Western Escarpment Research Articles

Was there a low-altitude Younger Dryas Stadial glacier in south-east Wales? Re-interpretation of landforms and palaeo-climatic inferences

A glacial origin for cirque-like hollows cut into the western escarpment of the Usk valley near Abergavenny, South Wales has become widely accepted. Associated supposed extensive moraine ‘festoons’ have been depicted merging and contemporaneous with Last Glacial Maximum (LGM) deposits formed by ice occupying the adjacent Usk valley. We re-interpret these festoons as the product mainly of rock slope failures (RSFs) emanating from the hollows. A cirque glacier origin is preferred to account for a compact double-ridge feature in one of the hollows. The equilibrium-line altitude (ELA) of the reconstructed glacier (357 m) is >60 m lower than all similarly small, presumed Younger Dryas Stadial (YDS; c., 12.9–11.7 ka) glaciers elsewhere in South Wales. To test whether this glacier nevertheless might date from the YDS, we apply three approaches to reconstruct annual palaeo-precipitation amounts at the ELA, two based on relationships between accumulation and ablation for modern glaciers and the third on a simple degree-day model (DDM) using likely climatic characteristics for this event. The DDM can be tailored to represent the recognised large-amplitude YDS annual temperature range rather than the much smaller one experienced by modern glaciers, making it our preferred approach. Although conditions along the Usk valley escarpment during the LGM would have been well suited to cirque glacier formation, the DDM approach, using the large-amplitude annual temperature ranges, suggests that a YDS age might also be possible. The results have implications for re-assessing the likely ages of some former small glaciers in South Wales.

InSAR-based landslide hazard mapping and identification of at-risk infrastructures in a selected district of North Shewa Zone, Ethiopia.

The devastating nature of landslides demands a thorough understanding of their spatial distribution and the risks they pose to human settlements and infrastructural assets. In this study, we employed a combination of Interferometric Synthetic Aperture Radar (InSAR) and Geographic Information System (GIS) techniques to explore the western escarpment of the Main Ethiopian Rift, with a focus on selected districts within the northern Shewa Zone, Ethiopia. By analyzing the SAR data, we derived 28 displacement maps and utilized them to create a comprehensive landslide hazard zonation map. The results indicated significant ground displacement, particularly along the rift margins and areas characterized by rugged terrain. The hazard zones were classified based on their level of risk, with 44% classified as very low, 24% as low, 5% as moderate, 13% as high, and 14% as very high hazard zones. The accuracy of our results was evaluated using receiver operating characteristic (ROC) analysis, which was conducted utilizing landslide inventory data. The analysis demonstrated a remarkable area under the curve (AUC) value of 0.848, providing strong evidence for the validity of our findings. Additionally, our study involved a spatial and statistical assessment of major infrastructure, revealing that 20 to 28% of these properties were in hazard zones ranging from moderate to very high levels, which calls for efficient risk-reduction actions. Therefore, this finding enables stakeholders to identify high-risk areas, prioritize mitigation efforts, and minimize the impact of landslide disasters.

Determinants of plant community along environmental gradients in Geramo forest, the western escarpment of the rift valley of Ethiopia.

Detailed information on plant community types, distribution, and their relationships with various environmental gradients is crucial for understanding forest dynamics and sustainable forest management because plant community types are influenced by various environmental factors. Thus, this study was conducted to investigate plant community types and species diversity in relation to various environmental gradients in Geramo Forest, which is a remnant forest in the western escarpment of the Rift Valley of Ethiopia. Vegetation data were collected in 96 nested plots (20 × 20 m2 and five 1 ×1 m2) laid systematically at a distance of 250 m along 16 line transects, which were laid 300 m apart. Environmental and disturbance variables were also collected from each main plot. Agglomerative hierarchical cluster analysis and Canonical correspondence analysis (CCA) with R software were used to identify plant community types and analyze the relationship between plant community types and environmental variables, respectively. The Shannon Wiener diversity index was used to compute species diversity among community types. Five significantly different (p ≤ 0.001) plant community types were identified. The CCA results showed that species diversity and community composition among different community types were significantly influenced by altitude, disturbance, soil organic carbon, slope, soil available phosphorus, and pH, which revealed the compounded effect of various environmental factors on species richness, diversity, and evenness among plant community types. The study also identified a significant level of anthropogenic disturbance and a strong reliance of the local community on the forest in the research area. Therefore, it is recommended that sustainable forest conservation interventions be implemented through awareness creation and the promotion of community-based approaches.

