This blog provides a commentary on landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings. The blog is written on a personal basis by Dave Petley, who is the Wilson Professor of Hazard and Risk in the Department of Geography at Durham University in the United Kingdom.

This blog is a personal project that does not seek to represent Durham University.

Friday, 31 October 2008

Did you hear the one about a goat in a landslide?

A bit of light relief over at the Highway 97 site in Canada, which continues to slip. Arthon have a pictorial report on their website of the rescue of a mountain goat that had fallen down the tension crack and become wedged 10 m below the surface (all images from the Arthon website):

Fortunately, the goat (now named Houdini) was spotted and a rescue was put in place. Enter the gallant abseilers (you wouldn't mess with these guys on a dark night):

They abseiled down and tranquilised the goat, who was then hauled back to safety:

Meanwhile the slope is still moving 10-15 mm per day and as a result the road is still closed. A water taxi has starts on Saturday morning to allow people to get around the blockage.

Hat tip - Andrew Giles again.

New book: Landslides and Engineering Geology of the Seattle, Washington, Area

Seattle is an area that has both a long history of landslides and a long history of landslide research. For example, there is a 1974 USGS report online examining landslides triggered in a 1972 rainfall event. In 1996-7 a series of large storms triggered multiple damaging slides in Seattle. As a result, the USGS and Seattle agreed to start a major project to produce a range of landslide hazard maps and associated forecasting tools. Part of this work has been the compilation of a database extending back to 1890 - there is a very nice report on this work on the Seattle Government website.

This work has been summarised in a new volume published yesterday by the Geological Society of America:

The book summary states that: "This volume brings together case studies and summary papers describing the application of state-of-the-art engineering geologic methods to landslide hazard analysis for the Seattle, Washington, area. An introductory chapter provides a thorough description of the Quaternary and bedrock geology of Seattle. Nine additional chapters review the history of landslide mapping in Seattle, present case studies of individual landslides, describe the results of spatial assessments of landslide hazard, discuss hydrologic controls on landsliding, and outline an early warning system for rainfall-induced landslides."

Baum, R.,L., Godt, J.W. and Highland, L.M. (eds) 2008. Landslides and Engineering Geology in the Seattle, Washington Area. Geological Society of America, 181 pp. ISBN: 9780813741208
Price: $30 for members, $60 for non-members. Available from here.

Thursday, 30 October 2008

Landslides in the 29th October Pakistan earthquake

The picture of the level of destruction in Pakistan resulting from yesterday's earthquakes remains slightly confused. The official death toll is now 215 people, but some reports suggest that the true number is about 400 as in smaller villages victims were buried before officials arrived. In terms of landslides, the picture is equally confused, but unverified reports indicate the following:
  • Some reports suggest that a village called Chali Dam in the Yuni Valley in Ziarat district was hit by a landslide that killed 61 people.
  • Relief web reports that some key highways are blocked by landslides.
  • The Pakistan news agency Dawn reports that "Most houses in the worst-hit villages of Ziarat were destroyed by boulders falling from mountains" and "He said the earthquake had left cracks in mountains and roads."
Hopefully the picture will become clearer today.

Highway 97: test blast

The latest report on the Highway 97 problem in Canada (see earlier posts here, here and here) is as follows:
  • The contractor, Arthon, released a statement to the press yesterday, the key points of which stated that "Highway 97 remains closed north of Summerland until further notice due to an unstable rock mass above the highway. The slope continues to move, therefore the highway is not safe to reopen. Safety is our top priority. The ministry is doing everything it can to reopen the highway as quickly as possible, but we won't open it until it's safe. We've built access roads to enable heavy equipment to reach the slope.
    Our first test blast took place this afternoon to help assess the stability of the rock mass.
    The geotechnical experts will now analyze the results of the blast and will have an update tomorrow afternoon. The results of the blasting will help the ministry finalize the work plan."
  • The tension crack extended by 8 millimetres overnight Tuesday-Wednesday, giving a displacement of 3.3 cm since Sunday.
  • The plan to move material from the crown to the toe of the landslide now appears to be the favoured solution. It is not clear how this will affect the road.
The cautious approach beiung adopted by the authorities is quite correct in my opinion.

Wednesday, 29 October 2008

A further Pakistan earthquake

At 11:32 UT there was a further earthquake in Balochistan, this time Mw=6.2 at 10 km depth. This is sufficiently large and shallow to cause considerable additional damage, including landslides. Unfortunately, this event is even closer to Ziarat, which seems to have borne the brunt the first time around. The epicentre is at 30.541°N, 67.457°E according to the USGS, which is shown below on Google Earth (click on the image for a better view):

Magnitude Mw=6.4 earthquake in Pakistan

News is coming in this morning of moment magnitude = 6.4 earthquake in Balochistan in Pakistan. According to the USGS, the earthquake occurred at 23:09 UT (04:09 local time) at a depth of about 15 km. The USGS have produced this map of the epicentre:

Fig. 1: USGS map of the location of the epicentre of the earthquake

This produces a map of shaking that looks like this:Fig. 2: USGS map of the intensity of shaking associated with this earthquake

This is a rugged and comparatively arid landscape (Fig. 3) with a population density of about 40 people per square kilometre. GDACS estimate that there are about 326,000 people living in a 50 km radius of the epicentre.

