Search

People’s vulnerability, exposure and capacity are key components of a risk assessment. Index-based methodologies have proved useful to document spatial variation in risk-controlling factors. The objective of this study is to propose a methodology to derive quantitative indicators of household vulnerability, exposure and capacity to assess household’s risk and its spatial variation. The method is applied to six unions of the coastal region of Bangladesh, including three offshore islands. Field data are collected by questionnaire survey of 609 households and 6 focus group discussions. Using conventional data conversion and aggregation methods and principle component analysis (PCA), the variables are summarized into a small set of dimensions to derive vulnerability and capacity scores. Result shows that households of islands are generally more vulnerable to natural hazards than nearby onshore unions. Unions of the central coast of Bangladesh are characterized by households with higher vulnerability and lower capacities than two other parts. The fatality rate of cyclone SIDR at village level is used to validate the spatial variation of household risk for one surveyed union. The proposed methodology and produced maps could support national to local government bodies in assessing household risk and identifying locations where to implement specific risk reduction measures.

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 (

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

Funder: VUB Strategic Research Program, Exposure to volcanic ash is a long-standing health concern for people living near active volcanoes and in distal urban areas. During transport and deposition, ash is subjected to various physicochemical processes that may change its surface composition and, consequently, bioreactivity. One such process is the interaction with anthropogenic pollutants; however, the potential for adsorbed, deleterious organic compounds to directly impact human health is unknown. We use an in vitro bioanalytical approach to screen for the presence of organic compounds of toxicological concern on ash surfaces and assess their biological potency. These compounds include polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dlPCBs). Analysis of ash collected in or near urbanised areas at five active volcanoes across the world (Etna, Italy; Fuego, Guatemala; Kelud, Indonesia; Sakurajima, Japan; Tungurahua, Ecuador) using the bioassay inferred the presence of such compounds on all samples. A relatively low response to PCDD/Fs and the absence of a dlPCBs response in the bioassay suggest that the measured activity is dominated by PAHs and PAH-like compounds. This study is the first to demonstrate a biological potency of organic pollutants associated with volcanic ash particles. According to our estimations, they are present in quantities below recommended exposure limits and likely pose a low direct concern for human health.

Uganda is regularly affected by multiple natural hazards, including floods, droughts, earthquakes, landslides and windstorms. This is due to a combination of natural biophysical factors such as steep topography, intense rainfall, variability of dry and rain seasons and high weathering rates. In addition, high population density, deforestation and other human-induced land use changes, and high poverty levels are believed to have an influence on the patterns of natural hazards and their impacts in the region. Despite this, there are limited studies that assess where and when natural hazards occur in Uganda, and a dearth of information on the processes involved. In addition, drivers and earth/landscape characteristics controlling the occurrence of natural hazards in the country remain poorly understood despite the high need for effective disaster risk reduction. Here, we present the ongoing methodological research framework and the first results of a study whose main objective is to understand the spatial and temporal occurrence of natural hazards that affect the Kigezi Highlands of south western Uganda and their interactions. To this end, the study is undertaking a comprehensive regional hazard inventory consisting of satellite image analysis, field surveys and exploration of literature and archives. Historical aerial photos and interviews with the elderly are important tools to analyze the impact of multi-decadal human-induced land use changes on natural hazard occurrences. Meanwhile, 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. Trained at using smartphone technology, they collect information (processes and impacts) on seven different natural hazards (droughts, earthquakes, floods, hailstorms, landslides, lightning, and windstorms) whenever they occur. During the first 12 months, 204 natural hazard events with accurate timing information have been reported by the geo-observers. Combined to field survey, these recent events have been associated mainly with the occurrence of > 3000 shallow landslides and 30 floods, frequently in co-occurrence and triggered by heavy rainfall. Additional inventory from Google Earth and Planet imagery covering a region much larger than that of the geo-observer network and a time window of more than 10 years shows an extra 230 landslide and flood occurrences, while archives and literature indicate 226 natural hazard events over the last 30 years. The preliminary results already demonstrate the value of citizen-science in producing highly detailed natural hazard inventory. A combination of different inventory methods improves the level of accuracy in understanding the spatial-temporal distribution of natural hazards.

The city of Goma is located in the eastern region of the Democratic Republic of Congo. With around one million inhabitants, it is built on lava flows, 15 km south of the active Nyiragongo volcano. Historically, the town was affected twice by eruptions, in 1977 and 2002 and severe destructions were reported. At that time, no volcanic risk preparedness and management tools had been implemented, and communication during and after the eruption was not consistent enough to avoid panic and human casualties. Without an appropriate and accurate risk communication, people may adopt a behavior which can put them at risk, by increasing their vulnerability. Nineteen years after the last disaster, risk management still have to develop an effective risk preparedness strategy and integrate risk awareness raising tools. The aim of this ongoing doctoral research is the assessment of risk culture, building upon a risk perception assessment and identification of risk reduction measures to be enhanced.A survey of 2224 adults among the general population of Goma was conducted in eight representative neighborhoods in order to assess the risk perception, the experience of the risk communication as well as the risk preparedness of inhabitants. We here present a first analysis of the results regarding the risk communication challenges. Goma is a dynamic town with a young population (80% are under 45 years old), living in relatively poor and large family (51% of households have 4-7 members and 31% 8-11 members; 57% of household have an income between 0-250$), with rather low education (47% is secondary level and 34% graduated). Language is one of the volcanic risk communication challenges in Goma: apart from French as the official language, Swahili as local, and English imposed by the large humanitarian sector, there are many dialects. Moreover, most communication tools are informal (social networks, friends and relatives…) and inhabitants mostly look for information on religion (22%), health (15%) and politics (12%), but not so much about risk reduction. Local radio (24%), television (14,5%) and social networks (13%) are the most preferred information channels. The city of Goma is also very dynamic: with a high migration rate, the population is growing and renewing itself regularly, to the point that risk communication must take into account the newcomers in order to be efficient. Additionally, our survey shows that experience of disasters and trust in decision-makers also provide a basis for effective risk communication.By presenting, as examples, the communication chain during the 2002 Nyiragongo eruption, as well as a more recent example of miscommunication due to the publication, in the general public press, of a scientific article with significant uncertainties in eruption forecast modelling (leading to misinterpretation by non-expert readers), we will demonstrate that the cascading reactions may have consequences putting risk decision-makers and scientists in a difficult position, by provoking a feeling of mistrust and doubt among the population. Based on the Goma case study, we will show that risk communication in the global south is a major risk management challenge with complex issues.

Volcano morphometry provides evidence for the magmatic and tectonic factors that control the growth of edifices and their spatial distribution in volcanic fields. We identified 731 volcanic edifices in the Philippine island arc using SRTM 30 m digital elevation models, and quantitatively described their morphology using the MORVOLC algorithm and their spatial distribution using Matlab GIAS and three-point analysis codes. A hierarchical classification by principal component analysis (HCPC) was used to morphometrically classify the edifices into four classes, which we interpret as small flat cones, small steep cones, large cones, and massifs. This classification is mainly based on edifice size and irregularity (PC1) and steepness (mean slope and height/basal width ratio; PC2), and to a lesser extent on the size of the summit region and edifice truncation (PC3), and edifice elongation (PC4). Both small flat cones and small steep cones have volumes of 3 with means of 3. The small flat cones have mean slopes of 3 (mean = 29 km3), whereas massifs have larger volumes: between 76 and 675 km3 (mean = 267 km3). Both classes have similar mean slopes with overall means of 15°.The morphometric classification, complemented by previously published geochemical data from some edifices, indicates continuous variation between volcano classes, which represent stages along an evolutionary trend. The small flat cones are mostly monogenetic, whereas the small steep cones represent an early growth stage of stratovolcanoes. Some small cones develop into large polygenetic cones, and these can grow laterally into massifs. Both large cones and massifs are mostly found on thickened crust. There is a trend towards more silicic compositions from small to large cones, perhaps due to larger edifice loads preventing mafic dykes from reaching the surface, that in turn drives magmatic evolution. More evolved and explosive magmas cause more silicic volcanoes to be less steep than andesitic volcanoes. The distribution and alignment of smaller edifices within eight volcanic fields shows that the dominant regional or local stress conditions and pre-existing structures influenced magma propagation and their spatial distribution. Associating morphometric classification with the stages of volcano growth will help in the initial assessment of the factors controlling volcano evolution, which might impact our assessment of hazards related to volcanoes.

