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Risk perception is an essential element to consider for effective risk management at time of eruption, especially in densely populated cities close to volcanoes. The city of Goma in the East of the DR Congo is one these cities highly exposed to volcanic hazards and highly populated. The perception of volcanic risk involves the processes of collecting, selecting and interpreting signals about uncertain impacts of volcanic hazards. Using a questionnaire survey, this study describes the spatial variation and factors influencing the individual volcanic risk perception of 2204 adults from height representative neighbourhoods of the city of Goma before the May 2021 Nyiragongo eruption. A composite risk perception indicator was built from the perceived likelihood of occurrence of volcanic hazards and of their impacts and from the perceived likelihood of being personally impacted. Statistical analysis of survey’s results shows that the risk perception is mostly shaped by risk cognitive and psychological factors rather than demographic factors (group, family status and previous risk experience). Perceived personal exposure to and predictive power of environmental cues (sights and sounds that are considered to indicate a hazard onset) positively shape risk perception. The higher the level of personal understanding and interest in seeking risk information, the higher the risk perception. In addition, risk perception leads to high level of anxiety. Finally, the spatial analysis shows that the highest level of risk perception was observed in the eastern part of the city, previously impacted by lava flows in 2002.

The movement of large, slow-moving, deep-seated landslides is regulated principally by changes in pore-water pressure in the slope. In urban areas, drastic reorganization of the surface and subsurface hydrology—for example, associated with roads, housings or storm drainage—may alter the subsurface hydrology and ultimately the slope stability. Yet our understanding of the influence of slope urbanization on the dynamics of landslides remains elusive. Here we combined satellite and (historical) aerial images to quantify how 70 years of hillslope urbanization changed the seasonal, annual and multi-decadal dynamics of a large, slow-moving landslide located in the tropical environment of the city of Bukavu, Democratic Republic of the Congo. Analysis of week-to-week landslide motion over the past 4.5 years reveals that it is closely tied to pore-water pressure changes, pointing to interacting influences from climate, weathering, tectonics and urban development on the landslide dynamics. Over decadal timescales, we find that the sprawl of urbanized areas led to the acceleration of a large section of the landslide, which was probably driven by self-reinforcing feedbacks involving slope movement, rerouting of surface water flows and pipe ruptures. As hillslopes in many tropical cities are being urbanized at an accelerating pace, better understanding how anthropogenic activity influences surface processes will be vital to effective risk planning and mitigation.

Geo-hydrological hazards (landslides and floods) are often associated with significant damages on physical infrastructure like buildings and roads. Understanding the factors controlling the extent of damage is a prerequisite for quantitatively estimating risk and its spatial distribution, and advising on measures to reduce vulnerability. In this study we document the impact of 64 landslide and six flood events in four selected districts in western Uganda for the period May 2019 - March 2021 through extensive fieldwork. We quantify in economic value the physical damage of landslide and flood hazards on exposed buildings, roads and bridges. We then analyse the physical vulnerability based on damage ratios and determine the factors (building material, hazard characteristics and age of the building) that control the degree of damage using fractional logistic regression. Out of the 91 buildings affected by landslides, 54% were totally destroyed, and only 10% not or minorly damaged, for an average damage cost of 3,179 USD/building. For the 212 documented buildings affected by floods, 35% were totally destroyed, 28% had severe to moderate damage and the rest were minorly or not affected, with an average damage costs of 1,755 USD/building. The physical vulnerability of buildings to landslides depends on the size of the landslide, age of the building, type of building wall material and the steepness of the slope cut to establish an artificial foundation platform. On the other hand, the physical vulnerability of buildings to flood hazards is largely controlled by the flood depth, the distance from the river channel, slope, size of flooded area and type of floor material. The physical vulnerability functions developed in this study are being used as a new inputs into a regional quantitative model of geo-hydrological risks. Combining the hazard estimates with the most accurate information on exposure of physical infrastructure, will facilitate the identification of the types of events and the locations that require most attention for risk reduction.

Disasters induced by natural hazards are increasing globally and have severe impacts. Some of these hazards, as volcanic eruptions, are related to the earth's interior mechanisms and cannot be prevented. Thereby, risk mitigation is the best strategy for reducing their impacts in densely populated areas, such as the city of Goma in the eastern Democratic Republic of Congo, exposed to volcanic threats from Nyiragongo. This requires the population to be prepared to respond to volcanic risk, by having a high state of awareness, anticipation, and readiness. “Living with a volcano” should be one of the life skills all Goma children acquire during their schooling, regardless of where they attend school. Therefore, this study used a mixed-method approach (questionnaire survey, focus group and written composition) to assess the awareness raising impact of two educational tools recently implemented in Goma for secondary students: the Hazagora serious game and the volcano museum. Several students (402 in total) from 12 schools participated in one of these risk awareness activities, while other students were assessed as controls. Results indicate that the tools have a positive impact on students’ volcanic disaster understanding, their risk perception, and their implication in DRR initiatives. Specifically, the volcano museum increases knowledge of volcanic process more than the Hazagora serious game; the latter increases more the perceived self-capacities and willingness of implementing protective measures. Risk perception raises almost identically with both tools. In general, participants indicate that they receive sufficient scientific information throughout the Hazagora serious game and the volcano museum visit to better understand the physical mechanisms of volcanic hazards and their impacts on human properties and livelihood. In addition, they claim to have received relevant information on protective measures and abilities, and to be willing to search for additional risk information. This study highlights that the two tools are complementary; thus, awareness raising through a diversity of tools can be more effective than a single and isolated activity.

