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.

Monday, 28 June 2010

New images of spillway at Attabad

Unfortunately I cannot access images from Attabad at the moment, but the Pamir Times has this morning published a set that are well worth a look.  The images are here.  Interestingly, they also note that the water level has reduced by 13 inches (about 33 cm) over the last two days, which is a promising sign.  Unfortunately I cannot validate these figures at the moment.

The images seem to show that the key constraint remains the point of the large boulder as before, although the water has now eroded around this, leaving it stranded in the middle of the channel:


The channel is clearly widening on both sides through slope failures, increasing the capacity of the channel, but there is still remarkably little sign of down-cutting.  Meanwhile downstream, the dam is continuing to lose mass through erosion, a process that we must watch carefully:


This loss of volume is very slowly weakening the barrier.  There are no signs at the moment that this is a cause for real concern, but close monitoring is needed as the flow rate increases.

Saturday, 26 June 2010

Attabad - situation as of 25th June,

NB I have updated this post, and changed the title.

Apologies for the lack of posts over the last few days - I have been in a meeting in Bermuda that has left little time to tend to this blog.  Meanwhile, although small scale blasting of the spillway has reportedly continued, as of yesterday the lake level at Attabad is continued to rise by 10 to 20 cm per day, with the effect of both further drowning houses, hotels and roads upstream, and increasing the volume of water in the lake.  Unfortunately I do not have any information about the blasting, or any pictures, but my analysis of the flow of the data is that the short term lake level graph now looks like this (correct to yesterday morning)


The lake level is now about 5.5 metres above the overtopping level, and at the moment there is little sign that this is reducing.  Thus, the long term lake level graph now looks like this:

Meanwhile, spillway discharge has  increased, driven primarily by a substantial rise in inflow:


I am intrigued to know whether this increased discharge has started to drive a new wave of erosion downstream.  Finally, this graph compares inflow and spillway flow over the last ten days or so:


It is clear that at the moment inflow and outflow are directly linked - i.e. that the increase in spillway flow is due at least in part to increasing inflow.  The grey line represents the point at which spillway flow equals inflow - i.e. the point at which the lake volume should stop increasing.  This does not account for seepage, but as this is now a tiny fraction of spillway flow this is not a major problem.  It is clear that recent increases in inflow were not being balanced by increasing outflow.

It should be expected that the inflow will continue to rise over the next few weeks, so this graph will be interesting to observe.  Hopefully the spillway operations will start to increase the outflow in a controlled manner in the next few days, such that the lake level starts to fall.

Tuesday, 22 June 2010

Blasting of boulders has begun at Attabad

Yesterday NDMA started the process of blasting the boulders in the channel at Attabad.  This image, from Focus, shows the state of the channel and the reconstructed access track:




One of the blasts yesterday was on the boulder at the entrance to the channel, visible on the left of the image above.  This image shows the crews drilling the blast holes:



Clearly this boulder is not the main issue in terms of the flow, but it may be that they are using this one, which is accessible, as a test.  Access to the other side of the channel is difficult, so the suggestion is that water cannon will be used to erode the softer material.  It will be interesting to see what they do today in terms of blasts.

Meanwhile the lake level rose by between 8 and 10 inches (20-25 cm) yesterday, suggesting that inflow has increased again.

Sunday, 20 June 2010

Attabad - a decision has been taken to blast

It appears that a decision has now been taken to attempt to blast the key boulders controlling the flow at Attabad, with suggestions now being made that blasts will begin tomorrow (Monday).  This is a brave decision by NDMA - and I wish them luck.  The context appears to be a combination of the continued exasperation of the local people about the lack or resolution of the situation, and the ongoing slow evolution of the spillway.  However, it should also be noted that there has been some change in the spillway over the last couple of days, as this Focus image (taken today) shows:


The Pamir Times published an alternative view taken on 18th June from the other side of the river, showing at the key boulder:


It is clear that the water has started to erode around the restriction.  By today the water had created a channel around the back of the block (image from Focus):


The importance of this boulder in controlling the flow remains very high, as this Focus overview image shows clearly:



Meanwhile, the level of landslide activity immediately upstream remains high (Focus image):

Friday, 18 June 2010

River flows at Attabad

Thanks to Dr David Archer of the University of Newcastle for an analysis of the dates of peak flows on the Hunza.  The analysis is for Danyor (sometimes spelt "Dainyore"), which is near to Gilgit downstream of Attabad (there is no hydrograph data for Attabad itself), but it provides a clear insight into the current vs maximum flow in the river.

