Meanwhile, elsewhere

Although all eyes, and increasingly those of the media (which is showing considerable interest in this blog), are on Attabad, other landslides are happening around the world as we enter the rainy season in many landslide prone areas of the Northern Hemisphere.  In the last few days a number of significant landslide events have occurred:


1. A landslide-induced rail crash in China this morning.
Xinhua reports that an 8000 cubic metre, rainfall-induced landslide derailed a train on the line between Shanghai and Guilin in Dongxiang county in Guangxi Zhuang Autonomous Region.  It is reported that 19 people were killed and a further 71 people were injured.  Xinhua has two images of the landslide, which appears to have occurred on a modified slope in deep, highly weathered soils:

Thus one may be the most telling, as it is clear that just above the top of the slide, on the right side, the slope has been regraded, and indeed there is clearly some fill in the exposed slope section, suggesting that the two of the slide was in a part of the slope that had been modified:

 2. The first serious rainfall event of the year has happened in Taiwan
In Taiwan there is deep concern about the likely impact of landfalling typhoons this year, given the devastating impact of Typhoon Morakot last August.  Those fears will have been heightened today as the first real rainfall event of the year occurred.  The Central Weather Bureau has published an image of the rainfall totals for the day:

Of course in most places such rainfall totals (>200 mm in a day) would represent an exceptional event.  In Taiwan this qualifies as a light shower, but nonetheless there has been some landsliding in the mountains, with the resort town of Tungpu being cut off as a result of rockfalls.  Taiwan is going to be very interesting to watch again this year; with continued inadequate means to manage slopes nationwide I fear for what might occur.


3. Sri Lanka is suffering its May landslide problem
Sri Lanka often suffers heavy rains in May as the SW monsoon starts up.  This year is no different, with a series of storms associated with Cyclone Laila triggering widespread flooding and landslides.  The Disaster Management Centre is reported to have said that 20 people have been killed, and 500,000 people have been affected.

I will post an update on Attabad tomorrow morning at about 7:30 am UT.

The mechanism of the Highway 3 landslide in Taiwan

That bastion of "quality" journalism, the Daily Mail, has an article about the Highway 3 landslide that includes a set of high quality images of the site:

tic

The article correctly identifies the failure as being a dip-slope slide:

"The hill had a dip slop [sic - should be slope] on the side nearest the motorway. The other side of dip slopes are steep and irregular, while the slope itself makes it easier for rocks to slide down, experts said.  The Ministry of Transportation said it as [sic] investigating up to 20 similar dip slopes near major roads in Taiwan."




A dipslope means that the beds in the slope were inclined sub-parallel to the slope surface, creating a plane of weakness on which sliding can occur, like this (from here):

The sliding surface can be clearly seen in the second image, though it was less steeply inclined than in the cartoon above.  The inclination of the beds parallel to this surface on the displaced block is very clear.  Excavation of the debris will have to be done very carefully indeed to avoid the upslope material slipping down onto the workers.

The lack of a trigger implies a progressive failure - but I am surprised in that case that signs of distress were not observed prior to failure. 

Finally, it is interesting that the Ministry of Transportation says it is investigating "up to 20 similar dip slopes near major roads in Taiwan".  Having spent a great deal of time in Taiwan I would be surprised if there were just 20 such slopes, but maybe these are just the very large ones by major highways.  The 18th August 1997 Lincoln Mansions landslide in Taipei, which killed 28 people, was also a dipslope failure, and the 2009 Shiaolin disaster was a wedge failure with a dipslope component.

The government really needs to get a grip of the management of slopes in Taiwan.

Images of the Highway 3 landslide in Taiwan

I have still not managed to track down some really good images of the Highway 3 landslide in Taiwan, but for now here are two pictures from the China Post:

More later I hope.

