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19 APRIL 2023

Torkham – a large rockslide in Pakistan (https://blogs.agu.org/landslideblog/2023/04/19/torkham-1/) Torkham – a large rockslide in Pakistan

On 18 April 2023, a large rockslide occurred at Torkham (https://tribune.com.pk/story/2412562/torkham-landslide-leaves-three-dead) in Pakistan (https://blogs.agu.org/landslideblog/?s=pakistan&submit.x=0&submit.y=0&mswhere=blog), very close to the border with Afghanistan. The landslide, which occurred in the early hours of the morning, struck a line of trucks waiting to cross the border. It is thought that about 20 trucks were buried in the accident. At the time of writing, three people are known to have been killed and a further eight people have been injured. Rescue operations continue, led by the army (https://www.bolnews.com/2023/04/19/politics/rescue-operation-at-torkham-landslide-site-continues-on-second- day/index.html).

The best image that I have found of this landslide has been tweeted by Pakistan Armed Forces News (https://twitter.com/PakistanFauj/status/1648248134068326406):-

The 18 April 2023 landslide at Torkham in Pakistan. Image tweeted by Pakistan Armed Forces News (https://twitter.com/PakistanFauj/status/1648248134068326406).

4/19/23, 7:12 AM Page 1 of 24

The image shows a rockslide – based upon the scar it appears that the landslide has mobilised a set of discontinuities inclined parallel or sub- parallel to the slope. The debris appears to have bulldozed the trucks, and there is some evidence of the aftermath of a fire. Rescue operations will be very challenging as the boulders are large and of course removal of debris at the toe risks creating instability in the debris pile.

The location of the landslide is [34.115, 71.102]. This is a Google Earth image of the landscape, collected in October 2021:-

Google Earth view of the site of the 18 April 2023 landslide at Torkham in Pakistan.

Of interest here is the indication that the toe of the slope has been cut as part of construction works. By comparison, here is an image from 2016:-

Archive (2016) Google Earth view of the site of the 18 April 2023 landslide at Torkham in Pakistan.

4/19/23, 7:12 AM Page 2 of 24

Archive (2016) Google Earth view of the site of the 18 April 2023 landslide at Torkham in Pakistan.

I have created a slider to allow the two images to be compared:-

It is unclear as to what has happened at the site since 2021 – there may be some evidence of the creation of concrete structures for the road – but a reasonable starting hypothesis could be that the cutting of the toe has enabled the instability.

News reports indicate that the landslide was triggered by a lightning strike. In most cases, such reports are erroneous, with the actual trigger being the very rainfall that accompanies the thunderstorm.

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18 APRIL 2023

Landslides as a dominant landscape process on icy satellites (https://blogs.agu.org/landslideblog/2023/04/18/icy-satellites-1/) Landslides as a dominant landscape process on icy satellites The journal Icarus (https://www.sciencedirect.com/journal/icarus) has a very interesting new paper (Mills et al. 2023 (https://www.sciencedirect.com/science/article/pii/S0019103523001112)) that considers why some icy satellites of large planets, such as those orbiting Jupiter and Saturn (in particular Ganymede, Europa, and Enceladus), have smooth surfaces with very few impact craters. There is a good plain English summary of this work on the Interesting Engineering website (https://interestingengineering.com/science/nasa-icy-moons-jupiter- saturn) too. Conventionally, the theory has been that the smooth surfaces have been created by the eruption of fluids from volcanoes.

The topography of Ganymede, an icy satellite of Jupiter.

JuxtaposeJS(http://juxtapose.knightlab.com)

4/19/23, 7:12 AM Page 3 of 24

The topography of Ganymede, an icy satellite of Jupiter.

The topography of Ganymede, an icy satellite of Jupiter. Image NASA via phys.org (https://phys.org/news/2015-10-jupiter-moon-ganymede.html)

Interestingly, these icy satellites are known to be geologically-active, resulting from the high gravitational forces from the planets, which generate planetary seismic events (the equivalent of terrestrial earthquakes). This geological activity has created ridges, with smooth surfaces between them. The authors test the hypothesis that the seismic events trigger landslides from these ridges, which then mantle the surface of the icy satellite to create the smooth topography.