Carbon stocks of Geramo forest, the western escarpment of the rift valley of Ethiopia

Forests play a vital role in the global carbon balance and combating global climate change by sequestering and retaining carbon from the atmosphere in their biomass and soil. Thus, this study aims to estimate the carbon stocks in the biomass and soil along with various environmental factors in the Geramo forest in southern Ethiopia. Ninety-six plots (20 × 20 m2) were laid at a distance of 250 m along 16 line transects that were laid 300 m apart. Five 1 × 1 m2 subplots (4 at the corner and 1 at the center) were laid inside each main plot for LHG and soil data collection. The results revealed that the estimated total carbon stocks and mean carbon stock densities of the study forest were 57994 Mg h−1and 604 ± 344 Mg h−1, respectively, with a mean CO2 equivalent of 2217 ± 1262 Mg h−1. This result indicates the remarkable role of the Geramo forest in carbon stock and sequestration potential compared with other remnant forests in Ethiopia. Thus, the Geramo forest plays a crucial role in climate change mitigation through carbon sequestration, and hence, this forest can generate carbon credits as financial benefits to the nearby population in the future. The results also revealed that anthropogenic disturbances were negatively associated with the carbon stocks of the forest. Therefore, sustainable forest conservation activities are needed to conserve forest resources, protect the forest from growing anthropogenic disturbances, and sustain its current global climate change mitigation and adaptation benefits.

Two new Poyntonophrynus species (Anura: Bufonidae) highlight the importance of Angolan centers of endemism

Abstract The pygmy toad genus Poyntonophrynus is endemic to southern Africa. The morphology of these small toads is conserved. They are usually dully colored, and are predominately adapted to arid conditions. During recent surveys in Angola we found Poyntonophrynus specimens that were not assignable to known species. Using an integrative approach, based on mitochondrial and nuclear DNA, morphology, osteology, biogeography and ecology, we identified three new lineages, and describe two of them as new species. All three lineages are closely related to P. pachnodes, an Angolan endemic species, but they are geographically isolated from it. The new species are morphologically distinguishable, and are associated with two of the most important Angolan centers of endemism: the western escarpment and the central highlands. In order to get a more comprehensive understanding of the osteology of the genus, we also provide an osteological characterization of P. dombensis, which was not available to date. Our findings i) increase the number of earless species in the genus Poyntonophrynus, ii) emphasize southwestern Africa as the cradle of diversification in this genus, iii) report the occurrence of Poyntonophrynus in humid environments, thus showing that these toads are ecologically more variable than previously thought, and iv) underline the importance of further biodiversity studies in Angolan centers of endemism.

Evaluate and analyze land cover change dynamics, driving force and their implications to biodiversity in the western escarpment of the Rift valley

AbstractLand use land cover (LULC) changes are caused by natural and human alterations of the landscape that could largely affect forest biodiversity and the environment. The study aimed to analyze LULC change dynamics and driving forces in the western escarpment of the rift valley of the Gamo Zone, Southern Ethiopia. Digital satellite images, which are downloaded from USGS, were analyzed using ERDAS Imagine (14) and Arc GIS 10.2 software and supervised image classification was used to generate LULC classification, accuracy assessment, and Normalized Difference Vegetation Index (NDVI). Drivers of LULC change were identified and analyzed. Four land classes were identified such as forest, farmland, settlement, and water‐wetlands. Settlement and farmlands have increased by 8% and 6%, respectively. On the other hand, both forest and water‐wetlands decreased by aerial coverage of 9% and 5%, respectively. The overall accuracy of the study area was 92.86%, 94.22%, and 94.3% with a kappa value of 0.902, 0.92, and 0.922, respectively. NDVI values ranged between −0.42 and 0.73. Agricultural expansion (31.4%), expansion of settlement (25.7%) and Fuelwood collection and Charcoal production (22.9%) were the main driving forces that affected the biodiversity of the vegetation in the study area. Integrated land use and policy to protect biodiversity loss, forest degradation and climate changes are deemed necessary.