Aerial video film of the Highway landslide in Taiwan

Youtube now has a helicopter video of the Highway landslide in Taiwan:



It is an extraordinary landslide, apparently being a deep translational slide that has displaced a great raft of material fronted by the cutslope shown in the previous post.  I will be interested to see some decent images in the morning!

The location of the Taiwan highway landslide

I have I think identified the location of the Taiwan highway landslide today.  Based upon this image (source):

The location appears to be here:

It appears that the failure has occurred on the cutslope shown in the centre of the image, with the margin of the slide being close to the bridge (which can be seen in the first image on top of the debris).  Thus, it appears to be a large cut slope failure.

This is certainly not the first time a cut slope has failed on a major highway, as these two examples show.  First, the Pigeon Gorge slide in North Carolina last year:

And second the 2003 Bukit Lanjan landslide in Malaysia:

However this slide in Taiwan is unusually large, with an interesting mechanism.

A huge landslide on Freeway No.3 in Taiwan

Taiwan today suffered an extraordinary landslide in Highway number 3, which links Taipei with Keelung.   The landslide appears to have completely buried the road for a distance of about 300 m.  The depth of burial looks to be more than 10 m.  There are reports that there were a number of cars on the road at the time - if so, the chances of survival are slim.

At the moment the available pictures of this event are poor - no doubt much better ones will emerge tomorrow as this will be a very big story in Taiwan.  The best I have been able to find so far are these picture from TVBS:

There is also a youtube video of a news report from the slide site, which you should be able to view below:



Compare the video above with this image of the site before failure to get an idea of just how large this slide is:

Interestingly, there was no recorded rainfall or earthquakes at the time of the collapse.  The mechanism and nature of the failure will be very interesting.

I have been arguing for some time that Taiwan needs to start managing its slopes better.  Will this finally see the authorities take some action?

Hat tip to Chingying Tsou of Kyoto University for pointing this one out and providing the links.

Hazard management in Taiwan

The Taipei Times has a very interesting editorial (17th April) that reflects upon hazard management in Taiwan.  It returns to the edtorial that I wrote for the paper last summer, based upon a posting that I put on this blog.  The need to take action to improvement the management of hazards in Taiwan is undeniable.  As we approach a new typhoon season the legacy of the continued inaction could be all too apparent again.

Framlingham College Presentation on the typhoon Morakot disaster in Taiwan

Last night I gave a public lecture on the Typhoon Morakot disaster in Taiwan. The talk may be viewed and downloaded here:

10_02 Framlingham comp

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The causes of the Shiaolin landslide disaster in Taiwan

The Shiaolin landslide disaster in Taiwan, which occurred during typhoon Morakot last August, has been the source of huge controversy. To recap, the landslide, which occurred during an exceptional rainfall event, wiped out Shiaolin village, killing about 500 people. The controversy centred on two key aspects - first, the perceived very slow response of the government to the disaster and second the possibility that tunneling associated with the Zengwen Reservoir project may have been a contributing factor to the slope failure. In response the Executive Yuan of Taiwan commissioned an investigation from the Public Construction Commission, which released its final report yesterday.

The report is of course in Mandarin, but very helpfully there is a powerpoint file available that summarises the findings and provides some illustrations of the key issues. This powerpoint file is available here (warning it is a large file in Powerpoint in pptx format):

http://www.pcc.gov.tw/pccap2/FMGRfrontendDownloadQuoteFile.do?fileCode=F2010020012

The report is available here:

http://www.pcc.gov.tw/pccap2/FMGRfronten/DownloadQuoteFile.do?fileCode=F2010020011

The key finding of the report is in my view correct - this is that the tunnel project was not the cause of this landslide disaster - they factor was the exceptional rainfall experienced in this event. The powerpoint file provides a dramatic illustrations of the magnitude and intensity of this rainfall:


Click on the image for a better view in a new window. The map on the left is the recorded rainfall for the storm, the table on the right is the total rainfall for a number of stations in the worse affected area. Note that the precipitation totals are extreme in every sense of the word - c.2500 mm (2.5 metres of rain) is the equivalent of three years total rainfall for the temperate area in which I live. This is the largest rainfall event ever recorded in Taiwan, and probably the most intense rainfall event worldwide for half a century.