Many volcanoes exhibit evidence of long-term deformation driven by gravity. This deformation influences the development of magmatic plumbing systems and volcanic vent locations, and it manifests as earthquakes and ground surface motions. Two end-member deformation styles are volcano sagging (flexure) and volcano spreading. Previous modeling studies indicated that the mechanical and geometric properties of basement rocks below the volcano can control whether a volcano spreads or sags, but these works differed on exactly how. Furthermore, evidence in nature that a volcano may progress from sagging to spreading as it grows has not been tested experimentally. Using Digital Image Correlation (DIC) and a revised scaling approach, we here revisit the classic experiments in which a sand–plaster cone is emplaced upon a basement comprising an upper brittle layer and a lower ductile layer. In a first experiment series, we emplaced the cone instantaneously. By normalizing both brittle and ductile layer thicknesses to cone height, we provide new insight into the dimensionless geometric controls on spreading and sagging. In a novel second experiment series, we emplaced the cone incrementally. We show that as a growing cone migrates through the dimensionless geometric parameter space, its deformation style changes successively in time from sagging to spreading. DIC shows that the horizontal velocity of the cone flank increases linearly or non-linearly during cone construction, but it decreases exponentially after construction ceases. Despite their geometric simplification and the omission of several sedimentological, magmatic, and regional-tectonic processes, our models' results are compatible with a range of observations of volcanoes on Earth and Mars. In particular, they help to explain: (i) why lithosphere-scale loading results in sagging rather than spreading, and (ii) why ocean island volcanoes of >2-3 km in height develop stellate forms and rift zones.

During a volcanic eruption generating lava flows, an effective risk reduction action is evacuation. However, if the eruption is not preceded by precursors, such as the 2021 Nyiragongo eruption, the population living near the volcano is confronted with the need to rapidly decide by themselves whether to evacuate or not; and if so, where and how. On the evening of 22 May, a red glow on the south flank of Nyiragongo alerted the population of Goma (East DRC) that an eruption had started. There were no clear instructions from the authorities. On that night, part of the population evacuated spontaneously, and returned the following day as the lava had stopped flowing. In the following week, intense seismic shocks affecting the city led the Governor to order on May 26 an evacuation of the eastern neighbourhoods. Using a qualitative survey associated with a quantitative one among 1.137 adults residing in both mandatory and non-mandatory evacuation zones, this study analyses individual evacuation decision making during both volcano-seismic phases of the 2021 Nyiragongo eruption. The results of the statistical analyses indicate that the population in the north-eastern neighbourhoods evacuated spontaneously on the night of the eruption without prior knowledge of their destination. Their preferred destination was relatives’ homes for resources, either outside the city or in another neighbourhood. The decision to evacuate was not influenced by an individual risk assessment, but by the family safety. Following the May 26 evacuation order, the majority of households evacuated while maintaining at least one person to house sit. Fear of earthquakes was the main reason for evacuation but those who did not evacuate considered the risk to be lower, compared to the 2002 experience. The results of this study will improve the Goma contingency and evacuation plans in the event of a new volcanic eruption.

The integration of indigenous knowledge into understanding disasters from natural hazards is hitherto hampered by the limited conceptualization of the process that shapes indigenous knowing. This study proposed a framework, structuring the processes that shape indigenous knowledge on disaster risk. Bearing that framework in mind, the evolution of disaster risk as understood by indigenous people was investigated based on the case floods in the Rwenzori. Data are collected using participatory ethnographic methods and analyzed through an inductive-analytical approach. Findings indicated indigenous knowledge framed along lived experiences, fostered by open knowledge production in the cultural institutions. This enabled rationalization of successive floods, over time, favoring a conceptualization of the context-specific processes through which flooding turns into disaster. This indigenous conceptualization not only exposes blind spots in the scientific evidence on context-specific processes of floods; it further illustrated how, through history, flood risk is a primary consequence of pressures that are sociopolitical and capitalist in nature. These pressures tend to undermine indigenous knowledge of flood risk specificities, favor watershed degradation, aggravate exposure, and hamper community-based investments that would enhance resilience. This exposition of distal pressures neglected by scientists highlights the indispensable role of indigenous perspectives in understanding context-specific disaster risk. Graphic abstract: Indigenous knowledge construction framework and its influencing factors in practice. [Figure not available: see fulltext.]

Tropical mountainous regions are commonly identified as landslide hotspots with particularly vulnerable populations. Anthropogenic factors are assumed to play a role in the occurrence and impact of landslides in these populated regions, yet the relative importance of these human-induced factors remains poorly documented. In this work, we explore the impact of forest cover dynamics, agricultural land management practices, urbanisation, roads, and mining/quarrying activities on the occurrence of landslides and their associated risk in the North Tanganyika–Kivu Rift, an area that stretches at the border of four countries in Africa. Using a holistic approach that combines extensive fieldwork, optical and SAR/InSAR satellite remote sensing, time-series analysis, UAS image acquisition, historical photograph processing, citizen science and geomorphic marker understanding, our study demonstrates the role of human activities on the frequency, size and deformation patterns of landslides in the region, in both rural and urban environments. The interaction between uplift associated with the continental rifting in the region, fluvial incision, and the (human-induced) landslides are also key elements that are considered in our analysis. Overall, we highlight the need to consider the human context when studying hillslope instabilities in regions under anthropogenic pressure.