Mills et al. (2023 (https://www.sciencedirect.com/science/article/pii/S0019103523001112)) have used the dimensions of the fault scarps to estimate the magnitude of the seismic events (the ranger is M=4.0 to 7.9), and then have modelled the resulting seismic accelerations. These accelerations were found to be sufficiently large to exceed the gravitational accelerations of the satellites, allowing mass movements to develop. The team has assessed the potential volumes of the resultant landslides, using two different models. The more recent of these suggests that for Ganymede for example, the landslide volumes could be in the range of 2.3 × 10 –1.4 × 10 cubic metres. It must be stressed that these are quite speculative – there are many assumptions implicit in that number – but it is a very interesting result.

There is much work to do on this idea, which will be greatly assisted by the forthcoming Europa Clipper and JUICE missions (https://astronomy.com/news/2023/04/two-missions-target-jupiters-moons), which are intended to “provide high-resolution surface imaging, including stereo imaging, along with subsurface radar sounding, for both Europa and Ganymede”.

This study is another illustration of the key role that landslides play in planetary systems.

Reference

Mills, M.M., Pappalardo, R.T., Panning, M.P. et al. 2023. Moonquake-triggered mass wasting processes on icy satellites (https://www.sciencedirect.com/science/article/pii/S0019103523001112). Icarus, 399, 115534. https://doi.org/10.1016/j.icarus.2023.115534 (https://doi.org/10.1016/j.icarus.2023.115534).

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17 APRIL 2023

The Arroyo Seco landslide in Monterey County, California (https://blogs.agu.org/landslideblog/2023/04/17/arroyo-seco-1/) The Arroyo Seco landslide in Monterey County, California

Over the last week, concerns have been raised about a landslide that has developed in Arroyo Seco in Monterey County (https://kion546.com/top- stories/2023/04/12/residents-in-arroyo-seco-say-looming-landslide-has-them-banding-together/) in California, USA. (https://blogs.agu.org/landslideblog/?s=california&submit.x=0&submit.y=0&mswhere=blog) The best image I have found of the setting of the landslide was tweeted by Karl Cooke, a journalist with KION 5/46 (https://twitter.com/KarlCooke16/status/1646278504047341568):-

An overview of the Arroyo Seco landslide in California.

6 9

4/19/23, 7:12 AM Page 4 of 24

An overview of the Arroyo Seco landslide in California.

An overview of the Arroyo Seco landslide in California. Image tweeted by Karl Cooke. (https://twitter.com/KarlCooke16/status/1646278504047341568)

There is a more detailed image of the landslide itself in a drone video of the landslide that was posted to Facebook by Felix Cortez, who is a reporter for KSBW Action News 8:-

A view of the Arroyo Seco landslide in California. Still from a drone video posted to Facebook by Felix Cortez.

A view of the Arroyo Seco landslide in California. Still from a drone video posted to Facebook by Felix Cortez (https://www.facebook.com/KSBWFelixCortez/videos/1306006936929989/).

The local authorities have rightly closed the road at the foot of the slope. The landslide is being monitored by the USGS (https://www.ksbw.com/article/geologists-monitor-assess-arroyo-seco-landslide/43595501).

The trigger for the landslide is not clear, but California has suffered a series of major rainstorms through the winter and the spring. In January, the high level of the river necessitated a helicopter rescue for a couple living in the area (https://news.yahoo.com/couple-dog-rescued-arroyo-seco- 080335022.html).

This landslide might well be a substantial headache for the inhabitants of the area and the people trying to keep them safe. Movement of the slope is likely to be hard to predict. One scenario is that the slope fully fails, creating a debris pile that can be removed, albeit at substantial cost. A more difficult scenario is that the slope does not fully fail, leaving a hazard on the slope that will place the road at risk. Experience from elsewhere suggests that decision-making in this situation is a challenge.

A tweet from KION News Channel 46 provides a really nice 3D view of the slope. It appears that the failure is occurring on geological strata that dip in parallel to the slope?