Lahars impose significant secondary hazards on highly populated volcanic islands by remobilizing volcanic ash deposits. Karthala, on Grande Comore Island, is a relatively young and poorly eroded basaltic shield volcano with sporadic occurrence of ash-forming phreatic eruptions. In 2005, two mildly explosive episodes emplaced tephra blankets on the summit area. Heavy precipitation subsequently triggered the repetitive occurrence of small-volume secondary lahars up to 2012. These lahars damaged roads and hundreds of houses, affecting thousands of inhabitants at the foot of Karthala volcano, but were poorly documented at the time of their occurrence. Their future hazard remains unclear as well. This study aims at gaining insights into the main characteristics of these lahars, as well as testing and comparing the effectiveness of two numerical tools to simulate the extent of these small-volume lahars. To understand the physical characteristics of the lahars, we first documented the spatial extent and characteristics of the debris deposits at the foot of Karthala volcano and in the ravines that guided the flows. Our observations suggest that the debris were emplaced by small-scale (volumes ≤ 105 m3), rain-triggered and predominantly low sediment concentration lahars. The spatial extent of the deposits served to calibrate and compare numerical lahar simulations from the widely used volume-limited LaharZ model with simulations from Q-LavHA, a probabilistic flow model originally developed for lava flows. Q-LavHA mitigates some limitations of LaharZ, such as its ability to simulate flow bifurcations and the transition from constrained to unconstrained flow but comparison demonstrates that Q-LavHA typically yielded lower simulation accuracies compared to LaharZ simulations. The obtained accuracy values represent a rather poor performance for both models compared to existing studies on larger-volume lahars on stratovolcanoes, and are inferred to result mostly from difficulties in delineating lahar flow paths on the smooth, poorly eroded topography of the volcanic edifice. We therefore also evaluated the potential to increase simulation accuracy by updating a 10 m resolution Digital Elevation Model (DEM) with channel topography measurements. By using such updated DEMs, the correctly delineated area improved for both models. This approach, however, did not prevent simulations to sometimes miss the hazard-prone position of settlements which were actually affected by the hazard in the past. Our study shows the limitations of numerical volcanic flow simulation strategies on young and poorly eroded volcanic edifices, such as active basaltic shields. The results indicate that accurate topographic representations and detailed documentation of spatial extent of the impacted area and lahar deposit thickness are needed to produce accurate lahar simulations, as well as the further adaptation of existing numerical simulation tools to better suit these particular environmental settings.

Goma city, at the eastern border of DRCongo, is highly exposed to natural hazards, especially from Nyiragongo volcano, located directly North of it. In January 2002, the city centre of Goma was devastated by lava flows and several thousands of people were temporarily displaced. Defining and quantifying population vulnerability to natural hazards, and lava flow hazards in particular, is a crucial element to evaluate and manage the risk. This paper aims at assessing the vulnerability of the population facing volcanic hazards in Goma, and its spatial variation across the city, in order to support volcanic risk prevention and management at the local levels. In this data scarcity context, two parallel methodologies are tested based on data collected through a large-scale household survey: the Social Vulnerability Index (SoVI) as defined by Cutter et al. (2003) based on a statistical data reduction; the other using fewer significant indicators in order to develop an Operational Vulnerability Index (OVI). Results show that the spatial distribution of the vulnerability levels with both approaches is quite similar, but the construction of an OVI can help to communicate the message more easily to political authorities for risk management actions – e.g. to target neighborhoods where to develop priority prevention programs – but also in terms of spatial urban planning – e.g. to identify areas where to act. Population vulnerability assessment, together with the lava flow hazard invasion probability and population exposure, is one of the crucial steps towards the lava flow risk assessment., SCOPUS: ar.j, info:eu-repo/semantics/published

Disaster risk zonation is often proposed as a long-term disaster risk reduction strategy by international treaties and academic research. This strategy has been implemented in the city of Limbe, which is known to be a disaster-prone one. Citizens are forced to settle in unsafe terrains, ranging from wetlands to unstable hillslopes due to the city’s geographical location and economic attraction. Following the fatal landslides and floods in 2001, a local crisis committee identified affected areas and declared them ‘risk zones’ to prevent further exposure. Empirically, this study narrates the production and implementation of risk zonation policy in the city of Limbe. Theoretically, it uses an urban political ecology perspective, which incorporates science and technology studies, post-political theory and disaster research to interpret the drivers and implications of the mismatch between research, policy and action. In this case study, we investigate the implications for disaster risk reduction by describing three underlying socio-political drivers of the risk zonation policy: (i) authoritarian science regime, (ii) post-political discourse, and (iii) blame diversion. We argue that authorities from national to local level use a post-political discourse to promote and implement disaster risk reduction in the city of Limbe through the development and the application of risk zonation policy. As a consequence, risk zonation leads to poor enforcement of the law and corruption, ultimately leading to risk accumulation in this case. This analysis allows us to draw broader conclusions on drivers and implications of the implementation of disaster risk zonation policy in urban areas that are primarily governed hierarchically and prone to corruption.

© 2018 Springer-Verlag GmbH Germany, part of Springer Nature Over the past decades, the global exposure of persons and assets to natural hazards, like landslides, has increased faster than that their vulnerability has decreased. Therefore, the Sendai Framework for Disaster Risk Reduction (DRR) made a call in 2015 for more investment in DRR. Recent studies exposed the lack of scientific evaluation data for selecting DRR measures. The objective of this research is to develop a participatory methodology for identifying appropriate DRR measures based on stakeholder groups’ perceptions. More specifically, we propose a social multi-criteria evaluation which combines a two-phased participatory multi-criteria analysis with an institutional analysis for its design and a discourse analysis for interpreting its outcomes. This method is then tested for a case study focusing on landslides in the Rwenzori Mountains region (Uganda) to illustrate both its relevance and practical challenges. The results from the case study highlight the perceived importance of the acceptability of measures above cost, feasibility and effectiveness criteria, by district and village stakeholder groups. Frequently recommended DRR actions, such as disaster risk zonation or relocation, are shown to be perceived negatively by local stakeholders despite being put forward in national policies. This study contributes to the DRR literature as it proposes a new method to support DRR-related decision-making. It also contributes to the understanding of landslide risk reduction in the Rwenzori Mountains region as it presents the first attempt to identify appropriate landslide risk reduction measures for the region. ispartof: Landslides vol:16 issue:9 pages:1793-1807 status: Published online

Nyiragongo volcano (D.R. Congo), in the western branch of the East African Rift System, is one of the most active volcanoes on Earth. Its eruptive activity is mainly characterized by the presence of a persistent lava lake in its main crater. As observed at other persistent lava lakes, the Nyiragongo lava lake level exhibits metric vertical variations in the form of minutes-to hour-long cycles, which we infer to be gas piston activity. To study this activity, we developed and tested a Stereographic Time-Lapse Camera (STLC) system, which takes stereo-pairs of photographs of the Nyiragongo crater at regular intervals. Each pair of gas- and steam-free images during daytime allows the production of a 3D point cloud. The comparison of the point clouds provides a measurement of topographic changes related to variations in lava lake level. The processing of a first dataset acquired between 18 and 20 September 2011, at an acquisition rate of 1 pair of images every 2 min, revealed cycles of vertical lava lake level variations reaching up to 3.8 m. Lava lake level variations >0.5 m are detected significantly. They are interpreted to result from gas accumulation and release in the lava lake itself. The limitations of the STLC approach are related to the number of cameras used and the atmospheric masking by steam and volcanic gas in the Nyiragongo crater. The proposed photogrammetric approach could be applied elsewhere or in other disciplines, where frequent topographic changes occur.