  Danyor (Dainyore) Bridge (from here)

This table shows the mean date of occurrence in the season of specific percentages of the peak flow based on the 33 year period from 1966 to 1998:

Flow                         Mean date                                 Standard Deviation (days)
Peak                         29th July                                   14
50% of peak             26th June                                  11
20% of peak             3rd June                                    9
10% of peak             18th May                                  11
5% of peak               2nd May                                    9

This suggests that on average the current flow would be somewhere between 20% and 50% of the peak summer flow - i.e. that the spillway is going to have to cope with a great deal more water yet this summer.  Assuming that the data are described by a normal distribution, we would expect that in 68% of years (representing 1 standard deviation) the peak flow would occur within 14 days of 29th July (i.e. between 15th July and 12th August.

A week of landslides around the world

Alongside the continuing Attabad crisis, here is a summary of the last week in landslide events (in no particular order).  The list is not exhaustive by any account, but these are the stories that caught my eye:



1.The Oliver debris flow in Canada
I covered this event in a post or two earlier in the week.  It is now clear that the trigger was the overtopping and eventual failure (through a breach) of a small earthen dam high in the catchment (image from here):


The authorities were warned by a hiker that the lake was overtopping two days before the failure.  It appears that there is now a great deal of soul searching occurring in Canada regarding the safety of these old and often poorly maintained structures.

2. A deadly landslide in Burma
No complaints please - I will not be drawn into using the other name for Burma imposed by the illegal and immoral junta that runs that country.  Anyway, Bangladesh and Burma both suffered very heavy rainfall this week, triggering landslides across a wide area.  In Burma a slide killed 56 people in Maungtaw and Buthidaung townships in Rakhine state, according to Xinhua.


3. Deadly landslides in Bangladesh
Meanwhile the same rainstorm caused chaos across a large part of the Cox's Bazaarand Bandarban areas of Bangladesh, with multiple landslides killing at least 55 people.  As is so often the case, the blame is being laid at the door of deforestation and slope cutting.


4. Two slope accidents in China
China also suffered two terrible slope accidents this week. In the first, on Monday, 24 people were killed when a debris flow hit vehicles on a road in Nanping, in eastern Fujian Province.  In the second, on Tuesday, a 40,000 cubic metre rockfall occurred at a hydroelectric project construction site in Pengta Town, Kangding County in Sichuan, killing 23 people.  Meanwhile, as a I write, reports suggest that another slide in China today has killed up to five people in Taohua Village, Chun'an County in Zhejiang Province.


5. An interesting hit pit wall collapse in Australia
ABC News carries a story today about a large scale high pit wall collapse in the Savage River iron ore in Tasmania:




Note the excavator at the pit bottom for scale.  The slide is reportedly 140,000 cubic metres in volume.  There were no injuries or fatalities in this event.


6. Landslides in Darjeeling, India.
The ever-impressive Savethehills blog reports on landslides this week triggered by heavy rainfall in Darjeeling.  One slide, in Tirpai, Kalimpong, killed three people.  Readers may be interested in the dramatic video on this page, which shows a small landslide in action, with the unfortunate effect of the loss of a truck:

Thursday, 17 June 2010

Attabad - locals taking the situation into their own hands

Several media outlets in Pakistan are reporting that the level of frustration amongst the displaced people at Attabad has reached the point that they have taken the situation into their own hands.  The Pamir Times has a pictorial record of what they have chosen to do - a large group have been working on the banks of the channel in an attempt to widen it.  There is a full gallery of images here, from which these are taken:



Unfortunately, the amount that they can do in actually widening the channel is limited, whist the risks to those undertaking this work are high.  Hacking away at the toe could destabilise the slope such that it collapses, dumping all of them in the water, and there is the potential for further slides from the slope behind.

Earlier reports suggested that people trying to join this effort from downstream has a confrontation with the police, and at least one person was injured.

I fear that this will ramp up the pressure on the authorities such that they will end up blasting the boulders without undertaking a full analysis.  I hope that this does not happen - but that a proper study is undertaken urgently.

