Mass movement mapping for geomorphological understanding and sustainable development: Tigray, Ethiopia

Mass movement topography characterises the escarpments and piedmont zones of the tabular ridges in the western part of the Mekelle outlier, Tigray, Ethiopia. Several types of mass movements can be distinguished. The first type is rockfall produced by 357 km rocky escarpments and cliffs during the rainy season. In the study area, every current kilometer of Amba Aradam sandstone cliff annually produces 3.7 m3 of rock fragments. However, this is an under-estimation of the actual cliff and escarpment evolution, which is also characterised by debris slides and small rock slides. In the debris flow class, three dormant flow types are recognised. The first type comprises preferential or undifferentiated mobilisations of the so-called plateau layers, the whitish sandy-clayey lacustrine deposits and the lower and upper basalts, and more especially, the swelling clays, derived from the basalts. These debris flows start on the nearly horizontal Amba Aradam Sandstone tabular extensions, jump over cliff recessions or even spurs, and go very far into the valley. In some instances parts of Amba Aradam sandstone and Antalo limestone cliffs are transported. Secondly, some debris flows take their origin in the Antalo limestone supersequence. It concerns deeply weathered layers resting upon aquicludes/aquitards. Finally, gigantic debris flows and rock slides occur around dolerite dyke ridges. About 20% of the total surface of the study area is occupied by landslide topography. Most of the landslides affect the steep edges of the table mountains or the dykes/sills. Mapping and listing of active and dormant mass movements increases knowledge in three domains which are crucial for sustainable development of the study area. The first one is geomorphological risk assessment. The distribution map of active rockfall and dormant landslides shows the areas where potential risks are located. Land use changes which improve the water infiltration capacity of dormant landslides, should be followed up. Secondly, the impact of global climate change on these risk areas can be assessed. The second domain is the water sector, which needs attention in the study area and in many parts of Africa. Landslides mobilised by hydrostatic pressures are related to the occurrence of aquicludes and aquifers. In the study area, landslide mapping led to the location of three aquitards, not described before. The third domain is the pedological mapping. In the study area, soil distribution is very well explained by the morphology and extension of dormant landslides. Finally, mapping of dormant landslides stimulates the academic debate on the geomorphological significance of mass movements in hillslope retreat in tropical areas.status: publishe

Soil–landscape relationships in the basalt-dominated highlands of Tigray, Ethiopia

Though knowledge about the distribution and properties of soils is a key issue to support sustainable land management, existing knowledge of the soils in Tigray (Northern Ethiopian Highlands) is limited to either maps with a small scale or with a small scope. The goal of this study is to establish a model that explains the spatial soil variability found in the May-Leiba catchment, and to open the scope for extrapolating this information to the surrounding basalt-dominated uplands. A semi-detailed (scale: 1/40 000) soil survey was conducted in the catchment. Profile pits were described and subjected to physico-chemical analysis, and augerings were conducted. This information was combined with information from aerial photographs and geological and geomorphologic observations. The main driving factors that define the variability in soil types found were: 1) geology, through soil parent material and the occurrence of harder layers, often acting as aquitards or aquicludes; 2) different types of mass movements that occupy large areas of the catchment; and 3) severe human-induced soil erosion and deposition. These factors lead to “red-black” Skeletic Cambisol– Pellic Vertisol catenas on basalt and Calcaric Regosol–Colluvic Calcaric Cambisols–Calcaric Vertisol catenas on limestone. The driving factors can be derived from aerial photographs. This creates the possibility to extrapolate information and predict the soil distribution in nearby regions with a comparable geology. A model was elaborated, which enables the user to predict soil types, using topography, geomorphology, geology and soil colours, all of which can be derived from aerial photographs. This derived model was later applied to other catchments and validated in the field.status: publishe

Sound therapy for cochlear implant users with tinnitus

Objective: Despite the positive effect of a cochlear implant (CI) on tinnitus in many patients, tinnitus remains a problem for a significant proportion of CI users. We investigated the acceptability and effect of sound therapy (a combination of natural background sounds and one concise tinnitus counselling session) on tinnitus and speech perception in CI users who still experienced tinnitus during CI use. Design and study sample: Thirty-two CI users (32–78 years) participated in phase 1: a test at the clinic to evaluate six background sounds provided by the sound processor. Eighteen out of the 32 CI users participated in phase 2: an optional take-home evaluation of 2 weeks without sound therapy, followed by 5 weeks with sound therapy, ending with an evaluation visit. Results: Thirty subjects (93.8%) found at least one background sound acceptable. In phase 2, a small improvement with sound therapy was found for tinnitus loudness, annoyance, and intrusiveness. 50% of the subjects subjectively reported benefit of sound therapy. Especially the sense of control on their tinnitus was highly appreciated. No detrimental effect on speech perception was observed. Conclusion: The background sounds were acceptable and provided tinnitus relief in some CI users with tinnitus during CI use