Fig. 3: Google Earth image of the region affected by the earthquake.
Click on the map for a better view in a new window.

In such an environment, landslides are very likely to have been triggered by the earthquake. Already there are one or two reports that landslides have occurred - for example:
  • AFP are reporting that "The deaths occurred in and around the hilly town of Ziarat, about 50 kilometres east of Quetta, in gas-rich Baluchistan province, police official Abdul Khaleq told AFP. Ziarat is a historic hill resort famed for its juniper forests. Most of the casualties were from two villages on the outskirts of the town which were built on steep ground and badly damaged in landslides triggered by the quake, which struck at a depth of 10 kilometres, officials said."
  • The Daily Telegraph is reporting that "One village, Wam Killy, was almost completely destroyed while many houses were buried in landslides triggered by the quake."
  • Bloomberg saya that "A landslide in Ziarat, a tourist resort about 100 kilometers east-northeast of Quetta, killed 17 people, said Dilawar Hussain Shah, an official at police control in Quetta. More deaths were reported from Pishin town and its neighboring villages, he said."
Fig. 4 shows a perspective view of Ziarat, whilst Fig 5 gives an idea of the terrain:

Fig. 4: Google Earth perspective view of Zierat, in which many landslides have been reported.
Click on the map for a better view in a new window.

Fig. 5: Flickr image from Worldwidetravelling of the landscape in Zierat

All of the above suggests that landslides are likely to be a serious issue in this earthquake. The diagram of area affected by landsliding derived by Keefer (1984) is helpful here (Fig. 6). The likely affected area is in the range of 200-2000 square kilometres, with a value towards the upper limit being more likely given the shallow focus of the earthquake and the rugged terrain. In my view, it is likely that the effects, although quite localised, could be quite high, with landslides being a major problem both in terms of causing losses and in terms of impeding the flow of assistance.

Fig. 6: Dave Keefer's 1984 plot of the area affected by landslides in earthquakes of different magnitudes, annotated to show the range of areas expected to be associated with this one.

I will post again as more information becomes available.

Keefer, D. 1984. Landslides caused by earthquakes. GSA Bulletin, 95, 406-421

Highway 97 latest update

The latest update on the Highway 97 landslide in Canada (see here and here) is as follows:
  1. The slope is still moving. Between 19:00 on Monday and 14:00 on Tuesday the mass moved about 15 millimetres (i.e. about 0.8 mm per hour). This is quite high for a large mass. The rate of movement is described as being constant;
  2. The mobile volume is now estimated to be 200,000 cubic metres;
  3. The road remains closed (unsurprisingly!);
  4. There are provisional plans to remove material from the top of the unstable slope and to move it to the toe. The aim here is to reduce the mass that is driving the movement and to increase the mass that is supporting it.
I am sure in the background there is an enormous amount of work going on. Analysis of the pattern of movement in time and space, especially by looking at vectors of movement and accelerations and decelerations will give a pretty good idea of what is happening in the slope. This gives a potential for providing a short term warning of an impending collapse, but does not really tell us how likely this is in the medium term.

Tuesday, 28 October 2008

Highway 97 update

Arthon have posted an update on their website of the situation at Highway 97 in Canada:

"Slight movement in Rock Mass overnight. Road likely closed until Thursday at a minimum. Options being considered for removal of rock"

There is also quite a nice news report with footage here. In the report there is a good description of the use of precursor indicators that can be used to warn of a large-scale failure. They are quite right that movement data, sounds, the opening of cracks and the occurrence of small falls can be used to indicate that a large slip might occur. However, they will need to understand the slope quite well before this option is adopted, and they will need to be particularly cautious when it rains or there is snow melt.

Arthon have published some excellent pictures, including a couple of aerial shots, here. The picture below is the best of them to give an oversight of the problem:

Click on the image for a link to the full size version. Note that a few metres below the main crack there appears to be a smaller tension crack running across the slide, perhaps suggesting that it is starting to break up a little.

Monday, 27 October 2008

Interesting slide on Highway 97 in Canada

Thanks to Andrew Giles for bringing this one to my attention. Highway 97 in British Columbia is currently being upgraded through the Okanagan Valley (Fig. 1). This project is being undertaken by Arthon - their project website describes this as:

"Four lane roadworks and 1,000,000 m3 rock removal over a 7 km section of BC's main north-south highway corridor. The B.C. Ministry of Transportation awarded Arthon Contractors Inc. a $38.6 MM contract to complete roadway construction by summer 2009".

Fig. 1: Google Earth image of the location of the problematic slope on Highway 97.

