2 July 2015
Darjeeling is an area of northern India that is probably most famous for a type of fine tea. Located in the Lesser Himalaya, and heavily affected by monsoon rainfall. Landslides have long been a significant hazard in this area, although there has also been increased concern of late that poorly planned development is greatly increasing the risk. This is so substantial that Darjeeling is unusual in having a citizens’ group dedicated to raising awareness of the problem, the wonderful Save the Hills organisation. They have campaigned tirelessly to raise awareness of the problems associated with poor slope management.
Yesterday the potential slope problems in Darjeeling came home to roost. Heavy rainfall overnight triggered a series of landslides across Darjeeling, damaging buildings and roads. The Indian Express reports at least 25 landslides across the district. The losses make grim reading:
According to officials in the state disaster management department, 22 deaths occurred in Mirik, where 13 people were also reported missing. The remaining 17 died in Kalimpong, Lava, Sukhia and Gorubathan areas, they said. Twenty persons were reported injured and 15 missing at 8 Mile and 11 Mile areas in Kalimpong, sources said, adding that extensive damage has occurred to NH-10 and NH-55.
The largest event appears to have occurred at Tingling village near to Mirik:
Google Earth does have a Tingling Tea Garden marked, so it is presumably one of the two adjacent villages:
Judging by this image from AFP, this appears to have been a highly mobile flow type landslide:
There is a full set of photos of the landslides on the Darjeeling Chronicle Facebook site, but please be careful as some are very graphic and quite disturbing. Unfortunately, overnight there were further landslides as the heavy rainfall continued, and there are some suggestions that the confirmed losses might now amount to 40 people.
I have no doubt that Save the Hills will provide a full account of the landslides in Darjeeling in due course. Yesterday they published some detail about the rainfall that triggered the landslides. They reported that at that point Kalimpong had received 226 mm of rainfall in a six hour period. And as Praful Rao has written:
“The worst part is we have at least 3 months of rainfall ahead.”
1 July 2015
An updated landslide density map from the Nepal earthquakes from the EWF project
The Earthquakes Without Frontiers project has published a revised landslide density map for the Nepal earthquakes, This map includes landslides triggered by both the 25th April and the 12 May earthquakes:-
Note the shaded areas are those obscured by cloud, so the dataset is not quite complete. The full landslide dataset is available to download from here:
- Approximately 5,600 landslides have been identified to date, including new landslides triggered by the 25 April 2015 Gorkha earthquake and the 12 May 2015 Dolakha earthquakes, as well as reactivations of landslides that were present before the earthquake sequence began.
- Major or disruptive landsliding is limited to a zone that runs east-west, approximately parallel to the transition between the Lesser and High Himalaya. This zone includes parts of the districts of Gorkha, Dhading, Nuwakot, Rasuwa, Sindhupalchok, Dolakha, Ramechhap, and Khavre.
- Landslides triggered by the 12 May Dolakha earthquake are included in this data set for the first time. The area of landslides triggered by the Dolakha earthquake overlaps with the eastern end of the area affected by landslides in the Gorkha earthquake. In general, locations that suffered from high landslide intensities after the Dolakha earthquake also suffered from widespread landsliding in the Gorkha earthquake. These areas have suffered damaging levels of shaking in two successive large (Mw 7+) earthquakes, and must be viewed as having a very high risk of failure during the 2015 monsoon season.
- There have been numerous reports of cracked ground in the affected areas. There is no single interpretation of cracks in slopes generated during earthquakes and how these cracks are likely to develop through the monsoon. We recommend establishing simple monitoring (distance measurements between stakes positioned across cracks), to establish if cracks are widening or if movement of the slope has ceased. Areas that exhibit continued or accelerating movement should be treated with extreme caution.