Bridging Ethnoarchaeology and Archaeology in the Ethiopian Gamo Highlands

ABSTRACT This article is a case study that applies long-term ceramic ethnoarchaeology to recent archaeological research in the Gamo region of Ethiopia. The region is located on the western escarpment of the Great Rift Valley. Today, an important cultural characteristic of the Gamo is their caste system. They divide society into occupational castes including Mala farmers and Tsoma artisans who are segregated in their access to land and food resources. Working collaboratively with Gamo Boreda elders, we located a historic Mala household at the archaeological site of Ochollo Mulato (1270–1950 CE) and an artisan household at the archaeological site of Garu (eighteenth and nineteenth centuries CE). The historic archaeological pottery assemblages from Ochollo Mulato and Garu are considered in light of thirty years of Gamo ceramic ethnoarchaeological research to understand changes in subsistence and social organization through time.

The Crystal-Wonder Cave System: A New Hotspot of Subterranean Biodiversity in the Southern Cumberland Plateau of South-Central Tennessee, USA

The Crystal-Wonder Cave System developed in the Western Escarpment of the southern Cumberland Plateau in the Interior Low Plateau karst region of south-central Tennessee, USA is a global hotspot of cave-limited biodiversity. We combined historical literature, museum accessions, and database occurrences with new observations from bio-inventory efforts conducted between 2005 and 2022 to compile an updated list of troglobiotic and stygobiotic biodiversity for the Crystal-Wonder Cave System. The list of cave-limited fauna includes 31 species (23 troglobionts and 8 stygobionts) with 28 and 18 species documented from the Crystal and Wonder caves, respectively, which represents five phyla, ten classes, nineteen orders, and twenty-six families (six arachnids, three springtails, two diplurans, three millipedes, six insects, three terrestrial snails, one flatworm, five crustaceans, and two vertebrates, respectively). The Crystal-Wonder Cave System is the type locality for six species—Anillinus longiceps, Pseudanophthalmus humeralis, P. intermedius, Ptomaphagus hatchi, Tolus appalachius, and Chitrella archeri. The carabid beetle Anillinus longiceps is endemic to the Crystal-Wonder Cave System. Sixteen species are of conservation concern, including twelve taxa with NatureServe conservation ranks of G1–G3. The exceptional diversity of the Crystal-Wonder Cave System has been associated with several factors, including a high dispersal potential of cave fauna associated with expansive karst exposures along the Western Escarpment of the southern Cumberland Plateau, a high surface productivity, and a favorable climate throughout the Pleistocene.

Petrological and geochemical characteristics of flood and shield basalts from Kesem-Megezez section, northwestern Ethiopian Plateau: Implication for their mantle source variations