The large-scale land use transformations since the 1990s in the Mekong Delta have had significant impacts on socio-economic conditions and livelihoods of local residents, potentially affecting their vulnerability to coastal hazards. This study presents an assessment of social vulnerability of households in the coastal Tran Van Thoi District of the Ca Mau Province, the lowest part of the Mekong Delta in Vietnam. The data of 21 socio-economic variables was extracted from a survey of 405 households and analyzed. The proposed household vulnerability index (HVI) is based on a Principal Component Analysis (PCA), which reduces the selected variables into seven independent factors. Results highlight the significant influence of some initial variables, especially education, income and housing quality, in the variation of the aggregated HVI. Households active in the agriculture and aquaculture are not significantly different in term of social vulnerability, whereas households working in the trade and service sector, or as temporary employees, are characterized by a significantly higher vulnerability. The coastal communes concentrate a higher proportion of vulnerable households, in agreement with the socio-economic statistics of these communes. It highlights the necessity to invest in priority in the enhancement of socio-economic conditions of these vulnerable groups for effective vulnerability reduction plans in the study area.

Having one of the most vulnerable coasts of the world to climate change, Bangladesh and India are facing new challenges to protect Sundarban, the largest mangrove in the world, from adverse impacts of climate-driven changes. In this study, unsupervised classification of mangrove density is performed on Landsat images of four time periods over 35 years (1975-77, 1989, 2000 and 2010) to identify the spatio-temporal evolution of the Sundarban mangrove, and infer the causes of observed changes. Specifically the influences of environmental and anthropogenic drivers on these changes are discriminated by correlating the observed change patterns with cyclones' tracks, erosion processes and areas of expected human influences as assessed by local stakeholders. Results highlight a very dynamic system, with rapid changes characterized by decreasing mangrove density, mainly in India, erosion and accretion. There is ∼1.2% (or 11,500 ha) net erosion in 35 years in Sundarban, which remains limited relative to the documented high rate of sea level rise of 6 mm/yr. Mangrove density changes are attributed to cyclones, increased salinity and anthropogenic influences. Based on interpretation of the spatial pattern of density changes by local stakeholders, we conclude that the zones accessible to human activities are significantly more affected by land cover changes. Management policies of Sundarban by Bangladeshi and Indian authorities should acknowledge the important role played by natural or global drivers like sea level change, cyclones in affecting the mangrove as well as manage the localized anthropogenic pressures.

Nyiragongo (Democratic Republic of Congo) erupts fluid, fast-moving, foidite lavas. Nearby Nyamuragira fre- quently erupts less mobile tephrite lavas. Nyamuragira flows rarely threaten urbanized areas, but Nyiragongo flows threaten Goma (pop. ~900,000) and surrounding villages, resulting in fatalities in 1977 and 2002. We report new laboratory measurements of viscosity evolution during cooling and crystallization from both volcanoes by con- centric cylinder viscometry. Melt viscosity is ~33 Pa s at the liquidus (~1220°C) for Nyiragongo lavas, similar to Hawaiian basalts. Lavas remain fluid over ~75°C of undercooling (φc ≤ 0.05) before rapid crystallization forms a crystal network inhibiting flow. Melt viscosity is ~40 Pa s at the liquidus (~1260 ◦C) for Nyamuragira lavas, which remain fluid over ~110 ◦C of undercooling (φc ≤ 0.11) before the onset of rapid crystallization. Low viscosity al- lows thin Nyiragongo flows to reach >10 ms-1 even at subliquidus temperatures on low slopes, posing great risk to Goma.

In the Arusha volcanic region in northern Tanzania, within the eastern branch of the East African Rift, water shortage is common and much of the surface water carries unacceptable levels of dissolved fluoride; hence groundwater is the main source of drinking water. Unfortunately, the quality of groundwater in this region is also very poor due to a high fluoride (F⁻) content because of natural contamination from the surrounding geological environment. Consumption of this water leads to dental and skeletal fluorosis among the local population. Existing borehole completion reports and field stratigraphic description of sub-surface sediments during the digging of new hand dug wells were used to characterise the geology of aquifers. On the western flank, the main aquifer is a fractured and weathered basalt while on the south-western and north-eastern flanks the aquifers are composed of volcanic deposits (ash, tuffs, pumice, lapilli) and fractured and weathered basalt. A total of 158 groundwater samples from 113 water points (61 hand-dug wells and 52 springs) were collected for chemical analysis. Laboratory results show Sodium (Na+) and bicarbonate (HCO3⁻) are the dominant ions hence the main water type in this area is Sodium bicarbonate (NaHCO3). Preliminary results show strong contrasts in pH, EC, TDS and F⁻ concentration across the study area, with some spatial patterns for water samples from springs (on the north-eastern flank) where pH, EC, TDS and F⁻ concentration increase with a decrease in elevation. In all 158 groundwater samples, 91% (143 samples) have F⁻ concentration higher than the WHO limit (1.5 mg/l) recommended for drinking water. The 9% (15 samples) with F⁻ concentration lower than the WHO limit are water from the springs found in the recharge area at higher elevation on the eastern flanks of Mount Meru inside the Arusha National Park. The chemistry of the groundwater shows that weathering and dissolution of silicate minerals (especially chemical weathering of Na-K-rich volcanic rocks), dissolution of fluoride-rich minerals and calcite precipitation play great roles on the chemical evolution of groundwater in the study area while long residence time and nature of the geological formations (including degree of weathering) play great roles in the groundwater fluoride contamination in the area.

Volcanoes display diverse morphologies as a result of the complex interplay of several constructive and destructive processes. Scaled analogue models offer a tool to isolate and characterize the different processes. Here, we investigate the interplay between volcano growth and deformation caused by an underlying strike-slip fault through simple analogue models. In particular, we analyze the morphometry of analogue volcanoes resulting from different growth-to-deformation ratios. Deformation elongates the volcano edifice at an angle of 10-45º from the fault trace along the extensional quadrants and generates a summit graben structure oriented perpendicular to the edifice elongation. The overall steepness of the edifice decreases, but steep slopes are preserved or increased on the lower compressional flanks, commonly related to small avalanches. Growth can partially to totally mask these features depending on the growth rate to strike-slip velocity ratio. The summit graben is easily masked even by low growth rates, whereas edifice elongation has the best preservation potential. Scaling of the experiments suggests that at volcanoes with growth rate (km3/yr) to strike-slip velocity (km/yr) ratios ≤ 3.8 km3/km, deformation features should be clearly preserved, whereas at volcanoes with ratios ≥ 15 km3/km, deformation features should be completely masked. The typical growth rates of volcanoes (0.01 to 1 km3/ka) and the typical velocities of strike-slip faults (1 to 20 mm/yr) suggest that in nature, growth rate to strike-slip velocity ratios can range over 3 orders of magnitude, spanning both types of end-members. Using examples of both active and inactive volcanoes located on strike-slip faults with variable elongation intensities and orientations, we highlight that the analogue models account for some of the morphometric variability observed at volcanoes in nature, although the role of vent distribution can be a key factor. Fil: Grosse, Pablo. Fundación Miguel Lillo. Dirección de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina Fil: Poppe, Sam. Vrije Universiteit Brussel; Bélgica Fil: Delcamp, Audray. Vrije Universiteit Brussel; Bélgica Fil: van Wyk de Vries, Benjamin. Université Clermont Auvergne; Francia Fil: Kervyn, Matthieu. Vrije Universiteit Brussel; Bélgica

Magma intrusions grow to their final geometries by deforming the Earth's crust internally and by displacing the Earth's surface. Interpreting the related displacements in terms of intrusion geometry is key to forecasting a volcanic eruption. While scaled laboratory models enable us to study the relationships between surface displacement and intrusion geometry, past approaches entailed limitations regarding imaging of the laboratory model interior or simplicity of the simulated crustal rheology. Here we apply cutting-edge medical wide beam X-ray Computed Tomography (CT) to quantify in 4D the deformation induced in laboratory models by an intrusion of a magma analog (golden syrup) into a rheologically-complex granular host rock analog (sand and plaster). We extract the surface deformation and we quantify the strain field of the entire experimental volume in 3D over time by using Digital Volume Correlation (DVC). By varying the strength and height of the host material, and intrusion velocity, we observe how intrusions of contrasting geometries grow, and induce contrasting strain field characteristics and surface deformation in 4D. The novel application of CT and DVC reveals that distributed strain accommodation and mixed-mode (opening and shear) fracturing dominates in low-cohesion material overburden, and leads to the growth of thick cryptodomes or cup-shaped intrusions. More localized strain accommodation and opening-mode fracturing dominates in high-cohesion material overburden, and leads to the growth of cone sheets or thin dikes. The results demonstrate how the combination of CT and DVC can greatly enhance the utility of optically non-transparent crustal rock analogs in obtaining insights into shallow crustal deformation processes. This unprecedented perspective on the spatio-temporal interaction of intrusion growth coupled with host material deformation provides a conceptual framework that can be tested by field observations at eroded volcanic systems and by the ever increasing spatial and temporal resolution of geodetic data at active volcanoes.

