Are satellite-based landslide hazard algorithms useful?

In some parts of the world, such as the Seattle area of the USA, wide area landslide warning systems are operated on the basis of rainfall thresholds. These are comparatively simple in essence - basically the combination of short term and long term rainfall that is needed to trigger landslides is determined, often using historical records of landslide events. A critical threshold is determined for the combination of these two rainfall amounts - so for example, it might require 100 mm of rainfall in hours after a dry spell, but 50 mm after a wet period. These threshold rainfall levels have been determined for many areas; indeed, there is even a website dedicated to the thresholds!

In 1997 NASA and JAXA launched a satellite known as TRMM (Tropical Rainfall Monitoring Mission), which uses a suite of sensors to measure rainfall in the tropical regions. Given that it orbits the Earth 16 times per day most tropical areas get pretty good coverage. A few years ago Bob Adler, Yang Hong and their colleagues started to work on the use of TRMM for landslide warnings using a modified version of rainfall thresholds. Most recently, this work has been developed by Dalia Bach Kirschbaum - and we have all watched the development of this project with great interest. The results have now been published in a paper (Kirschbaum et al. 2009) in the EGU journal Natural Hazards and Earth Systems Science - which is great because NHESS is an open access journal, meaning that you can download it for free from here.

Of course a rainfall threshold on its own doesn't tell you enough about the likelihood of a landslide. For example, it doesn't matter how hard it rains, if the area affected is in a flat, lowland plain then a landslide is not going to occur. To overcome this, the team generated a simple susceptibility index based upon weighted, normalised values of slope, soil type, soil texture, elevation, land cover and drainage density. The resulting susceptibility map is shown below, with landslides that occurred in 2003 and 2007 indicated on the map:


A simple rainfall threshold was then applied as shown below:

Thus, if an area is considered to have high landslide susceptibility and to lie above the threshold line shown above based upon an analysis using 3-hour data from TRMM, then a warning can be issued.

Kirschbaum et al. (2009) have analysed the results of their study using the landslide inventory datasets shown in the map above. Great care is needed in the interpretation of these datasets as they are derived primarily from media reports, which of course are heavily biased in many ways. Examination of the map above does show this - look for example at the number of landslide reports for the UK compared with New Zealand. The apparent number is much higher than in NZ, even though the latter is far more landslide prone. However, in New Zealand the population is small, the news media is lower profile, and landslides are an accepted part of life. However, so long as one is aware of these limitations then this is a reasonable starting point for analysing the effectiveness of the technique.

So, how did the technique do? Well, at a first look not so well:



In many cases the technique failed to forecast many of the landslides that actually occurred, whilst it also over-forecasted (i.e. forecasted landslides in areas in which there were none recorded) dramatically. However, one must bear in mind the limitations of the dataset. It is very possible that landslides occurred but were not recorded, so at least to a degree the real results are probably better than the paper indicates. Otherwise, the authors admit that the susceptibility tool is probably far too crude and the rainfall data to imprecise to get the level of precision that is required. However, against this one should note that the algorithm does very well (as indicated by the green pixels on the map above) in some of the key landslide-prone areas - e.g. along the Himalayan Arc, in Java, in SW India, the Philippines, the Rio de Janeiro area, parts of the Caribbean, and the mountains around the Chengdu basin. In places there is marked under-estimation - e.g. in Pakistan, Parts of Europe and N. America. In other places there was dramatic over-estimation, especially in the Amazon Basin, most of India, Central Africa and China.

All of this suggests that the algorithm is not ready for use as an operational landslide warning system. Against that though the approach does show some real promise. I suspect that an improved algorithm for susceptibility would help a great deal (maybe using the World bank Hotspots approach), perhaps together with a threshold that varies according to area (i.e. it is clear that the threshold rainfall for Taiwan is very different to that of the UK). Kirschbaum et al. (2009) have have produced a really interesting piece of work that represents a substantial step along the way. One can only hope that this is developed further and that, in due course, an improved version of TRMM is launched (preferably using a constellation of satellites to give better temporal and spatial coverage). That would of course be a far better use of resource than spending $4,500 million on the James Webb Space Telescope.