The rock removal appears to be a widening exercise in which a substantial amount of rock has been removed to create a platform. Unfortunately, last Friday the contractors noticed that a crack had appeared in the slope above the works at the location shown on Fig. 2.

Fig. 2: Google Earth perspective view of the area of the unstable slope before the slope cutting had commenced.

The crack in question is not insubstantial. I must note here that I am very impressed with the openness of those involved - the contractor has placed images on their website of the nature of the problem (Fig 3.), even showing comparison views of the crack opening.

Fig. 3: Arthon Ltd image of the crack on the slope (from the Arthon Ltd web page)

The block of rock that is moving is large - about 300,000 cubic metres (Fig. 4), with the crack at the rear extending downwards for at least 10 m.

Fig. 4: Arthon Ltd image of the mobile block (from the Arthon Ltd web page)

Unsurprisingly, the authorities have stopped both the work on the slope and the traffic on the road, and now it is a game of wait and see. One possibility is that the slope will collapse completely, it may keep creeping or it may stop. Whatever happens the authorities have quite a challenge on their hands to know how to deal with this slope. The pattern of displacement against time is one tool that could be used in this case.

I'll post again as this develops. In the meantime, congratulations to all for their transparency in this case.

Rockfall sequence in Yosemite has a spectacular sequence of images of a rockfall in progress in Yosemite National Park that are well worth a look. The images (which are explicitly copyrighted, so I have not reproduced them here) were collected by a well-known photographer, Herb Dunn, in the canyon of the Merced River.

The pictures show a fall from what appears to be a previously active rockfall scar. Below the scar there is a large area of rockfall debris. The falls appear to occur in granitic rocks, with the detachment being controlled by a series of large joints.

The failure in this case was apparently quite large - the bock was 30 m x 15 m - and appears to have come from a wedge failure at the top of the scar. As a result of the large fall height and substantial volume, the boulders have fragmented as they have impacted the slope, creating a spectacular plume of dust that rolls downwards. The rocks also disturb the accumulated and weathered scree that they hit, which means that the dust cloud starts to change colour in the third image as the discoloured material is kicked up. The fifth image captures some airborne blocks (see the bottom of the image in the centre), which are quite impressive.

Note that the failure has happened on a beautiful sunny day in August, so the trigger mechanism is not really obvious (thermal expansion maybe, or perhaps just progressive failure).

Friday, 24 October 2008

Forced to flee

IRIN, the UN Office for the Coordination of Human Affairs, has produced a rather nice video about the impact of lahars (a landslide in comparatively young volcanic materials) in the Philippines. The landslide occurred during Typhoon Durian (known in the Philippines as typhoon Reming) in 2006.

Wikipedia image of the track of typhoon Durian (Reming) in 2006. The orange dots indicate the locations at which the typhoon was at its maximum intensity

NASA image, derived from TRMM data, of the rainfall associated with typhoon Durian (Reming). Note that although 200 mm is very high, far greater rainfall totals are often associated with large typhoons.

Lahars surged down the flanks of Mount Mayon, killing over a thousand people. The film focuses on a comparatively affluent family whose house and land was hit by the lahar. The children's mother was killed, their house destroyed and their land inundated. In the aftermath the government declared the flanks of the volcano to be too hazardous, meaning that the family were moved into a refugee camp. The father of the family is relentlessly cheerful (except when he revisits his house and sees his wife's pillow), but his desperation is clear to see.

The film is available here.

Google Earth image of Mount Mayon, showing a lahar deposit. Click on the image for a full size view in a new window.

In many ways the most interesting aspect is the way that the film balances the hazards associated with the natural processes (i.e. the danger of another event) with the hazards associated with displaced people moving to new settlements that can quickly become slums. It is an interesting film that brings home some fundamental issues in a very real way, without presenting anything terribly new. It is certainly useful for teaching both in schools and at undergraduate level, and as a reminder to those of us working on hazards as to the complexity of the impact of decisions.

UNOSAT image of the impact of Typhoon Reming on Mount Mayon, showing in particular the multiple lahar tracks. Note the degree to which the lahars have impacted upon the towns.

Wednesday, 22 October 2008

Landslide crisis in Honduras

Although it has not received any substantial coverage in the west, it appears that there is a serious landslide crisis developing in Honduras. Over the last few days Honduras has experienced intense rainfall as a consequence of a stalled tropical depression. A state of emergency has been declared.

The most serious problem appears to lie in Corquin in Copan, in the very west of Honduras. Here, both La Prensa and La Tribhuna are reporting that massive landslides have occurred. A (very rough) translation of the key parts of the La Prensa article is as follows:

"A landslide caused by rains in two hills formed a gigantic dam on a river that buried two villages, whose inhabitants had been evacuated, in a municipality in the department of Copan, 550 km northwest of the Honduran capital, reported a local official on Tuesday.

