out by the afternoon of 16th June. In Kedarnath, hostels has started to collapse, probably as a result of erosion of the edges of the terrace on which the town was built. However, upstream above the eastern snout of the Charobari glacier a larger slope failure developed. This is shown clearly in the satellite image that I included in my earlier post:
An initially reasonably small failure quickly accumulated sediment and water, turning into a highly energetic debris flow that swept to the foot of the slope, and then ran along the margin of the glacier before sweeping into the town. Eye-witness reports suggest that this was probably at about 6:15 pm on 16th June. This is the account of Constable Kuldeep Singh Mehra of the Uttarakhand Armed Police:
At around 7pm, with the temple walls echoing with wails, prayers, and shrieks, large boulders began rolling into the town, slamming against the shrine. “My stomach turned with every thud,” says Mehra. “We all thought, this is it, there is an earthquake, and it will kill us all.” No one inside the temple slept that night. Mehra tried to peep outside, but could see nothing. He only heard the ominous sounds of gushing water, and every once in a while, earth-shattering claps that made the whole temple shake.
The debris flow swept down the Mandakini river to strike Rambara. Before the disaster the town reportedly consisted of about 100 shops and five hotels, although the image below suggests rather fewer. Whatever the total, all of them were destroyed.
Accounts from Rambara suggest that the debris flow struck the town soon after it impacted Kedarnath, also at about 6:15, suggesting both very high velocities and of course that it was the same event. The account of Ghanshyam Sharm is very harrowing:
People were scrambling up the mountainside in desperation as the water rose in volume and ferocity.“Then, I saw a little boy, 6-7 years old, who was trying to climb the mountain holding his mother’s hand slip and go sliding into the river,” said Ghanshyam. “The mother looked back and then fell herself.” Ghanshyam helped his wife up a few feet on the mountainside, the path below them fast dissolving. Both of them held on to little cracks in the rock, and wedged their feet where they could. A few feet above, trees offered more protection but neither had the energy to reach them. “Everywhere, people screamed ‘help me, save me,’” said Ghanshyam. “But no one could have helped anyone here. If anyone reached out to grab someone else, they would both fall to their death. People were falling off like pebbles.” Encouraged by the sight of those who managed to reach the trees, Ghanshyam and his wife hauled themselves up to the base of one. “We have no idea how. God helped.” They straddled a tree each—face down towards the slope, arms and legs entwined around the trunk, as the rain fell without a break, and rivulets of water ran down the slopes. “We were next to each other,” said Ghanshyam. “We were not going to move from there.” All night they saw people trying to make their way up or trying to find trails. All night they saw more people, the young and the old, slip to certain death, as the earth shook. “After a while, I just kept my eyes on my wife and stopped seeing anything else,” said Ghanshyam. “We did not expect to see the morning.”
Upstream at the western snout of the Charobari Glacier an even greater problem was developing. Retreat of the glacier in the last two centuries had left a rampart of moraine that impounded a seasonal lake, called Charobari Tal. This is an image of the lake before the disaster:
The combination of rainfall and snowmelt caused the lake to over top the moraine barrier, which failed catastrophically, releasing all of the impounded water. Three debris flows, consisting of a combination of water and glacial sediment that included large boulders, swept down the slopes below the glacier, picking up debris and water en route. The tracks of these flows are shown on the satellite image from my earlier post, where 1 is the location of the lake, 2 the breach and 5 the location of the town:
This very energetic and large debris flow swept into Kedarnath in the morning of 17th June, causing terrible devastation. Constable Mehra’s account is as follows:
On the morning of 17 June, at first light, Mehra walked out of the temple and met a scene he could barely comprehend. Boulders, rocks, sand and gravel had piled up high around the complex. Buildings had collapsed or were about to. People were everywhere, dazed, aimlessly walking. “Then I heard a piercing sound, like a storm hurtling towards us,” said Mehra. He ran back to the temple.“I screamed—run, run, run, get inside—and just as I entered the mandir, a huge wave threw me inside,” he says. “I was lifted so high that I was near the ceiling, and I grabbed the electric cables and held on.” He looked down to see heads bobbing up and down in the water, mouths twisted in screams, hands desperately reaching out for suspended bells, wires, anything. The water burst through a side door and carried away some pilgrims. Sand poured in, collecting 4-5ft deep.“Everything was over in seconds,” said Mehra. He jumped down into the sand and ran out. Outside, lodges and shops had been carried away, like they were toys. The buildings that stood were packed with sand and gravel to the ceiling.“I knew immediately that no one could have survived,” said Mehra …“Everywhere we looked there were dead bodies,” said Mehra. “Lifeless hands and legs stuck out of the sand-packed windows and doors. One had red bangles on it, the kind you wear when you are newly married.”The survivors began to gather. The Mandakini raged all around them, creating three channels that coursed through the temple town. They were on an island. The survivors collected wreckage, hauled tree trunks washed down by the river to try and make bridges. None held. Night came, and around a thousand people made their way inside the only lodge that wasn’t full of sand.
