Kenya Rift Research Articles

The tectonostratigraphic evolution of a Miocene half-graben, Kerio Valley Basin, East African Rift of Kenya: analysis of a 3 km thick volcano-sedimentary succession

The Kerio Valley Basin is a classic half-graben within the Eastern Branch of the East African Rift System, though to date its tectonostratigraphic evolution has only been interpreted through an incomplete stratigraphic record exposed along structural highs. This study examines a 3 km thick, volcano-sedimentary succession recorded within a hydrocarbon exploration well, Cheptuket-1, located within the hanging wall of the Kerio Valley Basin. A suite of silicic extrusive volcanic and volcaniclastic rocks are also recorded, calibrated by a dense collection of thin-sections from 84 side-wall cores. These volcanic rocks include phonolite lava flows. Through documentation of the well stratigraphy and integrating newly acquired 40 Ar/ 39 Ar age dates from outcrop, we detail a substantially revised, simpler tectonostratigraphic evolution of this basin. Cheptuket-1 penetrated a Middle Miocene to recent stratigraphic succession, bottoming in metamorphic basement, likely through a fault plane. Several phases of lake development are elucidated, including both pre- and syn-mechanical rifting, with the latter phase containing beds exhibiting high organic matter content. This study ultimately represents a rare insight into a near complete rift-basin hanging-wall succession, as well as detailing a workflow for characterising mixed volcanic and sedimentary successions.

Seroprevalence of dengue, yellow fever, and related flaviviruses among the rural human population in Nguruman and Kerio Valley, Kenya

BackgroundYellow fever virus (YFV) and dengue virus (DENV) are among the major re-emerging arboviruses that pose a significant threat to public health. Their associated burden and prevalence can be substantially underestimated due to insufficient surveillance and inadequate diagnosis. This study aimed to determine evidence of dengue, yellow and related flaviviruses circulation among the rural human populations residing in Nguruman (Kajiado County) and Kerio Valley (Baringo County), two dryland ecosystems in the Kenyan Rift Valley.MethodsSerum samples obtained from febrile patients between 5 and 85 years through a hospital-based cross-sectional survey from July 2020 – May 2023, were screened for neutralizing antibodies to YFV, DENV-2 and related flaviviruses, West Nile virus (WNV) and Zika virus (ZIKV) via Plaque reduction neutralization test (PRNT). The study sites and important demographic characteristics were obtained using a structural questionnaire and the data analyzed and seroprevalence compared. A multinomial logistic regression model was done to predict risk for each of the most prevalent viruses with covariates; age, gender, and occupation.ResultsOverall, 54.5% (50.1–59.0% 95% confidence interval (CI) of the samples tested positive for at least one of the four Flaviviruses. The percentage was significantly higher in Kerio Valley (64.34%, 184/286) than in Nguruman (40.2%, 78/194) (P<0.0001). YFV had the highest prevalence, followed by WNV (16.25%), ZIKV (5.2%), and DENV-2 (1%). Kerio Valley had a significantly higher YFV seroprevalence (51%) than Nguruman (6%) (P<0.0001), while DENV-2 was observed only in Nguruman with a low seropositivity of 2%. In contrast to Nguruman, where seropositivity rates were higher in males at 47.47% (P=0.049), in Kerio Valley, females showed considerably higher viral seropositivity at 60.82% than males (P<0001).ConclusionThe study suggests that there is significant circulation of Flaviviruses in both regions, posing a public health risk, that could potentially contribute to clinical disease. However, seropositivity rates vary for each specific site. Furthermore, there could be a risk of YFV, WNV, and ZIKV transmission in both sites with DENV transmission specifically noted in Nguruman. The study findings inform direct cost-effective actions (such as YF vaccines) and precise surveillance data of vector populations for improved disease risk prediction.