"El Suptal de Coquín and El Suptal de Belén are two communities that were nearby, one kilometer away from one to another, and they were buried, including two schools and all the houses disappeared". The mayor said that five other communities are at risk. Paz said that the land that slipped from two hills formed a dam on the river Coyol, which was formed a gigantic pool that has flooded the two communities. The earth dam is turning into mud that can slide easily endanger other five communities, which were evacuated. "The communities that are at risk are Mesitas, Pacaya, Ichotal, Higueral y El Coyol, all we have evacuated 100%, there are not a person, or anything, thank God," he said. He explained that "there is no access for machinery, or anything, the only way will be to blow it up but the thing is that as the hills are too sensitive and could cause more landslides." In the monitoring they did yesterday, the dam measured about 500 meters and the river Coyol is blocked. Every five minutes landslides occur that bring down trees and rocks, which increases the height of the blockage.

La Estrella is reporting that the landslide dam is 150 m high Needless to say a blockage like this is exceptionally concerning as it is inevitable that a breach will lead to a serious flood unless the landslide is mitigated. Urgent action may be needed to prevent a serious problem.

Tuesday, 21 October 2008

Sichuan Earthquake session at SinoRock 2009

Prof. ZuYu Chen has today emailed to bring to my attention a special conference session on the geohazards associated with the Wenchuan Earthquake. This will be held at the SinoRock 2009 conference in Hong Kong on 22nd May 2009. It will be followed by a field trip to the earthquake zone.

Beichuan New Town landslide. Source: This is Life Blog

Papers are due by 15th January 2009. Details of the session are available here.

Another landslide blog

Interestingly, I today came across another landslide blog, also housed on blogger:

Landslides under the microscope

The Blog appears to have been active since September this year, although it is not clear who is maintaining it. Nonetheless, someone is putting a great deal of time into it and there is some good stuff on the site. It has quite a strong Asian focus - especially Japan - so I guess that it is being hosted by someone from there.

It is a very welcome addition and I hope that it thrives.

Sunday, 19 October 2008

A strange report from Nigeria...

The Nigerian newspaper "The Punch" has been carrying a quite strange and intriguing story over the last few days regarding an apparently huge landslide in the Awgu area (i.e. at about 6.0046N, 7.4024E). The key points of the story (from the Punch) are:

"Residents of Ugwueme, Umuhu, Ugulesi Awgu and Ezinese Mgbidi communities in Awgu Local Government Area, Enugu State could not believe their eyes when they visited their farmland in the morning. Expansive farmlands measuring more than 20 square kilometres had been destroyed by a tremor. On account of the incident which was later explained as a landslide, there were huge cracks and depressions on the land as if a straying ballistic missile had exploded there. Some trees sank in the depression while others were completely uprooted."

The traditional Prime Minister of Awgu, Chief Stephen Onuorah, who visited the scene on the second day of the incident, said he felt a massive shaking and reverberations under his feet. He said he heard a noise that sounded like the roaring of a bulldozer. Surmising that it was an earthquake, he contacted the Chairman of Awgu Local Government Area, Chief Uche Anioke, who later led some officials to the site. Amazed at the level of devastation, the council boss contacted experts from the Federal Ministry of Mines and Steel Development, but the confusion over the incident was dispelled by the team of experts from the National Geo-hazards Monitoring Centre led by the director of the agency, Mr. Alex Nwegbu, and Prof Cornelius Nwajide, a lecturer at the University of Nigeria, Nsukka and consultant to Shell Petroleum Development Corporation.

The team which also included geologists, geophysicists and seismists, visited the farmland on Tuesday. They described the incident as a landslide which occurred on account of massive rainfall which “peculated into the land to an impermeable layer and caused land cracks”. Nwegbu in his preliminary report traced the remote cause of the incident to the geographical positioning of Awgu which was sitting on a ridge belt called clay star. The belt runs from Idah in Kogi State through Awgu to Arochukwu community in Cross River State, all of which are prone to geo-hazards.

The Chairman of the House Committee on Petroleum Resources and Environmental Management, Chris Ugwu, in a report sent to the state assembly, described the incident as an unusual disaster...Ugwu said that his committee, which visited the area, observed that large portions of land were compressed into crooked ridges and valleys."

This is intriguing because the area affected appears to be very large (>20 square kilometres) and the level of destruction appears to be high, even though the landslide has not been catastrophic in terms of movement. The terrain is question is not particularly steep or rugged, and this is not an area with notable seismicity. I would be very interested to hear more about this slide. I wonder whether this earlier report, although possibly covering a different area, might provide an indication of the root cause of the issue?