The Kesem-Megezez Section is located on the western escarpment of the main Ethiopian rift, central Ethiopia, part of the northwestern Ethiopia plateau, and hosts both flood basalts (Kesem Oligocene basalts) and shield volcano basalts (Megezez Miocene basalts) separated by an Oligo-Miocene silicic pyroclastic formation. Petrography, whole-rock trace, and major element data are presented for the Kesem Oligocene and Megezez Miocene basalts to assess their petrogenetic characteristics and the processes involved in their evolution. The Kesem Oligocene basalts are dominated by aphanitic textures, whereas the Megezez Miocene basalts are dominated by porphyritic textures. The Kesem Oligocene basalts are alkaline, whereas the Megezez Miocene basalts have transitional composition. The Kesem Oligocene basalts and Megezez Miocene basalts show distinct compositional differences. MREE/HREE and LREE/HREE show different depths of melt segregation and degrees of partial melting for the Kesem Oligocene basalts and the Megezez Miocene basalts. The geochemical differences (Zr/Nb, Rb/Zr, K/Nb, Ba/Zr and Nb/Zr) between Kesem alkaline basalts and the Megezez transitional basalts reflect the involvement of EMORB-like and OIB-like mantle sources in different proportion in their petrogenesis. Using primitive mantle, garnet- and spinel-bearing lherzolitic sources, a non-modal equilibrium melting model shows that the Kesem alkali basalt can be produced by equilibrium melting of ∼3–4% residual garnet and about 3% degree of partial melting. Whereas, the Megezez transitional basalts were formed by melting of ∼2–3% residual garnet and >3% degree of partial melting. Geochemical evidences envisioned a scenario in which magmatism started with the arrival of a mantle plume (OIB-like; aka Afar Plume), which comes across a sub-lithospheric geochemically enriched and fertile asthenospheric mantle component (EMORB-like). The upwelling of the hot mantle plume that impinging beneath the lithiosphere at ∼30 Ma generates OIB-type melts due to decompression. The thermal effect of the hot plume also triggered melting of the fertile E-MORB component in the asthenosphere at the garnet stability depth. Then, the interaction between more melts from the plume (OIB) and lesser melts from the E-MORB created flood basalts (Kesem basalts) in the Oligocene. During the Miocene, the progressive melting of OIB and E-MORB generates the plateau shield basalts (Megezez basalts).

Fern Cave: A Hotspot of Subterranean Biodiversity in the Interior Low Plateau Karst Region of Alabama in the Southeastern United States

The Fern Cave System, developed in the western escarpment of the Southern Cumberland Plateau of the Interior Low Plateau karst region in Northeastern Alabama, USA, is a global hotspot of cave-limited biodiversity as well as home to the largest winter hibernaculum for the federally endangered Gray Bat (Myotis grisescens). We combined the existing literature, museum accessions, and database occurrences with new observations from bioinventory efforts conducted in 2018–2022 to generate an updated list of troglobiotic and stygobiotic species for the Fern Cave System. Our list of cave-limited fauna totals twenty-seven species, including nineteen troglobionts and eight stygobionts. Two pseudoscorpions are endemic to the Fern Cave System: Tyrannochthonius torodei and Alabamocreagris mortis. The exceptional diversity at Fern Cave is likely associated with several factors, such as the high dispersal potential of cave fauna associated with expansive karst exposures along the Southern Cumberland Plateau, high surface productivity, organic input from a large bat colony, favorable climate throughout the Pleistocene, and location within a larger regional hotspot of subterranean biodiversity. Nine species are of conservation concern, including the recently discovered Alabama cave shrimp Palaemonias alabamae, because of their small range sizes, few occurrences, and several potential threats.

POWOJENNA ODBUDOWA ZAMKU KSĄŻĄT GRYFITÓW POMORSKICH W SZCZECINIE

Rebuilt in the years 1958-1980 in the Renaissance style with elements of Gothic, the Castle of the Pomeranian Dukes from the Griffin dynasty in Szczecin is located on a promontory of the high western escarpment of the Odra river valley, within the non-existent medieval perimeter walls of the city, in the area of today's Rycerska, Kuśnierska, Mściwoja and so-called Castle Route. Below the castle, there is a partly rebuilt lower town called Podzamcze. Reconstructed in Renaissance forms, the castle is one of the archaeologically and architecturally well-recognized objects of the Duchy of Gryfit. Szczecin's medieval Old Town was almost completely destroyed during American and British air raids on the Szczecin ship base in 1942. It caused the greatest destruction in the history of the Old Town and the castle located in its immediate vicinity. The degree of destruction of the Szczecin castle after the war, as well as the entire Old Town, was estimated at 85%. No elements of the interior furnishings of the castle have survived, except for individual pieces of furniture stored in the cellars. Valuable paneling and wooden furnishings were burnt down in a fire that lasted for many days after the bombing. The preserved buildings were completely unknown to Poles, not related to Polish tradition and history, so it was considered whether they should not be completely demolished, and the area cleared of rubble should be used for new buildings. This is what happened to a large part of the Old Town, where only a few buildings have survived, the technical condition of which allowed their further use. The reconstruction of the castle began in 1956 and was basically completed in 1985, taking into account new program elements, allocating the rooms of the castle, mainly for cultural purposes. In order to preserve the historic character of the building, scientific and conservation supervision over the reconstruction of the castle was carried out by art historians: Dr. Henryk Dziurla from Wrocław (until 1960) and residents of Szczecin: Dr. Zbigniew Radacki in the years 1960-1984 and Krystyna Kroman after 1984. A multi-stage renovation of the former duke's castle was started in 2005, combined with the modernization and change of the technical equipment of the rooms. The unknown stone foundations dating back to the 12th century were discovered under the main courtyard of the Pomeranian Dukes' Castle in 2012.