Volcanic edifices are dynamic landforms whose morphology encodes the long-term (thousands to millions of years) interaction between construction and erosion. Short-term episodes of volcanic activity that cumulatively build topography compete with long-term erosive processes associated with climate and mass wasting to degrade edifices, generating a variety of morphologies from simple, cone-like edifices to complex, non-axisymmetric volcanoes. However, separating the signatures of these processes using topography remains elusive as both volcanic and climatic processes are often spatially-heterogeneous and temporally-varying. Despite this, disentangling edifice morphologic histories provide new avenues to better discern an edifice’s volcanic record, assess potential hazards, and quantify the role of climate in landscape evolution.Here, we aim to understand the long-term interaction between volcanic and erosional processes in driving edifice morphology using numerical landscape evolution modeling and comparing modeled landscapes to the morphology of the Kaua`i shield volcano. Kaua`i has been built over the past 5 Myr by series of lava flows that have non-uniformly altered both topography and surface erodibility. Coupled with this, a strong precipitation gradient across the island has influenced basin-scale erosion rates, impacting drainage development and making Kaua`i a natural laboratory to test the effects of spatially- and temporally-varying construction and degradation processes.We analyze the interaction of these processes by first characterizing the impacts of lithology and precipitation gradients on edifice morphologies over 5 Myr timescales by employing the TopoToolbox Landscape Evolution Model. Starting with an initial, simplified edifice geometry, we test the effects of both singular and multiple parameter gradients through space and time over a broad parameter space. We then quantify edifice degredation and evolution using a series of metrics that include topographic hypsometry, basin geometries, drainage density, and , showing that such parameter gradients create asymmetric landforms with spatial heterogeneities related to the geometry and configuration of basins and channel networks. Afterwards, we consider edifice morphologic evolution within the framework of Kaua’i. By constraining the spatiotemporal model parameter configurations with the geologic and precipitation data of the volcano, and comparing modeled landscapes to the current morphology of Kaua’i, we determine likely parameter ranges that contribute to its evolution.

The way people perceive the volcanic risk and how this leads them to take protective measures is an essential topic in volcanology. We apply the Protection Motivation Theory (PMT) to analyse the threat and coping appraisal of individuals living at different distance ranges from Volcán de Colima, Mexico. We assessed respondents’ perceived vulnerability, the severity of the volcanic threat, their perception of the efficacy of protection measures, their ability to implement them, and how this influences their level of implementation. We collected data from 224 individual inhabitants from twelve different villages. People living closer to the volcano have a higher threat appraisal but a lower level of implementation of protective measures. Perceived severity of the threat, the efficacy of the recommended measures, and the respondents' self-efficacy were significantly related to the implementation of protective measures. However, the relationship for self-efficacy was strongest. As such, risk management in the Colima area should focus on improving self-efficacy to enhance the implementation of protective measures. Priority should be given to communities closest to the volcano.

About 350 maar craters, tuff rings, and tuff cones are spread along the Manyara rift escarpment, and clustered around the Hanang and Kwahara volcanoes in North Tanzania. They lie in the East African Rift, an active extensional setting, where the magma composition is moderately to highly alkaline and carbonate-rich. We present newly-collected depositional characteristic observations, grain size distributions, and texture analyses of tephra deposits from selected maars, tuff rings and tuff cones of alkaline composition in Manyara to illustrate the range of the associated eruption dynamics and eruptive styles. We observed deposits with some evidence for water-magma interaction and deposits without. We attribute this range to varying magma ascent conditions and water availability along intrusive paths. Magma is guided by fractures allowing it to rise fast and to exsolve gas only near the surface. If water was available within a fracture, a moderate phreatomagmatic eruption was triggered and formed a shallow maar. In a dry fracture, the magma was fragmented by gas exsolution near the surface resulting in a tuff ring or a tuff cone. Several tephra deposits show similarities with kimberlite deposits, notably so the spherical and ellipsoidal shape of the juvenile lapilli and the presence of cannonball bombs.

The long-term (ka to ma) degradation of a volcanic edifice is controlled by both regional (e.g., climate, tectonics) and local factors (e.g., original morphology, lithology), resulting in both long-lasting weathering and river incision and short-term hazardous events, such as flank collapses and lahars. Trends among the morphometry of stratovolcanoes, their drainage network, denudation, and regional factors were recently characterised for composite volcanoes along the Indonesian arc. Denudation was shown to be negatively correlated with drainage density; the across-arc variations expose a tectonic control on the level of denudation and volcanoes’ irregularity. This study applies the same method on age-constrained volcanoes in Japan to find coherent trends between arcs despite the different local and regional factors. We aim to better understand the factors that control erosion rates and patterns, and the evolutionary phases of volcano degradation. We first compile a dataset of 35 singular, non-complex composite volcanoes with known eruption ages and spatially spread throughout the Japanese Island arc system. Using 30m TanDEM-X Digital Elevation Models, morphologies, and drainage metrics (e.g., volume, height, slopes, irregularity index, Hack’s Law exponent, and drainage density) are extracted for each volcano, using the MORVOLC algorithm adapted in MATLAB as well as the newly developed DrainageVolc algorithm. Correlations between the morphometric parameters and potential controlling factors (e.g., age, climate, lithology, and tectonics) are analysed to determine quantitative relationships of edifice degradation throughout the arc. Finally, we compare relationships and correlation values of the Japanese Arc system to those from the Indonesian Arc. The analysis shows that volcano age is positively correlated with irregularity and negatively correlated with height and volume. From the drainage parameters, we find that basins become wider and merge, resulting in lower drainage densities. The variation in erosion rates along the Japanese arc provides evidence for the degree of climatic control on the volcano degradation. The between-arc comparison shows which trends are susceptible to arc-scale variations and highlights consistent trends that have the potential to be extrapolated to other volcanic arcs and be used as a relative age determination tool for composite volcanoes.