Exploring the Influence of Export Environment on Market Standard Dimensions and Horticultural Market Growth in South Rift, Kenya

The inclusion of rural smallholder farmers in the export of horticultural products has two major implications: increased household income through a promising global market, which is a catalyst for productivity, cumulatively growing Gross Domestic Product (GDP) and foreign exchange. So far, there are an estimated 2500 smallholder farmers who participate in the export of horticulture in Kenya. As a result, the current study sought to establish the influence of export environment on the relationship between market standard dimensions and export market growth of the horticultural products from small scale farmers in south rift of Kenya. The study collected quantitative data using a structured questionnaire from a sample of 334 small-scale horticultural farmers who were randomly selected. Validity and reliability tests were performed before the main study. Then, descriptive and multiple regression was used to analyze the data. Export environment was measured through: government support and services for export, government regulations and certifications and trade agreements and market access. Findings indicated that there was a statistically significant influence relationship between market standard dimensions and the growth of horticultural export market, where export environment on each predictor variable had the highest influence on market dynamics, followed by quality control, traceability and post-harvest handling practices being the least. This implies that the export environment plays a critical role in making the smallholder farmers’ products more competitive in export market. The study concluded that, appropriate policies, regulations and trade agreements were critical in market standards compliance. The government should create a framework to effectively disseminate information on trade agreements so as to benefit farmers and in addition establish collaboration between farmers, the government and private sector in export intervention measures. Keywords: Export, Horticulture, quality, Post-harvest, Traceability, Market

Growth of Horticultural Export Market: The implication of Post-harvest Handling Practices among Small Scale Farmers in South Rift, Kenya

The inclusion of rural smallholder farmers in the export of horticultural products has two major implications: increased household income through access to a promising global market and enhanced productivity, cumulatively contributing to the growth of Gross Domestic Product (GDP) and foreign exchange. Currently, there are an estimated 2,500 smallholder farmers participating in horticultural exports South Rift of Kenya. Consequently, this study aimed to investigate the relationship between post-harvest handling practices by smallholder farmers and the growth of the horticultural export market. Quantitative data were collected using a structured questionnaire from a sample of 334 small-scale horticultural farmers, randomly selected for the study. Validity and reliability tests were conducted prior to the main study. Descriptive statistics and simple linear regression were employed to analyze the data. Post-harvest handling practices were assessed through the utilization of packaging materials, storage facilities, energy supply, hygiene, and transportation facilities. The findings indicated a statistically significant relationship between post-harvest handling practices and the growth of horticultural export markets. However, deficiencies were observed among small-scale farmers in South Rift, Kenya, in managing horticultural products after harvest. The study recommended for strategic interventions for the adoption of modern technologies in every stage of the supply chain and establishes collaborations with key stakeholders in order to minimize cost of investment per farmer and ultimately enhancing market standards compliance and competitiveness in the fruit and vegetable export market. Keywords: Post harvest, storage, packaging, Hygiene, Export, Markets

Active deformation in the central section of the East African Rift from tectonic, volcanic, and hydrologic processes: Observations from satellite geodesy

The East African Rift System (EARS) is an active continental rift zone that hosts a diverse range of processes that result in recent and ongoing crustal deformation. To analyze these processes, we used Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) to complement the sparse GNSS velocity field with high resolution measurements of line-of-sight (LOS) deformation between 2015 and 2022. A broad survey approach was employed to detect new signals within the central section of the EARS, and to establish a baseline for future studies focused on tectonic, volcanic, and/or hydrologic deformation and change spanning geodetic time scales. With this regional approach, we were able to resolve signals varying over time-spans of a few weeks to several years that have magnitudes greater than ∼1 cm/yr. Our resulting deformation field shows a diverse range of signals related to the processes listed above as well as other unknown sources. This includes up to 8.5 cm/yr of groundwater-related subsidence in Nairobi, up to 70 cm of LOS displacement during the eruption of Nyiragongo in 2021, and steady uplift in the Manyara basin with a rate of 2.8 cm/yr. We update previously published InSAR measurements of Mount Suswa volcano, and the geothermal fields in Olkaria. We also show LOS change ranging between 2 and 5 mm/yr over a distances of approximately 200 km spanning the Kenya Rift with the greatest differential rates occurring south of Lake Turkana. More generally, our results highlight the ambiguity of relying solely on the sparse network of GNSS for studies such as those characterizing tectonic motion and rift opening. Such studies are likely missing many important signals and/or includes sites that are contaminated with signals unrelated to the target process.