Petrogenesis of Butajira-Kibet Quaternary basaltic rocks; Central Main Ethiopian Rift

Major and trace element data are presented for Quaternary basalts from Butajira-Kibet area, close to the western escarpment of the Central Main Ethiopian Rift to investigate the petrogenetic processes involved and the nature of mantle source compositions. The data indicate that the basalts are mildly alkaline characterized by moderate to high contents of MgO (6.85-9.00 wt. %) and TiO2 (2.40-2.92 wt. %). In the primitive mantle-normalized multi-element diagram, they exhibit troughs at Th, U, Rb and K and peaks at Ba, Nb, Ta, La, Pb and Sr with positive Eu/Eu*(1.01-1.17). Incompatible element ratios e.g., Ba/Nb (8.92-16.25), Rb/Nb (0.42-0.70), K/Nb (233.00-340.00) and Nb/U (47.97-61.05) suggest that the basalts are unaffected by crustal contamination. The acquired data do not evidence fractionation of plagioclase and clinopyroxene. On the other hand, relationships between major elements and their ratios (e.g., Na2O and Ca2O/Al2O3) and trace element ratios (e.g., Zr/Y and (La/Sm)N) indicate partial melting of a clinopyroxene - rich mantle at medium pressure. Chondrite - normalized REE diagram is characterized by relatively flat HREE (TbN/YbN=1.73-2.13) and significantly enriched HREE (higher than 10-times chondritic values) patterns. LREE/MREE versus MREE/HREE modelling of non-modal batch melting indicates that the basalts are formed by 1.5-3% partial melting of spinel peridotite mantle source with minor contribution from garnet-bearing peridotite. Primitive mantle-normalized multi-element diagram and trace element ratios, such as Nb/Zr, Nb/U, Ba/La, Rb/Zr and Ba/Nb, suggest that the studied basalts are not affected by carbonatite and/or hydrous phase metasomatism. Rather, they are closely similar to the OIB source (mainly EM-I) and the SCLM. They are most likely the result of significant interaction of melts from a mantle plume and the SCLM.

Middle Pennsylvanian (Desmoinesian) Fusulinids of the Bug Scuffle Limestone Member of the Gobbler Formation, Sacramento Mountains, South-Central New Mexico