Although Nanka has bared the brunt of the erosion-based devastations, it has however not been relegated only to Nanka. Other towns have been faced with their unfortunate share of these hellish gullies. Enugu Ukwu is another town ravished by gully erosion. According to a 1993 State report on the state of gully erosions in Anambra, “the number of gullies presently pervading and ravaging the lands of Enugu Ukwu defies solution”. The story of the gullies in Enugu Ukwu begins with the Etti-Umuatulu-Osili Enugu Ukwu gully networks which starts from Etti Awobu village and gallops down a slope stretching down into Umuatulu Awobu where it splits into two branches; to run into Obuagu Osili where it converges to a point where the gully depth stands at about 80meters. The gully network within the Urukpaleke and Akama Osili areas originate which is reported to have been aggravated by a flood from a faulty drainage line constructed along Enugu-Onitsha road. The same gully stretches to another Akama Osili village and joins Urukpaleke gully. According to Inter Press Service New Agency who was one of the many New Agencies that reported on the incident, “the inhabitants of Umuchiana, one of the villages that make up Ekwulobia community in Anambra state, were woken up at night by a noise only to find some houses at the edge of the village giving way to landslide. They deserted their homes, taking refuge in nearby forest and villages. By the time they returned to their village the following morning, several houses, a church and some roads were washed away. Their farmlands, palm and cashew trees were not spared either. Though nobody died in the incident, more than 250 families (made up of more than 1,500 persons) were displaced.

Friday, 17 October 2008

Retaining wall collapse, Uganda

On Tuesday morning a collapse occurred in a retaining wall being constructed for the foundations of a new tower block in the capital of Uganda, Kampala. Two images have been published online of the failure, which buried nine workers, killing eight of them:

Monitor online image of the Pensions Towers collapse site

New Vision image of the Pensions Towers collapse site

Collapses like this are now quite rare in more developed countries, though not unknown (see here, here and here for example). However, a properly designed retaining wall, based on good site investigation and laboratory data, and a properly executed design, should not collapse in this way. So it will be interesting to find out what has gone wrong in this case. There will be a formal investigation, so we will wait and see, but the pictures and reports do point to a couple of issues.

First, the pictures above show a very red soil. This is of course characteristic of deep weathering - the red is iron oxide. Deep, tropical residual soils like this are often problematic materials because they can be weak and also highly variable. Experienced engineers know to treat them with respect.

Second, the pictures show that the excavation is deep (one of the newspaper articles suggests it was 25 m high!). The wall was being supported, but it appears that this was with nothing more than "wood, iron bars and wire mesh" see here). The images suggest that the wall was just being faced, not supported properly. This is surprising. However, the reasons behind this are perhaps explained by this:

"At the heart of the queries will be NSSF’s decision to change building plans which KCC insists it had advised the developer against. In building Pension Towers, NSSF had initially planned an eight-storey tower consisting of two-basement parking levels. The Fund subsequently changed the plans for the complex, into a 26 storey complex and tripled its costs from Shs36b to Shs120b."

The suggestion being that as a result of the extra storeys on the tower the excavation was deepened from two to four storeys without taking into consideration the need to change the design of the wall. It has also turned out that:

"The developers of the Pension Towers, whose retaining wall collapsed on Tuesday killing eight people, had earlier ignored a warning from Kampala City Council advising against using unapproved building plans."

The state of play at the site might be indicated by this report into the aftermath of the collapse:

"When the New Vision visited the site around 11:00am, the horrified workers of [the] construction company were desperately trying to dig out their buried colleagues, using spades and hoes. Enraged onlookers demanded that the two bulldozers on the site be used to remove the soil. As fate would have it, the wheel chain of one of the bulldozers broke off as soon as the engine was started by a volunteer as its operator had vanished, while the second bulldozer developed a mechanical fault and caught fire. A third bulldozer had to be rushed in from site. "

Finally, the interplay between western and traditional views of disaster causation on sites like this is nicely captured here:

"Foreman Hajji Kigongo said the accident could have been prevented if they had sacrificed three bulls before construction began. He scolded this boss for failing to perform the ritual, a common practice in Buganda. Susan Kataike, the works ministry spokesperson, said prior to the works, they had tested the soil to establish if it could hold a building of that size."

Tuesday, 14 October 2008

The Lifan landslide - from natural disaster to cover up

In China this summer there have been two big mining-related flowslides. The second, at Linfen County in Shanxi Province attracted a great deal of publicity (see my blog reports here and here), not least because of the very high death toll. However, the story of the first, which happened on 1st August at Lifan, also in Shanxi Province, is a great deal more murky, but details are now emerging.

On the day after the slide there were a series of reports that it had occurred and that 11 people had been killed. I picked up a Xinua report for example that stated that:

"More than 100 rescuers are clearing the landslide debris under which 11 people have been confirmed buried in north China's Shanxi Province. The landslide was in the early hours on Friday at Sigou Village in Loufan County. An initial investigation showed seven houses and11 villagers were buried, according to rescuers. Rescuers were working in shifts with excavators to clear the debris of stone and earth with an estimated volume of more than 100,000 cubic meters. The landslide site has resumed power and communications supply. "

Note that there is no mention here that the failure occurred in the dump from an iron ore mine, and the suggestion is that there was a large-scale and rapid response. In late August to mid September a different picture started to emerge. This suggested that in fact the failure had been a flowslide from an iron ore mine and, more importantly, that there had been a cover-up by the authorities, who had failed to search for a substantially higher number of victims. Over the next few days a recovery operation was launched, and eventually it was ascertained that 44 people had been killed.