27 June 2013
The Indian National Remote Sensing Centre has released a new set of images of the Kedarnath area, collected using the RISAT-1 instrument. These are very high quality images that allow a proper analysis of the events that caused the disaster. These can be viewed in their excellent GIS system, Bhuvan. In a post two days ago I suggested that the disaster might have been caused by two different events, first a landslide induced debris from that came from the area of the glacier to the northeast; second a glacial-related flow that came from the glacier to the northeast. In this post I am going to take a look at each of these. However, I’ll start with an image of the town itself. Note that all of the images shown here are taken from the Bhuvan system. This is the town, showing the flows that have come from the north:
The very high level of damage to the town is clearly evident. Also clear is the two flows:
- To the north-east, a flow that has come down the margin of the glacier (the large dark grey mass at the top of the image) and then spread out to hit the town.
- To the north-west, a flow that has come from the other glacier to strike the town. Note that much of this flow has passed to the west of the town, but it is also clear that a portion struck it directly.
My interpretation is the that the flow from the northwest occurred after the one from the north-east, based on the juxtaposition of the sediments. I’ll now take a look at the source of the flow to the northeast. Upstream the area looks like this:
What is clear from this high resolution image is that the debris flow here was initiated by a landslide high on the hillside, which then ran down the slope entraining debris en route. At the slope toe it was channelized by the glacier into a narrow gully. It is clear that the flow eroded out a large amount of material is this area. Upon exiting the channel it spread out across the flood plain before striking the town. Rough parameters from Google Earth suggest a height difference from the crown of the landslide to the channel below of about 500 metres, and a length of about 1200 metres. The scar width is about 75 m, I think, so this is a large landslide. The area downslope of the failure was already a zone of active erosion, so the likelihood of entrainment was very high.
The second event, which came from the glacial area to the northwest, is very different. This was the area of greatest uncertainty, but the images tell us exactly what happened. This is the source area of the debris flow:
The key area here is the source zone, so I’ve enlarged and annotated this below:
This is my interpretation of what happened in this case – the bullet numbers refer to the numbers on the image above:
- In this area fresh, muddy sediment can be seen. This suggest to me that the moraine had created a blocked basin in this area, allowing water to build up in a pool.
- Eventually this pool overtopped the moraine barrier – the site of the breach can be seen at 2. Once overtopping of the barrier occurred, it catastrophically breached. This generated a very rapid release of the impounded water.
- The flow was so large that it over-topped the moraine on the other side of the glacial area, such that three flows were formed. One went southwest to join the valley from the earlier debris flow before swinging to the south to strike the town. This exploited an existing channel. The second was a much smaller flow that reoccupied an palaeo-channel. The volume of water and sediment that entered this channel was small, but note that it appears to have entrained debris en route (the channel widens downslope).
- Most of the debris flow traveled south down the main channel. The flow must have been huge as there is very substantial erosion in the area of 4. This is the source of many of the boulders now seen in the town. The flow traveled southwards, eventually starting to spread and deposit sediments before striking the town.