Analysis of fusulinids from the Bug Scuffle Limestone Member of the Gobbler Formation along the western escarpment of the Sacramento Mountains in south-central New Mexico demonstrates that all four Desmoinesian regional fusulinid zones documented in Midcontinent and Southwest North America are present in the stratigraphic unit. Earliest Desmoinesian (Df1 Zone) fusulinids from the basal Bug Scuffle limestone beds suggest that the carbonate unit transgressed northward on the Sacramento Shelf, with Beedeina insolita in basal beds of the southernmost canyon exposures, and the slightly more advanced B. hayensis and B. curta in basal limestone beds of more northern outcrops. Late early Desmoinesian (Df2 Zone) fusulinids are common and widespread throughout the escarpment outcrop belt indicating that it was the time period with the most widespread normal marine shelf paleoenvironmental conditions. The diverse assemblage of the Df2 Zone is characterized by Beedeina novamexicana, B. euryteines, B. leei, B. socorroensis, B. joyitaensis, Wedekindellina euthysepta, and W. excentrica. The microprobematical branching fossil Komia is also common in this zone. Wedekindellina and Komia do not range above the mid-Desmoinesian CSB1 composite sequence boundary. Above that sequence boundary, the early late Desmoinesian Df3 Zone is characterized by sparse Beedeina haworthi, and the closely related B. illinoisensis and B. tumida. The late late Desmoinesian Df4 Zone is represented by a diverse assemblage of fusulinids in the uppermost part of the Bug Scuffle Limestone Member in the southern canyon exposures, including Beedeina acme, B. megista, B. mysticensis, B. lonsdalenesis, B. bellatula, B. gordonensis, and B. vintonensis. No Beedeina identifiable to species were found in upper part of the Bug Scuffle Limestone Member in the northernmost canyon exposures, demonstrating that late Desmoinesian paleoenvironments became more restricted marine northward along the Sacramento Shelf. Above the CSB2 composite sequence boundary in the uppermost Bug Scuffle Limestone Member, the lower part of the uppermost depositional sequence continues to contain latest Desmoinesian Df4 Zone fusulinids in the southern canyon sections. Early Missourian conodonts have been reported in a limestone unit near the top of the Gobbler clastic detrital member in the north-central part of the outcrop belt(Wahlman and Barrick 2018; Lucas et al. 2021), but no early Missourian conodonts or fusulinids have been reported yet from the uppermost Bug Scuffle Limestone Member in the southern canyons.

Vegetation Structure and Regeneration Status of the Western Escarpment of the Rift Valley of the Gamo Zone, Southern Ethiopia

Understanding the structure and regeneration of forest resources contributes to identifying the elements of diversity, endemism, threatened and endangered species. This study was conducted in the western escarpment of the Rift valley of the Gamo Zone, Southern Ethiopia. The main objective was to investigate structure and regeneration status of the study area. A systematic sampling method was used to collect vegetation data from a total 102 quadrats, each 20 × 20 m (400 m2) and five 1 × 1 m (1 m2) sub-quadrats were established at the four corners and at the centre for sapling and seedling estimation. Tree and shrub species were listed; Height (H ≥ 1.5 m) and DBH ≥ 2 cm were measured and recorded. R-statically software and Microsoft Excel were used to record and analyse the data. A total of 126 plant species belonging to 43 families and 90 genera were identified. The most dominant families were Fabaceae, followed by Anacardiaceae and Euphorbiaceae. Most frequent species were Euclea divinorum (84.3%), followed by Rhus natalensis (83.3%), Terminalia brownii (74.5%). DBH class ≤ 5cm had highest density (63.6%) and DBH ≥ 25.1 cm had the lowest density (0.87%). Three population patterns have been observed; inverted J, J-shaped and irregular shaped. 93% of species had IVI values b/n 1 - 4, 65% of species IVI values Pappea capensis, Combretum molle, Terminalia brownii, Euclea divinorum had highest IVI values. In the vertical stratification, lower story was 91.3% of the individuals. Only a few species contributed to the high density of saplings (440.2/ha) and seedlings (825.49/ha) while most had very little or no saplings and seedlings at all. Thus, in order to revert the current forest structure and regeneration to the previous natural state, it is considered important to minimize the influence of the human interference, grazing and raising awareness to surrounding community.

Evaluation of Chemical Application as Pilot to Improve Oil Production from High Viscous Oil in Sandstone Reservoir