So what happened to expose this incident? Well, a Chinese newspaper, the Guangzho Daily, has now published an account together with an interview with the reporter who exposed this event. This interview has been translated and published with photographs here. The reporter, Sun Chunlong published an article in late August pointing out that there had been a cover up. He based the article on an undercover visit to the site in which he compiled a list of 41 victims from family members. It turns out that many of the victims were migrant workers for whom the local authorities seem to have had little regard. He then followed his article with a post on his blog on 14th September in the form of an open letter to the governor of Shanxi province. This letter (which is translated at the end of the article here) came to the attention of the Chinese Premier, Wen Jiabao, who ordered a recovery operation and allowed the new to emerge officially. Between 22nd and 29th September they uncovered many victims, providing a final toll of 41 bodies and six partial remains.

Now, a formal investigation has been launched both into the landslide itself, which is just one of a catalogue of mining-related fatal accidents in China, and of the subsequent cover-up.

Thursday, 9 October 2008

Young River Landslide, New Zealand

Interesting news from New Zealand, where for the last few months there has been some concern about a landslide dam on South Island. The landslide itself occurred in a fairly remote area of the Southern Alps at 4:40 am on 29th August 2007. The landslide, which is well-described in a GNS Science poster here (there are some great images and some good data on that poster), blocked the river valley to a depth of about 100 metres. This was a big debris slide, with a volume of about 11 million cubic metres and a runout distance of about 1.8 km. Interestingly it does not appear to have created an air blast as large slides of this type often do. This may mean that the mass moved as a series of events closely spaced in time, rather than one big, instantaneous failure.

Over time a lake built up behind it, finally overtopping on 5th October 2007. Understandably, there was concern about the possibility of an outburst flood. In this case there are few human assets at risk downstream, but this is a popular hiking area, potentially putting people on the trails at risk. As a result, the trails were closed by the Department of Conservation whilst the landslide was monitored in real time by GNS Science and Otago Regional Council. Unfortunately, such a closure was not good for the local community as it reduced the number of tourists.

The images below show the landslide from the downslope side. I have annotated it below to show the key features. Note that the deposit has banked up on the right side (from this view). The natural spillway that has formed is just on the lee of this banked up deposit. This deposit is coarse-grained (bouldery), which may well be the reason why the channel has not eroded downwards to release the water.

The image below is from the landslide dam itself looking across the lake. Note the size of the boulders - these are part of the landslide deposit. This does show that if the landslide dam is stable then the resultant lake can in some circumstances become an asset.

This week it was reported here that a decision has now been taken to reopen the trails downstream of the landslide from 1st November (i.e. just before the start of the summer). Unsurprisingly, the local people are rather pleased: "Makarora Residents Association deputy chairman Devon Miller said the closed valley had affected some of the tourist operators in the township, so the decision to re-open was a welcome one."It's a good positive announcement and the community is happy," he said." (Otago Daily Times).

The decision to reopen the trails but to maintain some restrictions in heavy rain, using a new warning system, appears to be sensible. So often landslide management is about balancing risks - i.e. what is the risk of a collapse of the dam affecting someone on a trail compared to the risk to the local communities associated with the loss of tourism, etc. In this case the stability of the dam suggests that this risk has now dropped to close to the residual level. Note that this does not mean that there is no risk - there are hazards associated with spending time in remote mountains. The risk from the landslide dam is no greater, and may be substantially less, than those other risks.

All-in-all the approach taken by the parties involved in New Zealand has been exemplary, in terms of picking up the event in the first place, in terms of the ways that they have monitored it and in terms of the decision-making process to minimise risk.

Volcanic flank collapse and tsunamis

A few years ago the media got rather excited about a paper that suggested that there was the potential for a giant flank collapse on the Cumbre Vieja volcano in the Canary Islands. A model of the resultant tsunami suggested that it could be sufficiently large to cause huge losses throughout the coastal areas of the North Atlantic. Most scientists now believe that this tsunami was something of an exageration of a worse case scenario, (see for example this critique) but the potential for a flank collapse to generate a local tsunami event is very real, albeit comparatively rare. As a result, there is considerable interest in trying to understand these events better.

At the GSA Annual Meeting this week, Matthew Hornbach from the University of Texas presented a rather interesting study that has just been undertaken on the island of Tongatapu in Tonga. Tongatapu is located in the South Pacific with a number of active volcanoes nearby (Fig 1).

Fig. 1: Google Earth image of the island of Tongatapu showing the location of three unnamed submarine volcanoes to the west.

Hornbach found that on Tongatapu there are seven coral boulders located up to 400 m from the current coastline (Fig. 2). The largest of these boulders has a mass of about 1200 m. The boulders have clearly been lifted from the coral that fringes the island - Science News reports that for the largest boulder the point in the reef from where it has been removed is clear.