Tuesday, 15 June 2010

Attabad - remarkable stability on the spillway - and some thoughts on what to do next

I will shortly post the latest update on the monitoring site, which shows that the lake level is continuing to rise at about 5 cm per day as inflow exceeds outflow.  The spillway continues to show a remarkable level of stability.  These two images compare an image from Sunday (left side) with one taken 24 hours later on Monday (right side).  Whilst it is tempting to play spot the difference, the reality is almost no change:


So what to do now?  Well, it is clear that there is a huge social cost to the current situation, which probably cannot continue for much longer.  It is also surely clear that the current monitoring team cannot maintain the current level of activity for long given their living conditions.  So here is my suggestion for a way forward. Please note this is not advice, and should not be treated as such, but rather it is a starting point for discussion.

1. NDMA sets up a detailed, integrated data collection system based upon, but enhancing, the current Focus activities.  This should include the following measurements at 6 hour interval:, with the first measurement each day being taken at dawn
  • The flow rate in the spillway
  • The seepage rate
  • The lake level
  • Landslide activity
  • The inflow rate
  • Temperature
  • Seismic activity
2. An expert group meets just after dawn each day and integrates that data with the weather forecast to issue guidance on the stability of the dam.  If the group considers that conditions are safe, the boat service is allowed to operate, and people are allowed onto the red zone - i.e. the land below the dam - during the hours of daylight, so long as they are within earshot of a siren.
3. This is backed up with real time monitoring, preferably automatic, of inflow, landslide / rockfall activity at strategic points along the lake, and outflow, feeding a warning system.  A command centre is established that would operate the alarm system should landslide flow rate increase.  Boat crews and people in the red zone are trained as to what they should do if the alarm sounds.
4. The expert group meets at dusk each day to plan for the next day. 
5. Alongside this a study is implemented immediately of management options for the spillway.  This study should be undertaken properly, with international input, and will be made openly available when complete.  A timetable is placed on the production of this report, and on the decisions that will be made on the basis of it.
6. All of this is backed up with a transparent communication strategy that explains the risks and benefits of the current situation, and of the various options.

This would seem to me to be the best balance between maintaining safety and allowing people to start to rebuild their lives.  Of course this strategy will increase the risk that people face from the dam - but there are real risks associated with their displaced state too that we need to start to reduce.  However, I must emphasise that to do this safely NDMA must use expert advice - this cannot be done any other way.

The strange similarity between the Attabad and the landslide in Oliver

Yesterday I posted in both the ongoing situation at Attabad (and I am glad to say that it now seems likely that the reported landslide at Shimshal was a false alarm) and the mud and debris flow at Oliver in Canada.  It is now reported that the Oliver slide was caused by the failure of an embankment retaining a small irrigation lake.  If that is the case then I assume that the lake is this one:


The damage, shown below in an image from the Vancouver Sun, does serve to demonstrate the destructive potential of lake collapses, and thus our ongoing concerns about Attabad:


Has anyone seen any decent images of the path that the flow took between the lake and the valley floor?

Monday, 14 June 2010

Impressive mud and debris flow in Oliver, British Columbia

Thanks to a number of people for bringing this one to my attention.  The community of Oliver in British Columbia yesterday suffered an impressive mud and debris flow that is reported to have destroyed five homes (images from the Vancouver Sun):




The flow has clearly come out of a deeply incised gully in the mountains:


A perspective view of the excellent Google Earth imagery of this area is rather helpful:


Two things to note here (the flow hit the area just above the "97" on the image above).  First the community that has been hit by this flow is located on a small fan that has been formed by this type of flow.  Second, the very narrow, deeply-incised channel mouth is the classic location for this type pf flow, where a blockage allows debris and water to accumulate, before collapsing to generate a flow.  It is interesting to note that this area has reportedly experienced unusually heavy rainfall this spring and early summer.

