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August 31, 2025<\/p>\n
3 min read<\/p>\n
Huge Cracks in the Earth Are Slicing through Cities, Swallowing Houses and Displacing Thousands of People<\/p>\n
Hundreds of thousands of people are at risk of losing homes, businesses\u2014and lives\u2014as giant \u201cgullies\u201d expand into cities across Africa<\/p>\n
A view of a deep urban gully in Kamonia in the Democratic Republic of the Congo. More than 3,000 people are at risk of this gully expanding.<\/p>\n
Ruben Nyanguila\/Anadolu via Getty Images<\/p>\n
Gigantic trenches known as gullies are opening up in cities in Africa, swallowing up homes and businesses, sometimes in an instant, a study has found.<\/p>\n
About 118,600 people, on average, in the Democratic Republic of the Congo (DRC) alone were displaced between 2004 and 2023, according to researchers reporting their findings in Nature.<\/p>\n
Without urgent action, researchers estimate that hundreds of thousands of people across Africa are likely to be displaced within the next 10 years, including more than one-quarter of the 770,000 or so people in the DRC living in the expected expansion zone of these gullies.<\/p>\n
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\u201cIt\u2019s an underestimated and severely under-researched hazard,\u201d says study co-author Matthias Vanmaercke, a geographer at the Catholic University of Leuven (KU Leuven) in Belgium. It is caused by \u201ca combination of natural and human factors,\u201d he says, but this is \u201cnot at all unavoidable.\u201d<\/p>\n
Gullies are expanding across cities that are built on sandy soils and lack adequate drainage. When there are heavy rains, water accumulates on roads and rooftops. When the drainage systems are inadequate, the water finds its way into unprotected ground, carving deep holes that can stretch for hundreds of metres. Over time, the gullies swallow houses and other infrastructure, and sometimes even result in deaths.<\/p>\n
Vanmaercke and his colleagues used satellite images taken between 2021 and 2023 to identify 2,922 urban gullies in 26 of 47 cities, covering a cumulative distance of nearly 740 kilometres. The team cross-checked these images with historical aerial photographs stored at the Royal Museum for Central Africa in Belgium and found that only 46 of the gullies were present in the 1950s. This \u201cgave the first clear indication that this is indeed attributable to the ongoing urbanization,\u201d Vanmaercke says.<\/p>\n
A woman and a boy look through the collapsed wall of a house left by the collapse of one of the main roads in the Mont Ngafula district in Kinshasa, the capital of the Democratic Republic of Congo on November 4, 2021.<\/p>\n
Alexis Huguet\/AFP via Getty Images<\/p>\n
In 99% of cases, the gullies had expanded by at least 10 square metres between 2004 and 2023. The average gully was 253 metres long and 31 metres across at its widest point, and nearly all of them were linked to the road network. \u201cThe water cannot infiltrate, and it concentrates along these roads which basically become big canals that turn into rivers,\u201d says Vanmaercke.<\/p>\n
The researchers then combined data on population density with the gully maps. This enabled them to estimate that an average of 118,600 people were displaced because of gullies over the period \u2014 with displacement rates more than doubling after 2020.<\/p>\n
Guy Ilombe Mawe, a geomorphologist at the Official University of Bukavu in the DRC and a co-author of the paper says that the widening of gullies can be catastrophic and even fatal, and that families living near gullies often have no safe alternatives.<\/p>\n
In November 2019, the researchers visited Kinshasa, the DRC\u2019s capital and one of the most affected cities, with 868 urban gullies stretching over a total of 221 kilometres. There they met a mother whose home stood near a gully edge. Two days later, several of her children were killed while sheltering at a relative\u2019s house, when an expanding gully collapsed overnight. At least 40 people in Kinshasa died that night.<\/p>\n
As African cities expand, the threat of expanding gullies is likely to increase. The continent\u2019s population is expected to nearly triple by 2050, and rainfall intensities in tropical Africa could increase by up to 15% in the coming decades.<\/p>\n
The site of a house in Kinshasa where a family lost several children to gully formation. People tried to prevent the gully from expanding using sand, cement and sticks.<\/p>\n
The authors note in their study that preventing gullies from forming is more effective and affordable than is stabilizing them after they form, which can cost upwards of US$1 million per gully. \u201cThe trick would be to have interventions that are well thought of and installed in time. But there\u2019s such a huge lack of money and resources that usually when something is done, it\u2019s either inadequate or too late,\u201d says Vanmaercke.<\/p>\n
Ana Mijic, a hydrologist at Imperial College London, says that governments and private-sector organizations need to step up their investments in interventions such as sufficient drainage systems. But high costs and maintenance of long-term solutions act as barriers.<\/p>\n
Gina Ziervogel, a geographer at the University of Cape Town in South Africa, says that governments should prioritize sustainable infrastructure. \u201cWe need to understand the role of the environment and resources in cities \u2014 soil and water particularly \u2014 and so engaging experts from those fields is really important.\u201d She adds that involving the affected communities in planning interventions \u201cwould go a long way to understanding their insights, both on the experience of living with this and on potential solutions.\u201d<\/p>\n
\u201cThe sooner we can invest, the better, because we know that the later we leave it, the bigger the scale of the challenge,\u201d says Ziervogel.<\/p>\n
This article is reproduced with permission and was first published on August, 27 2025.<\/p>\n
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