KION News Channel 46

4/19/23, 7:12 AM Page 5 of 24

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30 MARCH 2023

Buriticupu: a town with a chronic gully and landslide problem in Brazil (https://blogs.agu.org/landslideblog/2023/03/30/buriticupu-1/) Buriticupu: a town with a chronic gully and landslide problem in Brazil

Buriticupu is a town in municipality in Maranhão in Brazil (https://blogs.agu.org/landslideblog/?s=brazil&submit.x=0&submit.y=0&mswhere=blog), located on a plateau with steep slopes, founded in 1994. Its population is about 73,000 people. Reuters has a very nice video about a chronic landslide problem that is affecting the town (https://www.youtube.com/watch?v=ak59DYIVWUc), with the issues rapidly escalating over the last year:-

KION News Channel 46 @KION546 · Follow

ARROYO SECO FACES POSSIBLE LANDSLIDE Read more: kion546.com/top-stories/20…

Watch on Twitter

10:00 PM · Apr 12, 2023

52 Reply Share

Read 3 replies

Families in fear as rains worsen landslides in Brazil

4/19/23, 7:12 AM Page 6 of 24

Google Earth imagery (the town is at [-4.327, -46.457]) shows that the town has landslide problems on many slopes -some reports suggest 26 different locations. The image below is one of the worst affected areas, as captured in 2014, before the problem became too serious:-

Google Earth imagery of the site of some of the landslide problems at Buriticupu in Brazil. Image from 2014.

This is the same site in July 2022:-

Google Earth imagery of the site of some of the landslide problems at Buriticupu in Brazil. Image from July 2022.

4/19/23, 7:12 AM Page 7 of 24

I have created a slider to allow the sites to be compared:-

Estadao has a short article about the issues in Buriticupu in Portuguese (https://www.estadao.com.br/brasil/buracos-vocorocas-gigantes-ameacam- cidade-maranhao-calamidade-nprm/). It includes this image:-

One of the landslides at Buriticupu in Brazil.

One of the landslides at Buriticupu in Brazil. Image by Mauricio Marinho via Reuters and Estadao (https://www.estadao.com.br/brasil/buracos- vocorocas-gigantes-ameacam-cidade-maranhao-calamidade-nprm/).

These issues at Buriticupu are primarily rapid headward and lateral erosion of gullies, driven by toe erosion and then slope failure, as the image above shows. The materials appear to be deeply weathered (hence the red colour), and thus will be weak. The Estadao article (https://www.estadao.com.br/brasil/buracos-vocorocas-gigantes-ameacam-cidade-maranhao-calamidade-nprm/) ascribes the problems to ‘deforestation, disorderly occupation, relief and sandy soil’.

In my experience, these problems are often associated with inadequate water management in the towns, both in terms of water supply and sewage disposal, and the control of surface drainage from the roads and pavements. It would be interesting to know if that is the case here. Unfortunately, once these problems start they are difficult to stop unless there is substantial engineering intervention into the gullies themselves, along with good water management in the town.

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29 MARCH 2023

The Novato landslide in California: digital elevation model data demonstrates a much older, larger

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4/19/23, 7:12 AM Page 8 of 24

The Novato landslide in California: digital elevation model data demonstrates a much older, larger landslide (https://blogs.agu.org/landslideblog/2023/03/29/novato-landslide-2/) The Novato landslide in California: digital elevation model data demonstrates a much older, larger landslide

Loyal reader and long time online friend Funkenbeachin has extracted the 1 metre digital elevation model (DEM) data for the site of the Novato landslide in California (https://blogs.agu.org/landslideblog/2023/03/27/novato-1/). He has made a a video that shows the site (https://www.youtube.com/watch?v=ij6YCIu0aA4), which he’s posted to Youtube:-

This video really demonstrates the power of DEM data, which highlights beautifully that the most recent slide is a reactivation of the lower portion of a much larger, ancient landslide. I wonder whether the engineers who designed and constructed the slope on the uphill side of the road were aware of this. This landslide can clearly be seen in the still from the video below:-

1 m DEM data for the site of the Novato landslide in California.

