For decades, the layers of earth on the slopes of Bukavu have been gradually sliding down – but the slow erosion in the big city in the Democratic Republic of the Congo seems to be moving faster since the city has grown a lot. As Antoine Dille from the Royal Belgian Institute of Natural Sciences in Brussels and his team report in the journal "Nature Geoscience", it could be related to the fact that the settlements have changed both the surface and the watercourses underground.
The Bukavu population has more than quadrupled since 1995. One reason: Due to violence in the surrounding regions, many people fled into the city. Bukavu was founded on the banks of Lake Kivuse, but now the place has also spread to the surrounding slopes. A third of Bukavu therefore lies on large, deep and slowly eroding layers of earth.
Antoine Dille and his colleagues have now used satellite and aerial images to investigate how fast the slopes have moved over the past seven decades. They found that the soil layers slide down the slope more and more rapidly over the decades, especially in places where the groundwater flow near the surface has been changed. Some sections would move three times faster than in the 1970s.
As the study authors suspect, the slope slip does not result from increased precipitation or earthquakes, but the many house buildings destabilize the soils. Because the fastest way to move the rapidly urbanized areas - about 0.7 meters per year - because buildings and streets intervene in the course of the water outflow. However, residents could reduce the risk of a devastating, fast landslide by improving the drainage of the surface water, the authors write.