- Thus, it is clear that Kedarnath was struck by an earlier from from the northeast, then a later flow from the northwest. The latter was highly efficient, in part because of the earlier events and in part because the flow struck the town from two directions simultaneously.
It is also worth noting what happened below Kedarnath. Downstream of the town, the flow was contained within the channel. As a result there was massive erosion of the riverbanks, as seen in the image below:
Compare this with the image (also from Bhuvan) from before the disaster:
Although the focus has been on Kedarnath, downstream some of the smaller villages have been utterly destroyed by this event. This is the village of Rambara before the debris flow:
And this is how it looked afterwards:
There is nothing left of the village.
26 June 2013
The death toll from the Kedarnath debris flows continues to rise, with 127 bodies being found yesterday alone, bringing the total there to about 600 and the overall total across Uttarakhand to 822. The total number killed across northern India continues to be uncertain, with estimates ranging from 1000 to 5000. The uncertainly may well be primarily because so many victims are buried in debris. Continued heavy rains are hampering the rescue efforts, and there were reports yesterday that two further people died in landslides. In addition, a rescue helicopter crashed close to Kedarnath, killing all 20 people on board.
The lack of coherent information from the government continues to amaze me, especially when compared with the clarity of data that is produced in similar situations in other poor countries, most notably the Philippines. Take a look at the Indian National Disaster Management Agency web page – as far as I can see it provides no useful information about this event other than the control room telephone numbers. The NDRRMC in the Philippines in contrast shows how this can and should be done. The website of the DMMC in Uttarakhand is a little better than its national equivalent, but still lacks detailed information. Sadly, this lack of clarity will be adding to the stress for those involved, and for their relatives.
What is emerging slowly is a better understanding of what has happened beyond Uttarakhand. It is clear that landslides have been triggered across a very wide area. The next valley to the east of Kedarnath shows this very clearly – this is the Landsat 8 image of that area (the same images as I used in my post yesterday), showing the multiple small debris flow gulleys:
The following images have also appeared in various news reports and on Twitter. Interestingly, there is a vast range of landslide types represented. These first three images were taken from an Indian Air Force helicopter and are on the Flickr site of Shivaroor:
This image is on the Twitter feed of Ushinor Majumdar. The caption is: “Ndrf, army warn flood survivors of falling rocks in landslide zone during Uttarakhand evac”:
Finally, this image from the Deccan Chronicle shows some of the challenges that the landslides are posing to the rescue and recovery efforts:
There are also some videos that supposedly show the landslides in action, but at least some of these seem to be relabeled examples from early events.
25 June 2013
Robert Simmon of the Earth Observatory at NASA has very kindly made two Landsat 8 satellite images available to me of the Kedarnath area,, affected by exceptionally heavy rainfall ten days ago. The first was taken on 22nd May 2013 – i.e. before the debris flow – whilst the second was collected on Sunday (23rd June). They are both 15 m resolution, so are very helpful. I should also note that this is the first time that I have used Landsat 8, which was only commissioned last month.
This is the image before the event:
And this is the image afterwards:
One obvious difference is the amount of snow across the landscape – of course we can just ignore this. It is also helpful to take a look at the Bing image, which was taken in the summer months but much earlier than either of these two:
The area of real interest is the zone around and upstream of the Kedarnath temple. This is a zoom into the Landsat 8 image before the disaster:
And this is after the disaster:
There are some dramatic changes. One is that on the post-disaster image the town has almost disappeared. Another is that all of the channels now have fresh sediment in their beds. Although the resolution makes interpreting the processes quite difficult, enough is visible here to get a pretty good idea of what has gone on. First, it doesn’t appear that there has been a mass flow down either glacier. It does appear that on the western glacier, there has been mobilisation of moraine at the end of the ice flow, and that this debris struck the town. I have put the two images of this area side by side below; the northern edge of the town is on the lower portion of the images, just to the right of centre:
It looks to me as if a large amount of sediment in this region failed and transitioned into a debris flow that then ran down slope into the town. However, this is not all. On the other side of the valley we see this feature, again shown in the pre- and post-disaster images:
In this case it appears that there is a large area of erosion, or even a landslide, right up the valley side. This has also transitioned into a debris flow that has struck the town – indeed if you look at the location of the town on the left image, it appears that much of the damage may have been from this flow. This is the same area on the high resolution Bing image:
The source area of the erosion / landslide is visible, but it is nothing like as active as it was in the disaster. The route through which the debris from this slide was able to strike the town is clearly evident.