1 m DEM data for the site of the Novato landslide in California. Still from a video posted to Youtube by loyal reader funkenbeachin. (https://www.youtube.com/watch?v=ij6YCIu0aA4)

Novato Landslide 2023, Redwood Boulevard, US-101, California, v1, 3D Slope Map Draped…

4/19/23, 7:12 AM Page 9 of 24

This is landslide country – there are many other landslides visible in the image above, a consequence of active tectonics that have created a dynamic landscape, weak rocks, regular high intensity rainstorms and occasional earthquakes.

There are certainly lessons to be learnt from the Novato landslide.

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28 MARCH 2023

Alausí: a massive landslide in Ecuador (https://blogs.agu.org/landslideblog/2023/03/28/alausi-1/) Alausí: a massive landslide in Ecuador The 26 March 2023 landslide at Alausí in Ecuador (https://blogs.agu.org/landslideblog/?s=ecuador&submit.x=0&submit.y=0&mswhere=blog) has attracted considerable attention, having buried a neighbourhood of the town. At the time of writing the confirmed loss of life is seven people, with a further 23 having been injured. It is reported that 64 people are missing, although there will be considerable uncertainty in that number. Earlier reports of 16 fatalities are now thought to be incorrect. (https://www.dw.com/es/gigantesco-alud-deja-decenas-de-desaparecidos-en-ecuador/a- 65144812)

The best overall view of this very large landslide is a drone video collected by Edwin Salazar that has been widely tweeted (https://twitter.com/canarvaezm/status/1640328603198971907):-

https://twitter.com/canarvaezm/status/1640328603198971907

The drone successfully captures a very deep-seated, rotational landslide in comparatively homogenous, but clearly weak, rocks. I would suspect that these might be volcanic materials?

Meanwhile, AP has a remarkable image of the toe of the landslide (https://andina.pe/agencia/galeria-deslizamiento-sepulta-un-barrio-alausi-centro- los-andes-ecuador-18518.aspx), and the immense damage that it has caused to the town of Alausí:-

The toe of the very large 26 March 2023 landslide at Alausí in Ecuador.

The toe of the very large 26 March 2023 landslide at Alausí in Ecuador. Image by AP via Andina (https://andina.pe/agencia/galeria-deslizamiento- sepulta-un-barrio-alausi-centro-los-andes-ecuador-18518.aspx).

4/19/23, 7:12 AM Page 10 of 24

This is roughly the same perspective from Google Earth, giving an idea of what has been lost in this lower portion:-

Google Earth image of the site of the very large 26 March 2023 landslide at Alausí in Ecuador.

The location of the landslide is [-2.193, -78.843]. This is the best image that I have found that shows the entire landslide:-

The very large 26 March 2023 landslide at Alausí in Ecuador.

4/19/23, 7:12 AM Page 11 of 24

The very large 26 March 2023 landslide at Alausí in Ecuador.

The very large 26 March 2023 landslide at Alausí in Ecuador. Image by REUTERS/Karen Toro (https://www.reuters.com/world/americas/landslide- kills-least-16-ecuadors-andes-2023-03-27/).

Reports indicate that the area has suffered heavy rainfall in recent days (https://www.20minutos.es/noticia/5113512/0/deslizamiento-tierras- fallecidos-desaparecidos-ecuador/), which is also hindering the rescue operations. The area has been on yellow alert for landslides since 15 March 2023.

In terms of Alausí itself, there are reports that cracks started to appear in the area of the landslide in December 2022, and that irrigation water had ceased to flow in the area. The reports also indicate that some monitoring was ongoing at the site.

It is interesting to take a wider perspective on the area around Alausí:-

Google Earth image of the landscape around Alausí in Ecuador.

This is a landscape dominated by landslides. On the left side of the image are multiple shallow failures on steep slopes, many of which are affecting the road. But on the steep slopes around Alausí there are multiple arcuate scars that probably mark the source zones of previous landslides, many of which would have been much larger than the event on Sunday. The largest of these might lie in the upper portion of the in the centre of the image, where there is a very large, arcuate scar and, downslope to the right, the possible remains of a degraded landslide block. This is, of course, only a hypothesis – more detailed mapping would be needed to confirm the theory.