The Kigezi highlands, southwestern Uganda, is a mountainous tropical region with a high population density, intense rainfall, alternating wet and dry seasons and high weathering rates. As a result, the region is regularly affected by multiple natural hazards such as landslides, floods, heavy storms, and earthquakes. In addition, deforestation and land use changes are assumed to have an influence on the patterns of natural hazards and their impacts in the region. Landscape characteristics and dynamics controlling the occurrence and the spatio-temporal distribution of natural hazards in the region remain poorly understood. In this study, citizen science has been employed to document and understand the spatial and temporal occurrence of natural hazards that affect the Kigezi highlands in relation to the multi-decadal landscape change of the region. We present the methodological research framework involving three categories of participatory citizen scientists. First, a network of 15 geo-observers (i.e., citizens of local communities distributed across representative landscapes of the study area) was established in December 2019. The geo-observers were trained at using smartphones to collect information (processes and impacts) on eight different natural hazards occurring across their parishes. In a second phase, eight river watchers were selected at watershed level to monitor the stream flow characteristics. These watchers record stream water levels once daily and make flood observations. In both categories, validation and quality checks are done on the collected data for further analysis. Combining with high resolution rainfall monitoring using rain gauges installed in the watersheds, the data are expected to characterize catchment response to flash floods. Lastly, to reconstruct the historical landscape change and natural hazards occurrences in the region, 96 elderly citizens (>70 years of age) were engaged through interviews and focus group discussions to give an account of the evolution of their landscape over the past 60 years. We constructed a historical timeline for the region to complement the participatory mapping and in-depth interviews with the elderly citizens. During the first 24 months of the project, 240 natural hazard events with accurate timing information have been reported by the geo-observers. Conversion from natural tree species to exotic species, increased cultivation of hillslopes, road construction and abandonment of terraces and fallowing practices have accelerated natural hazards especially flash floods and landslides in the region. Complementing with the region’s historical photos of 1954 and satellite images, major landscape dynamics have been detected. The ongoing data collection involving detailed ground-based observations with citizens shows a promising trend in the generation of new knowledge about natural hazards in the region.

Ol Doinyo Lengaï (OL) in north Tanzania is the only active volcano in the world emitting natrocarbonatite lavas. This stratovolcano (2962 m a.s.l) is mostly characterized by effusive lava emissions since 1983. However, on the 4th of September 2007, explosive events marked the beginning of a new eruptive style that lasted until April 2008. This new phase involved short-lived explosive eruptions that generated volcanic ash plumes as high as 15 km during its paroxysmal stage. This explosive activity resulted in the formation of a 300 m wide and 130 m deep crater in place of the growing lava platform that had filled the crater since 1983. Since then the effusive activity at OL resumed within the crater and has been partially filling it over the last 14 years. Due to the remote location of the volcano there is a lack of monitoring of its activity and, hence, its eruptive and morphological evolution over the last years is not well constrained (e.g., emission rates, number of vents, unstable areas). This absence of monitoring, preventing the detection of features, such as instabilities of the summit cone, could have hazard implications for the tourists regularly visiting the summit area.In this study, we quantify the evolution of OL crater area over the last 14 years by reconstructing its topography at regular time interval. We collated several sources of optical images including Unoccupied Aircraft Systems (UAS) images, videos and ground-based pictures that have been collected over the period 2008-2021 by scientists and tourists. Those data have been sorted by year and quality in order to reconstruct the most accurate topographical models using Agisoft Metashape Pro, a software for Structure from Motion (SfM) photogrammetry, and CloudCompare a 3D point cloud processing software. This enables estimating the emitted volume of lava, the emission rate and the remaining crater volume available before crater overflow. It also allows identifying punctual events, such as hornito formation or destruction, and partial crater collapses. Our results indicate that the main lava emission area has repeatedly moved over the years within the crater floor and that OL’s effusion rate has been increasing over the last few years, with more than two times higher lava emission in the period 2019-2021 compared to 2017-2019. Assuming a similar lava effusion rate in the coming years, the crater could again be filled within the next decade leading to new lava overflows. There is thus a need for periodic assessment of the situation at OL. New cost- and time-effective photogrammetry techniques, including UAS and SfM processing, offer a solution to improve the monitoring of such remote volcanoes.

Risk perception is an essential element to consider for effective risk management at time of eruption, especially in densely populated cities close to volcanoes. The city of Goma in the East of the DR Congo is one these cities highly exposed to volcanic hazards and highly populated. The perception of volcanic risk involves the processes of collecting, selecting and interpreting signals about uncertain impacts of volcanic hazards. Using a questionnaire survey, this study describes the spatial variation and factors influencing the individual volcanic risk perception of 2204 adults from height representative neighbourhoods of the city of Goma before the May 2021 Nyiragongo eruption. A composite risk perception indicator was built from the perceived likelihood of occurrence of volcanic hazards and of their impacts and from the perceived likelihood of being personally impacted. Statistical analysis of survey’s results shows that the risk perception is mostly shaped by risk cognitive and psychological factors rather than demographic factors (group, family status and previous risk experience). Perceived personal exposure to and predictive power of environmental cues (sights and sounds that are considered to indicate a hazard onset) positively shape risk perception. The higher the level of personal understanding and interest in seeking risk information, the higher the risk perception. In addition, risk perception leads to high level of anxiety. Finally, the spatial analysis shows that the highest level of risk perception was observed in the eastern part of the city, previously impacted by lava flows in 2002.