Density structures of the upper mantle in the East African Rift System: implications for the evolution of intracontinental rifting

The East African Rift System (EARS) provides an ideal natural laboratory for studying the mechanisms of tectonic plate breakup and continental drift, as well as a unique perspective for exploring the maturation process of continental rifting and its drivers. This study combines high-resolution satellite gravity data and seismic tomography model with an integrated geophysical approach to reveal the density structures in the upper mantle of the EARS. The results show that the northeastern to central Congo and Zimbabwe Craton exhibit significant high-density anomalies extending up to 250 km, which is indicative of a thicker and more intact lithosphere. In contrast, the Uganda, Tanzania, eastern and southern Congo, and Kaapvaal Craton show shallow high-density anomalies underlain by low-density anomalies that are clearly derived from the deeper mantle, indicating a thining of the lithosphere with some degree of possible melting at the base. The various rift segments of the EARS exhibit different rift morphologies. The Main Ethiopian Rift and the Kenya Rift of the Eastern Rift Branch show strong low-density anomalies, indicating intense melting, which is much stronger than that observed in the Western Rift Branch. However, the two rifts may have originated from the same mantle uplift in which the low-density anomalies of the Eastern and Western Rift Branches connected in the deep upper mantle. The lower portion of the Malawi Rift exhibits weaker low-denstiy anomalies, which can be observed to the south of the Malawi Rift, extending further south as a continuation of the EARS. Combining the results of previous kinetics simulations and our density perturbation results, it can be inferred that the Eastern Rift Branch is mainly affected by active rifting, while the Western Rift Branch is affected by both active and passive rifting.

Formation mechanism of ground fissures in the Kenyan Rift: tectonics, sediments, and erosion

Formation mechanism of ground fissures in the Kenyan Rift: tectonics, sediments, and erosion

GIS-based AHP model for selecting the best direct use scenarios for medium to low enthalpy geothermal resources with hot springs in central and Western Kenya

Medium to low enthalpy geothermal resources (MLEGRs) in various Eastern African countries, Djibouti, Ethiopia, Kenya, Uganda, Tanzania, Rwanda, and Malawi, have received little attention from policymakers in the energy sector. Policymakers from these countries prioritize developing high-enthalpy resources for electric power production. Hence, many MLEGRs remain unused since they are assumed to pose higher risks of drilling unproductive deep wells. Besides, funding institutions prioritize high-enthalpy geothermal resources. Some MLEGRs have warm-to-hot springs with considerable flow rates and chemical constituents with varying concentrations. This study introduces a novel approach, using hydrogeochemical analysis of hot spring waters and a GIS-based AHP model, to select the best direct use scenarios for the warm/hot springs emanating from MLEGRs in central and western Kenya. The model is validated by contemporary commercial usage of the hot springs and similar studies in the study area. The stable isotope analysis revealed that the hydrothermal systems in Kenya are majorly recharged by meteoric water. In contrast, Kenya Rift Valley endorheic lakes, such as Lake Naivasha, Lake Nakuru, Lake Magadi, Lake Baringo, Lake Bogoria, and Lake Turkana, partly recharge some. Hence, they pose low risks of drying up during development and exploitation for thermal energy. The over 150 hot springs in Kenya produce warm to hot water with a thermal capacity of over 275 MWt. Hence, by harnessing the hot spring resources, Kenya can raise its direct use capacity from the current 18.5 MWt to about 100–200 MWt without drilling shallow or deep wells. The hot springs best suited for domestic use and aquacultural pond heating were selected as Narosura, Majimoto, Olchorro, Kipsegon, Kijabe, and Eburru. Those best suited for spas, bathing/ swimming pools, and volcanic geotourism were Lake Bogoria, Arus, Homa Hills, and Kariandusi. Overall, Lake Bogoria, Homa Hills, and Narosura hot springs were rated the best for direct use of hot springs.