Reference
Kirschbaum, D. B., Adler, R., Hong, Y., and Lerner-Lam, A. 2009. Evaluation of a preliminary satellite-based landslide hazard algorithm using global landslide inventories. Natural Hazards and Earth System Science, 9, 673-686.

Images of landslides and other damage from the Sichuan earthquake part 4 - the Mianyuanhe area

This is the fourth part of my photographic description of damage caused by the Sichuan earthquake. The other parts are as follows:

Part 1: Beichuan town
Part 2: The Tangjiashan landslide
Part 3: Hanwang town
Part 4 (this part): The Mianyuanhe area
Part 5: The Xingyiu area

First a location map. The Mianyuanhe area is a fairly large river valley that cuts through the Longmen mountain chain, with its mouth as Hanwang as shown in the Google Earth image (which predates the earthquake) below:

As you may know, it has been shown that the earthquake was associated with movement on two different thrust faults (and an additional strike-slip fault that sits between the two). The Mianyuanhe shows the surface expression of the two thrust faults. I have annotated a perspective Google Earth view of the Mianyuanhe area to show the approximate position of the two faults below:

This image also gives an idea of the terrain in this area. The surface features of these two faults is pretty clear. This is the Jiangyou-Guanxian fault (JGF) - the car has tilted as it crosses the crest of the fault scarp:

The displacement on the Yingyou-Beichuan fault (YBF) is much larger:

The presence of these two faults has meant that this is an area that has been pretty badly affected by the earthquake, with a large amount of building damage and many, many landslides. It is also an area with some active mines (coal mines I think) - for example, this mine, located just on the hanging wall side of the JGF, has been pretty badly damaged by the earthquake:

Coal mining in China has a dreadful environmental and safety record, so one wonders what happened to the miners when the earthquake struck. In fact, the impact that the mine is having on the environment is pretty clear - the red colours here are acid mine drainage, associated with acidic water coming from the underground workings. Note the extensive earthquake triggered shallow rockslides in the background too:

There has also been a huge amount of damage to buildings, such as this school:

Unfortunately, destroyed buildings create a huge volume of waste material that is very hard to dispose of without causing real environmental damage:


The electricity infrastructure was seriously damaged, as this pylon shows:

And of course the roads are in a very sorry state in places:

However, there is a surprising and very impressive amount of rebuilding going on, some of which is now quite advanced:

In this valley the earthquake triggered a vast number of highly destructive landslides, some of which are quite large. This photo, taken just on the hanging wall side of the YBF, shows gives an idea of the number of slides, as well as the level of damage to buildings:

The second largest mass movement triggered by the earthquake, the Wenjiagou landslide, occurred in this area. It is located between the two faults. This is an overview of this large and complex slide:


The source is a dip-slope failure high up on the left side of the image. The picture below shows the source area more clearly:

Note that on the steep scarp on the centre-left side of the image dust being blown up from ongoing rockfalls is clearly visible. The landslide slide down the dip-slope, turned to the left and travelled down the valley, and then turned to the right before running out. The movement rate must have been very high as the landslide super-elevated (banked up) as it went around the second turn, as this image clearly shows:

About 45 people were killed by the landslide. There is now a problem here with ongoing debris flow activity - more on this below.

There were also some very impressive valley blocking landslides. The most visually dramatic is this one, which has created a large barrier lake:

The slide mass is evident in the gap between the cliffs on the upper centre right of the image. These barrier lakes are causing considerable difficulties (although they are not dangerous now). For example, they are causing flooding of properties and roads:

Even the natural vegetation is being killed:

There are several of these very large valley blocking landslides, such as this one (which is different from the one above):

Note the multiple landslides in the background.

One of the most interesting slides lies on a tributary valley to the main one. This is a c.1 km long rockslide that has created a very tall but restricted debris pile:

This slide appears to have originated as a wedge failure controlled mainly by a bedding plane that has then changed direction and slid into the valley. In the foreground is a school - it is lucky that the slide did not spread. The bedding plane is pretty clear on this image:

The landslide blocked the valley to a height of over 50 m. A lake built up behind the blockage, but in this case drainage has not been necessary as water flowed through the rock dam. The muddy sediments laid down in the lake show this very clearly:

And there are natural markings and pieces of debris showing the old lake levels on the valley sides:

Finally one of the major problems that lies ahead is that of ongoing landslide and debris flow activity, and the resultant impact on the river systems. There are already plenty of signs that these problems are very serious indeed:


Your comments, thoughts and corrections, and indeed you general impressions, are very welcome. Please feel free to use the pictures in lectures and seminars, but please do acknowledge me. I retain copyright on the images.

