Rates and Timescales of Fractional Crystallization from 238U-230Th-226Ra Disequilibria in Trachyte Lavas from Longonot Volcano, Kenya

A suite of peralkaline trachytes from Longonot volcano, Kenya,which erupted during the last 6000 years, has been analysedfor major and trace elements, Pb and Nd isotopes, and U–Th–Radisequilibria. The lavas are divided into three stratigraphicgroups of trachytes (Lt²a, Lt²b and Lt³), and hybrid lavas,designated LMx¹ and LMx², which, respectively, pre-date andpost-date the Lt² lavas. Major and trace elements are consistent,with up to 37% within-group fractional crystallization of predominantlyalkali feldspar. The parental magma for the different trachytegroups had a more mafic composition—probably hawaiitic.Nd and Pb isotopes show minimal variation, both within and betweenmagma groups, and indicate that up to 10% comendite magma fromthe neighbouring Olkaria volcanic field may have intermixedwith the Longonot magma. (²³⁰Th/²³⁸U) disequilibria indicatethat limited U/Th fractionation occurred during the past 10kyr, whereas (²²⁶Ra/²³⁰Th) disequilibria reflect the effectof alkali feldspar fractionation >8 kyr ago in the Lt²a lavas,between 3 and 7 kyr ago in the Lt²b lavas and in the past 3kyr for the Lt³ lavas. (²²⁶Ra/²³⁰Th) disequilibria in the Lt²blavas are interpreted using a model that combines the equationsof radioactive decay and in-growth with Rayleigh crystallizationto give fractionation rates of about 0·2 x 10^–4/yearfor the evolution of hawaiite to trachyte, but more rapid ratesof up to 3 x 10^–4/year for fractionation within the trachytesequence. (²²⁶Ra/²³⁰Th) from two whole-rock–alkali feldsparpairs are interpreted to show the crystals formed at 5800 yearsBP (Lt²b) and 2800 years BP (Lt³), implying that phenocrystformation continued almost up to the time of eruption. The resultsstrongly indicate that fractionated magmas can be stored forperiods on the order of 1000–2500 years prior to eruption,whereas other magmas were erupted as fractionation was proceeding. KEY WORDS: trachyte; magma chambers; u-series; Kenya     

Neotectonics and extension direction of the Southern Kenya Rift, Lake Magadi area

The Magadi area, located in the southern part of the Kenya Rift, is a seismically active region where rifting is still in progress. The recent tectonic activity has been investigated through a seismological survey and the study of neotectonic joints found in Lake Magadi sediments, which were deposited some 5000 years ago. The structural analysis of these open fractures was combined with a quantitative analysis of the orientation and size characteristics of imagery faults. The gathered data demonstrate (1) that the majority of the systematic joints have straight and parallel trajectories with a common en echelon mode of propagation displayed through a rich variety of patterns, and (2) that there is a self-similarity in fault and joint principal directions recognised at the different telescopic scales. SPOT image (1:125,000), aerial photos (1:76,000), and outcrop fieldwork reveal two important structural orientations which are N015°E and N015°W. The N015°E regional direction is consistent with the orientation of the southern segment of the Kenya Rift. Structural analysis is supported by results of a joint microseismic investigation in the Lake Magadi area. Obtained focal mechanism solutions indicate an E–W to ESE–WNW normal faulting extension direction.     

Forced Evictions in Kenyan Cities

Forced evictions are widespread in Kenyan cities and are, on the surface, caused by conflicts in land rights, non–payment of excessive land and house rents, and urban redevelopment. But, more fundamentally, evictions are due to factors embedded in the country's political economy, in particular, the grossly inequitable land ownership structure which makes it difficult for the poor to access land and decent shelter. Evictions cause significant socioeconomic hardship to individuals, affecting cities and whole nations. To avoid evictions, I argue that Kenya must make its political economy more inclusive, implement land reform, domesticate its municipal planning and related by–laws, and create a proactive slum settlements policy. This paper is based on secondary data, largely drawn from the extensive coverage of urban evictions in recent decades in Kenya's leading newspapers.     