Chemical injection stimulation is one of worldwide proven technologies for viscosity reduction and mobility enhancement. The principle mechanism is to reduce heavy oil viscosity by injecting of active chemical agent solution into reservoir as huff and buff practice, the agent solution is act at near wellbore area by remove plugging of heavy organic material, Energy support due to large quantity of stimulation liquid being injected into the formation, viscosity reduction by emulsification and micro-emulsion which will greatly enhance oil mobility; therefore, accelerate oil recovery and reduce interfacial tension (IFT); therefore, increase oil recovery. as global oil industry many technologies introduced to Sudanese oil fields such as chemical which had been implemented in 2018 to increase oil production by developing high viscous oil reservoirs. The pilot was done in two wells in Moga and Fula fields; they are located at southern part of western escarpment trend of Fula sub-basin, Main oil-bearing distributes in Aradeiba, Bentiu and Abu Gabra formations. Bentiu formation was selected for pilot, it is consolidated medium productive sand stone reservoir as per well test interpretation productivity index is 0.05 to 0.2 bbl/day/psia, PVT features: low bubble point pressure, low gas oil ratio (GOR), viscosity at initial pressure between 396–5902 mPa.s and 8986–13880 mPa.s at surface pressure and 29°C, permeability lab test results show strong heterogeneity formation. This paper discusses the chemical injection as enhanced oil recovery (EOR) application in block-6, investigate and evaluate pilot results, then discuss lesson learned from this pilot. Basic reservoir engineering principles and lab test result had been used to calculate production and reservoir parameters before and after implementation. The results of first well shows instantaneous downhole fluid level (DFL) raising about 129 m and remain stable while same pump speed was maintained after the chemical injection, the water cut dropped from 64% to 42% and Oil rate jumped from 95 BOPD to 204 BOPD. second well shows bad performance post the chemical injection and the oil rate decreased from 60 to 40 BOPD and WC increased from 70% to 93% due to well located in the down dip close to OWC and strong reservoir pressure support.

AHP based analysis of groundwater potential in the western escarpment of the Ethiopian rift valley

ABSTRACT This study investigated groundwater potential in the Western escarpment of the Ethiopian Rift valley, taking Dijo catchment as a case study, an area that is known for its critical shortage of water. Different thematic layers were used to determine the groundwater potential of the catchment. PCI Geomatica and Rockwork were used to automatically extract lineament and lineament orientation, respectively. Weights of parameters were computed using the analytical hierarchy process (AHP). Rank was assigned to each feature class for each thematic map according to their characteristics and interrelationship with groundwater. Once the mapping was done, validation of the estimated result was done. Accordingly, the result indicates that there is a matching between the analysis results and samples taken from boreholes with an accuracy result of 79.2%. The results revealed that nearly half of the catchment was found to have high-to-very-high groundwater potential while the remaining exhibiting limited potential for groundwater. Despite the high potential, there is a critical shortage of water. This is partly attributed to poor planning and limited capacity in identifying water resource potential. Thus, we suggest that efforts should be made to exploit the available water resources thereby to solve the societal problem.

Erosion rates and weathering timescales in the eastern Great Escarpment, South Africa

The eastern escarpment in South Africa has a combination of geology and climate that is unique in the entire Great Escarpment. Yet, no studies have been undertaken before to quantify the landscape changes at this locality. In this study, we assess the denudation history of the eastern escarpment using cosmogenic beryllium-10 (10Be) on quartz from rock outcrops and river sediments, and carry out uranium‑thorium‑helium ((U,Th)-He) and argon‑argon (40Ar/39Ar) dating of Fe-oxides and Mn-oxides, respectively, in the soils. The erosion rates obtained on the eastern escarpment vary from 1.8 m/Ma to 24 m/Ma and are similar in range to values from the entire Great Escarpment. We found that the catchment-averaged erosion rates of the gentle catchments above the eastern escarpment are lower, whereas those from steep catchments draining the escarpment edge are higher. We also determined that the catchment-average erosion rates of the eastern escarpment are similar to those of the western escarpment in Namibia, lower than those of the Drakensberg Escarpment and lower than those of the Lowveld adjacent to it. The 40Ar/39Ar dating of cryptomelane-bearing Mn nodules yield Palaeoproterozoic ages unrelated to the pedogenic processes, and might indicate that these nodules are not pedogenic, but inherited from weathered bedrock. The (U,Th)-He ages of goethite concretions range from 0.85 Ma to 1.05 Ma and they date the last period of intensive chemical weathering on the eastern escarpment, which coincides with the Mid-Pleistocene Transition from humid to more arid conditions on the southern African subcontinent. Given the low erosion rates above the escarpment, an area that experiences intensive chemical weathering, and the high erosion rates down the escarpment we conclude that at the eastern escarpment, pediplanation is a more important driver of denudation than peneplanation.