Co-auteur étranger; International audience; This study investigates the localities of low and high F- groundwaters in the aquifer system on the flanks of Mount Meru to come up with guidelines to provide groundwater that can be used for drinking water supply without health impacts on the population. Our study focuses on parts of the flanks which were only partially or not at all covered by previous research. Results show that the groundwater chemistry of F--rich NaHCO3 alkaline groundwater in the area is controlled by dissolution of weathering aluminosilicate minerals, dissolution of F--bearing minerals, the precipitation of carbonate minerals as secondary products and the dissolution of magmatic gases. The low F- groundwaters which can be used for drinking water supply without health impacts under the WHO limit (1.5 mg/L) are the low-fluoride springs from the high altitude recharge areas on the eastern and north-western flanks of Mount Meru inside Arusha National Park, whereas on the western flank the groundwater meets the Tanzanian limit (4.0 mg/L). On the south-western flank, the shallow aquifer composed of alluvium deposits at lower elevations, shows F- values that meet the Tanzanian limit. One of the three investigated deep boreholes on this flank also meets the Tanzanian limit, suggesting a possibility of finding relatively low F- groundwaters in the deep aquifer. Yet, in general, the deposits at lower elevations are found to contain high to very high F- values, whereas the deposits at high elevations contain groundwater of low F- values. Thus, the internal texture and grain size of geological formations, the burial depth of these formations and the water residence times are the factors determining the groundwater mineralisation and F- concentrations in the area. The study identified that the deep hydrothermal system has influence on the high F- groundwaters on the eastern and north-eastern flanks of Mount Meru.

A water quality problem exists in populated areas along the flanks of Mt. Meru in northern Tanzania, with excessively high fluoride (F-) concentrations exceeding the WHO drinking water standards (1.5 mg/L). Little is known about the potential sources of F-among the various rocks types forming the Meru aquifers. Nineteen samples (Debris avalanche deposits (DAD n=4), lava flows n=6, brecciated lava n=4, pumice n=2, scoria n=1, ash n=1, carbonitic n=1) representative of the materials covering the slopes of Mt. Meru were characterized for their mineralogical, chemical, and total and water-soluble F- compositions. Mt. Meru is mainly composed of alkaline volcanic rocks of basaltic to phonolitic composition. The total F- analysis indicated that F-occurs in all rock types with a mean value varying per rock type from 0.6 to 3.2 g/kg. The DAD in the east and northwest of Mt.Meru contained the highest amount of F- (mean 3.1±0.17 g/kg), whilst the lava flow samples had the lowest mean value (0.6±0.25 g/kg). Water rock-interaction experiments further revealed the highest release of F- in the analyzed DAD samples, possibly associated with their weathering status that progressively converted the primary minerals into secondary clay-bearing minerals assemblage, and favoring F- release into the interacting water. Unlike DAD, pumice and ash have a moderately high level of total F- (1.76±0.04 g/kg) yet; release a minimal amount of it through leaching. Petrographic observations showed that the analyzed volcanic rocks consist of volcanic glass and rare F--bearing accessory minerals (amphibole, titanite, biotite, and apatite), among others. Using electron microprobe analysis, the F- concentrations were found to be as high as 3- 6.5 g/kg in the glassy groundmass and up to 4 g/kg, 5 g/kg, and 45 g/kg in accessory phases of titanite, amphibole, and fluorapatite, respectively. Comparing the abundance and the composition of the glassy groundmass with the mineral phases, the former harbors most of the total F-content. The findings of leaching experiments are congruent with past water quality which show that, low F- is found in water from lava and tephra-dominated areas at higher altitudes and Mt. Meru west, respectively. This new information could guide future explorations for safer locations to place wells for water consumption. Itcould also be of interest for other East African Rift sectors and similar volcanic settings.Keywords: Northern Tanzania, East African Rift, Meru volcano, fluoride contamination, volcanic rocks, leaching