30 June 2015
The Araniko Highway in Nepal
The Araniko Highway is the main road that links Nepal with Tibet and China, heading initially eastwards from the Kathmandu Valley and then turning north into stunningly beautiful landscape:-
This road is of crucial importance to Nepal as it carries a very large amount of goods from China. However, even before the earthquake this was a very landslide prone section of road, and indeed it was closed for much of last summer by the Sunkoshi landslide. But in particular the 20 km or so of road leading up to the border is to all intents and purposes dominated by landslides.
Unfortunately this area was hit very hard by the earthquakes of May and June 2015, and landslides proved to be a major problem. The EWF blog has a map of the mapped earthquake-induced landslide density from the earthquake – the Araniko Highway is marked on the map to the northeast of Kathmandu:-
The Araniko Highway must have been a terrible place during the earthquakes, as some of the images that have emerged indicate:
And now as the monsoon cranks up in Nepal this road is starting to cause major concerns. After a marathon effort to try to get the road reopen and serviceable, the Chinese authorities started to release goods stored close to the border late last week. However, this remains vert problematic – the customs post has been relocated closer to Kathmandu for example. And yesterday My Republica reported that landslide present an “existential threat” to the area around Tatopani:-
The road stretchbetweenChakutoLiping Bazaar is full of landslides and very risky to drive through…Faults had appeared on boulders, land stretches were split and a number of dry landslidesweretrigged during the aftershocks and in the aftermath. Though, these had subsided with the decreasing frequency of the aftershocks lately, continuous rainfall in the cracked area, have made it more prone to landslides.Sludge like landslideshas been flowing down theTatopani,Kodari andLiping Bazaar. The debris brought along by the landslides has accumulated along the road in many places. Mud and clayis deposited in homes and the river is floating against its course, at some places even on the road itself. The houses thatwere spared by the quake now face serious threats from the landslides.Over 3000 Larcha and Liping residents of the area were evacuated following the May 12 aftershock and were relocated in make shift tents in Kathmandu. The latest landslide fear has seriously dashed off their hope to get back home.
The Miteri Bridge that connects both the nations has been padlocked. The busy commercial town of Khasa Bazaar remains empty and closed since the past three months. Billions worth Nepali traders’ assets are in danger. 430 consignment containers are stuck on the Chinese side. Efforts of Nepali businessmen to clear the landslides and start the transportation have failed to bear fruit due to the fresh landslides, almost every day “With the commerce going down in Tatopani, Nepali traders have started facing hardships,” Arjun Sapkota, a Khasa based trader said while elaborating on the impact of quake and the most recent landslides on the business.
29 June 2015
Daning River landslide
The video seems vaguely familiar so I am unsure as to whether it is actually this event. Certainly the shape of the failure and the type of landslide looks to be correct:
Does anyone have any further information? The landslide is now believed to have killed two people.
27 June 2015
Lac du Chambon
On the banks of the Lac du Chambon in the French Alps a 1 million cubic metre landslide is rapidly developing. This landslide is making the international news because it has caused the organisers of the Tour de France to reroute perhaps the most famous section of all – the Alpine stage that ends with the lung-bursting climb to the ski resort of Alpe d’Huez.
The slope in question on the edge of the Lac du Chambon is important because the road along the edge of the lake bypasses it via a tunnel that passes through the landslide mass. This is a Google Earth perspective view – the road is the yellow line, with the tunnel section being the part of the road that is missing:
Interestingly, there is no obvious indication of instability in this image (from 2009), but there is a large landslide scar on the left side of the mass (the tunnel portal is clearly located on the edge of the landslide scar). The landslide itself is now heavily disrupted, as per these images from 3France:
In recent days the movement rate of the landslide has accelerated from 5 to 15 cm per day, suggesting that the landslide might be in a tertiary creep phase. However, as the Mount Mannen landslide in Norway last year demonstrated, predicting failure is very challenging, and the team monitoring the landslide are sensibly making no firm predictions. Of course, it will be very challenging for the authorities if the slope does not collapse.