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27 MARCH 2023

Novato: an interesting landslide triggered by heavy rainfall in California (https://blogs.agu.org/landslideblog/2023/03/27/novato-1/)

4/19/23, 7:12 AM Page 12 of 24

(https://blogs.agu.org/landslideblog/2023/03/27/novato-1/) Novato: an interesting landslide triggered by heavy rainfall in California

Last week, the latest in a long series of large storms struck California (https://blogs.agu.org/landslideblog/? s=california&submit.x=0&submit.y=0&mswhere=blog), triggering another round of flooding and landslides. One particularly interesting slope failure occurred at Novato in Marin County. The San Francisco Chronicle has a nice image of the aftermath (https://www.sfchronicle.com/bayarea/article/novato-road-damage-bay-area-storms-17856032.php):-

The aftermath of the landslide in Novato, California.

The aftermath of the landslide in Novato, California. Image from the San Francisco Chronicle. (https://www.sfchronicle.com/bayarea/article/novato- road-damage-bay-area-storms-17856032.php)

A Tweet (https://twitter.com/sarah_klieves/status/1639077493432008705) by Sarah Klieves (https://twitter.com/sarah_klieves), a senior producer for NBC Bay Area, provides the best perspective though:-

Sarah Klieves @sarah_klieves · Follow

Our @nbcbayarea SkyRanger flew over a landslide that crumpled a section of Redwood Blvd near Olompali State Historic Park. This is the only public road into the park, so rangers say it will be closed for awhile.

Watch on Twitter

6:31 PM · Mar 23, 2023

322 Reply Share

4/19/23, 7:12 AM Page 13 of 24

This is a view from that video, showing the landslide:-

The landslide at Novato, California.

The landslide at Novato, California. Image from a Tweet by Sarah Klieves of NBC Bay Area (https://twitter.com/sarah_klieves/status/1639077493432008705).

The location of the landslide appears to be [38.1444, -122.5652]:-

Google Earth image of the site of the landslide at Novato, California.

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4/19/23, 7:12 AM Page 14 of 24

Google Earth image of the site of the landslide at Novato, California.

Interestingly, Redwood Boulevard, which is the road damaged by the landslide, was constructed in 2015. A Google Earth image from March that year shows that the slope at the site of the landslide was cut and reprofiled, and that drains were installed:-

Google Earth image of the site of the landslide at Novato, California in March 2015, showing engineering works underway at the site.

It is interesting that at this site the slope is a little steeper than in the adjacent areas, which presumably is the reason for the additional works, including the drains. That failure is a classic slump. Fortunately the toe has not extended to the main highway, and the limited mobility of the debris has meant that this road is unaffected. However, the landslide has caused disruption to a watermain and to a gas pipeline.

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24 MARCH 2023

A remarkable landslide at Karl Marx village, in Jalpak-Tash, Kyrgyzstan (https://blogs.agu.org/landslideblog/2023/03/24/jalpak-tash-1/) A remarkable landslide at Karl Marx village, in Jalpak-Tash, Kyrgyzstan

On the night of 22 March 2023 a landslide was triggered at Karl-Marx village in Jalpak-Tash rural municipality, Uzgen in Kyrgyzstan. The landslide is reported to be 1 million cubic metres. AKI Press has a posted a drone video of this event onto Youtube (https://www.youtube.com/watch? v=08nM4eCU23w) – it is breathtaking:-

Өзгөндө 1 000 000 куб метр жер көчтү: Өзгөчө кырдаал режими жарыяланды

4/19/23, 7:12 AM Page 15 of 24

This is a still from the video:-

The 22 March 2023 landslide at Karl-Marx in Jalpak-Tash rural municipality in Kyrgyzstan.

The 22 March 2023 landslide at Karl-Marx in Jalpak-Tash rural municipality in Kyrgyzstan. Still from a video posted to Youtube by AKI Press (https://www.youtube.com/watch?v=08nM4eCU23w).

The image below shows the upper portion of the landslide, including the source area:-

The source area of the 22 March 2023 landslide at Karl-Marx in Jalpak-Tash rural municipality in Kyrgyzstan.