Note also that there was very active erosion in all of the other gulleys, but these do not seem to have been responsible for the disaster.
So, in conclusion, I suggest that the town was struck by debris flows from both the east and the west valleys (see here for my earlier speculation on this). On the west side the main issue seems to have been failure and mobilisation of glacial sediment; on the east side it was active erosion of slope materials. Faced with this sort of onslaught, the town stood little chance.
Comments and thoughts very welcome.
23 June 2013
The level of loss at the Kedarnath Temple in the debris flow remains unclear. Indeed, the situation remains surprisingly chaotic, with rumours about the magnitude of the losses sweeping across Twitter, but little objective information to validate them. A week on from the accident, this seems like an unacceptable situation, even allowing for the challenges that the rescuers are facing. What is clear is that the damage to the temple and its surroundings is very serious. There are some images and indeed videos of the inside of the temple, but it is also clear that these images have caused considerable upset for religious reasons, so I won’t reproduce them here. There is an excellent gallery of the state of the area around the temple on the Indian Express website, which includes this image:
It is very unclear as to what actually happened at Kedarnath to generate this very large debris flow. There I think several possibilities, which I will try to outline below. The starting point is that we know that the event was triggered by prolonged heavy rainfall interspersed with at least one “cloud burst” type event. We also know that the debris came from above the town in the formerly-glaciated valleys, and that there was no shortage of sediment in those valleys. The above image appears to show a deeply incised channel on the margin of the glacial moraine, whilst the one below (also from the Indian Express) shows very fresh sediments in the other glacial valley above the town:
Of some help is an image, released by the ISRO, of the site, taken on 18th June. It is available on their Facebook site:
It is worth comparing this with the pre-disaster Bing imagery from a similar angle:
So let’s look at the possible scenarios (this list is not intended to be exhaustive):
1. The collapse of a moraine-dammed lake
This is the simplest and most obvious explanation, and it has been proposed elsewhere. In this scenario there is a lake upstream of the town, with meltwater from the glacier impounded by glacial debris. In the extreme rainfall the barrier failed, releasing a huge flood that struck the town. Unfortunately though, I cannot see such a lake on the above images. Maybe I have missed it, or maybe it formed since the images were collected. However, I also cannot see an obvious location for such a lake on the more recent ISRO image.
2. A catastrophic landslide onto, and then down, the glacier
This scenario is entirely possible in such a landscape. Here, a collapse event on the valley walls above the glacier transitioned into a flow that swept down the ice. This then picked up debris and water below the glacier, and turned into a debris flow. This is entirely possible, and might account for the morhology of the right hand glacier in the ISRO image. However, the morphology of the area upstream of the town doesn’t really suggest that this is what happened.
3. A landslide below the glacier created a dam, which then ruptured, releasing the flood
On the ISRO image there is an interesting area that I have highlighted as 1 below:
There seems to be quite a lot of change is this area, which could indicate a blocking event in this region,perhaps from a failure on the lower part of the valley wall. However, this area is more likely to have been scoured from some other event.
4. A landslide event in a higher valley that became a channelised debris flow:
It is entirely possible that a landslide elsewhere in the catchment became a debris flow that struck the town. I have highlighted a possible scar as 2 in the annotated image above, although this could just be an area of erosion, or something similar. There are other areas with similar features.
5. A simple case of too much rain on a large catchment, and a misplaced town
The final scenario is that there was simply too much rain across the large catchment, resulting in flows across all of the channels, which exceeded their channels. As a result, large volumes of water reached the town simultaneously, having picked up huge amounts of loose sediment en route. The location of the town at the confluence of these channels meant that the disaster was inevitable.
