1 June 2022
Multiple landslides at Mibei village in Guangdong during heavy rainfall in 2019
Between 10 and 13 June 2019 a period of intense rainfall triggered multiple landslides in the vicinity of Mibei village in Longchuan County, Guangdong Province, China. Fortunately there were no reported fatalities. A paper just published in the journal Landslides (Feng et al. 2022) describes and investigates this event, which caused damage to 7.2 km of roads and four houses. The economic loss in Mibei village is estimated to have been 120 million yuan. Interestingly, the local government reportedly evacuated 377 residents on day two of the rainstorm.
The article includes the following image, collected by a UAV, of the landslides triggered in this rainstorm:-
Interestingly, this cluster of landslides can also be seen on Google Earth. The location of Mibei is, I believe, 24.6479, 115.3053. This is the image of the area:-
These landslides are interesting. For the most part the crown of the landslide is quite high on the slope, in many places reasonably close to the ridge or another break of slope. They have occurred in forested areas. They are shallow and planar, with a long debris trail. The material appears to be deeply weathered soil or regolith – the authors describe this as a residual soil created by long-term weathering of granitic rocks.
Feng et al. (2022) have recorded 327 landslides in the vicinity of Mibei village. They found that the landslides are indeed shallow – typically 1.5 to 3 m in depth, with very few exceeding 5 m. Through an experimental programme, they have shown that the intense rainfall induced saturation in the shallow layers of the soil, influenced by the permeability boundary between the more intact underlying granites and the shallow, weathered regolith. This induced sliding, with a transition to fluidised flow as the soil underwent deformation.
It seems to me that the landslides probably entrained considerable volume of material in the lower portions of the slope (note the long debris trails, often to the foot of the slope), and Feng et al. (2022) also noted some toppling around the crown of the landslides, suggesting some retrogression too.
Interestingly, the authors note that there appears to have been a lag between the most intense rainfall and the occurrence of most of the landslides, perhaps being attributable to the time taken for seepage forces to develop.
These types of landslide clusters are increasingly common in intense rainfall events, especially on the granitic areas of SE China. Similar events have been recorded in Hong Kong. It is important that analyses are undertaken of them in order to reduce future losses, so this study is welcome. In this case, the timely evacuation of the residents was an important success.
Feng, W., Bai, H., Lan, B. et al. 2022. Spatial–temporal distribution and failure mechanism of group-occurring landslides in Mibei village, Longchuan County, Guangdong, China. Landslides. https://doi.org/10.1007/s10346-022-01904-9