The report shows that disturbance associated with the tunnel is not sufficient to be a factor in the landslide - a conclusion that I support. Instead, they show that the slope underwent a dip slope failure that led to a massive rockslide that destroyed the village. The report suggests that the landslide had a maximum depth of about 86 m and a volume of 2.5 million cubic metres. From what I can tell the slide itself was a wedge failure with a dip-slope defining part of the wedge.

There is only one aspect of the report that continues to cause concern. This is the interpretation of the mechanism of failure. This slide shows a long profile of the landslide site, which shows bedding parallel to the slope right down to the river (section A-A'):

This just doesn't seem to accord with what Chris Massey and I observed on site at the toe of the slope:

This picture is taken from the north end of the toe of the slope looking upstream - note the bedding on the far side of the valley - this is near vertical.

This picture was taken at the site of the old bridge abutment at the toe of the slide (the concrete in the middle of the image is this abutment I think) - again, note the very steeply dipping rocks at this point.

The final point to make is that the Shiaolin landslide was of course not the only failure to occur in the area during Morakot. Mapping of this region has identified 880 landslides covering an area of 2058 hectares (20.88 square kilometres).

There can be no doubt that Morakot was an extraordinary event.

The damage caused by landslides during earthquakes

Below is the presentation file of the keynote lecture that I gave today at the Chilean Geological Congress in Santiago. I have removed a few of the figures as they have not yet been published.

You should be able to download and to view the file below:

Damage caused by earthquake landslides

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The powerpoint file is hosted on Authorstream, which also holds many more of my presentations here:

http://www.authorstream.com/user-presentations/Dr_Dave/

The role of landslides in coral reef destruction

Loss of coral reefs is a widely reported and serious problem, caused by a range of factors including changes in sea temperature and chemistry; pollution; fishing; development; and mining. Reefs are often also damaged by severe storms. It is is thus unsurprising to read this report of serious damage to the coral reefs at Orchid Island, to the south-east of Taiwan, as a result of Typhoon Morakot:

"Coral reefs off Taiwan will need up to 100 years to recover from Typhoon Morakot, which lashed the island in early August killing more than 600 people, a scientist said Tuesday...Some of the shallow-water coral reefs look as if they've been crushed by road rollers," said Chen Chaolun, a researcher at the institution. "They will need up to 100 years to recover."...The live coral coverage near Orchid Island has tumbled from 68 percent to less than 18 percent, he said."

However, the cause of the damage is a surprise:

"The reefs, popular with diving enthusiasts, were damaged by driftwood thrust into the sea by the typhoon and mudflows crashing into the ocean from coastal areas."

This driftwood, which accumulated on the beaches of Taiwan and even choked harbours in Japan, was released from the hillsides by the huge numbers of landslides triggered by the typhoon, and then carried out to sea by the rivers. The volume of driftwood was extraordinary, as this Guardian image shows:

I have not seen previous reports of landslide-released driftwood causing coral reef destruction, so this is an interesting new landslide impact.

Debris flow damage from Typhoon Morakot in Taiwan

In addition to visiting the Shiaolin landslide in Taiwan at the weekend, we also managed to visit a couple of other places that had suffered damage during typhoon Morakot. Damage from debris flows and river floods occurred extensively throughout the upland areas of southern Taiwan, as these images show:


The government has set aside about US$5 billion for reconstruction. Unfortunately this area is threatened by another typhoon, called Parma:

Photos and text from a visit to the Shiaolin landslide in Taiwan

The aim of this post is to present an initial interpretation of the Shiaolin landslide, based upon a couple of days of fieldwork by Chris Massey and myself over the past two days. The interpretation here, which I have written (so don't blame Chris!) should be considered to be provisional at best. At the end of the post there are some thoughts about future work. We have no intention at this stage of publishing our analysis - that is for others to do - and so are happy for others to develop the ideas presented here. If so, we would just ask for acknowledgement in any resulting publications and that you let us know what you have found.