Tectonic conditioning revealed by seismic refraction facilitates deep-seated landslides in the western escarpment of the Main Ethiopian Rift

Landslide is a geo-hazard phenomenon that has been taking lives and causing severe property damages all over the world mostly in mountainous areas. The Main Ethiopian Rift has a unique tectonic setting with complex geological and geomorphological features, coupled with continuously deteriorating environmental conditions, which made its escarpments vulnerable for landslides. The study area is located near the Debre Sina town, within the Yizaba Wein locality, which has been severely affected by frequent landslide problems. This work was carried out using a multidisciplinary approach based on geological, geomorphological, kinematic analysis and geophysical survey. Seismic refraction investigations were carried out along the Yizaba Wein landslide main scarp to determine the depth to the bedrock and to the failure plane, to assess the stability of the slope, to locate possible structural features and to identify the extent of recent landslide activity, and to study the subsurface situation. The seismic measurements were made along three nearly orthogonal survey lines in the recently affected area. A high-resolution 2D P-wave survey was conducted using a 24-channel seismic unit. The seismic refraction results revealed four layers of geomaterials with distinct physical characteristics that contained a subsurface landslide anomaly within the layers. The layers were interpreted according to the major lithological units, from top to bottom: (i) clay, loosely cemented colluvial sediments and highly weathered agglomeratic basalt; (ii) highly to moderately fractured porphyritic basalt, ignimbrite-volcanic ash and rhyolite/trachyte; (iii) moderately to slightly fractured ignimbrite, rhyolite/trachyte and basalt and (iv) very strong, massive, fresh rock/bedrock. Faults and weak zones have also been identified in the bedrock based on the abundance of fractures and subsidiary faults resulting from damage of rocks and change of lithology due to variable fault rock formation strongly influencing the wavefield distribution which usually causes a local decrease of the velocity value. The main findings show that the landslide in the Yizaba Wein locality was caused by its complex geological-structural setting and downslope movement of the underlying pyroclastic sediment facilitated by heavy rainfall. Considering the similar geological and tectonic settings, similar mechanisms can be assumed for other landslides along the rift margins and associated highlands of Ethiopia.

Evaluating escarpment evolution and bedrock erosion rates in the western Guadalupe Mountains, West Texas and New Mexico

The Guadalupe Mountains tower above surrounding plains and basins in western Texas and southeast New Mexico. Although this mountain range is extensively studied for the Permian stratigraphy related to the petroleum reservoirs in the adjacent Delaware Basin, little is known about the geomorphic history. The western escarpment, in particular, rises abruptly from the Salt Basin to the west of the range, and Guadalupe Peak rises ~1600 m above the surrounding landscape. This study investigates how geologic processes create and maintain the steep profile of the escarpment on the western boundary of the Guadalupe Mountain Range. In-situ produced cosmogenic nuclides were used to quantify erosion rates across the steep western front of the range to assess how tectonic, climatic, and lithologic forces influence the escarpment profile. Erosion rates range from 1 to 73 m/Myr. Faster erosion rates in the southern area of the escarpment coincide with more frequently mapped faults, higher elevations at the top of the Rim, and locations with colder temperatures and higher precipitation. Topographic profiles across the western escarpment surfaces indicate greater retreat from the original positions of fault surfaces at the north end of the mountain range. Faster erosion rates in the mountain range are linked to greater uplift and more recent activity in the southern end of the Guadalupe Mountains.

Othonna koos-bekkeri, a new succulent shrub from northern Namaqualand and southern Richtersveld, (N. Cape Province, South Africa)

Othonna koos-bekkeri is a new shrubby Othonna from the mountains of the western escarpment in the Northern Cape. It is immediately recognized by its ascending rod-like stems and lateral ascending spreading spur-shoots and sub-umbellate yellow flower heads, the latter flowering during autumn when the plants are leafless. In the past, it was often confused with Othonna arbuscula, a smaller species widespread in the Succulent Karoo Biome.