Cyclone Idai: evidence of the impact of landslides and debris flows

As the true magnitude of the likely costs of Cyclone Idai across southern Africa becomes clear, some images are emerging that indicate that in some areas landslides may have been a significant part of the problem, in Zimbabwe at least.  This is directly indicated in a few news reports – for example, it has been widely noted that two boys were killed when a landslide struck the dormitory of a school:-

“Two pupils and a worker at a secondary school in the area were among those killed after a landslide sent a boulder crashing into their dormitory.  Soldiers on Sunday helped rescue the surviving nearly 200 pupils, teachers and staff who had been trapped at the school in Chimanimani.”

But reports also suggest that landslide and debris flows might have played a much larger role.  The same report indicates that:-

“Agony is etched in Tapiwa Chanyawo’s face as he tells of the night the storm came, a mudslide swept away their home, and his family died.  Their home, in the eastern Zimbabwean town of Chimanimani, lay in the path of Idai — a gigantic tropical cyclone that may have left more than a thousand dead in its wake.  “My father, my mother, my two sisters including the elder one and her child, they all died,” Chanyawo told AFP from his bed at a local hospital, counting the numbers on his fingers.”

This report contains the following image, which includes very clear landslide scars in the hills and, perhaps, the aftermath of a channelised debris flow:-

The aftermath of Cyclone Idai in Zimbabwe. Image by AFP Photo/Zinyange AUNTONY, via Yahoo News.

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Meanwhile, Povo News has posted this image, which I believe is the village of Ngangu, close to Chimanimani:-

The aftermath of Cyclone Idai. This image appears to be the village of Ngangu, close to Chimanimani. Image via Povo News

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There is no doubt that this image shows the aftermath of debris flows, with clear landslide scars in the hills in the background.  It appears that there are multiple examples of this type of event:-

The aftermath of Cyclone Idai. This image appears to be the area around the village of Ngangu, close to Chimanimani. Image via Povo News.

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Elsewhere there is evidence of other, more conventional, landslides, which have caused extensive damage to the road network:-

Landslides in the he aftermath of Cyclone Idai, close to Chimanimani. Image via Povo News.

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Note here the multiple small landslides have combined in the channels.  This process is probably the origin of the debris flows; a mode that is very familiar from Japan, Colombia and elsewhere.  The destructive power of the resulting debris flows is well illustrated by the famous video from Lantau Island.