Influence of prickly pear cactus (Opuntia stricta) on the socio-economic status of pastoral livelihoods of rangelands in the Northern Rift Valley of Kenya

This study aimed to evaluate the influence of the prickly pear cactus on the socio-economic status of pastoral livelihoods of rangelands in the Northern Rift Valley of Kenya. The prickly pear cactus (Opuntia stricta) is one of the most widespread and naturalized invasive species in the arid and semi-arid areas of Kenya, with serious negative consequences on rural livelihoods and the environment. The invasiveness of O. stricta is due to its productive and competitive advantages under marginal conditions, limited availability of pests and pathogens, and high reproductive potential. A descriptive survey design was used in this study. In this study, the socio-economic impact of the prickly pear cactus was examined in two sites located in the northern rangeland of the Rift Valley in Kenya. A purposive sampling technique with semi-structured questionnaires administered through an Open Data Kit was used to generate the primary data. In order to examine the influence of O. stricta on the socio-economic status of livelihoods, the study used linear regression analysis. The study concluded that an increase in cactus thicket negatively affects the livelihoods of the pastoral communities. This study recommends that support to the local communities from the government, as well as other developing agencies operating within the region, is necessary for the effective management of the invasive species. Furthermore, development plans for the region must also take into account the socio-ecological impact of the prickly pear cactus in the region.

Influence of mantle plume on continental rift evolution: A case study of the East African rift system

Mantle plume is an essential component of the mantle convection system, and its influence on the geodynamics of continental rifts is of great significance for understanding the crust–mantle interaction. The East African Rift System, as the largest continental rift in the Cenozoic and in the initial stage, provides an excellent option for studying the interaction between the mantle plume and the continental crust. Based on the data such as GPS, seismic tomography, and global crustal model, a viscoelastic-plastic 2D thermodynamic numerical model is established to reconstruct the evolution of the Afar depression, Ethiopian Rift, and Kenyan Rift. By comparing the differences between the models of the Afar depression, Ethiopian Rift, and Kenyan Rift, the relationship between the mantle plume and pre-existing structures and their influence on the evolution of continental rifts are discussed. The results show that the mantle plume can increase the depth of the rift faults, concentrate the distribution of the faults, and strengthen the control of main faults on the rifts, allowing the possibility of narrow rifts. Pre-existing structures control the fault styles and symmetry of the rifts and also the morphology of the mantle plume.

The >250-kyr Lake Chala record: A tephrostratotype correlating archaeological, palaeoenvironmental and volcanic sequences across eastern Africa

Regional tephrostratigraphic frameworks connect palaeoclimate, archaeological and volcanological records preserved in soils or lake sediments via shared volcanic ash (tephra) layers. In eastern Africa, tracing of tephra isochrons between geoarchaeological sequences is an established chronostratigraphic approach. However, to date, few long tephra records exist from sites with continuous depositional sequences, such as lake sediments, which offer the potential to connect local and discontinuous sequences at the regional scale. Long lake sediment sequences may also capture more complete eruptive histories of understudied volcanic centres. Here, we present and date the tephrostratigraphic record of a >250,000-year (>250-kyr) continuous sediment sequence extracted from Lake Chala, a crater lake on the Kenya-Tanzania border near Mt Kilimanjaro. Single-grain glass major and minor element analyses of visible and six cryptotephra layers reveal compositions ranging from mafic foidites and basanites to more evolved tephri-phonolites, phonolites, trachytes and a single rhyolite. Of these, nine are correlated to scoria cone eruptions of neighbouring Mt Kilimanjaro or the Chyulu volcanic field ∼60 km to the north; seven are correlated to phonolitic eruptions of Mt Meru, ∼100 km to the west; and four to voluminous trachytic eruptions of Central Kenyan Rift (CKR) volcanoes located ∼350 km to the north. The only rhyolitic tephra layer, a cryptotephra, correlates to the 73.7-ka BP (before present, taken as 1950 CE) Younger Toba Tuff (YTT) from Sumatra. Two of the CKR tephra layers provide direct ties with terrestrial sequences relevant to Middle Stone Age archaeology of the eastern Lake Victoria basin in Kenya. Absolute age estimates obtained by direct 40Ar/39Ar dating of 10 tephra layers are combined with six 210Pb and 162 14C dates covering the last 25-kyr and the well-constrained known age of the YTT to build a first absolute chronology for the full Lake Chala sediment sequence. The uninterrupted >250-kyr Lake Chala sedimentary archive represents a unique tephrostratotype sequence for eastern Africa, optimising the chronological value of tephra correlations in regional palaeoenvironmental, archaeological and volcanological research. Further study of cryptotephra in the Lake Chala sequence and additional geochemical characterisation and dating of ancient volcanic eruptions from nearby and further afield may eventually produce a regionally connected and detailed tephrostratigraphic framework for eastern equatorial Africa.