Attabad - a further twist in the tail

Over the weekend the water level in the lake at Attabad has started to rise once again (see the monitoring site), presumably indicating that the warm weather in the Hunza region is increasing the rate of snowmelt, and therefore of inflow to the lake.  The continued choke on flow being imposed by the large boulders in the channel is clear.  The channel itself continues to evolve slowly through widening (image from Focus as per usual):


 The amount of scour in the downstream portion of the channel is remarkably impressive:


 It would appear that development of the the channel continues to be impeded by a small number of critical boulders, one of which may well be below the water level, protecting the stream bed against downcutting.  The Pamir Times images of the site, available in this gallery, are quite instructive.  This composite image in particular is interesting, clearly showing how the boulders are controlling the discharge:


Meanwhile, landslides continue to occur with a high frequency in the Attabad area (Focus image):

Friday, 11 June 2010

Two very interesting galleries of recent landslides

I am now trying to catch up on everything that has been pushed aside by the Attabad landslide saga.  Whilst all of this has been going on there have been a number of other substantial landslide events.  Two of these have impressive galleries of images available, both of which are worth a look:

1. Tropical Cyclone Agatha in Guatemala
The landfall of Tropical Cyclone Agatha on 29th May triggered extensive landslides over a wide area in that country, killing over 150 people.  One of the affected areas was the town of San Antonio Palopo.  A group of the expatriates have set up a website appealing for assistance (I have no idea as to the legitimacy of this appeal, but also have no reason to disbelieve them).  They have put a gallery of images online here.  An example of the images is this:


2. Lanckorona, Poland
Meanwhile, the town of Lanckorona in Poland is being slowly destroyed by a large, slow moving landslide, with terrible consequences for the inhabitants.  At the time of writing, a second phase of movements has been reported.  There is a couple of decent videos of the town here, but most impressive (and dreadful) is the extensive gallery of images here, including these two:


Both sets of images are worth a look

The continued threat posed by landslides at Attabad

Attention continues to be focused upon the state of the spillway at Attabad, and in particular the likely impact of the increase in flow we might see over the next few weeks.  Yesterday's images from Focus showed that slow evolution of the spillway continues, with the lake level reported to have dropped only by a:n inch (2.5 cm):




However, we must not lose sight of the potential for other failure mechanisms.  Given that seepage appears to now be constant, the greatest concern may well be associated with the potential for a further landslide into the lake.  The high water levels and (comparatively) warm temperatures render this a possibility (but not in any way a probable event).  This remarkable set of images, taken at 6:14 to 6:16 pm last night (10th June) by the Focus geologists, clearly illustrates the ongoing threat:

Thursday, 10 June 2010

Attabad spillway video

Thanks to a number of people for drawing my attention to the Hunzaonline video on youtube that shows the spillway in action.  The caption indicates that this was collected on the 8th June:



Three observations about this video:
  1. It shows that the major restriction on flow is still the large boulder at the saddle of the spillway;
  2. A second boulder has formed  substantive constriction downstream as well, but this is not controlling the overall flow
  3. There is still considerable scour occurring, especially on the downstream side of the boulder, upstream of the boulder towards the neck of the channel, and elsewhere on the banks of the channel.
Meanwhile, the Pamir Times reports that "An international expert reportedly suggested the government to blow two large boulders present in the spillway but the government has decided to act against the suggestion".

In case anyone was wondering, that expert is not me!   Whilst I wouldn't completely rule out the possibility of a controlled blast, this would need to be undertaken with extreme care, and only after a full analysis of the consequences had been undertaken.  I would in particular want to see an evaluation of the likely flood that the blast might trigger, and the potential for triggering further slides on the sides of the valley.  However, this is not an excuse for inaction - NDMA really need to move quickly now to evaluate the range of options, and to communicate the pros and cons more widely.

As per my post yesterday, I will use the Hunza Monitoring Site to host updates on the situation at Attabad, and this site to provide a commentary.  I will put a new set of data on the monitoring blog later this morning.

Wednesday, 9 June 2010

Slowing evolution of the spillway at Attabad

Once again I am grateful for Focus Humanitarian Assistance for sending the latest photos of the spillway at Attabad.  The rate of change new seems to be slowing as flow is being controlled by the large boulders at the head of the channel.  This pair show the downslope side of the channel - the left hand image was taken on 7th June and the right hand image a day later:


Allowing for the slight change in camera angle, there is little indication of major change between the two images.  The large boulder on the left side of the upper part of the channel bank has slipped into the water on the right hand image, presumably indicating that channel widening is continuing.  Of course there may well be some continued erosion of the bed that would is not visible here.

In the upper channel there is comparably little evidence of change also.  The inset image is from 7th June, the main image a day later:


It may be that a more detailed inspection on the ground would reveal a more dynamic system.

It is my intention to stop duplicating posts on the two sites from today, with the Hunza Monitoring Blog being used once again to present data on the state of the dam and the lake, and Dave's Landslide Blog to provide a commentary.  On DLB I will also start covering other landslide events again.

