Giant landslides in Palu from the 2018 Sulawesi earthquake

As decent satellite imagery starts to become available, the landslides in the vicinity of the city of Palu, triggered by the 2018 Sulawesi earthquake, are becoming clear.  The picture is fascinating and tragic, providing an explanation for some of the remarkable footage that we have seen.  There is a key message here – although it is the tsunami that has attracted most of the attention, three very large landslides in Palu have caused very high levels of loss.  These three landslides are remarkable.

So, starting from the south, let’s take a look at these three slides.  The first appears to be in the vicinity of an area called Tinggede, on the outskirts of Palu.  This is the Planet Labs image of the landslide:-

The Tinggede landslide on the outskirts of Palu. Image via Planet Labs, used with permission.

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This is the landslide that was caught on the video with the transmission tower.  This is a very large slide – I estimate that the headscarp is about 1 km across, and the slide is over 3 km in length.  On the east side of the scarp is a canal, which has breached, but my reading of the situation is that the breach happened because of the slide, not vice-versa.  This is a flow type slide (rather than a lateral spread), with many houses being involved.  The level of destruction is almost complete, judging by the imagery.  I find it hard to believe that there was not significant loss of life here.

If that is bad, the second landslide in the area of Palu is worse:-

The Palu airport landslide from the 2018 Sulawesi earthquake. Planet Labs image, used with permission.

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This landslide is just to the south of the Palu airport runway.  Again, it is very large.  I estimate that the scarp width is about 1.5 km, and the length is over 2.5 km.  There are two main components, and the image needs careful inspection.  What captures the eye initially is the area of bare soil in the landslide source.  But look to the west of this – you will see a lobe structure extending almost to the edge of the image, which is the landslide deposit.  This consists of soil and debris from the landslide, but also huge numbers of buildings, compressed together and wrecked.  There is a second lobe, albeit smaller, to the south.  The level of destruction to vast number of properties is vast.  Again, it is hard to believe that there is not very significant loss of life here.

The third landslide is smaller, but far from trivial.  This landslide is close to the city centre, with movement from the west towards the east:-

The landslide close to the centre of Palu, triggered by the 2018 Sulawesi earthquake. Planet Labs image, used with permission.

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This landslide in Palu is about 500 m wide and about 1km long.  Again, the bare soil of the source draws attention, but the vast number of houses compressed into a debris zone to the east is also evident, extending to the edge of the image. The level of destruction is very high.

All three of these landslides in Palu appear to be shallow slides on comparatively low angle slopes.  All are close to the fault trace.  In this area there are few other large landslides (there may be many other ones that cannot be resolved on this imagery).

Further to the south there are huge numbers of smaller landslides.  These will feature in a future post.

Reference

Planet Team (2018). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://api.planet.com