Disclaimer - please note that this is a personal assessment based on a very provisional walk over survey. Far more work is needed to produce a definitive evaluation - this is not that! Please do not use this in any formal sense - that is not its purpose.

Geological setting
The basic geology of the landslide is an interbedded sandstone and mudstone sequence. The structure is quite complex - on the west side of the river the beds are steeply dipping, as the image below shows. The steeply dipping bedding is clearly evident on the left (west) side of the image:


Steep dips are also seen at the toe of the slope on the east side of the river near to the location of the old bridge. Further up the slope the bedding is difficult to discern, and we did not have time to get that far. There are clear planar surface visible - we interpreted these as being bedding, perhaps dipping approximately parallel to the slope, although these could have been joints. On the south edge of the landslide bedding is visible, but as the slope is steep we could not get a proper idea of the dip and dip direction. The upshot of this is that it is clear that the simple geological sections that appear to indicate a simple syncline and with failure occurring as a dipslope may not be supported by field evidence. An initial interpretation would be that there is a fault running through the valley close to the toe of the slope (probably on the right side of the image above), but this needs a great deal more detailed work.

Landslide morphology
This is an attempt to calculate some crude initial details and statistics of the landslide:

Landslide type: Rock-slide/debris-flow
Volume: 30 to 45 million cubic metres
Source area: 1.4 square kilometres
Depth (average): 20 to 30 m
Distance from crown to assumed toe (western side of river): 3,400 m
Vertical fall: 1,000 m
Angle of reach: 16°

The morphology of the slide is indicated below. To the left is the original image, to the right is the same image with annotation. The labels are meant to be indicative only - a much more robust mapping exercise would be needed to do this properly.

(Base image taken from a helicopter by Mr Chi)

The key points are as follows:

1. There are effectively two slides at this site - the main one to the south (in the centre of the image above), and the other to the north, which is a much smaller (though still very substantial) slide. The slides are divided by a bedrock ridge for essentially their entire length;
2. The main slide is a structurally controlled failure in bedrock. A large promontary high on the slope has failed and collapsed. At this point the failure is quite deep. The detachment surfaces are likely to be joints and/or bedding.
   
3. The debris from the main failure has travelled directly downslope, unfortunately through the location of the village. In this central part the landslide appears to have been highly disrupted and to have bulldozed everything in its path;
4. Most of the debris was deposited in the river channel. The river was blocked near to the old bridge, but there would also have been substantial amounts downstream. Much of this debris has been removed in the subsequent flood. It is likely that this is also the case for the remains of the village;
5. The main rockslope failure was followed by a complex series of debris flows that have deposited finer grained, matrix supported materials on top of, and on the flanks of, the main slide deposit. The flows form distinct lobes that could be mapped. In some cases there is intact vegetation associated with them;
6. The final phase of deposition was of fluvially reworked sediments.
   

The main rockslide
The main event appears to have been a catastrophic failure of a large area of the upper part of the landslide. Failure was without doubt structurally controlled, as evidenced by the surfaces visible in the scar:


This failure transitioned into a high speed failure that ran straight down the hill, across the first terrace and into the river, taking the lower terrace with it. The remains of this deposit are clear, including large boulders This one is on the river bed, hence the fine sediment and the rounding):


The deposit is clast (i.e. rock) supported, implying a rockslide mechanism, although there is some finer material, primarily derived from crushing and fragmentation. There are some highly shattered tree remains visible as well:


This part of the landslide appears to have run across the upper terrace, leaving some rockslide material behind, without eroding the terrace substantially. In places terraces gravels are still visible, overlain with rockslide material and underlain by bedrock:

The lower terrace has been mostly removed, and there is little evidence of debris from the village.This might indicate that it was incorporated into the landslide mass that was deposited in the river channel. Most of this debris has been removed by the dam break flood.