Fig. 2: Science News image of one of the boulders on the island of Tongatapu.

Now, this island is flat, meaning that the boulders cannot have rolled there. Hence, Hornbach has concluded that these boulders were emplaced by a huge tsunami, which they have provisionally dated to have occurred in the Holocene (i.e. in the last 10,000 years). This is potentially the largest tsunami deposit so far recorded - the wave must have had a run up of >40 m vertical distance. Hornback believes that the source of this tsunami was a submarine volcano located to the west of the island (Fig. 1). They report that bathymetric surveys of this feature show that it rises to to the water surface - some reports suggest within 65 m. This large volcano apparently has a section missing from the east side, which Hornbach interprets as being the result of a flank collapse - i.e. a giant landslide in which the side of the volcano collapses. Flank collapses undoubtedly can cause very large, localised tsunamis.

As an aside, it is interesting to note that the major population centres are on the sheltered north and east side of the islands (Fig. 3) . I wonder if this is a coincidence?

Fig. 3: Google Earth image of Tongatapu .

Wednesday, 8 October 2008

8th October 2008 - two important dates

The third anniversary of the Kashmir Earthquake
Today is the third anniversary of the Kashmir earthquake disaster, in which over 79,000 people were killed. Of these, about a third (i.e. about 26,000) were killed either directly or indirectly by landslides. To mark the occasion, the images below, which I took in January 2006, show some of the slope failures that occurred.

Whilst Pakistan has undoubtedly put a great deal of effort into earthquake reconstruction, hardship is still the norm in the earthquake affected areas. The two major towns, Muzaffarabad and Balakot are still only partially rebuilt, whilst many of the outlying villages are in an even more desperate state. Over 2000 people still live in refugee camps as a result of losing their land and properties to landslides and disruption to the road network from failures is still a daily occurrence.

Photo 1: Shallow rockslides on the road from Muzaffarabad up the Neelum Valley. Note the complete destruction of the village in the foreground.

Photo 2: Landslides on a main road close to Muzaffarabad. The bravery of the bulldozer drivers was and is incredible.

Photo 3: Houses on an active landslide near to Hattian Bazaar. The cracks are the result of movement of the slope in the earthquake. Note that the large house is in a graben feature (i.e. on a block that has dropped down as a result of the landslide movement). This has cause the house to crack, but as the washing shows it was still inhabited. Note that rebuilding is occurring in this incredibly dangerous location.

Photo 4: A collapsed terrace in Hattian Bala. When the terrace collapsed the buildings on the edge fell into the river, killing the occupants.

An irony: the International Day for Natural Disaster Reduction

The second Wednesday in October (i.e, today) is designated by the United Nations as the The International Day for Natural Disaster Reduction. Worldwide activities today are focused on raising public awareness, and thus preparedness, for natural disasters. Yesterday, the Secretary General of the United Nations urged greater investment in disaster preparedness. Today in which the UK government has agreed to plough yet another £50 billion to prop up the banks for their earlier follies. Just to put that into context - in the aftermath of the Kashmir earthquake, which made over 3.3 million people homeless, the International Community donated a grand total of $5.8 billion (£3.3 billion) - i.e. 6.6% of the amount that the UK government has today invested in the banks, not even counting the £450 billion that has been made available as loans to the banks.

Tuesday, 7 October 2008

Hull Geographical Association talk

On 7th August I gave a talk to the Geographical Association in Hull. The box below is the Powerpoint file. It can be downloaded by clicking on the link marke "Dr_Dave" below the file. If you cannot see it here then you can download it here.

The talk is loosely based on my presentations in New Zealand, but it has been updated somewhat.

Uploaded on authorSTREAM by Dr_Dave

Sunday, 5 October 2008

Scottish landslide study

August 2004 was unusually wet in, with some areas of the country experiencing three times the long term average rainfall for the month. The most memorable manifestation of that time was a series of landslides that hit the road network. In particular, on 18th August a series of debris flows the hit a main road , the A85, in Glen Ogle. This is widely seen as a pretty near miss as over 50 people were trapped between two landslides and had to be rescued by search and rescue helicopters (see below, image from the Scottish Government).

In the aftermath of that event, Transport Scotland promised to undertake a detailed study of the threats posed to the road network by landslides. Tomorrow (Monday) that report will be published at last. It will be very interesting to see what it says, but the Sunday Herald appears to have leaked the main findings. These are as follows:
  • Records suggest there have been about 175 major landslides in Scotland over the last century
  • The occurrence is increasing with time (note there are many reasons why this might be the case, or might appear to be the case)
  • 380 kilometres of the trunk road network are at high risk of landslides.
  • 67 locations have been identified with the highest level of hazard (though it is not clear at present whether this is actually high risk in a global sense)
  • The A82, A83, A86, A87 A9 are the roads with the biggest hazards
  • Parts of the country's key trunk roads, such as the A1, A7, A77, M74 and M90, are also at risk.
The highest risk area is apparently the A82, which runs from Glasgow to Inverness via Fort William. Apparently 16 stretches of the A82 were identified as at high risk, with a 13 km stretch along Loch Lochy, north of Fort William, being rated as the most hazardous (see below from Google Earth).