It is hard to say which of these scenarios, if is right. If I was a betting man (and I am not) I would be tempted by scenario 5, but I would not be confident of seeing my money again.
We need a much better, high resolution image of the site to understand what has happened. Hopefully such an image will be collected soon. This site needs a proper forensic investigation by a team that understands such processes, not least because there are many other sites in the Himalayas that are at risk of such events.
21 June 2013
Information about impacts of the early monsoon floods and landslides in Uttarakhand in northern India is slowly emerging. The tardiness of the information flow undoubtedly reflects both the exceptionally difficult terrain in this area and the magnitude of the damage, with for example few roads having been left intact. What is emerging is that the losses of this disaster are high – probably much higher than the current estimate of about 170 people – although at this stage it is hard to know if this will be a few hundred or more. A search on Twitter for either Uttarakhand or Kedarnath (see below) brings home the likely consequences. There are numerous reports, and photos, of people (and in some cases whole families) who have not been heard of since the disaster. In some cases there are young children missing,
One of the largest impacts appears to have occurred at Kedarnath, a Hindu shrine high in the mountains, which at this time of year is an important pilgrimage destination. The site is just a short distance from the snout of two mountain glaciers, as this image from 50 or so years ago shows:
A couple of things to note here – first, the amount of debris below the glacier on the left side of the image suggests a pretty active, and quite steep, sediment transport system. Second, there are rocks and boulders in the fields in the foreground.
Given the number of people who make the pilgrimage to this site each summer, a degree of development around the temple was inevitable, although the pre-disaster images suggest that this has occurred in an entirely haphazard manner. There are some excellent images of the town here, from which this one is taken. The temple is on the right side of the image, surrounded by buildings:
The level of destruction of the town by the debris flow is very high, and is quite shocking. There are several images of this floating around the internet, such as this one:
The upslope end of the temple, which has survived the flood intact though damaged, is buried in debris. Many of the surrounding buildings have been entirely destroyed. Given that many of these were hotels and hostels, which would have been full at this time of year, the high level of potential loss is clear.
The question of course is what happened. Many Indian newspapers have a commentary, although it is not clear as to whether this is based on fact or speculation. Up-valley from Kedarnath, above the western glacier shown above, is a peak known as Kedar Dome. The suggestion is that the rainfall triggered a collapse event on the mountain, which turned into a debris flow downstream that struck the town. Certainly some of the images suggest that the debris flow came from this valley above the town, so the account is credible, but the degree to which it is verified is unclear. Unfortunately, the Google Earth imagery of this area was taken in winter, so it is covered in snow. Bing has a better image, which shows the geometry of the glaciers and peaks up-valley from the town (which is marked with the blue dot):
In terms of lives lost, this is probably the worst landslide since the August 2010 Zhouqu landslide in China. There are some similarities between the events.
18 June 2013
Over the last few days rainfall across northern India and Nepal has been unusually high, inducing widespread flooding and landslides, at a substantial cost to the local population. The TRMM seven day rainfall map for Asia shows the affected area:
According to media reports the worst-affected areas have been in Uttarakhand, where the death toll to date is about 40 people, with more reported missing. Rainfall totals here have exceeded 340 mm, leading to some dramatic videos of rivers in flood, and in particular of houses being lost to riverbank erosion. Sky News have this dramatic video (which I cannot embed), whilst this television news report (not in English) video has a wider perspective on the floods and at around the 50 seconds mark shows a landslide in action and at 2:50 has a dramatic rockfall:
The best gallery of images that I have found is on the Daily Mail website:
The far west of Nepal has also been seriously affected by this rainfall, with a family of seven being killed by a landslide in Malika in Dailekh, a family of five being killed by a landslide at Siddheswor in Baitadi, two people being killed and three injured by a landslide at Kuntiwandali in Achham , and five young women being killed by the Trishuli River in Trishuli.
Whilst mid-June is monsoon season in this area, the most intense rainfall usually occurs later than this. Unfortunately, tis high intensity rainfall event will have saturated the ground in these areas, making them more vulnerable to landslides later in the summer.