Making Rift Valley Fever Viral Particles Fluorescent.

Rift Valley fever virus (RVFV) is a mosquito-borne pathogen that represents a significant threat to both human and veterinary public health. Since its discovery in the Great Rift Valley of Kenya in the 1930s, the virus has spread across Africa and beyond, now posing a risk of introduction into Southern Europe and Asia. Despite recent progresses, early RVFV-host cell interactions remain largely uncharacterized. In this method chapter, we delineate the procedure for labeling RVFV particles with fluorescent organic dyes. This approach makes it feasible to visualize single viral particles in both fixed and living cells and study RVFV entry into host cells. We provide additional examples with two viruses closely related to RVFV, namely, Toscana virus and Uukuniemi virus. Furthermore, we illustrate how to utilize fluorescent viral particles to examine and quantify each step of the cell entry program of RVFV, which includes state-of-the-art fluorescence-based detection techniques such as fluorescence microscopy, flow cytometry, and fluorimetry.

Magma‐Assisted Continental Rifting: The Broadly Rifted Zone in SW Ethiopia, East Africa

AbstractThe Gofa Province and Chew Bahir Basin in the Broadly Rifted Zone (BRZ) between the southern Main Ethiopian Rift (sMER) and the northern Kenya Rift (nKR) record early volcanism and associated faulting in East Africa; however, the spatiotemporal relationships between volcanism and faulting remain poorly constrained. We applied apatite (U‐Th)/He (AHe) and zircon (U‐Th)/He (ZHe) thermochronometry to Neoproterozoic basement rocks from exhumed footwall blocks of the extensional Gofa Province and Chew Bahir Basin, and analyzed our result in the context of well‐dated regional volcanic units in the BRZ to unravel the interplay between tectonic exhumation, faulting and volcanism. Single‐grain AHe ages ranging from 1.0 to 136.8 Ma were recorded in 32 samples, and single‐grain ZHe ages from three samples range between 142.2 and 335.6 Ma. The youngest AHe ages were obtained from the Chew Bahir Basin and the narrow deformation zone in the Gofa Province. Our thermal modeling results reflect little or no significant regional crustal cooling prior to extensive volcanism, which started at about 45 Ma. Conversely, new and previously published thermal history models suggest that widespread crustal cooling related to regional extension occurred between ∼27 and 20 Ma. Thermal modeling results from subsets of samples indicate that following this initial diffuse extensional deformation, renewed exhumation occurred along a narrow zone within the Gofa Province and the Chew Bahir Basin during the middle to late Miocene (15‐6 Ma) and Pliocene (<5 Ma), respectively. The crustal cooling phases follow a regional trend in volcanic episodes. For example, initial cooling between 27 and 20 Ma corresponds with the end of widespread flood‐basalt volcanism (45–28 Ma), suggesting that spatially diffuse normal faulting may have initiated shortly after the emplacement of voluminous and areally extensive flood basalts. The Miocene and Pliocene shifts in deformation along the Mali‐Dancha and Bala‐Kela basins in the Gofa Province and the Chew Bahir Basin, respectively, may indicate strain localization during the late stage of rifting and ongoing tectonic interaction between the sMER and the nKR. Our results support the notion of crustal weakening by massive volcanism as a precursor to widespread extensional faulting, and thus offer further insights into magma‐assisted deformation processes in the East African Rift System.