The role of indigenous knowledge in increasing context specificity and exposing blind spots in scientific understanding is widely evidenced in disaster studies. This paper aims to structure the processes that shape indigenous knowledge production and its optimisation using the case of floods. An inductive analytical approach is applied among riparian indigenous communities (focus on the Bayira) of the Rwenzori region of Uganda where plenty of indigenous flood practices have been recorded. Indigenous knowledge of floods is found to be based on intimate comprehension of local hydrometeorological regularities. Insofar as these regularities follow natural dynamics, indigenous socio-epistemic processes are noted to be consistent with the laws of nature. Coupled with regular open sociocultural deliberations, the conceptualisation of hydrometeorological regularities induces an indigenous ontology and empiricist epistemology. This, together with the techniques used, is the driver of crucial epistemic virtues which enable indigenous knowledge to provide disaster solutions that are adapted, pragmatic, and holistic.يتضح الدور الذي تلعبه المعرفة الأصلية أو التقليدية في زيادة خصوصية السياق وكذلك الكشف عن النقاط العمياء في الفهم العلمي على نطاق واسع في مجال دراسات مخاطر الكوارث. كمساهمة في تعزيز هذا الدليل، تهدف هذه الدراسة إلى هيكلة العمليات التي تشكل إنتاج المعرفة الأصلية وتحسينها بناءً على حالة الفيضانات. تم استخدام نهج استنتاجي تحليلي للتحقيق في مظاهر معرفة السكان الأصليين وتنظيم عملياتهم الاجتماعية المعرفية. يتم تطبيق هذا النهج بين مجتمعات السكان الأصليين ل باييرا(التركيز على باييرا) في منطقة روين زوري حيث يتم تسجيل الكثير من ممارسات السكان الأصليين بشأن الفيضانات. تظهر النتائج أن معرفة السكان الأصليين بالفيضانات تستند إلى فهم وثيق لانتظام الأرصاد الجوية المائية المحلية. وبقدر ما تتبع هذه التنظيمات المحلية الديناميكيات الطبيعية، يُلاحظ أن العمليات الاجتماعية المعرفية الأصلية تتبع ضمنيًا قوانين الطبيعة. بالاقتران مع المداولات الاجتماعية الثقافية المنتظمة المفتوحة، فإن وضع تصور لانتظامات الأرصاد الجوية المائية المحلية يستحث نهجًا تجريبيًا وجوديًا أصليًا. هذا النهج جنبًا إلى جنب مع التقنيات المستخدمة هو المحرك للفضائل المعرفية الحاسمة مثل الاستناد إلى النتائج الملموسة والتفكير المنهجي. هذه الفضائل هي التي تمكن المعرفة الأصلية من توفير حلول محلية متكيفة وعملية وشاملة للكوارث مثل الفيضانات. الكلمات الدالة: الفلسفة العرقية، الطريقة الأصلية، العلوم الأصلية، المخاطر الطبيعية، الطبيعة الاجتماعية.在灾害风险研究领域，越来越多的证据表明，土著知识有助于增加背景特异性以及揭示科学理解盲点。本研究的目的是根据洪水案例，构建土著知识产生和优化的过程，进一步丰富相关证据。本文采用归纳分析方法，调查土著知识表现形式和社会认知过程的构建。这种方法应用在鲁文佐里地区的河岸原住民社区（主要是巴伊拉人），那里许多土著人对洪水的做法得到了记录。结果表明，关于洪水的土著知识是基于对当地水文气象规律的深入了解。由于这些地方性的规律在某种程度上遵循着自然的动态变化，因此土著社会认知过程是遵循自然规律的。再加上定期的公开社会文化审议，当地水文气象规律的概念化引发了本土本体论和经验主义方法。这种方法结合所使用的技术，构成了关键美德认知论的驱动力，美德认知论是基于可靠结果和系统思维。正是这些美德使土著知识能够提供适合、务实和全面的当地解决方案，以应对洪水等灾害。 关键词：民族哲学，土著方法，本土科学，自然灾害，社会科学.

Understanding of the aquifer structure and its hydraulic properties provides comprehensive knowledge for proper groundwater utilisation and management. This study delineated the aquifer structure using lithohydrostratigraphical cross-sections, and estimated the hydraulic parameters using single well pumping tests for various locations on and around Mount Meru. Results show that, the aquifer system on the flanks of Mount Meru is a sloping aquifer with sloping beds. On the far east of the eastern flank, the aquifer is composed of debris avalanche deposits, while on the north-eastern and west flanks the aquifer is composed of weathered fractured lava, whereas on the south-western flank, the aquifer is composed of different layers: pyroclastics on the top, weathered fractured lava, weathered pyroclastics, and weathered fractured lava at the bottom. The aquifer is semi-confined on the north-eastern and western flanks; on the north-eastern flank, the overlying debris avalanche deposits acting as an aquitard, while on the western flank, the overlying layers: pyroclastics and unweathered lava acting as an aquitard and aquiclude, respectively. The aquifer is unconfined on the far east of the eastern flank and south-western flank. The transmissivity of the aquifer on the north-eastern flank is substantially increasing with increasing depth, while variable, both at the shallow depth of hand-dug wells and the larger depth of boreholes, on the south-western flank; indicating aquifer heterogeneity. On the north-eastern flank, the topmost part of the aquifer, exploited by hand-dug wells, has a low transmissivity (T = 1.3 m2/d) and potential for smaller withdrawals for local water supply with limited consumption, while the upper part of the aquifer, captured by boreholes, has an intermediate transmissivity (T = 35 m2/d) and potential for local water supply, whereas the deeper part of the aquifer has a high transmissivity (T = 788 m2/d) with potential of somewhat regional importance. On the western flank, the aquifer has a verylow transmissivity (T = 0.4 m2/d) and potential for local water supply with limited consumption. On the south-western flank, on average, the topmost part of the aquifer, exploited by hand-dug wells, has very low to intermediate transmissivity (range of T: 0.3–21 m2/d), leading to variable potential for smaller withdrawals for local water supply (private consumption), whereas the deeper part of the aquifer, captured by boreholes, has low to intermediate transmissivity (range of T: 9–43 m2/d) and potential for local water supply.