The study of rift basin's morphology can provide good insights into geological features influencing the development of rift valleys and the distribution of volcanism. The Kivu rift segment represents the central section of the western branch of the East African Rift and displays morphological characteristics contrasting with other rift segments. Differences and contradictions between several structural maps of the Kivu rift make it difficult to interpret the local geodynamic setting. In the present work, we use topographic and bathymetric data to map active fault networks and study the geomorphology of the Kivu basin. This relief-based fault lineament mapping appears as a good complement for field mapping or mapping using seismic reflection profiles. Results suggest that rifting reactivated NE-SW oriented structures probably related to the Precambrian basement, creating transfer zones and influencing the location and distribution of volcanism. Both volcanic provinces, north and south of the Kivu basin, extend into Lake Kivu and are connected to each other with a series of eruptive vents along the western rift escarpment. The complex morphology of this rift basin, characterized by a double synthetic half-graben structure, might result from the combined action of normal faulting, magmatic underplating, volcanism and erosion processes.

Landslides affect millions of people worldwide, but theoretical and empirical studies on the impact of landslides remain scarce, especially in Sub-Saharan Africa. This study proposes and applies a method to estimate the direct impact of landslides on household income and to investigate the presence of specific risk sharing and mitigation strategies towards landslides in a tropical and rural environment. An original cross-sectional household survey is used in combination with geographical data to acquire detailed information on livelihoods and on hazards in the Rwenzori mountains, Uganda. Ordinary least squares regressions and probit estimations with village fixed effects are used to estimate the impact of landslides and the presence of mitigation strategies. Geographical information at household level allows to disentangle the direct impact from the indirect effects of landslides. We show that the income of affected households is substantially reduced during the first years after a landslide has occurred. We find that members of recently affected households participate more in wage-employment or in self-employed activities, presumably to address income losses following a landslide. Yet, we see that these jobs do not provide sufficient revenue to compensate for the loss of income from agriculture. Given that landslides cause localized shocks, finding a significant direct impact in our study indicates that no adequate risk sharing mechanisms are in place in the Rwenzori sub-region. These insights are used to derive policy recommendations for alleviating the impact of landslides in the region. By quantifying the direct impact of landslides on household income in an agricultural context in Africa this study draws the attention towards a problem that has been broadly underestimated so far and provides a sound scientific base for disaster risk reduction in the region. Both the methodology and the findings of this research are applicable to other tropical regions with high landslide densities. publisher: Elsevier articletitle: The direct impact of landslides on household income in tropical regions: A case study from the Rwenzori Mountains in Uganda journaltitle: Science of The Total Environment articlelink: http://dx.doi.org/10.1016/j.scitotenv.2016.01.171 content_type: article copyright: Copyright © 2016 Elsevier B.V. All rights reserved. ispartof: Science of the Total Environment vol:550 pages:1032-1043 ispartof: location:Netherlands status: published

Monogenetic volcanoes are widespread in the East African Rift. Their morphologies are diverse with positive (scoria and tuff cones) and negative reliefs (tuff rings and maars). The Manyara Rift (Tanzania) and Albertine Rift (Uganda) are characterised by a singular abundance of negative volcanic reliefs with about 300 and 350 maars and tuff rings, respectively, covering a surface of about ∼3000 km 2 in each country. Such high density of explosive craters is not observed elsewhere in the East African Rift. We perform spatial distribution and alignment analyses using two different approaches (Two Point Analysis and Point Alignments) to study the link between the distribution of the monogenetic volcanic vents, the rift structures, and the stress field. Both methods give similar results although the Point Alignments perform better for large radius of investigations. Volcanic alignments in the Manyara rift suggest a dominant control of the old basement and rift structures on dyke emplacement and distribution of volcanic vents, under an oblique rifting. However, data further suggest that this influence is reducing, and the rift is entering a more mature phase with orthogonal rifting. On the other hand, volcanic alignments in the Albertine rift imply a dominant control of the stress field on dyke emplacement and on the distribution of volcanic vents under orthogonal rifting. This suggests that the Albertine rift is a mature rift since at least the past 50 000 yrs. We further tested the influence of rift structures and stress field on maar and tuff ring morphologies. Most of the craters are near-circular, or a least not strongly elongated, and show minor complexities in shape which we attribute to lateral migration of explosions. Few maars and tuff rings in Manyara show that lateral migration have followed pre-existing faults. In general, we advise not to fit an ellipse to individual maars and tuff rings to assess the orientation of the feeder intrusions.

Mount Elgon in Eastern Uganda is one of the most landslide-prone regions in Africa. This extinct shield volcano is characterized by steep slopes, intense precipitation, and fertile lands supporting a dense human population. As a result, landslides frequently cause damage and many fatalities. Apart from the need for a landslide susceptibility assessment, insight into the landslide mobilization rates [ton/km2/y] is required to assess the geomorphological importance of landslides. Such quantitative information is scarce for many regions around the world and particularly for Africa. We therefore compiled a calibration dataset of 653 landslides (514 slides and 139 rockfalls). Additionally, a second dataset of over 400 landslides was independently collected for validation purposes. To determine a logistic landslide susceptibility model, we used Monte Carlo simulations that selected different subsets of the calibration dataset to test the significance of the considered environmental variables. Susceptibility maps for all landslide types and for rockfalls were constructed for the Mount Elgon region in Uganda. In both maps, topography is by far the most significant factor controlling landslide susceptibility. Including lithology and soil moisture, further improved the model predictions. The models explain about 55% and 85% of the observed variance in landslide occurrence for all landslide types and for rockfalls respectively. The average calculated landslide frequency and mobilization rate for the landslide affected area are respectively 0.04 landslides/km2/y and 750 ton/km2/y. Landslide size is only weakly positively correlated with landslide susceptibility. Therefore, observed larger landslide mobilization rates correlating with higher landslide susceptibilities result from larger landslide numbers rather than from larger landslides. Our research highlights the relevance of detailed and long-term landslide mapping at the regional scale in data-scarce areas for regional planning and risk reduction strategies, as an improvement to continental and global susceptibility models, but also to assess the geomorphological importance of landslides as an erosion process.

Natural hazards have a large impact on household livelihoods worldwide, especially in the Global South. Yet, literature on the adoption of risk reduction measures at household level remains scattered and inconclusive. This study combines geographical data with an original cross-sectional household survey to investigate the relation between individual land use plans and both exposure to and experience with a natural hazard. Regressions are used to test the protection motivation theory (PMT) and to investigate the link between intentions to plant trees to reduce landslide risk and past experiences, actual exposure, perceived threat and perceived capacity to prevent the occurrence of landslides. The results show that respondents in our study area in Uganda are well aware of landslide risk and believe trees are effective in landslide susceptibility reduction. Yet, those farmers that would benefit most from reducing landslide susceptibility by planting trees have the lowest intention to do so. A low self-efficacy among exposed farmers is proposed to explain this result. This finding has important implications for disaster risk reduction and land use policies and leads to recommendations on how governments and development agents should communicate about landslide risk.

Land use is rapidly changing within the Mekong delta due to decisions of local actors. This study aims at understanding the factors influencing the understanding of inhabitants about the concepts, causes and effects of land use and cover changes (LUCC), as well as how they perceive and act about LUCC management. A Knowledge-Attitude-Practice (KAP) survey was carried out on a sample of 330 households in the Tran Van Thoi District, Ca Mau Province in the Mekong Delta, Vietnam. The respondents were surveyed on their knowledge of the conceptualization of LUCC, how LUCC are caused and what their consequences are. The results highlight the political, socio-demographic, economic and environmental causes and effects considered as meaningful by the respondents for understanding LUCC process. Multiple logistic regression (MLR) models with nested cross-validation were developed for investigating the factors influencing the knowledge, attitude and practice of individual households. Although variation exists in the significant predictors of the different K-A-P components, educational level, age, participation in group activity, access to communication mean, and occupation (farming or permanent employment) are shown to be the main influencing variables. The knowledge of the concept of LUCC, and to a lower extent of its causes and consequences, highly correlates with the Attitude and Practice regarding LUCC management, indicating the necessity of disseminating and enhancing LUCC understanding among local actors before implementing land use management projects.