Evaluation of in-situ stress orientations within the Central Kenyan rift, through analysis of borehole images of wells drilled in Menengai Geothermal field, Kenya

The Menengai Caldera is in a complex structural zone within the Kenyan Central Rift and hosts the Menengai Geothermal Field. In assessing the subsurface characteristics of many geological resources, knowledge of in-situ stress orientations and magnitudes at depth is essential. Acoustic televiewer logging campaigns carried out in Menengai Geothermal Field between 2018 and 2019 in the production zones of three geothermal wells, have provided an on-site assessment of horizontal in-situ stress orientation in an area lacking such data. Data generated from drilling-induced features in the Menengai Geothermal Field revealed that the average SHmax orientation for MW-34 is NW-SE, whereas the average SHmax orientation for MW-20B is NE-SW, and the average SHmax orientation for MW-15A is NNE-SSW. Subsurface variations of in-situ stress orientations are related to large-scale features such as fractures, fissures, and fault architecture in the geothermal field. The NW-SE SHmax in-situ stress orientation around MW-34 agrees with the Molo (TVA) structural orientation, the Menengai pre-caldera shield orientation, and the Aswa shear zone. The NNE-SSW strike direction of the southern Kenyan Rift Valley, which changes orientation at the triple junction, is compatible with the NE-SW and NNE-SSW SHmax orientations of MW-20B and MW-15A. MW-34 is aligned to the Solai TVA/Graben because of its NE-SW Shmin orientation. In addition, the MW-15A's almost E-W Shmin orientations coincide with the Kenyan Rift's extension direction, which corresponds to the orientation of the E-W striking horsetail fracture inside the Menengai caldera. Localized stress perturbations manifest as rotations of BOs or DITFs orientations along the well as a function of depth.

Influence of Inherited Brittle Fabrics on Continental Rifting: Insights From Centrifuge Experimental Modeling and Application to the East African Rift System

AbstractThe presence of pre‐existing fabrics at all lithospheric scales has been proven to be of primary importance in controlling the evolution of continental rifts. Indeed, observations from natural examples show that even in conditions of orthogonal rifting, when extension should result in simple fault patterns dominated by normal faults orthogonal to extension vectors, inherited fabrics induce complex arrangements of differently‐oriented extension‐related structures. This paper explored the influence of inherited fabrics on rift‐related structures by using a series of analog models deformed in a centrifuge. The models reproduced a brittle‐ductile crustal system and considered the presence of pre‐existing discrete fabrics in the brittle crust in conditions of orthogonal narrow rifting. These fabrics were reproduced by cutting the brittle layer at different orientations with respect to the extension direction. Modeling shows pre‐existing fabrics have a significant influence on rift‐related faults, provided that the angle between inherited fabrics and the rift trend is less than 45°. In these conditions, fabrics cause prominent segmentation of rift‐related faults and induce the development of isolated depocenters. Pre‐existing fabrics strongly influence the geometry of extension‐related structures, resulting in curved fault patterns and en‐echelon arrangement of oblique faults. These findings provide insights into the development of continental rift systems in nature: our modeling shows indeed significant similarities (i.e., peculiar fault architecture and geometries) with the faults in different sectors of the East African Rift System (e.g., the Magadi and Bogoria basin, Kenya Rift), testifying that reactivation of inherited fabrics is a paramount process in shaping continental rifts.

Controls on Quaternary geochemical and mineralogical variability in the Koora Basin and South Kenya Rift