From Shiny Shoes to Muddy Reality: Understanding How Meso-State Actors Negotiate the Implementation Gap in Participatory Forest Management

Recent research on participatory forest management (PFM) in the global south has highlighted the existence of a widespread “implementation gap” between the ambitious intent enshrined in legislation and the often partial, disappointing rollout of devolved forest governance on the ground. Here, through an ethnographic case study of forest officers (FOs) in Kenya, we draw on a framework of critical institutionalism to examine how key meso-level actors, or “interface bureaucrats,” negotiate and challenge this implementation gap in everyday forest governance. We go beyond consideration of institutional bricolage in isolation or as an aggregate category, to analyze how bricolage as aggregation, alteration, and/or articulation is variously driven, shaped, and constrained by FOs’ multiple accountabilities and agency. Our analysis highlights the locally specific, contingent, and mutually reinforcing nature of accountability, agency and bricolage, and their explanatory power in relation to the performance and nature of “actually existing” PFM.     

肯尼亚交通优势度及其空间分异格局分析

基于2018年肯尼亚铁路、公路、机场、港口等交通基础设施数据,设定交通优势度指数及交通网络连接度指数和交通对外通达度指数2个分指数,采用探索性数据分析法对肯尼亚交通优势度及其空间分异格局进行分析,并对其影响因素进行探讨。研究发现：① 肯尼亚交通优势度空间差异十分显著,以内罗毕、蒙巴萨和基苏木为主要交通节点的铁路沿线地区交通优势度水平明显高于其他地区;② 肯尼亚交通优势度空间分异格局总体上呈现出较强的非均衡性,交通网络连接度呈现出以内罗毕为核心,以铁路沿线为轴带呈圈层状向四周递减的空间分异格局,而交通对外通达度呈现出北部和西北部较低而南部和东南部较高的空间分异格局。③ 地形地貌、气候、水文、人口集聚、经济发展等是形成肯尼亚交通优势度空间分异的主要影响因素。对交通基础设施空间分布进行优化调整,积极引导经济空间合理布局,是推动肯尼亚经济健康持续发展的重要途经。     

Random walk, zonation and the food searching strategy of Terebralia palustris (Mollusca, Potamididae) in Kenya

Terebralia palustris is a common mud-whelk present at a particularly high density in all Indo-West Pacific mangroves. Young snails feed on nothing but mud while larger specimens are able to feed on fallen leaves too. In Kenya (Mida Creek) under the canopy, competition for mangrove leaves can be very high due to the high density of Sesarmidae crabs. On open exposed muddy platforms, no Sesarmidae occur but the leaf density is very low because the leaves are only randomly present as they are deposited and removed twice a day by the tide. However, the snail density is always very high, raising the question as to whether the snails use a special searching strategy to optimize their resource finding rather than a purely random movement. By analyzing the snails' movements on a uniform area at different levels and comparing them with simulated random paths, we could show that the snails' movements are not purely random. The distribution of different size classes of T. palustris in Mida Creek was known to be quite odd: the same simulation approach suggests that the zonation asymmetry could reasonably be due to the stochastic recruitment of juveniles in space and time and maintained by a substantial long-lasting spatial inertia.     

The dynamics of vulnerability: locating coping strategies in Kenya and Tanzania

We investigate how smallholder farmers at two sites in Kenya and Tanzania cope with climate stress and how constraints and opportunities shape variations in coping strategies between households and over time during a drought. On the basis of this analysis, we draw out implications for adaptation and adaptive policy. We find that households where an individual was able to specialize in one favoured activity, such as employment or charcoal burning, in the context of overall diversification by the household, were often less vulnerable than households where each individual is engaged in many activities at low intensity. Many households had limited access to the favoured coping options due to a lack of skill, labour and/or capital. This lack of access was compounded by social relations that led to exclusion of certain groups, especially women, from carrying out favoured activities with sufficient intensity. These households instead carried out a multitude of less favoured and frequently complementary activities, such as collecting indigenous fruit. While characterized by suitability to seasonal environmental variations and low demands on time and cash investments, these strategies often yielded marginal returns. Both the marginalization of local niche products and the commercialization of forest resources exemplify processes leading to differential vulnerability. We suggest that vulnerability can usefully be viewed in terms of the interaction of such processes, following the concept of locality. We argue that coping is a distinct component of vulnerability and that understanding the dynamism of coping and vulnerability is critical to developing adaptation measures that support people as active agents.     