Shield volcanoes are described as low-angle edifices built primarily by the accumulation of successive lava flows. This generic view of shield volcano morphology is based on a limited number of monogenetic shields from Icelandand Mexico, and a small set of large oceanic islands (Hawaii, Galápagos). Here, the morphometry of 158 monogenetic and polygenetic shield volcanoes is analyzed quantitatively from 90-meter resolution SRTM DEMs using the MORVOLC algorithm. An additional set of 24 lava-dominated ?shield-like? volcanoes, considered so far as stratovolcanoes, are documented for comparison. Results show that there is a large variation in shield size (volumes from 0.1 to >1000 km3), profile shape (height/basal width (H/WB) ratios mostly from 0.01 to 0.1), flank slope gradients (average slopes mostly from 1° to 15°), elongation and summit truncation. Although there is no clear-cut morphometric difference between shield volcanoes and stratovolcanoes, an approximate threshold can be drawnat 12° average slope and 0.10 H/WB ratio. Principal component analysis of the obtained database enables to identify four key morphometric descriptors: size, steepness, plan shape and truncation. Hierarchical cluster analysis ofthese descriptors results in 12 end-member shield types, with intermediate cases defining a continuum of morphologies. The shield types can be linked in terms of growth stages and shape evolution, related to (1) magma composition and rheology, effusion rate and lava/pyroclast ratio, which will condition edifice steepness; (2) spatial distribution of vents, in turn related to the magmatic feeding system and the tectonic framework, which will control edifice plan shape; and (3) caldera formation, which will condition edifice truncation. Fil: Grosse, Pablo. Fundación Miguel Lillo. Dirección de Geología. Instituto de Minerología y Petrografia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina Fil: Kervyn, Matthieu. Vrije Universiteit Brussel; Bélgica

We report on spectral reflectance measurements of basaltic lava flows on Tenerife Island, Spain. Lava flow surfaces of different ages, surface roughness and elevations were systematically measured using a field spectroradiometer operating in the range of 350–2500 nm. Surface roughness, oxidation and lichen coverage were documented at each measured site. Spectral properties vary with age and morphology of lava. Pre-historical lavas with no biological coverage show a prominent increase in spectral reflectance in the 400–760 nm range and a decrease in the 2140–2210 nm range. Pāhoehoe surfaces have higher reflectance values than ʻaʻā ones and attain a maximum reflectance at wavelengths &lt, 760 nm. Lichen-covered lavas are characterized by multiple lichen-related absorption and reflection features. We demonstrate that oxidation and lichen growth are two major factors controlling spectra of Tenerife lava surfaces and, therefore, propose an oxidation index and a lichen index to quantify surface alterations of lava flows: (1) the oxidation index is based on the increase of the slope of the spectral profile from blue to red as the field-observed oxidation level strengthens, and (2) the lichen index is based on the spectral reflectance in the 1660–1725 nm range, which proves to be highly correlated with lichen coverage documented in the field. The two spectral indices are applied to Landsat ETM+ and Hyperion imagery of the study area for mapping oxidation and lichen coverage on lava surfaces, respectively. Hyperion is shown to be capable of discriminating different volcanic surfaces, i.e., tephra vs. lava and oxidized lava vs. lichen-covered lava. Our study highlights the value of field spectroscopic measurements to aid interpretation of lava flow characterization using satellite images and of the effects of environmental factors on lava surface evolution over time, and, therefore, has the potential to contribute to the mapping as well as dating of lava surfaces.

Detailed historical records of rift volcanism are scarce. Such information is, however, of a great importance to study the role of magmatism and volcanism as forces contributing to continental rifting. Nyamulagira (or Nyamuragira) volcano, located in the western branch of the East African Rift System, is one of the most active volcanoes on Earth and, hence, represents a good case study to investigate the spatial and temporal evolution of eruptive activity in a youthful extensional setting. Since 1882, Nyamulagira produced at least 42 eruptions, offering a dense historical record for that time period. Using scientific literature, including colonial scientific documents archived at the Royal Museum for Central Africa in Belgium, field data and a detailed mapping of the volcanic field, the spatial and temporal evolution of the eruptive activity of Nyamulagira is studied in order to 1) review the current state of knowledge on eruption history and dynamics at that volcano, and 2) infer the influence of the rift on factors controlling the location, occurrence and characteristics of Nyamulagira eruptions. The results show that the duration and location of eruptions allow the distinction of four eruption groups: summit/upper-flank, classical flank, long-lived flank and remote eruptions. The interpretation of these groups suggests that Nyamulagira eruptions are related to the main crustal magmatic system and are strongly influenced by the gravitational stress field induced by the main central edifice. However, remote eruptions (1904, 1912, 1948, 1991–1993) are not influenced by this edifice loading and seem directly related to deeper magma reservoirs. The 1938–1940 eruption is also atypical, but is related to an important drainage of the upper magma plumbing system, which triggered a caldera collapse. No tectonic trigger of eruption is evidenced, but cone and eruptive fissure alignments suggest that rift structures can also influence the eruption location. In addition, the present study suggests that the major eruptions of Nyamulagira along structural axes close to Nyiragongo can induce a change in the eruptive activity of the latter hazardous volcano. Hence, the historical eruptive activity of Nyamulagira highlights the complex interplay between the magmatic system and the local and regional stress fields in controlling the location and characteristics of eruptions, in this youthful extensional tectonic setting where main volcanic edifices developed.

With its exceptionally steep topography, wet climate, and active faulting, landslides can be expected to occur in the Rwenzori Mountains. Whether or not this region is prone to landsliding and more generally whether global landslide inventories and hazard assessments are accurate in data-poor regions such as the East African highlands are thus far unclear. In order to address these questions, a first landslide inventory based on archive information is built for the Rwenzori Mountains. In total, 48 landslide and flash flood events, or combinations of these, are found. They caused 56 fatalities and considerable damage to road infrastructure, buildings, and cropland, and rendered over 14,000 persons homeless. These numbers indicate that the Rwenzori Mountains are landslide-prone and that the impact of these events is significant. Although not based on field investigations but on archive data from media reports and laymen accounts, our approach provides a useful complement to global inventories overlooking this region and increases our understanding of the phenomenon in the Rwenzori Mountains. Considering the severe impacts of landslides, the population growth and related anthropogenic interventions, and the likelihood of more intense rainfall conditions, there is an urgent need to invest in research on disaster risk reduction strategies in this region and other similar highland areas of Africa.

The main objective of this study is to assess the spatio-temporal dynamics of land cover/land use changes in the lower Mekong Delta over the last 40 years with the coastal Tran Van Thoi District of Ca Mau Province, Vietnam as a case study. Land cover/land use change dynamics are derived from moderate to high spatial resolution (Landsat and SPOT) satellite imagery in six time intervals ranging from 1973 to 2011. Multi-temporal satellite images were collected, georeferenced, classified using per-pixel method, validated, and compared in post classification for the land use/land cover change detection in decades. Seven major land cover/land use classes were obtained, including cultivated lands, aquaculture ponds, mangrove forest, melaleuca forest, built up areas, bare lands, and natural water bodies. The accuracies of the land cover/land use maps for 1973, 1979, 1989, 1995, 2004, and 2011 were 81%, 82%, 86%, 87%, 89%, and 89%, respectively. The results show that the area of cultivated lands reduced over the period 1973–2011, however, it still represents the dominant land use in the case study. Aquaculture ponds were almost absent in 1973 but greatly increased from 1995 to 2004, to represent 20% of the land surface in 2011. Overall, from 1973 to 2011, bare lands, cultivated lands, mangrove forest, and melaleuca forest decreased by 104 km2, 77 km2, 61 km2, and 5 km2, respectively. In contrast, aquaculture lands and built up areas increased by 123 km2 and 120 km2, respectively. Temporal analysis highlights that these changes took place mostly between 1995 and 2004. This study is a first step to identify the main drivers of land use changes in this delta region, which include economical policies as well as demographic, socio-economic, and environmental changes.