The South Kenya Rift is comprised of a series of N-S-oriented grabens with sediments that preserve an approximate one-million-year environmental history that reflects the interplay of climate, tectonism and volcanism. This study attempts to disentangle the relative roles of these major controls by comparing the geochemical records preserved in three sedimentary basins. The study focuses on the Koora Basin using bulk geochemical data in a 139-m-long core. This record is then compared with geochemical data and environmental histories from a 196-m-long core at Magadi and outcrops in the Olorgesailie Basin. Four climatic phases (1000–850; 850–470; 470–400; 400–0 ka) are recognised at Koora, which can also be distinguished in the Magadi and Olorgesailie Basins. However, inter-basin contrasts also suggest that additional, non-climatic factors influenced these geochemical histories, particularly during four intervals. These include 1) the Magadi Transition (MT; ∼770–700 ka), 2) the Magadi Tectonic Event (MTE; ∼540 ka), 3) the Koora Instability Period (KIP; ∼325–180 ka), and 4) the Trona Precipitation Period (TPP; ∼105–0 ka). Prior to the MT, Zr/TiO2, La/Lu, Mo, As, V and Na/Ca in Magadi and Koora cores were similar but afterwards diverged. Major reductions in transition metals at Magadi during the MTE reflect tectonically-induced cross-rift drainage diversion. This contrasts with the Koora and Olorgesailie basins where these metals were constant from ∼1000 to 300 ka. The KIP represents a significant increase in volcanic inputs to the Koora Basin and increased geochemical variability. Bromine (Br), which reflects peralkaline volcanic activity and/or evaporative concentration, is elevated during the KIP at Koora but is below detection limits in the rest of the Koora core. Br in the Magadi core does not correlate with that in the Koora record, suggesting contrasting accumulation processes. The TPP represents a phase of trona precipitation at Magadi but not at Koora. This difference partly reflects increased magmatic CO2 rising along faults in the Magadi basin during a period of increasing aridity. Rare-earth element patterns indicate a major change at Magadi with many anomalies after about 325 ka to the present, caused by the development of hypersaline waters, which did not occur at Koora or Olorgesailie. The geochemical data from the three basins help to partially separate climatic controls from those related to volcanism, tectonism and local geomorphology.

The evolution of gully erosion in the Rift Valley of Kenya over the past 50 years

Gullies are common in areas of unconsolidated deposit soil, and relatively steep-sided erosion that spread quickly in depth and width over short periods may occur during heavy or extended rainfall and. Soil erosion has been recognized as the major cause of land degradation worldwide, especially in the East African Rift Valley of Kenya where thick layers of volcanic ash have been deposited. This paper reports the results of studying the evolutionary process of gully erosion and types of gullies in the East African Rift Valley in Kenya over the last 50 years using remote sensing images, field investigations, and UAV (Unmanned Aerial Vehicle) aerial photography. Forward expansion, backward expansion, new gullies, and road culvert gullies were classified according to their morphological evolution characteristics and then identified throughout the history of the valley over the past 50 years. The erosion length increase from forward expansion was the largest of the four categories, followed by backward expansion, new gullies, and road culvert gullies. Human activity and rainstorms are the main factors of gully erosion in the study area. Additionally, four types of gullies were also categorized according to their causes of formation via field investigation and testing: physically-induced gullies, artificially-induced gullies, pipe erosion-induced gullies, and fissure-induced gullies, and artificially-induced and fissure-induced gullies were the most common type of gully in the study area. The evolution of gullies poses a serious threat to the ecological environment since it can lead to grassland degradation, segmentation of landscape ecology, and the erosion of the survival environment of wildlife. In this regard, man-made and fissure-caused gullies are the most severe and should be investigated further.

Spatial and temporal control of the volcanic activities over the distribution of sediments in the Magadi basin, Kenya Rift