Finally, just a reminder that this is the fourth part of my photographic description of damage caused by the Sichuan earthquake. The other parts are as follows:

Part 1: Beichuan town
Part 2: The Tangjiashan landslide
Part 3: Hanwang town
Part 4 (this part): The Mianyuanhe area
Part 5: The Xingyiu area

A Powerpoint presentation on earthquake-induced landslides

On Monday I gave a presentation to staff and students at the State Key Laboratory for Geohazards at Chengdu University of Technology - the topic was the lessons that can be learnt about earthquake-induced landslides from the Taiwan (1999) and Kashmir (2005) earthquakes. This is the presentation:


Uploaded on authorSTREAM by Dr_Dave

I ask only that you acknowledge me in any use that you might make of it.

Sendai presentations

The following are my presentations from the World Landslide Forum Satellite Conference in Japan on 11th and 12th November 2008. In each case, you should be able to download the Powerpoint show from the link below the file. I am more than happy to send copies of the papers to anyone who might like them, and will post them online next week.

I also welcome any comments that you might have.

Keynote address on landslides and climate in S. Asia:

Uploaded on authorSTREAM by Dr_Dave

Wishart Mitchell's paper, which I presented on his behalf, on the Keylung Serai Rock Avalanche:

Uploaded on authorSTREAM by Dr_Dave

My other presentation on the occurrence of fatal landslides in 2007:

Uploaded on authorSTREAM by Dr_Dave

The Frank Landslide, 29th April 1903

As today is the 105th anniversary of the Frank Landslide in Canada, it seems appropriate to revisit this most interesting event. The town of Frank is located at about 49 degrees 35 minutes North and 114 degrees 24 minutes West at an elevation of about 1300 m in Alberta, Canada. The town on the back of coal deposits at the foot of Turtle Mountain to the west of the town (Figure 1). These were exploited by coal mines at the foot of the hill.

Figure 1: Google Earth image of the Frank landslide, Turtle Mountain, Alberta, Canada.

The landslide is fairly easy to see on Figure 1. The first signs of problems came in the weeks leading up to the collapse, when the coal tunnels started to show signs of movement. The final collapse occurred at 4:10 am when a block of about 650 m in height, 900 m in width and with a maximum thickness of about 150 m thick broke off the hillside and thundered into the valley below. The failure, which had an estimated volume of 30 million cubic metres, apparently took about 100 seconds, killing 76 people. Most of the victims were killed in their beds and their bodies could not be recovered as they were buried to a depth of about 30 m. Figure 2, from Natural Resources Canada, captures the scale of the event quite well. The landslide deposit extended over about 3 sq km, blocking the river and flooding about 2 km of the railway line. Seventeen coal miners were buried in the coal mine by the landslide but were able to dig themselves out over a 14 hour period.

Figure 2: Natural Resources Canada photograph of the Frank landslide, Turtle Mountain, Alberta, Canada.

The Frank landslide remains of great interest for a number of reasons:

1. There has been considerable controversy over the cause of the landslide. Initially the blame was pinned squarely on the mining activities, but more recently it has been increasingly accepted that in fact the geological structure, which was unfavourable for stability, was probably the primary cause. The mining probably did not help, and other factors such as rainfall may have also had a role.
2. There has also been a great deal of speculation over the the rate at which the landslide debris spread itself over such a large area. This very rapid runout behaviour is a somewhat enigmatic process in many large rockslides. Theories have abounded over the role of air entrainment, reduced basal friction, etc. The jury is still out - this remains one of the great questions in landslide science.
3. Parts of the mountain are probably still potentially unstable. In 1911 part of the town was relocated over fears about the stability of the slope. Today, real time monitoring is undertaken by the Alberta Geological Survey using a wide range of sensors. The aim is not to prevent a failure event but to provide a warning that it might occur. This is fine for a progressive failure or for one triggered by rainfall, but it offers little if there should be a large earthquake. Nonetheless, this is important work that is undertaken to a world leading standard. The work is described exceptionally well here