The age of past lava flows is crucial information for evaluating the hazards and risks posed by effusive volcanoes, but traditional dating methods are expensive and time-consuming. This study proposes an alternative statistical dating method based on remote sensing observations of tropical volcanoes by exploiting the relationship between lava flow age and vegetation cover. First, the factors controlling vegetation density on lava flows, represented by the normalized difference vegetation index (NDVI), were investigated. These factors were then integrated into pixel-based multi-variable regression models of lava flow age to derive lava flow age maps. The method was tested at a pixel scale on three tropical African volcanoes with considerable recent effusive activity: Nyamuragira (Democratic Republic of Congo), Mt Cameroon (Cameroon) and Karthala (the Comoros). Due to different climatic and topographic conditions, the parameters of the spatial modeling are volcano-specific. Validation suggests that the obtained statistical models are robust and can thus be applied for estimating the age of unmodified undated lava flow surfaces for these volcanoes. When the models are applied to fully vegetated lava flows, the results should be interpreted with caution due to the saturation of NDVI. In order to improve the accuracy of the models, when available, spatial data on temperature and precipitation should be included to directly represent climatic variation. Copyright (c) 2017 John Wiley & Sons, Ltd.

The 28 March to 22 April 1999 eruption of Mount Cameroon volcano in southwest Cameroon occurred from multiple vents along fissures at two sites. Vents opened first at the upper site 1 (2650 m) and were more explosive than vents at the lower site 2 (1500 m), which were more effusive. Earthquakes, lava flows, tephra fall, ballistics and gas emissions affected the volcano's west and south flanks, including forests, plantations, stock animals, water supplies, coastal communities and their people. Through an analysis of existing published data and new interview data, we provide an overview of the environmental, social and economic consequences of these hazards on infrastructure, human health, and socio-economic and agricultural activities of the four coastal communities most affected by the eruption: Batoke, Bakingili, Debundscha and Idenau. The collected data provide a more detailed description of the short- and long-term direct and indirect effects of the eruption and response than has been provided to date. Sedimentation of tephra and ballistics from site 1 produced both short-term and long-lasting impacts on people, through the contamination of plants and water supplies, which induced impacts on human health and commercial activities. A ~9.2 km long lava flow erupted from site 2 received significant short-term attention as it severed the only arterial coastal highway, forced the evacuation of some 600 residents of Bakingili, and interrupted commerce between communities. The agricultural sector also suffered due to burning of crops and soils. The only obvious significant benefit of the eruption appears to be that the long lava flow has become a tourist attraction, responsible for bringing in money for food, drink and lodging. However, the long-term cascading effects caused by the hazards have proven to be more severe than the immediate direct and indirect effects during the eruption.

We present an integrated, spatially-explicit database of existing geochemical major-element analyses available from (post-) colonial scientific reports, PhD Theses and international publications for the Virunga Volcanic Province, located in the western branch of the East African Rift System. This volcanic province is characterised by alkaline volcanism, including silica-undersaturated, alkaline and potassic lavas. The database contains a total of 908 geochemical analyses of eruptive rocks for the entire volcanic province with a localisation for most samples. A preliminary analysis of the overall consistency of the database, using statistical techniques on sets of geochemical analyses with contrasted analytical methods or dates, demonstrates that the database is consistent. We applied a principal component analysis and cluster analysis on whole-rock major element compositions included in the database to study the spatial variation of the chemical composition of eruptive products in the Virunga Volcanic Province. These statistical analyses identify spatially distributed clusters of eruptive products. The known geochemical contrasts are highlighted by the spatial analysis, such as the unique geochemical signature of Nyiragongo lavas compared to other Virunga lavas, the geochemical heterogeneity of the Bulengo area, and the trachyte flows of Karisimbi volcano. Most importantly, we identified separate clusters of eruptive products which originate from primitive magmatic sources. These lavas of primitive composition are preferentially located along NE-SW inherited rift structures, often at distance from the central Virunga volcanoes. Our results illustrate the relevance of a spatial analysis on integrated geochemical data for a volcanic province, as a complement to classical petrological investigations. This approach indeed helps to characterise geochemical variations within a complex of magmatic systems and to identify specific petrologic and geochemical investigations that should be tackled within a study area.

Mapping lava flows using satellite images is an important application of remote sensing in volcanology. Several volcanoes have been mapped through remote sensing using a wide range of data, from optical to thermal infrared and radar images, using techniques such as manual mapping, supervised/unsupervised classification, and elevation subtraction. So far, spectral-based mapping applications mainly focus on the use of traditional pixel-based classifiers, without much investigation into the added value of object-based approaches and into advantages of using machine learning algorithms. In this study, Nyamuragira, characterized by a series of > 20 overlapping lava flows erupted over the last century, was used as a case study. The random forest classifier was tested to map lava flows based on pixels and objects. Image classification was conducted for the 20 individual flows and for 8 groups of flows of similar age using a Landsat 8 image and a DEM of the volcano, both at 30-meter spatial resolution. Results show that object-based classification produces maps with continuous and homogeneous lava surfaces, in agreement with the physical characteristics of lava flows, while lava flows mapped through the pixel-based classification are heterogeneous and fragmented including much “salt and pepper noise”. In terms of accuracy, both pixel-based and object-based classification performs well but the former results in higher accuracies than the latter except for mapping lava flow age groups without using topographic features. It is concluded that despite spectral similarity, lava flows of contrasting age can be well discriminated and mapped by means of image classification. The classification approach demonstrated in this study only requires easily accessible image data and can be applied to other volcanoes as well if there is sufficient information to calibrate the mapping.

As a disaster prone country, Bangladesh is regularly hit by natural hazards, including devastating cyclones, such as in 1970, 1991 and 2007. Although the number of cyclones’ fatalities reduced from 0.3 million in 1970 to a few thousand or fewer in recent events, loss of lives and impact on livelihoods remains a concern. It depends on the meteorological characteristics of cyclone and the general vulnerability and capacity of the exposed population. In that perspective, a spatially explicit risk assessment is an essential step towards targeted disaster risk reduction. This study aims at analyzing the spatial variation of the different factors contributing to the risk for coastal communities at regional scale, including the distribution of the hazards, exposure, vulnerability and capacity. An exploratory factor analysis method is used to map vulnerability contrasts between local administrative units. Indexing and ranking using geospatial techniques are used to produce maps of exposure, hazard, vulnerability, capacities and risk. Results show that vulnerable populations and exposed areas are distributed along the land sea boundary, islands and major inland rivers. The hazard, assessed from the density of historical cyclone paths, is highest in the southwestern part of the coast. Whereas cyclones shelters are shown to properly serve the most vulnerable populations as priority evacuation centers, the overall pattern of capacity accounting for building quality and road network shows a more complex pattern. Resultant risk maps also provide a reasonable basis from which to take further structural measures to minimize loss of lives in the upcoming cyclones.

Meru volcano is located within the Northern Tanzanian Divergence Zone where the east branch of the East African Rift splits into several branches. The 4565-m-high Meru volcano is breached on the east flank by a horseshoe-shaped scar following a major collapse associated with the Momella debris avalanche approximately 9000 years ago. Remote sensing combined with detailed field mapping allowed the characterisation of the Momella debris avalanche deposit, structure, and texture. Hummocks, ridges, lineaments, lobes, grabens and shear zones are observed on the surface of the deposit. The most common facies observed are the mixed facies with indurated and shattered outcrops and the matrix facies. The collapse involved a volume of 20 ± 2 km 3 with a deposit that spread over an area of 1250 km 2, up to the base of Kilimanjaro. Based on field evidence, we suggest that water played a key role in the deformation, facies formation, avalanche emplacement and mobility of the entire deposit but to a lesser extent south of Ngurodoto complex. The deformation and emplacement of the avalanche were accommodated by both extension and shearing on a water-fluidised basal layer.