High-velocity layers in basins with significant sub-basalt coverage, such as the Magadi basin, can impede geophysical imaging of potential subsurface hydrocarbon deposits. Using magnetic and gravity methods, this study examines the influence of volcano-tectonic processes and the basement on the evolution of the Magadi basin. Regional-residual separation analyses identified key structures and signatures. Lineaments and depths of the causative sources were determined using Euler deconvolution. Butterworth low-pass filters on aeromagnetic data isolated depth-varying magnetic layer responses. The study demonstrates a westward displacement of volcanic flows in the Magadi basin, originating from nearly all volcanic plugs. Depocenters near the western boundary fault are more affected by westerly movements of the volcano-tectonic flows than depocenters near the eastern boundary fault. The Rift underwent internal compartmentalization, resulting in depocenters with unique and intermittent tectonic and sedimentary occurrences. Rift segmentation led to modifications in catchment areas, which caused sudden variations in sediment flux, ultimately leading to the isolation of the depocenters. This study identifies the initial compartmentalized depocenters of Nguruman, Koora, and Forty-six. The initial Nguruman depocenter is oriented SW-NE and spans approximately 2512 sq. km with a sediment thickness range of 2000–4000 m. The presence of horsts in the southern and northern parts precludes volcaniclastics from the depocenter. Active tectonics and inversion caused the initial Nguruman depocenter to split into two halves: the northern Musenke depocenter and the southern Pakase. Euler depth analysis indicates sedimentary formations are thicker in compartmentalized depocenters in Magadi's western and southern regions than near the eastern boundary fault. The sediment thickness range in the Koora basin is approximately 1000–3000 m, while Pakase on the western flank has a sediment thickness range of 2000–3800 m.

Diffuse soil CO2 emissions at rift volcanoes: Structural controls and total budget of the Olkaria Volcanic Complex (Kenya) case study

Continental rift systems are first-order emitters of deep-sourced CO2 but their impact on the global budget is largely unknown. For instance, the estimate of the total amount of deep-sourced CO2 released by the East African Rift (EAR) is largely undocumented due to the small number of direct measurements available and the impracticability of remote sensing methods induced by atmospheric noise. This study explores the degassing budget and the structural control of soil CO2 emissions at an active rift volcano aiming to implement the database of available direct measurements of EAR's volcanoes. We investigated soil CO2 degassing at the Olkaria Volcanic Complex, a large, multicentred, geothermally exploited volcanic complex in the southern portion of the Kenyan Rift. A total of 1158 soil CO2 flux measurements were collected on fumarolic fields or crosscutting unaltered major faults. The contribution of multiple sources of CO2 (biogenic background vs magmatic/hydrothermal) was tested using both graphical statistical analysis and the carbon isotopic signature (13C-CO2). Soil CO2 fluxes reached up to ∼5500 gm-2d-1. The emission of deep-sourced CO2 coupled with the structurally controlled hydrothermal fluid circulation, sums up to ∼280 tCO2 released per day by the entire complex. Finally, we provide an estimate of the total budget for soil CO2 of the rift, summing up the contributions of all volcanoes in the EAR.

Out of the Palaearctic: the Helophorus water beetles of the Afrotropical Region (Coleoptera: Helophoridae)

Helophorus Fabricius, 1775 (Coleoptera: Hydrophiloidea: Helophoridae) is an old and largely Holarctic genus of beetles, with most extant diversity concentrated in the Palae­arctic. As with a number of primarily northern temperate lineages, the genus has colonised the Afrotropical Region, with species described from the Ethiopian Highlands and southern Africa. Here, the Afrotropical Helophorus fauna is revised, based on a study of all primary types and additional material, including extensive recent collections from South Africa. The known Afrotropical fauna is shown to be comprised of six species, only three of which were previously described: H. aethiopicus Régimbart, 1907, from southern highland areas of Ethiopia, H. aethiops J. Balfour-Browne, 1954 known from summer and year-round rainfall areas of South Africa and Namibia and H. cooperi Orchymont, 1948, stat. nov., described as a subspecies of H. aethiopicus and still only known from the type locality in Ethiopia. To these, three new species are added: H. brumopluvialis sp. nov., widespread in winter rainfall areas of the Western and Northern Cape Provinces of South Africa, H. nyandaruaensis sp. nov. from mountains of the East African Rift in Kenya and H. simiensis sp. nov. from the Simien Mountains of northern Ethiopia. All species are (re)described in detail and illustrated with high-resolution photos. Known distributions are mapped and a key to species provided. It is suggested that the two South African species may have speciated allochronically, due to seasonal shifts in life cycle associated with the development of the winter rainfall regime in the Cape during the Plio-Pleistocene. Helophorus are hypothesised to have colonised the Afrotropics on at least two occasions from separate Palaearctic ancestors.