Monday, 7 June 2010

Latest image of the spillway at Attabad

The wonderful people at Focus have provided an image of the state of the spillway at Attabad that is very instructive.  This was taken today:



The current state of play is I think as follows.  Flow appears to be constrained by two blockages but, as a commenter has noted, one is a rock spur out of the channel.  The blockage appears to have formed a small waterfall / rapid.  Downstream of the blockage the channel has widened dramatically - and indeed a section of the track has now been lost.

To me this suggests that the crisis may be far from being over.  In particular, the loss of this barrier could cause a rapid increase in flow rate that could be highly erosive.  It is however important to stress that interpreting the state of play from photos is difficult.

Attabad - an increasingly difficult hazard to manage

Apologies to all who emailed and left messages over the weekend requesting updates. 

FWO data collected at 8 am on Saturday suggests that the rate of flow was 124.6 cumecs, whilst the Pamir Times reported yesterday that it was 131.7 cumecs.  If so, the discharge time graph looks like this:


Thus, the discharge is apparently stabilising.  Various media reports from the site itself suggest that downward erosion of the channel has now reduced, but that some lateral erosion is still occurring.  I have not seen any images to confirm this though.  The lake has stopped rising for now.

It is hard from here to assess the current position with regards to the dam, or to forecast what will happen next.  However, from the start I have held the view that managing this hazard would be somewhat challenging if stable flow became established.  The chronic hazard has not gone away, although the acute hazard may have reduced.  As there is still a vast quantity of water stored in the landscape, the dam remains vulnerable to a series of processes, including:
  1. An unexpected increase in erosion rate;
  2. Erosion during flood events (the discharge of the Hunza will rise substantially in the next few weeks);
  3. A further landslide on the banks of the lake, which could trigger a wave;
  4. A seismic event.
Thus, NDMA have a huge challenge ahead in deciding when to allow people to move back into the high hazard area.  They will also need to decide whether to initiate erosion through the use of a controlled blast.  This is not an unenviable decision to make.  Inevitably, there are some exerting pressure to initiate a breach to drain the lake, whilst others are happy with the status quo.

Meanwhile, of course those on the upstream side remain isolated, with a huge lake impeding access.  The Karakoram Highway remains closed indefinitely, although the boat service has been resumed.  During summer floods, when inflow may briefly exceed outflow, the lake level could rise again by a small amount, unless progressive erosion of the spillway serves to lower the lake level.  Thus, overall, many challenges remain at Attabad.; it will be interesting to see how NDMA responds to them.

Friday, 4 June 2010

Attabad: spillway flow update of 08:30 this morning

There is a mass of confusing and contradictory information about the state of flow in the Attabad spillway, but the FWO data appears to be consistent at the moment.  The latest data, again via Dr Sadiq,  is that flow was 3700 cusecs (105 cumecs) at 08:00 local time this morning.  This makes the graph look like this:


This suggests that we are still seeing an incremental increase in flow.  However, interestingly, the rate of inflow and the rate of outflow now appear to be balanced, such that the lake level should stop rising (for a while anyway).  If this happens, and spillway flow continues to increase, we will know that erosion is developing.

Photos of the development of the situation at Attabad

Focus have kindly provided a new set of images of the situation at Attabad with respect to the spillway.  I think that these images were taken yesterday.

Most importantly, here is an overview image of the spillway:


It is helpful to compare this with the image of the spillway from 1st June (right hand image):


It is clear that the situation has developed considerably over the last few days.  The flow along the spillway has increased greatly, and the lower part of the channel has widened and deepened.  Flow appears to still be controlled by the large boulder in the middle of the channel, although the lowering of the channel downstream will be steadily undercutting this.The development of the spring on the channel edge is also interesting.

A closer view of the spillway clearly shows how widening is occurring:


The flow is undercutting the banks, which are then progressively failing.  Note also just how much scour is occurring even though the bed of the channel is boulder-strewn - it is clear that at the moment the boulders are not armouring the channel.

A view from the downstream side of the channel is fairly dramatic:


This gives the impression that there is a huge volume of water flowing.  However, a look downstream towards the old landslide deposit at Salmanabad (that is the big pile of debris upper right) shows that this is not really the case:


It is clear that the flow is still rather modest, despite the huge amount of erosion that the water has achieved.