Өзгөндө 1 000 000 куб метр жер көчтү: Өзгөчө кырдаал режими жарыяланды

4/19/23, 7:12 AM Page 16 of 24

The source area of the 22 March 2023 landslide at Karl-Marx in Jalpak-Tash rural municipality in Kyrgyzstan.

The source area of the 22 March 2023 landslide at Karl-Marx in Jalpak-Tash rural municipality in Kyrgyzstan. Still from a video posted to Youtube by AKI Press (https://www.youtube.com/watch?v=08nM4eCU23w).

Whilst the image below shows the landslide track:-

The track of the 22 March 2023 landslide at Karl-Marx in Jalpak-Tash rural municipality in Kyrgyzstan.

The track of the 22 March 2023 landslide at Karl-Marx in Jalpak-Tash rural municipality in Kyrgyzstan. Still from a video posted to Youtube by AKI Press (https://www.youtube.com/watch?v=08nM4eCU23w).

The head scarp area of the Jalpak-Tash landslide shows a reasonably deep seated landslide source, with possibly a minor rotational component to the failure. The main part of the landslide track appears to me to be an earthflow. The video seems to indicate that the landslide was still creeping at the time of the failure.

The location of this landslide is unclear to me, but research suggests that it might be close to Kurbu-Tash, which is at [40.611, 73.293]. This area suffered a large landslide that I highlighted in 2017 (https://blogs.agu.org/landslideblog/2017/05/03/kurbu-tash/), which was not dissimilar to the 22 March 2023 event. This remains to be confirmed.

An AKI Press article reports that an emergency situation has been declared for the village (https://akipress.com/news:698326:Emergency_situation_declared_in_Karl_Marx_village_after_landslide/), with the residents of 18 houses having been evacuated (https://akipress.com/news:698327:Drone_films_giant_landslide_in_Uzgen/), but that the risk is considered to be low. The rate of movement has been recorded at about 3 metres per hour.

The trigger for this landslide is not given, but this will be snowmelt season in this part of Kyrgyzstan. The 2017 landslide also occurred in the Spring.

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4/19/23, 7:12 AM Page 17 of 24

23 MARCH 2023

Planet animations of a paraglacial landslide on a tributary of the Klutlan Glacier in Alaska (https://blogs.agu.org/landslideblog/2023/03/23/klutlan-glacier-1/) Planet animations of a paraglacial landslide on a tributary of the Klutlan Glacier in Alaska

A very interesting area of current research is the ways in which slopes are behaving in the vicinity of glaciers in high mountain areas. In most such environments, glaciers are retreating. There is some evidence that some slopes respond by deforming, possibly assisted by the thawing of permafrost at some times of the year.

Bretwood Higman, known as Hig, is a geologist and data scientist based in Alaska (https://blogs.agu.org/landslideblog/? s=alaska&submit.x=0&submit.y=0&mswhere=blog) (there is a great profile of Hig on YourStory (https://yourstory.com/2018/01/techie-tuesdays- bretwood-higman)) who has been studying these processes for a number of years. Hig recently contacted me to highlight a site in Alaska, on a tributary of the Klutlan Glacier, that he has identified that is displaying very active deformation. The location is [61.4881, -141.1884] – there is a really good image on the Living Atlas site:- (https://livingatlas.arcgis.com/wayback/#ext=-141.20920,61.48351,-141.17552,61.49310&active=57965&active=44873)

A landslide on a tributary of the Klutlan Glacier in Alaska.

A landslide on a tributary of the Klutlan Glacier in Alaska. Image from the Living Atlas site. (https://livingatlas.arcgis.com/wayback/#ext=-141.23656,61.46866,-141.10181,61.50705&active=57965&active=44873)

Hig has made the following observation about the landslide:-

In some ways this is a very typical landslide – a rotational failure with a very steep head scarp extending well beneath the surface of a thinning glacier. I’ve documented dozens of similar sites around Alaska. However, the retrogressive nature of the initial failure, opening huge tension cracks, is unusual. More typical would be antiscarps indicating a flexural topple.

