The Ghana Institution of Geoscientists (GhIG) is concerned about the recent occurrences of rockfalls, slope failures, and landslides some of which may be rainfall induced and its consequential dangers to life and property. Indeed, we are sitting on a looming danger and the need to address these issues now is important. It is also equally important to educate the general public to be good stewards of the environment
The recent heavy rains triggering landslides and rock-falls on the Akwapim-Togo Range, with the most recent one that occurred on the Aburi-Ayi Mensah stretch has caused several inconveniences to pedestrians and motorists and near life-threatening misses, even though thankfully, no fatality has been recorded.
The Aburi-Ayi Mensah dual-carriage road used to be a single lane until it was redesigned into its current state to ease access to and from the Aburi for motorists. During the construction of the dual-carriage way, the footwall of the hill was cut back without adequate assessment of the geological structures and the general geodynamics of the hill.
Similar areas in the country where there is looming danger, include the Kasoa Tollbooth, Ablekuma, MacCarty Hill, Gbawe, Kwabenya, Ofankor, Nkawkaw scarp, Voltaian Scarp (Camp), Jamase-Ashanti Mampong, Gambaga-Nakpanduri Road, Larteh Road and their surrounding areas which all falls part of a mountainous range, are subject to the risk of possible rockfalls and landslides. The occurrence of these natural catastrophic events may be accelerated by heavy rains, earth tremors and earthquakes as well as the surge in un-controlled, non-standardized and indiscriminate human activities.
The GhIG wishes to inform the Honourable Ministers responsible for Works and Housing, Roads and Highways and the general public of the need to collaborate in the sustainable development of projects in the country in other to forestall or minimize the effects of these disasters in our communities. This also calls for regulated zoning of our communities based on geological and geodynamics of rock formations both surface and sub-surface on which rests development projects.
The mountain range over-looking Accra which was at a point declared a green-belt zone, where human activities were to be controlled, but subsequently, massive developmental projects, including buildings sprang up without any consideration to the geological structures that host these development projects.
In summary, the geodynamics of the Akwapim-Togo range within the vicinity of Accra, comprises of the rock units such as quartzites, slates, sandstone and phyllites and is structurally controlled within numerous faults, joints and bedding planes.
These rock types are key factors in determining slope stability. In areas, where competent rocks like quartzites are interbedded or intercalated with weaker or incompetent phyllite, siltstones or mudstones, the incompetent rock which often has a veneer of clayey materials that are relatively easily weathered and eroded, creates weaker zones with the consequence of lowering their shear strength.
Website Officer: Jude Ontonyi
Thus, prolong rainfall could cause the above phenomenon to occur and in this instance, the competent quartzites in the Aburi area slided over the weaker phyllites which caused movement of the rocks down slope.
As indicated earlier, the Akwapim–Togo Range has been known to be seismically active due to its intersection with the Coastal Boundary Fault. Thus, earth tremors and earthquakes can trigger rock movements leading to landslides along these slopes particularly in the case of the Aburi-Ayi Mensah road where sections of the slope dip toward the road.
In addition, the rock formations are heavily jointed which facilitates their easy movement. There are two major joint directions almost perpendicular to each other. Where the joints are in the same direction as the dip direction, any shock or trigger can facilitate movement of the mass of rocks in the dip direction.
The design and construction of the Aburi-Ayi-Mensah dual-carriage road was deficient in the application of geodynamics to the rock formations in the area. The toe of the hill (with the rocks steeply dipping towards sections of the road) is in direct contact with the road without any safety buffer. The road should not have been constructed facing the dip direction of the rocks but rather on the other side of the hill. Besides, these high walls which are in close proximity to the road were not benched so that the berms created due to the multiple benching would act as safety bays for any rock fall.
The uncontrolled construction of buildings and access roads on top of the heavily fractured hill aggravated the problem that led to slope failure, facilitating the movements of rocks down slope.
Clearing of the vegetation for farming along the slope, exposed the rock surface to water seepage into the fractures together with surface runoffs, and this can lead to rock fall, slope failures and potential landslides
Mining of dimension stones for building purposes along the Range can also lead to disturbances in the structure of the rock’s units affecting the slope stability leading to the rockfall Illegal quarry activities on this Range also causes instability of the slope base resulting in the weakening of the stability of the rocks.
The Ghana Institution of Geoscientists wishes to recommend that as a matter of urgency, safety buffer zones should be created from the road to the toe of the hill and thereafter stabilize any steep slope along the stretch through multiple benching.
Where necessary, various rock support techniques should be incorporated, such as rock or cable bolting, retaining walls, geosynthetics and the appropriate wire meshing. As a way forward and in order to minimise and forestall future occurrences of similar geohazards and other geoengineering activities, the GhIG hereby suggest that:
a. All materials for road construction, buildings and other civil works must be certified by a qualified Geoscientists. This is to ensure that these materials do not contain any injurious minerals that may not be suitable for the required building or civil works.
b. The GhIG stands in readiness to partner any governmental agency in the standardization of geomaterials suitable for road, buildings and any construction works so that all stakeholders will have value for money, safety, environmental stewardess that would ultimately lead to sustainable development.
Signed:
General Secretary-GhIG
(Crisler Akwei Ankrah)
0244 962 162
Public Affairs Officer
(Dr. Yvonne Sena Loh)
0244 878 847