Spatial and gender inequality in the Kenya certificate of primary education examination results

Kenya's 8-4-4 system of education consists of 8 years of primary education, 4 years of secondary education, and 4 years of university education. The system was introduced in 1985 with the primary aim of better aligning Kenya's education system with its development aspirations. In particular, the system sought to reduce youth unemployment by offering them life skills training as well as technical and vocational skills. At the completion of 8 years of primary education, students take the national Kenya Certificate of Primary Education (KCPE) exam which tests students in five courses: English, Kiswahili, mathematics, science, and social studies and religious education (SSR). However, since the adoption of the 8-4-4 system, no comprehensive study of the spatial distribution of KCPE exam scores, especially by gender has been done. Thus, this study examines nationwide performance on the 2011 KCPE exam by gender using Geographic Information Systems (GIS) and spatial statistics. Examination scores derived from approximately 17,217 public primary schools and 630,625 students were used in the study. Point pattern analysis was subsequently used to extract useful information from the dataset. A hot spot and cold spot analysis was then performed to see if unusual concentrations of scores exist in space in terms of overall performance, performance by gender, and individual subject scores. Our results show an existence of significant variability in terms of overall performance, performance by gender, and individual subject scores; with males outperforming females in mathematics, science, and SSR. Additionally, we found that proximity to major road networks and urban centers positively influences student performance on the KCPE exam probably because these factors influence the availability of educational resources (such as books and teachers), masterly of English (the language of instruction), teacher supervision, and child teachability.     

Impact of lake‐level changes on the formation of thermogene travertine in continental rifts: Evidence from Lake Bogoria,Kenya Rift Valley

Travertine is present at 20% of the ca 60 hot springs that discharge on Loburu delta plain on the western margin of saline, alkaline Lake Bogoria in the Kenya Rift. Much of the travertine, which forms mounds, low terraces and pool‐rim dams, is sub‐fossil (relict) and undergoing erosion, but calcite‐encrusted artefacts show that carbonate is actively precipitating at several springs. Most of the springs discharge alkaline (pH: 8·3 to 8·9), Na‐HCO₃ waters containing little Ca (<2 mg l^?1) at temperatures of 94 to 97·5°C. These travertines are unusual because most probably precipitated at temperatures of >80°C. The travertines are composed mainly of dendritic and platy calcite, with minor Mg‐silicates, aragonite, fluorite and opaline silica. Calcite precipitation is attributed mainly to rapid CO₂ degassing, which led to high‐disequilibrium crystal morphologies. Stratigraphic evidence shows that the travertine formed during several stages separated by intervals of non‐deposition. Radiometric ages imply that the main phase of travertine formation occurred during the late Pleistocene (ca 32 to 35 ka). Periods of precipitation were influenced strongly by fluctuations in lake level, mostly under climate control, and by related changes in the depth of boiling. During relatively arid phases, meteoric recharge of ground water declines, the lake is low and becomes hypersaline, and the reduced hydrostatic pressure lowers the level of boiling in the plumbing system of the hot springs. Any carbonate precipitation then occurs below the land surface. During humid phases, the dilute meteoric recharge increases, enhancing geothermal circulation, but the rising lake waters, which become relatively dilute, flood most spring vents. Much of the aqueous Ca²⁺ then precipitates as lacustrine stromatolites on shallow firm substrates, including submerged older travertines. Optimal conditions for subaerial travertine precipitation at Loburu occur when the lake is at intermediate levels, and may be favoured during transitions from humid to drier conditions.