Just upstream from the old bridge (and from the village) the river channel is quite narrow. Landslide debris is found on top of the terrace on the far side of the river. Above this debris the slope has been stripped of trees and vegetation. This could be the outcome of a possible displacement wave. It appears that the main channel was blocked at this location by the landslide debris:

Subsequent debris flows
There is lots of evidence of subsequent debris flows overlying the main rockslide debris. These vary in character but all have a fine matrix with clasts. Some of these debris flows appear to contain little vegetation other than very splintered wood:

However, in other locations large amounts of vegetation are present, some of it still quite green with foliage:


On the margins of the slide these flows have bifurcated, leaving areas with in situ vegetation in place. In some cases there is evidence that rocks have travelled over these vegetated surfaces, leaving blocks caught in tree remains:


The dam break and flood
We did not really spend much time examining the remains of the subsequent flood. However, there are two houses left standing from the southern edge of the village. These show the after effects of the flood very clearly, even though the river was very wide at this point:

Downstream the effects are severe, with damage to bridges, embankments and even the river bed. For example, the central spans of this bridge have been washed away:

Future studies
The text here is no substitute for a detailed examination of this site. We are sure that this is being undertaken by our colleagues in Taiwan. For example, to understand this landslide properly there is a need for a full geological and geomorphological mapping exercise, including a structural geology assessment. It would be great to see an attempt to reconstruct the multiple events by mapping out the different lobes. The landslide should also have been recorded on the seismometer network, so an analysis of this might help to constrain what happened, and indeed to allow the event to be tied to the rainfall events that have been recorded from this storm. An interpretation of stallite and aerial imagery from before the slide would also be good. There is a need to reconstruct the terrain before and after the slide - using aerial images from before and ideally LIDAR data from the present. This would allow a calculation of the mass balances of the slide and of the geometry. Later on stability assessment based upon geotechnical testing could be undertaken, and ultimately even full modelling (although it is not clear what purpose this would serve). We are sure that all of the above is planned or under way (and a lot more as well) - the results will be very interesting.

A final disclaimer
All of the above is based on no more that a brief walk over survey. None of what is written here should be considered to be authorative or a substitute for a detailed survey. What is written here is the personal opinion of the author only and should not be used formally in any way.

Comments and thoughts welcome of course!

First images from a visit to the Shiaolin landslide

Today, with two colleagues, I have visited the site of the Shiaolin landslide in Taiwan, which killed about 500 people on 8th August. I will write a longer analysis soon (we are due to go back tomorrow), but for now I will just provide a before and after image.

Before:


After (the village was at the foot of the slope):


And this is the aftermath of the flood caused by the collapse of the landslide dam:

After Morakot

A new blog, called After Morakot, has been started to highlight the impact of Typhoon Morakot in Taiwan. The most recent post describes a journey by the author into the village of Namsia, which was one of the most seriously affected villages in the typhoon. The images and the commentary are remarkable.

I reproduce here two of the images, of the village of Mintsu - there are many more on the blog:

Special session on Typhoon Morakot in Taiwan

This afternoon at the Chi-Chi earthquake conference in Taiwan the organiser laid on a special session on the impact of Typhoon Morakot in August. This is of great interest to me, given the impact of the landslides, so I thought I'd give summary of the key points. Apologies for the note form - I have done this Twitter-style!

1. The magnitude of the typhoon
For Taiwan this was an extraordinary event. It appears that in terms of river discharge the floods were the largest since records began - over 200 years ago. For example, Prof. Tsai of the National Cheng Kung University showed that for the Gaoping River the peak discharge was 29,100 cubic metres per second. That is the equivalent of the daily water needs of 150,000 people - each second in a single river! These huge floods were driven by extraordinary rainfall. At Chiayi the statistics are as follows:
Total storm rainfall: 3005 mm
Maximum hourly rainfall: 136 mm
Max 3 hour: 325 mm
Max 6 hour: 548 mm
Max daily: 1623 mm

This is close to but not actually quite, the world record rainfall.