The Philippine Island Arc has a large number of volcanoes with diverse morphologies, making it an ideal location to study the factors controlling the morphology and spatial distribution of island arc volcanoes. We have identified 731 volcanic edifices using the SRTM 30 m digital elevation model, and computed their quantitative morphology using the MORVOLC algorithm. Hierarchical classification by principal component (PC) analysis distinguishes four volcano types: small flat cones, small steep cones, large cones, and massifs, with mean volumes of 0.2 km3 (

Granular materials are a useful analogue for the Earth’s crust in laboratory models of deformation. Constraining their mechanical properties is critical for such model’s scaling and interpretation. Much information exists about monomineralic granular materials, such as quartz sand, but the mechanical characteristics of bimineralic mixtures, such as commonly-used quartz sand mixed with gypsum powder (i.e. plaster), are largely unconstrained. We used several mechanical tests (density, tensile, extension, shear) to constrain the failure envelope of various sand-plaster mixtures. We then fitted linear Coulomb and parabolic Griffith failure criteria to obtain cohesions and friction coefficients. Tests of the effects of emplacement technique, compaction and humidity demonstrated that the most reproducible rheology is given by oven-drying, pouring and mechanically compacting sand-plaster mixtures into their experimentation container. As plaster content increases, the tensile strength of dry sand-plaster mixtures increases from near zero (pure quartz sand) to 166±24 Pa (pure plaster). The cohesion increases from near zero to 250±21 Pa. The friction coefficient varies from 0.54±0.08 (sand) to 0.96±0.08 (20 weight% plaster). The mechanical behaviour of the resulting mixtures shifts at 20-35 weight% plaster from brittle Coulomb failure along a linear failure criterion, to more complex brittle-plastic Coulomb-Griffith failure along a non-linear failure criterion. With increasing plaster content, the brittle-plastic transition occurs at decreasing depth within a pile of sand-plaster mixture. We infer that the identified transitions in mechanical behaviour with increasing plaster content relate to (1) increasing porosities, (2) increasing grain size distributions, and (3) a decrease in sand-sand grain contacts and corresponding increase in contacts of anisotropic gypsum-gypsum grains. The presented characterisation enables a more quantitative scaling of the mechanical behaviour of sand-plaster mixtures, including their tensile strength. Sand-plaster mixtures can thereby realistically simulate brittle-plastic properties of the Earth’s crust in scaled laboratory models., info:eu-repo/semantics/published

Freshly erupted volcanic ash contains a range of soluble elements, some of which can generate harmful effects in living cells and are considered potentially toxic elements (PTEs). This work investigates the leaching dynamics of ash-associated PTEs in order to optimize a method for volcanic ash respiratory hazard assessment. Using three pristine (unaffected by precipitation) ash samples, we quantify the release of PTEs (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V, Zn) and major cations typical of ash leachates (Mg, Na, Ca, K) in multiple simulated lung fluid (SLF) preparations and under varying experimental parameters (contact time and solid to liquid ratio). Data are compared to a standard water leach (WL) to ascertain whether the WL can be used as a simple proxy for SLF leaching. The main findings are: PTE concentrations reach steady-state dissolution by 24 h, and a relatively short contact time (10 min) approximates maximum dissolution; PTE dissolution is comparatively stable at low solid to liquid ratios (1:100 to 1:1000); inclusion of commonly used macromolecules has element-specific effects, and addition of a lung surfactant has little impact on extraction efficiency. These observations indicate that a WL can be used to approximate lung bioaccessible PTEs in an eruption response situation. This is a useful step towards standardizing in vitro methods to determine the soluble-element hazard from inhaled ash.

Effective disaster risk reduction is often hampered by a general scarcity of reliable data collected on disastrous events, particularly in the Global South. Novel approaches are therefore necessary to alleviate this constraint, particularly with regard to reducing extensive risks. A geo-observer network, consisting of 21 reporters, was established in the Rwenzori region (Uganda) in February 2017 to collect data on eight different disasters using smartphone technology. Within the first 15 months of operation, a total of 319 disaster reports were submitted. A large majority of the reported disasters were reached by the geo-observers within 2 days after their occurrence. The analysis of reporting activity shows a large divergence, with one third of the most active geo-observers accounting for nearly 75% of all reports. By using an existing landslide susceptibility map as a proxy of expected landslide prevalence, this reporting divergence is demonstrated to be at least partially driven by a difference in disaster occurrences. This is confirmed by the results of a survey held among the geo-observers. Survey results also showed that the participants are more driven by non-pecuniary benefits rather than financial compensation. The data collected during the first 15 months of operation indicates that extensive risks in the region are underestimated and demonstrates the added value of participatory sensing to compensate for the current lack of well-functioning official data collection mechanisms. This pilot project is a proof of concept for participatory sensing to collect high quality data even in remote contexts where smartphone technology is not generally adopted. It can serve as a precedent or example for other regions where extensive risks are poorly understood but pose significant threat to the population.