© 2017, © The Author(s) 2016. The overall objective of this review is to gain insights into landslide risk reduction measures that are applied or recommended in tropical landslide-prone countries, and the challenges at play. More specifically, this review aims to (i) presenting an overview of recent studies on landslides and landslide risk reduction in these countries, (ii) exploring the factors controlling the publication output on landslides and landslide risk reduction, (iii) reviewing the various landslide risk reduction measures recommended and implemented, and (iv) identifying the bottlenecks for the implementation of these strategies. A compilation of recommended and implemented landslide risk reduction measures in 99 landslide-prone tropical countries was made, based on an extensive review of scientific literature (382 publications). The documented measures are analysed using a scheme of risk reduction measures that combines classifications of the Hyogo Framework for Action and the SafeLand project. Our literature review shows that the factors influencing the number of publications on landslides and landslide risk reduction per country are (in order of importance) the absolute physical exposure of people to landslides, the population number and the Human Development Index of a country. The ratio of publications on landslide risk reduction versus publications on landslides for landslide-prone tropical countries does not vary much between these countries (average: 0.28). A significant fraction (0.30) of all known landslide hazard reduction measures are neither implemented nor recommended according to our review. The most recommended landslide risk reduction component is ‘risk management and vulnerability reduction’ (0.38). However, the most implemented component is ‘risk assessment’ (0.57). Overall, the ratio of implemented versus recommended landslide risk reduction measures in the tropics is low (

International audience; Mount Cameroon is characterized by an elongated summit plateau, steep flanks, and topographic terraces around its base. Although some of these features can be accounted for by intrusion-induced deformation, we here focus on the contribution of edifice-scale gravitational spreading in the structure of Mount Cameroon. We review the existing geological and geophysical data and morphostructural features of Mount Cameroon and surrounding sedimentary basins. Volcanic ridge gravitational spreading is then simulated by scaled analogue models on which fault formation is recorded using digital image correlation. Three sets of models are presented (i) models recorded in cross section (Type I), (ii) models recorded from above with a uniform (Type IIa), and (iii) nonuniform ductile layer (Type IIb). Type I models illustrate the formation of faults accommodating summit subsidence and lower flank spreading. Type IIa models favor displacement perpendicular to the long axis, with formation of a summit graben and basal folds, but fail to reproduce the steep flanks. Type IIb models investigate the effect of spatial variations in sediment thickness and/or properties consistent with geological evidence. Directional spreading of the volcano's central part perpendicular to the long axis is accounted for by a sediment layer with restricted lateral extent and increasing thickness away from the volcano axis. The later model closely reproduces key features observed at Mount Cameroon: steep upper flanks are accounted for by enhanced lateral spreading of the lower flanks relative to the summit. The relevance of these findings for understanding flank instabilities at large oceanic volcanoes is finally highlighted.

Volumetric depletion of a subsurface body commonly results in the collapse of overburden and the formation of enclosed topographic depressions. Such depressions are termed sinkholes in karst terrains and pit craters or collapse calderas in volcanic terrains. This paper reports the first use of computed X-ray microtomography (mu CT) to image analog models of small-scale (similar to< 2 km diameter), high-cohesion, overburden collapse induced by depletion of a near-cylindrical ("stock-like") body. Time-lapse radiography enabled quantitative monitoring of the evolution of collapse structure, velocity, and volume. Moreover, mu CT scanning enabled nondestructive visualization of the final collapse volumes and fault geometries in three dimensions. The results illustrate two end-member scenarios: (1) near-continuous collapse into the depleting body; and (2) near-instantaneous collapse into a subsurface cavity formed above the depleting body. Even within near-continuously collapsing columns, subsidence rates vary spatially and temporally, with incremental accelerations. The highest subsidence rates occur before and immediately after a surface depression is formed. In both scenarios, the collapsing overburden column undergoes a marked volumetric expansion, such that the volume of subsurface depletion substantially exceeds that of the resulting topographic depression. In the karst context, this effect is termed "bulking," and our results indicate that it may occur not only at the onset of collapse but also during progressive subsidence. In the volcanic context, bulking of magma reservoir overburden rock may at least partially explain why the volume of magma erupted commonly exceeds that of the surface depression.

Of the features that characterize large shield volcanoes on Mars, flank terraces remain the most enigmatic. Several competing mechanisms have been proposed for these laterally expansive, topographically subtle landforms. Here we test the hypothesis that horizontal contraction of a volcano in response to the down-flexing of its underlying basement leads to flank terracing. We performed a series of analogue models consisting of a conical sand–plaster load emplaced on a basement comprising a layer of brittle sand–plaster atop a reservoir of viscoelastic silicone. Our experiments consistently produced a suite of structures that included a zone of concentric extension distal to the conical load, a flexural trough adjacent to the load base and convexities (terraces) on the cone’s flanks. The effects of variations in the thickness of the brittle basal layer, as well as in the volume, slope and planform eccentricity of the cone, were also investigated. For a given cone geometry, we find that terrace formation is enhanced as the brittle basement thickness decreases, but that a sufficiently thick brittle layer can enhance the basement’s resistance to loading such that terracing of the cone is reduced or even inhibited altogether. For a given brittle basement thickness, terracing is reduced with decreasing cone slope and/or volume. Our experimental results compare well morphologically to observations of terraced edifices on Mars, and so provide a framework with which to understand the developmental history of large shield volcanoes on the Red Planet.

As for many other effusive volcanoes, Mount Cameroon (MC) is a volcano for which only limited information exists on lava flow properties and emplacement dynamics for recent eruptions. This study provides new quantitative constraints for rheological and dynamic characteristics of lava flow effusion for the 1982 and 2000 eruptive events, used to calibrate the FLOWGO thermo-rheological model for these lava flows. The FLOWGO 1-D physical model is used to simulate down-flow evolution of the geometry and rheology of channel-contained cooling-limited lava flows. Morphometric data from historical lava flows were acquired from the field, e.g. channel geometry, levee and background slope, in order to estimate lava yield strength, velocity and effusion rate. Lava density and viscosity were also estimated from compositional data and laboratory methods. To account for uncertainty in the input rheological and geometrical data, three end-member scenarios were used to bracket the potential range in lava channel initial dimension, initial lava temperature and phenocryst content. For each of these scenarios, two crustal growth models were used: one assuming strong insulation due to lava flow surface crusting, the other a much lower crusting rate. Twelve numerical simulations were made per flow and the results were compared against the channel geometry, microlite content, yield strength and viscosity estimates from field and laboratory investigations. Best-fit models where obtained for both the 1982 and 2000 lava flows using a low rate of surface crusting, high initial temperature and low phenocryst content. Model-predicted lengths were within 5% of the actual lengths. Modelled mean effusion rates for the 1982 (52–64 m 3 s − 1 ) and 2000 (10 m 3 s − 1 ) flows closely matched field data derived estimations (26–68 and 9.5 m 3 s − 1 respectively). FLOWGO model results are highly sensitive to initial channel dimensions, phenocryst content and the FLOWGO model is unable to reproduce the observed rapid near-vent increase in microlite content. Near-vent rapid cooling induced by lava degassing is yet to be fully documented and integrated into numerical lava flow models such as FLOWGO, but obtained results already provide valuable insights for lava flow hazard assessment at Mount Cameroon.

Over the past 50 years, at least seven major flash floods have affected catchments of the Rwenzori Mountains. The Rwenzori Mountains are not only subject to flash floods; forest fires, earthquakes and landslides occur as well. Many of the flash floods therefore co-occurred with other hazards. One of the most devastating of these events occurred on May 1st 2013, in the Nyamwamba catchment. Here we reconstruct the circumstances under which this flash flood event was triggered and its effects in this multi-hazard region. This includes the identification and characterization of different processes acting upon the catchment dynamics, their controlling and triggering factors and the estimation of the damaging effects of the flash flood within the catchment. The combined occurrence of intense rainfall, a forest fire having burned 18% of the catchment area and the occurrence of 29 landslides providing debris to the river system, induced a debris-rich and very destructive flash flood which caused several fatalities, the destruction of 70 buildings, several bridges, a hospital and a school, a tarmac road and several life lines. Peak flow discharge is estimated between 850 and 1300 m3/s. This case-study demonstrates that flash floods in the region should not be considered as self-determined phenomena but as a result of several cascading and interacting hazard processes including wildfires and landslides, occurring within a short time period.