2. Why was it so intense?
Prof. Jou of the Taiwan Meteorological Agency suggested that there were two key reasons why the typhoon was so intense. First, the storm slowed down as it crossed the island. Before it made landform it was moving at 20 km per hour. When it came ashore it moved only about 50 km in 24 hours. This led to very high rainfall accumulations. Second it appears that as it formed the typhoon interacted with a substantive monsoon trough, which drew in moisture from the inter-tropical convergence zone to the southwest. This meant that the typhoon generated huge rainfalls on the south edge of the storm which is where the maximum damage occurred. Interestingly, he admitted that one of their dynamic models run the day before the typhoon struck forecast 1900 mm of rainfall. However they didn't trust the model.

3. Landslide impacts
Very little was presented on the impact of the landslide at Siaolin, but Meei-Lin Ling stated that the death toll was 491 people. She stated that at the moment they have records of 1349 landslides, 46 debris flows and 298 road slope failures. I suspect that that many of the landslides may be classified as debris flows? These landslides cover an area of over 50,000 hectares. Prof. Jenn-Chuan Chern the Deputy CEO of Morakot Post-Disaster Reconstruction Council, suggested that the volume of sediment is 56 million tonnes (I wonder if this is rather low though?). Tainan County had the largest number of failures (515) the Kaohsiung (288) and Chiayi (216). The landslide distribution closely reflects the rainfall distribution. In Sinkai village 32 people were killed by a debris flow. There was also very extensive damage to the highway network - there is some doubt as to whether the road to Alishan (a major tourist area) can be repaired.

4. Other damage and impacts
Coastal flooding was a major impact. The peak of the storm coincided with a high Spring tide, causing major inundation. These flooded areas and those affected by river floods, have had major problems from silt accumulation. In some cases over a metre of slit has had to be removed from houses. This is quite straightforward, but clearing the water and sewage pipe network has been a major headache. Over 500,000 tonnes of wood has been deposited and is having to be removed. This is a substantive task.

5. Human costs
Human impacts are 701 fatalities with another 58 missing. 120,000 houses were flooded, 310,000 houses damaged. 4489 people are being housed in army barracks even now; reconstruction is going to be complex. At present 55 aboriginal tribal villages have been displaced. Government evaluations suggest that 31 of these are permanently unsafe. Therefore resettlement is not simple - the aboriginal communities want to reconstruct their villages in order to maintain their culture (e.g. through targeted schooling), but given the dangers of the sites this is not simple. Government land is being earmarked and NGOs are helping to liaise to find an appropriate solution.

6. The elephant in the room - climate change
None of the speakers wanted to ascribe this event to climate change - there was a real sense of caution about saying anything unwise. This is sensible. The point was made that in recent years the number of landfalling typhoons has been high compared with historic record and also that a dramatic increase in precipitation intensity has been noted. The floods met and even the calculated probable maximum flood of the rivers. Thus, it appears that the rainfall that is now happening is different from the historic record. Is this climate change? They key factor seems to be the interaction of the typhoon and the monsoon. A discussant implied that this could be because the monsoon front is moving. Whether it is climate change or not it does seem sensible to plan for more intense rainfall events. This is going to be very challenging in a place like Taiwan.

7. Meteorology
The final interesting comment was a note that classifying typhoon intensity by wind, which is the convention, is meaningless when most of the damage is done by rainfall. They suggested that a new classification is needed that combines both wind and rainfall, allowing better forecasting of landslide and flood impacts. Frustratingly I submitted a grant application to DFID ten years ago to develop a scheme to do exactly this, tied to a terrain classification scheme. They didn't fund it.