There is some interesting footage of the inside of the tunnel in the video embedded in this web page, which should be visible below:
This is a still from the video, showing the level of internal deformation that is occurring within the landslide:
This is of course a wonderful opportunity to get a better understanding of both the dynamics of a large slope failure and the way in which the displacement wave will develop and propagate. I hope that it will be possible to collect a detailed dataset and some video of the development of the failure.
25 June 2015
Daning River landslide
A very significant landslide occurred yesterday (Wednesday) evening on the Daning River, a tributary of the Yangtze, in Wushan County, Chongqing. Global Times has an image of the landslide site:
The landslide triggered local tsunami waves on the river that swamped a number of fishing boats:
Fortunately as the landslide occurred at 6:40 most of the vessels were reported to have been vacated. Nonetheless one person is reported missing and a further four were injured.
The landslide is intriguing. The images seem to show a low river level (possibly the river level is being drawn down in preparation for the rainy season?) and there is no mention of a rainfall trigger. The materials forming the landslide scar seem to be fine-grained and quite homogeneous. The fortunate element is that the landslide did not affect the houses located nearby.
The site of the landslide is only 110 km upstream of the Three Gorges Dam, such that the river level has been elevated by the impoundment of the reservoir. This case is likely to further raise fears of the potential for significant landslides on the banks of the lake.
22 June 2015
Landslide-induced sediment production after the Sabah earthquake in Malaysia
The Mw=6.0 5th June 2015 Sabah earthquake in Malaysia, which killed 18 people in rockfalls on Mount Kinabalu, generated landslides that have released large volumes of sediment. The heavy tropical rainfall in Sabah means that this sediment is now starting to enter the river systems in the form of mudflows and sediment-rich flash floods. So, for example, last week villages around the town of Ranau were struck by a series of mudflows. In particular, Mesilau was very badly affected, during a period of heavy rainfall last Monday. Mesilau lies on the flanks of Mount Kinabalu, but is some way from the main massif:
The AsiaOne website has an interesting gallery of images of the landslides that occurred last week:
Notable here is the amount of timber in the river – to me this suggests that there must have been quite extensive landslides in the forested areas on the lower slopes of the mountain. I have not seen detailed reports or images of these landslides. The threat that this timber provides to the water supply and to the river itself is clear. The post-seismic landslides from the Sabah earthquake are also moving quite large volumes of sediment, including large boulders. Typically the riverbeds will aggrade (the bed level will rise as sediment is deposited), which will greatly increase the threat of flooding and damage to infrastructure. This slug of sediment will work its way down the river, extending the effects of the earthquake well outside the area affected by the high ground accelerations. In effect this will extend the effects of the earthquake in time and space.
The rainy season in Sabah starts in October, so this will be the main hazardous time. However, in the tropical environment of Sabah heavy rainfall can occur at any point in the year.
Fortunately Malaysia has an excellent slope management organisation, JKR, part of the Public Works Department.
21 June 2015
Tbilisi flood – 14th June 2015
A week ago, on Sunday 14th June, a flash flood ripped through a part of Tbilisi, the capital city of Georgia, causing a very significant amount of damage:
The floods are known to have killed 19 people and to have injured a further 457 people. Three people remain missing. The flood inundated Tbilisi Zoo, killing large numbers of animals and releasing many more:
Earlier this week it was reported that a tiger that escaped from the zoo killed a man before being shot. Another tiger was thought to be on the on the loose, but I am unsure as to whether it has been recaptured. News reports also suggest that one of the penguins in the zoo made a bid for freedom. In an effort that is somewhat reminiscent of a scene from The Great Escape it was finally recaptured 60 km downstream.
