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Volume 12, Issue 2, April - June 2023
CONTENT
Chair's Foreword
Landslides in Africa - an increasingly frequent geohazard event
Earth Science Events
References and selected reading
Chair's Foreword*
We revisit the topic of geohazards in Africa and reflect on the increased frequency of landslides and mudslides due to climate warming. The link between climate changes and increased frequency of these events is firmly established. Less clear, is the type extent and magnitude of these changes in response to climate changes[1].
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| Road collapse due to landslide. Kwa Zulu Natal, South Africa [Source: AllAfrica.com] |
Landslides in Africa - an increasingly frequent geohazard event
Recent years have seen the increasing threat of geohazards to Africa, due to climate change. As seen recently in the case of rainfall events in West Africa, we now have a new way of looking at how climate events are related to climate change by judging the likelihood of such events occurring, without human-impacted climate warming [1].
Landslides, in particular, are a very commonly occurring geohazard in Africa representing great loss of lives, high annual costs of disruption to daily life and destruction of infrastructure. Most recently, flash floods in parts of East Africa have been a trigger for landslides in the region[2]. On 2 May 2023, heavy rainfall led to flash flooding in parts of Rwanda and Uganda. The downpours continued for two days, ending on 4 May. Rwanda's Sebeya River burst its banks. This led to several landslides across the hilly Rwanda landscape with a reported 127 deaths, 5,100 homes destroyed and 2,500 homes partially damaged.
As Garriano and Guzzetti [3] describe a landslide as a kind of mass wasting process that acts on natural and engineered slopes. It is the movement of a mass of rock, debris, or earth down a slope, under the influence of gravity[4]. Landslides involve flowing, sliding, toppling, falling or spreading and often exhibit a range of different kinds of movement. Different phenomena influence slope stability including rainfall, temperature, snow melt, earth tremors, etc. However, from this and many other studies the effect of moisture in the form of pore pressure changes induced by rain and runoff, is the most important factor influencing slope stability. This is also the case in the instance of long-term, deep-seated landslides, as the authors state and which is supported by the work of Rianna et al [5] in 2014, which investigated a slow moving deep-seated landslide in clay soil.
A recently researched example of a large area, long term landslide sits under the city of Bukavu in Democratic Republic of Congo[6]. The study maintains that the movement of large, slow-moving, deep-seated landslides is regulated by changes in pore-water pressure. The study concludes that surface and subsurface hydrology in urban areas ( e.g., due to roads, housing, drainage changes) can alter the surface hydrology and hence the slope stability. Satellite and (historical) aerial images were combined and used to quantify how 70 years of urbanisation changed the seasonal, annual and ten-yearly dynamics of a large, slow moving landslide under the city of Bukavu. The increase in landslides Africa is witnessing currently, dictates that we must urgently revisit the problems of these large long-term landslides that may suddenly and catastrophically accelerate, in addition to the ongoing monitoring of more typical cases.
Earth Science Events
August 9-10, 2023
International Conference on Tectonic Geomorphology and Paleoseismology
VISION: https://waset.org/tectonic-geomorphology-and-paleoseismology-conference-in-august-2023-in-lagos
VENUE: Lagos, Nigeria
November 4-5, 2023
International Conference on Agricultural Engineering
VISION: https://waset.org/agricultural-engineering-conference-in-november-2023-in-cape-town
VENUE: Cape Town, South Africa
December 13-14, 2023
International Conference on Theoretical and Computational Seismology
VISION: https://waset.org/theoretical-and-computational-seismology-conference-in-december-2023-in-cairo
VENUE: Cairo, Egypt
References and selected reading
[1] Otto, F., et al, Climate exacerbated heavy rainfall leading to large-scale flooding in highly vulnerable communities in West Africa, ResearchGate, 2022.
[2] Faye Hulton, Weather Tracker: Flash floods and landslides hit parts of East Africa, The Guardian, May, 2023.
[3] Gariano, S.L, Guzzetti, Landslides in Changing Climate, Earth Science Reviews, April 2016.
[4] Cruden, D.M., Barnes, D. J., Landslide Types and Processes, In Turner, A.K., Schuster, R.I., (Eds.), Landslides Investigation and Mitigation, Special Report 247. Transport and Research Board, Washington, D.C., pp.36-75.
[5] Rianna, G., Zollo, A.L., et al., Evaluation of the Effects of Climate Change on Landslide Activity of Orvieto Clayey Slope, Procedia Earth. Plan. Sci., 9, 54-63.
[6] Dill, A., Dewitte, O., Handwerger, A.L., et al, Acceleration of large deep-seated tropical landslide due to urbanisation feedbacks, Nature Geoscience, 15, 1048-1055, 2022.
*Board of the Society of African Earth Scientists: Dr Enas Ahmed (Egypt), Osmin Callis (Secretary - Guyana/Nigeria), Mathada Humphrey (South Africa), Ndivhuwo Cecilia Mukosi (South Africa), Damola Nadi (Nigeria), Dr Chukwunyere Kamalu (Chair - Nigeria).