All-in-all a fascinating set of presentations that really helped in the understanding of this extraordinary event.

Your questions and thoughts are welcome!

Presentation at the International Conference in Commemoration of the 10th anniversary of the 1999 Chi-Chi earthquake

Below is my presentation from the conference in Taiwan. The file is on authorstream (my authorstream page is here - there are several of my presentations there). You should be able to play or download the presentation below or from the authorstream site. As ever, please acknowledge anything that you use from it.

The paper was a review of the key things that we have learnt from research into landslides triggered by this earthquake. However, at the start there is some more general material on earthquake-triggered landslides worldwide, which might be of some interest.

Feedback welcome of course!

09_09 Chi-Chi conference Petley blog

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The geological structure of the Hsiaolin slide

Thanks to reader Chingying Tsou, who has answered my request for information about the geological structure of the Hsiaolin landslide. He has provided a link to the website of the Sino-Geotechnics Research and Development Foundation, which provides the key information. The page is in Chinese, but the diagrams are really helpful, as is the Google translation.



So here is a topographic map of the landslide site, with the major faults and of course the landslide itself marked on:

You will note two cross-section lines on the map, one of which (A-A') runs down the axis of the landslide. This cross-section is reproduced below:


It is clear from this that the landslide is a dipslope failure - i.e. the slide has occurred on beds that are orientated parallel to the slope, and thus facilitate failure. The cross-section indicates that the rocks are a mixture of sandstone and shale. This can often cause problems as the shale is weak, impermeable and prone to weathering, whereas the sandstone is often stronger but allows the accumulation of water (i.e. pore pressure generation). The presence of the fault is an additional factor - it may well be that the movement on the fault has caused the beds to be disrupted and thus weakened. It should also be noted that this cross-section is probably only indicative. It would not surprise me to find that the river has actually eroded out the lower portions of these beds, then filled in the spaces with the terrace deposits upon which the village was built, further weakening the slope.

The Hsiaolin landslide slope before failure

In an earlier post I highlighted a satellite image of the Hsiaolin landslide site. I have trimmed this a little below:


This image is rather helpful as it starts to allow the site of the landslide before failure to be examined using Google Earth, which has good quality imagery of this area. This is, as close as I can get it, the same slope prior to failure:

Click on the image for a better view in a new window.

There are a couple of things to note here. First, the slide ran out straight across the village, removing all trace as the earlier photographs showed. Second, the rivers clearly underwent huge amounts of flooding.

A perspective view of the site is a little more helpful:


I have annotated the image below to locate the approximate boundaries of the landslide, using the satellite image above plus the photographs of the site that are now available (see this post)



You may need to click on the image to be able to see the boundaries properly. These boundaries are at the moment very much indicative, but they give the general idea. The landslide is intriguing because the slope was not showing obvious signs of instability as far as I can see, bar a depression in the head scarp area the could be a tension crack? The river has clearly undercut the toe of the slope, which could have been a factor? It would be interesting to know more about the underlying bedrock, and in particular the dip direction. Can anyone provide any more information?

Comments welcome.

Eyewitness account of landslides triggered by Typhoon Morakot in Taiwan

Aerial image of Hsiaolin from CNR-IRPI

I have today returned from my holiday, so normal service should be resumed. Interestingly, the number of readers of the blog appears to have increased in my absence. There is a lesson there I think! Anyway, I have a large backlog of things to post, but unfortunately also have a large backlog of other work as well, so it may take some time.

Anyway, to get things moving, there is a very interesting eyewitness account of landslides triggered by Typhoon Morakot on a blog run by Rich Matheson, a resident of S. Taiwan. The account is at the following link:

http://liefintaiwan.wordpress.com/2009/08/18/typhoon-morakot/

It is well worth a read.

Thanks to Richard Foster of http://barking-deer.com/ (a company that runs adventure tours to the fabulous landscape of S. Taiwan) for bringing this to my attention.