Now, in many ways none of the above is terribly surprising. The most interesting part though is this (quoting from the Sunday Herald article):

"The Transport Scotland report pointed out that major engineering solutions such as re-routing roads or constructing retaining walls were expensive and intrusive. "It is anticipated that relatively few locations would justify this kind of expenditure," it concluded. Instead, the report suggested that more should be done to improve the public's awareness of the problem. There should be better road signs, improved weather forecasts and more road closures."

It will be interesting to see how this plays out tomorrow, and indeed of course what the report actually states. However, my experience is that the public and the media are rarely happy to have an apparently substantial level of hazard pointed out, but the recommendation then being to do little more than make the public aware. This is the point at which the public and/or the media often adopt a zero tolerance to risk. Incidentally, being told there will be more road closures is unlikely to go down well either. Presumably Transport Scotland will manage this rather carefully!

Wednesday, 1 October 2008

September 2008 fatal landslide map

For the first time in recorded history the monthly fatal landslide map is actually on time!

Below is the map for September 2008. First the statistics:
Number of recorded fatal landslides: 59
Number of recorded fatalities: 1290

September has been a quite bizarre month, with fatal landslides occurring at a level that is much higher than expected. As such this continues the trend for August, which was also above average, but it bucks the trend for the rest of the year. At present I am not sure of the reason for this change - that will require some considerable analysis. It is very interesting indeed.

Comparison with previous years is difficult. In 2004 there were catastrophic landslides in Haiti that killed three thousand people. If this is included then the average across the period 2002-2007 is 808 - high, but still much less than in 2008. Excluding that single event in Haiti yields an average of 202 people. Note that 550 of the fatalities in 2008 were also in Haiti due to mudflows created by two tropical cyclones. Other large events were the Manshiyet Nasser landslide in Cairo, Egypt (107 fatalities) and the Shanxi flowslide (270 deaths).

So, here is the map for September 2008. As ever, you will need to click on the map to get a decent view of it:

A few things to note:
  1. The very strong cluster along the Himalayan Arc is once again very evident. Nepal in particular is suffering an intense period of landslides.
  2. There is also a clear cluster in the Caribbean as the Hurricane season continues to have a high impact. Note that in Haiti the cluster is a multiple event.
The map of the year to date is shown below. Again, click on the map for a decent view. The normal clusters are now well developed. Compare this map with that from 2007 (see here). The similarity between the two patterns is now very clear.

As usual I welcome any comments, corrections and clarifications.

Mars Odyssey image of landslide

Although landslides on other planets have not been a major theme of this blog, there is an interesting area of science that focuses on these intriguing phenomena. Of course a great deal of this research is quite difficult given our poor knowledge of the conditions on and in the slopes when they occur. The availability of increasingly high resolution imagery is however helping in the understanding of these features. There is a hope that we might understand terrestrial landslides better if we can see how slides operate in other environments, although to date I must admit that I am unconvinced that this has really happened.

Yesterday NASA released the image below, which shows an area of Mars with a quite interesting landslide. It was collected by Mars Odyssey THEMIS (acknowledgement to NASA/JPL/Arizona State University):

Fig 1: Mars Odyssey THEMIS (acknowledgement to NASA/JPL/Arizona State University) image showing a landslide on Mars.

At first the landslide might not be obvious, but look closely on the centre right side - it is clear that the slide is a ridge failure with a reasonably long run-out. I have zoomed into the image to show the landslide below (Fig. 2):

Fig 2: Enlargement of Mars Odyssey THEMIS (acknowledgement to NASA/JPL/Arizona State University) image showing a landslide on Mars.

I have processed and annotated the image (Fig. 3) to highlight some key features. I think (though this is unconfirmed) that the landslide is about 2 km wide and 6 km long. Note that the presumably more resistant material that forms the ridge appears to be intact on the landslide body. The landslide has two smaller failures on its flank. Finally, it also appears to have a few small craters on it, which presumably means that it is not too recent (UPDATE: thanks to Dr Mauri McSaveney for pointing out that not too recent in this case probably means 2-3 billion years old).

Fig 3: Annotated enlargement of the Mars Odyssey THEMIS (acknowledgement to NASA/JPL/Arizona State University) image showing a landslide on Mars (Click on the image for a better view in a new window).

Similar landslides do occur on Earth. For example, Fig. 4 shows the Frank landslide, which I have described before. Note that in the Mars case the slipped block has only partially broken up, whilst at Frank it disintegrated completely to form a rapid flow. I am sure that there are better examples from Earth, but I cannot think of them at the moment. Can anyone come up with one?

Fig 4: Natural Resources Canada photograph of the Frank landslide, Turtle Mountain, Alberta, Canada.