Hig has put together a Planet (https://www.planet.com/) animation that shows the development of the Klutlan Glacier landslide, which you can see here (https://www.planet.com/stories/klutlan-trib-landslide-LruA13-VR). It’s really cool:-

https://www.planet.com/stories/klutlan-trib-landslide-LruA13-VR

As you can see, the landslide started to develop in July 2022. Before the landslide disappeared below the winter snow, it was about 400 m from

4/19/23, 7:12 AM Page 18 of 24

As you can see, the landslide started to develop in July 2022. Before the landslide disappeared below the winter snow, it was about 400 m from crown to the junction with the glacier and about 650 m wide.

It will be fascinating to see how this develops over the coming spring and summer – based on last years imagery of the area of the Klutlan Glacier, it is likely to start to re-emerge in April and May.

Acknowledgement Thanks to Hig for his work on this great site.

Planet Team (2023). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/ (https://www.planet.com/)

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21 MARCH 2023

First Planet satellite images of the landslides in Malawi from Cyclone Freddy (https://blogs.agu.org/landslideblog/2023/03/21/malawi-2/) First Planet satellite images of the landslides in Malawi from Cyclone Freddy Yesterday, I highlighted that Cyclone Freddy has triggered multiple damaging landslides in Malawi (https://blogs.agu.org/landslideblog/2023/03/20/mtauchira-1/). I have started to look at the Planet imagery (https://www.planet.com/) of the potentially affected areas, particularly in the area of Chiradzulu, which is reported to have been badly impacted. This is an area that is heavily affected by cloud, so obtaining good imagery is not straightforward. It is likely that it will be some days or even weeks before we get a full picture.

However, this is the Chiradzulu Forest Reserve, with an image collected on 19 March 2023. The centre of this image is at about [-15.693, 35.161]:-

The area affected by landslides triggered by Cyclone Freddy in Chiradzulu Forest Reserve, Malawi. Image copyright Planet (https://www.planet.com/), used with permission, collected on 19 March 2023.

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For reference, this is the same area in an image collected before Cyclone Freddy, on 21 February 2023:-

The area affected by landslides triggered by Cyclone Freddy in Chiradzulu Forest Reserve, Malawi. Image copyright Planet (https://www.planet.com/), used with permission, collected on 21 February 2023.

I have created a slider to allow the images to be compared easily:-

The Planet (https://www.planet.com/) satellite imagery shows multiple long run out flows, most of which appear to have initiated as shallow landslides on the higher slopes. Many have involved multiple landslide sources that have merged in channels to form more destructive landslides on the lower slopes. In several locations the landslides have impacted the settlements, as shown in this area of the image:-

JuxtaposeJS(http://juxtapose.knightlab.com)

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One of the areas most affected by landslides triggered by Cyclone Freddy in Chiradzulu Forest Reserve, Malawi. Image copyright Planet (https://www.planet.com/), used with permission, collected on 19 March 2023.

There is also evidence of landslides in other parts of the area too. On the western flanks of Mount Soche to the south of Blantyre, there is the landslide shown below (the location is [-15.842, 35.018]). Whilst the image is affected by cloud, and the landslide is on the very edge of the area captured, it appears that this landslide has run out through the urbanised area:-

A landslide triggered by Cyclone Freddy on the flanks of Mount Soche in, Malawi.

A landslide triggered by Cyclone Freddy on the flanks of Mount Soche in, Malawi. Image copyright Planet (https://www.planet.com/), used with permission, collected on 19 March 2023.

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ABOUT DAVE

Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.

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Whilst the imagery is insufficiently good to be sure, I am reasonably confident that there are further landslides in Malabvi Forest Reserve, located at [15.846, 35.136]. This post on Facebook (https://www.facebook.com/LisanjalaSDAchurch/posts/pfbid0nKopvp64yzwsUtaJxXR7FwrBhMHrpYMYYuX6n7oxqN9EdAaAZSBRwvL8FGijiidkl) would seem to support that assumption.

Whilst we await better imagery, it is clear that this area has been affected by dreadful landslides. Sadly, this is not the first time. Loyal reader Yannick Thiery from BGRM in France kindly contacted me to note that a similar landslide was triggered near to Chiradzulu by Cyclone Idai in March 2019. The location was reported to be [-15.683, 35.674].

Reference and acknowledgement

Planet Team (2023). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/ (https://www.planet.com/)

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