This recent disaster presents a proper platform for scientific research relating to landslide hazards in the Freetown peninsula. Such a study would prevent future failures and perhaps mitigate such hazards by predicting possible failures.
First of all, I would refuse to accept the notion that it was a mudslide seeing the type of materials that were displaced from the many photos I have seen. With the volume of rock material contained in the displaced materials I wonder then how it was classified as a ‘mudslide’. I would refer readers who disagree with me to read up on the worldwide accepted nomenclature for landslide classification. This however, shows a lack of knowledge in the area of landslide studies by whoever came up with the term to describe the event.
At the rate at which construction activities are going on in Freetown, we expect more of such disasters to occur in the near future if we do not take such studies seriously. I am not a prophet of doom but it is very evident that with the improper planning and erratic construction of buildings on the hills, we would expect to have more of such disasters occurring.
In the case of the event of 14th August, massive construction activities at the base of the slope could have initially put the slope in marginal stability waiting for a trigger as this could have caused an increase in stress on the slope. Then came the high rainfall with great intensity the nights preceding the event, which could have triggered the landslide. According to studies by Wieczorek (1996), shallow landslides in soils and weathered rock are often generated on steep slopes during the more intense parts of a storm and thresholds of combined intensity and duration may be necessary to trigger them. The rapid infiltration of rainfall causing the saturation of the soil could have brought about a rise in the pore water pressure bringing about loss in the shear strength of the soil thus leading to failure. What also need to be investigated is whether this was a palaeo landslide that was reactivated.
If we as a nation are not serious about this, then we would see more of such disasters occurring every rainy season. I have observed people with no knowledge in landslide studies or Engineering Geology have suddenly become experts in this field overnight.
God help us!
About the author
Dr. Egerton Hingston, from Sierra Leone, has been an academic for over 20 years in geology and applied geology. During this period, he has been involved in several mapping projects, mineral exploration, landslide studies, slope stability investigation, teaching and research. He holds a PhD in Engineering Geology from the University of Leeds, United Kingdom and is currently employed by the University of KwaZulu-Natal, Durban, South Africa, as a lecturer in Engineering Geology. His research interests lie in the understanding of landslides and slope stability problems and the geotechnical uncertainties associated with such studies. He also works on rock engineering problems in underground mines. He is also interested in waste disposal management and the use of geological materials in the construction industry.