This study characterises high-fluoride groundwater in the aquifer system on the flanks of Mount Meru, focusing on parts of the flanks that were only partially or not at all covered by previous research. Additionally, we analyse the impact of rainwater recharge on groundwater chemistry by monitoring spring discharges during water sampling. The results show that the main groundwater type in the study area is NaHCO3 alkaline groundwater (average pH = 7.8). High F− values were recorded: in 175 groundwater samples, the concentrations range from 0.15 to 301 mg/L (mean: 21.89 mg/L, median: 9.67 mg/L), with 91% of the samples containing F− values above the WHO health-based guideline for drinking water (1.5 mg/L), whereas 39% of the samples have Na+ concentrations above the WHO taste-based guideline of 200 mg/L. The temporal variability in F− concentrations between different seasons is due to the impact of the local groundwater recharge. We recommend that a detailed ecohydrological study should be carried out for the low-fluoride springs from the high-altitude recharge areas on the eastern and northwestern flanks of Mount Meru inside Arusha National Park. These springs are extracted for drinking purposes. An ecohydrological study is required for the management of these springs and their potential enhanced exploitation to ensure the sustainability of this water extraction practice. Another strategy for obtaining safe drinking water could be to use a large-scale filtering system to remove F− from the groundwater., info:eu-repo/semantics/published

Mt. Meru, in the northern Tanzania divergence zone within the East African Rift System, is a historically active volcano, with its last eruption in 1910 CE. The flank deposits of Meru are dominated by lava flows, debris avalanche deposits as well as major pyroclastic formations indicative of Plinian-style eruptions. The stratigraphy, spatial extent, and chronology of these pyroclastic deposits have, however, not been systematically studied. Here we report on the detailed reconstruction of the stratigraphy and eruptive dynamics of Late Quaternary Meru explosive eruptions, based on field investigations, geochronological and geochemical analyses. The findings indicate that Meru had at least three moderate-to-large-scale explosive eruptions over the past 40,000 years. The oldest Meru explosive event we recognize (MXP1) generated pyroclastic density currents (PDCs), while the second (MXP2) and the third, most intense explosive event (MXP3) generated both pyroclastic fallout and PDCs. Conventional radiocarbon dating of 6 palaeosols underlying MXP2 and MXP3, dated at ~34.1–38.5 ka cal BP and ~31.5–36.9 ka cal BP respectively, suggest these two eruptions may have followed each other relatively close in time. The compositional range of pumice lapilli of both MXP2 and MXP3 is limited to tephriphonolite-phonolite. Dispersal and thickness data of the better preserved and larger MXP3 deposits suggest a minimum bulk volume of 2.5 km3 of pumice fallout and 1.2 km3 of PDCs, respectively, which corresponds to a total erupted mass of at least 2.7 × 1012 kg and a magnitude of 5.4. Similar large-scale eruptions in the future would have a considerable impact on the nearby large urban population in Arusha city and its suburbs. This new information is, therefore, vital for the long-term volcanic hazard assessment in Northern Tanzania.

Risk management is used in societies to mitigate the potentially dramatic effects of natural hazards. Local authorities and managers use different indicators in elaborating rescue and urbanism plans, which are not always efficient in reducing impact in the time of the crisis. This highlights society’s vulnerability in the particular context of global environmental and climate changes. This interdisciplinary research aimed at identifying reliable risk indicators and societal responses regarding natural hazards and climate change impacts, to provide a governance framework for disaster risk reduction. Different societies face diverse risks and do not necessarily have the same level of local awareness confronting them. Two sites were thus selected from the Mediterranean basin, one from the South coast (North Morocco), other from the North coast (the Italian island of Sardinia). North Morocco, the region of multi-risks, is characterized by high demographic and economic pressures; West Sardinia counts for remarkable biodiversity of wetlands and is characterized by high environmental and agricultural pressures, which in both cases intensify the vulnerability of the coastal areas. Testing for the local population’s preparedness for future financial protection showed the importance of risk awareness sessions as an indicator of risk management. The significance of risk awareness sessions is demonstrated in a quantitative part of the study with the local population, and their importance is also discussed with other stakeholders in North Morocco in a qualitative part of the study. Based on these findings, further ideas on a new series of less descriptive, more dynamic, and more user-friendly indicators are suggested. How can risk sessions be a dynamic indicator of a resilient society? The obtained results could serve in future governance frameworks for the mitigation of natural hazards in the Mediterranean region and wider. Finally, the urgent need for continuous work to overcome the communication gap between the scientific community, risk administrators, civil society and the general population is encouraged.

The population of the semi-arid areas of the countries in the East African Rift Valley (EARV) is faced with serious problems associated with the availability and the quality of the drinking water. In these areas, the drinking water supply largely relies on groundwater characterised by elevated fluoride concentration (> 1.5 mg/L), resulting from interactions with the surrounding alkaline volcanic rocks. This geochemical anomaly is often associated with the presence of other naturally occurring potentially toxic elements (PTEs), such as As, Mo, U, V, which are known to cause adverse effects on human health. This study reports on the occurrence of such PTEs in the groundwater on the populated flanks of Mt. Meru, an active volcano situated in the EARV. Our results show that the majority of analysed PTEs (Al, As, Ba, Cd, Cr, Cu, Fe, Mn, Ni, Se, Sr, Pb, and Zn) are within the acceptable limits for drinking purpose in samples collected from wells, springs and tap systems, suggesting that there is no immediate health risk associated with these PTEs. However, some of the samples were found to exceed the WHO tolerance limit for U (> 30 μg/L) and Mo (> 70 μg/L). The sample analysis also revealed that in some of the collected samples, the concentrations of total dissolved solids, Na+ and K+ exceed the permissible limits. The concerning levels of major parameters and PTEs were found to be associated with areas covered with debris avalanche deposits on the northeast flank, and volcanic ash and alluvial deposits on the southwest flanks of the volcano. The study highlights the need to extend the range of elements monitored in the regional groundwater and make a more routine measurement of PTEs to ensure drinking water safety and effective water management measures. ispartof: SCIENCE OF THE TOTAL ENVIRONMENT vol:807 issue:Pt 1 ispartof: location:Netherlands status: published