Basaltic eruptions have been observed to produce structurally complex, compound 'a'ā lava flow fields but their morphometry has only rarely been systematically documented. We document the morphology and structures that developed during the emplacement of the 1982 basaltic lava flow field at Mount Cameroon (MC) volcano over a period of one month. Topographic cross-sections (13 in total) were made from the main vent (~2700 m above sea level (a.s.l)) down to a distance of 5.5 km on the cooled lava surface. Details obtained from these cross-sections include: channel width and depth, levee slope, lava surface morphology and structures. These details enabled us to describe the physical characteristics of the 1982 lava flow field. The inclined (12° - 19°) underlying slopes on which this flow field was emplaced resulted in a characteristic channelized basaltic 'a'ā flow field morphology. This includes a proximal zone characterised by reduced flow width and depth with no subsidiary channels. Slab-crusted lava dominates the proximal channel distinctively bent into convex upward shapes. 7 secondary vents were observed for the first time ~2.5 km from the main vent, with heights of 3 - 15 m. This is a very significant observation since it points to the fact that the flow field emplacement may have been a product of 2 eruption sites as observed at other historical MC lava flow fields. This supposition was ruled out by further evidence obtained from other surface features within the flow field. The presence of these secondary vents still has an important bearing in lava flow hazard assessment. Field observations also revealed the presence of tumulus. This is a novel feature for MC lava flow fields. It displayed a close similarity to those observed at other basaltic volcanoes occurring in association with clinker 'a'ā lava, lava tubes, squeeze-ups and pressure ridges. Channels are well-defined, bounded by levees. Accretional and overflow levees dominate in this flow field. This lava flow-field attained a final length of 7.5 km, an area of 2.6 × 106 m2 and volume of 1.3 × 107 m3. The presence of tumulus indicates internal inflation together with structures such as pressure ridges and squeeze-ups which are also attributed to compressive forces. Our observations suggest that real-time monitoring of compound lava flow fields evolution at MC may reveal the emplacement mechanisms of complex structures such as the secondary vents (~2180 - 2011 m a.s.l.) observed within the flow field. In addition, documenting the occurrence, morphology and link between lava tubes, tumulus and squeeze-ups may allow us to determine the risk of reactivation of a stalled flow front. This will thereby enhance the ability to track and assess hazards posed by lava flow emplacement from MC-like volcanoes.

The Virunga Volcanic Province (VVP) represents the most active zone of volcanism in the western branch of the East African Rift System. While the VVP’s two historically active volcanoes, Nyamulagira and Nyiragongo, have built scoria cones and lava flows in the adjacent lava fields, several small phreatomagmatic eruptive centers lie along Lake Kivu’s northern shoreline, highlighting the potential for explosive magma-water interaction. Their presence in the densely urbanized Sake-Goma-Gisenyi area necessitates an assessment of their eruptive mechanisms and chronology. Some of these eruptive centers possess multiple vents, and depositional contacts suggest distinct eruptive phases within a single structure. Depositional facies range from polymict tuff breccia to tuff and loose lapilli, often impacted by blocks and volcanic bombs. Along with the presence of dilute pyroclastic density current (PDC) deposits, indicators of magma-water interaction include the presence of fine palagonitized ash, ash aggregates, cross-bedding, and ballistic impact sags. We estimate that at least 15 phreatomagmatic eruptions occurred in the Holocene, during which Lake Kivu rose to its current water level. Radiocarbon dates of five paleosols in the top of volcanic tuff deposits range between ∼2500 and ∼150 cal. year BP and suggest centennial- to millennial-scale recurrence of phreatomagmatic activity. A vast part of the currently urbanized zone on the northern shoreline of Lake Kivu was most likely impacted by products from phreatomagmatic activity, including PDC events, during the Late Holocene, highlighting the need to consider explosive magma-water interaction as a potential scenario in future risk assessments.

This study analyses the behaviour and mobility of major and some trace elements during the physical and chemical development of landslide-prone soil profiles in Limbe, SW Cameroon. The soils result from in situ weathering of Tertiary basaltic and picrobasaltic rocks. Textural and chemical characterisations, together with two mass balance models are applied to understand the mobility and redistribution of elements during the weathering of pyroclastic cones and lava flows. Weathering indices are used to estimate the extent of weathering. The chemical composition of the samples is evaluated by Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP–OES) and their mineralogical composition by X-Ray Diffraction (XRD) analyses. It is observed that intensive weathering results in thick meta-stable soils in which significant loss of Ca, K, Mg, Na and Sr has taken place. There is a noticeable relative enrichment in all analysed trace elements (Ba, Zr, Y, Sc, V, Ni, and Co). Ti, Fe, Al, Mn, P and Ce tend to be leached in some horizons and concentrated in others. Zr, Ti, and Ce concentrations are greater in the soils than in the bedrock but show slight fluctuations in the soil and saprolites hence cannot be used as immobile elements for mass balance evaluations. Y increases progressively with advanced weathering. Major secondary mineral phases developed through weathering are a mixture of expanding (smectites) and non-expanding clays (kaolinite, halloysite and mica). The profiles show the presence of textural heterogeneities that can be exploited as slip surfaces. Data plotted in Si–Al–Fe diagram point out that the most advanced stage of weathering noted in these profiles is the kaolinisation stage.

Volcanic cones are the most common volcanic constructs on Earth. Their shape can be quantified using two morphometric ratios: the crater/cone base ratio (Wcr/Wco) and the cone height/width ratio (Hco/Wco). The average values for these ratios obtained over entire cone fields have been explained by the repose angle of loose granular material (i.e. scoria) controlling cone slopes. The observed variability in these ratios between individual cones has been attributed to the effect of erosional processes or contrasting eruptive conditions on cone morphometry. Using a GIS-based approach, high spatial resolution Digital Elevation Models and airphotos, two new geomorphometry datasets for cone fields at Mauna Kea (Hawaii, USA) and Lanzarote (Canary Islands, Spain) are extracted and analyzed here. The key observation in these datasets is the great variability in morphometric ratios, even for simple-shape and well-preserved cones. Simple analog experiments are presented to analyze factors influencing the morphometric ratios. The formation of a crater is simulated within an analog cone (i.e. a sand pile) by opening a drainage conduit at the cone base. Results from experiments show that variability in the morphometric ratios can be attributed to variations in the width, height and horizontal offset of the drainage point relative to the cone symmetry axis, to the dip of the underlying slope or to the influence of a small proportion of fine cohesive material. GIS analysis and analog experiments, together with specific examples of cones documented in the field, suggest that the morphometric ratios for well-preserved volcanic cones are controlled by a combination of 1) the intrinsic cone material properties, 2) time-dependent eruption conditions, 3) the local setting, and 4) the method used to estimate the cone height. Implications for interpreting cone morphometry solely as either an age or as an eruption condition indicator are highlighted.

Limbe town and surrounding areas, on the SE foot slopes of the active Mt Cameroon Volcano, have experienced numerous small-scale shallow landslides within the last 20 years. These resulted in the loss of *30 lives and significant damage to farmland and properties. Landslides and their scars are identified in the field, and their geometry systematically measured to construct a landslide inventory map for the study area. Specific landslides are investigated in detail to identify site-specific controlling and triggering factors. This is to constrain key input parameters and their variability for subsequent susceptibility and risk modeling, for immediate local and regional applications in land-use planning. It will also enable a rapid exploration of remediation strategies that are currently lacking in the SW and NW regions of Cameroon. Typical slides within the study area are small-scale, shallow, translational earth, and debris slides though some rotational earth slides were also documented. The depletion zones have mean widths of 22 m ± 16.7 m and lengths of 25 ± 23 standard deviation. Estimated aerial extents of landslide scars and volume of generated debris range from 10 1 to 10 4 m 2 and 2 to 5 9 10 4 m 3 , respectively. A key finding is that most slope instabilities within the study area are associated with and appear to be exacerbated by man-made factors such as excavation, anarchical construction, and deforestation of steep slopes. High intensity rainfall notably during localized storms is the principal triggering factor identified so far. The findings from this case study have relevance to understanding some key aspects of locally devastating slope instabilities that commonly occur on intensely weathered steep terrains across subtropical Africa and in the subtropics worldwide and affecting an ever denser and most vulnerable population.