Understandably, the flood has been very controversial in Georgia. Whilst I am not really able to comment on the factors that underlie the event, it is clear that the flood itself was caused by the collapse of a landslide dam created on the Vere River near to the village of Akhaldaba. The Georgian Government has produced a video animation of the landslide and flood. Unfortunately due to a hosting problem associated with upgrading the software that hosts this site, I cannot embed videos at present. However, you can access it via the Youtube website. Although it is not in English, the sequence of events is clear, representing a classic cascading sequence of heavy rainfall, slope failure, valley-blockage, lake formation, dam collapse and catastrophic flood / debris flow.
The landslide is estimated to have had a volume of about 1 million cubic metres. This still from the video above shows the slide:
The landslide appears to be a shallow failure for the post part, possibly with a rotational component in the headscarp area. There appears to be a lot of water on the shear surface. Interestingly, Tbilisi also suffered devastating floods on a number of previous occasions, and the zoo has been destroyed by floods on the Vere River at least once before. It would be interesting to know if these earlier events were also due to landslide dams on the Vere River .
15 June 2015
Aberfan: 7 pianos, percussion, voice and tools of rescue
Laura Siersema is a composer and poet based in western Massachusetts in the USA. In the aftermath of the terrible 1966 Aberfan landslide disaster in Wales, in which 116 children and 28 adults were killed when a coal mine spoil heap collapsed and buried a school, her mother wrote a folk song “In a town called Aberfan”.
As we approach the 50th anniversary of the disaster next year, Laura has been working on anew, much longer piece about the disaster entitled Aberfan (7 pianos, percussion, voice and tools of rescue). In Laura’s words:
“My mother wrote a folk song, “In a Town Called Aberfan,” in the wake of the tragedy, that I used to hear when I was a child. I have been compelled for years to work on an adaptation of my own. Using excerpts of melody and lyric from my mother’s song, as well as portions of hymns sung earlier that morning and at the funeral one week later, Aberfan is now a full modern piece incorporating movements of Rain, Sunrise, Rubble, Rock, Hymns, Interludes, Trauma, Silence and a Field, and their alterations.”
This is a sponsored project of the New York Foundation for the Arts (NYFA). Two samples of the piece can be played online via Laura’s blog: First Hymn – Rock Sequence and Altered Rain. Laura also has posted some reflections on writing the piece on her blog.
Laura is seeking funding to record the full piece later in 2015, ahead of the anniversary of the Aberfan disaster next year. Details are on her website.
8 June 2015
The Mount Kinabalu rockfall
The Mount Kinabalu rockfall on Friday, triggered by a shallow M=6.0 earthquake, is thought to have killed 19 people. A significant number of them appear to have been children from Singapore on a school trip to climb the mountain. They were truly in the wrong place at the wrong time, a real tragedy.
Whilst there appears to have been multiple landslides on the mountain, and indeed elsewhere, much of the loss seems to have come from the collapse of a rock pillar that formed one half of the “Donkey’s Ears” on the mountain. This is an image of this unusual rock formation before the earthquake:
And this is how they look now (via Twitter):
The column that collapsed is much larger than it might appear from the images. By coincidence, Planet Mountain ran an article late last week about new climbing routes on the Donkey’s Ears:
Interestingly, just below the climber in the image above there is a clear discontinuity inclined towards the right. About 20 m down there is another with a very similar inclination. I wonder if one of those was the detachment plane?
Whilst the image above shows that rockfalls on this column were far from uncommon (there is a huge amount of rockfall debris at the foot of the column, much of which is very large), this collapse event is very interesting. The column above would appear to be really vulnerable to the effects of seismic shaking, such that it is quite surprising that it has not collapsed previously. Does this indicate that the shaking associated with this seismic event was unusual in some way? The key is likely to be the very shallow nature of this earthquake, and its proximity to the mountain. This is the location, as given by the USGS, with Mount Kinabalu marked as well:
Such an earthquake could generate high Peak Ground Accelerations, but only over a very small area. These accelerations could have been amplified at the summit of the mountain. Thus. the key was probably the proximity of the earthquake event to the mountain and the shallow nature of the event. As such it may well prove to be an extraordinary but deeply tragic fluke.