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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.

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 (

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

The Mt Cameroon volcano is the highest and most active volcano of the Cameroon Volcanic Line. Little geological information is available for improving the understanding of the structure of this large volcanic system and its relationship to regional tectonics. After reviewing the tectonic evolution of the region, the analysis of a Digital Elevation Model and results from a field campaign dedicated to mapping geological structures in the summit area and at the SE base of Mt Cameroon are presented. Mt Cameroon is a lava-dominated volcano with long steep (over 30°) flanks. It is elongate parallel to its well defined rift zone. The summit plateau is bordered by 10 m high cliffs formed by summit subsidence along normal faults. Geological profiles were measured along rivers cutting through a topographic step at the SE base of Mt Cameroon. This step is associated with deformed Miocene sediments from the Douala basin that are overlain by volcanic products. Weak sediments of this area are deformed by 050°–060° and 020°–030° trending asymmetrical folds verging toward the SE, and thrusts faults related to the spreading of the volcano over its mechanically weak substratum. Combined remote sensing and field observations suggest that spreading is accommodated by summit subsidence and flanks sliding. Both slow spreading movements and catastrophic collapses of the steep flanks are interpreted to result from complex interactions between the growing edifice, repeated dyke intrusions, the weak sedimentary substratum and tectonic structures.

The volcano–tectonic architecture of the Rungwe Volcanic Province in SW Tanzania, part of the East African Rift System, was studied with integrated remote sensing imagery. A Shuttle Radar Topography Mission Digital Elevation Model was draped with geo-referenced geological and topographical maps and air photos. The entire RVP region was inspected systematically for tectonic lineaments and volcanic vents. Tectonic lineaments show two distinct directions, NW–SE and NNE–SSW, consistent with the idea of a current stress regime of local NE–SW compression. We find that there is tectonic control on the regional location for at least two of the three major volcanoes as well as for local distribution of eruptive vents on each of these three volcanoes. Field data show that major volcano instability events occurred in the Holocene for Ngozi caldera and Rungwe. These instability events are possibly associated with the faults controlling the location of both volcanoes. This study highlights the need for monitoring RVP tectonic and volcanic activity.

This study focuses on the compound pahoehoe lava flow fields of the 2000 eruption on Mount Cameroon volcano, West Africa and it comprehensively documents their morphology. The 2000 eruption of Mount Cameroon took place at three different sites (sites 1, 2 and 3), on the southwest flank and near the summit that built three different lava flow fields. These lava flow fields were formed during a long-duration (28th May–mid September) summit and flank eruption involving predominantly pahoehoe flows (sites 2 and 3) and aa flows (site 1). Field observations of flows from a total of four cross-sections made at the proximal end, midway and at the flow front, have been supplemented with data from satellite imagery (SRTM DEM, Landsat TM and ETM+) and are used to offer some clues into their emplacement. Detailed mapping of these lava flows revealed that site 1 flows were typically channel-fed simple aa flows that evolved as a single flow unit, while sites 2 and 3 lava flow fields were fed by master tubes within fissures producing principally tube-fed compound pahoehoe flows. Sites 2 and 3 flows issued from ∼ 33 ephemeral vents along four NE–SW-trending faults/fissures. Pahoehoe morphologies at sites 2 and 3 include smooth, folded and channelled lobes emplaced via a continuum of different mechanisms with the principal mechanism being inflation. The dominant structural features observed on these flow fields included: fissures/faults, vents, levees, channels, tubes and pressure ridges. Other structural features present were pahoehoe toes/lobes, breakouts and squeeze-ups. Slabby pahoehoe resulting from slab-crusted lava was the transitionary lava type from pahoehoe to aa observed at all the sites. Transition zones correspond to slopes of > 10°. Variations in flow morphology and textures across profiles and downstream were repetitive, suggesting a cyclical nature for the responsible processes. Copyright © 2010 John Wiley & Sons, Ltd.

This paper investigates the relative timing of solid Earth tides and thermal anomalies associated with volcanic activity at Oldoinyo Lengai (OL), Tanzania, from 2000 to 2008. The low viscosity of OL's carbonatite magmas may make it particularly susceptible to tidal stresses. Thermal data from the Moderate resolution Imaging Spectroradiometer (MODIS) were filtered using the MODLEN algorithm and Earth tides were modeled using TSoft. Application of the Schuster and Chi-squared tests resulted in apparent correlations between times of thermal anomalies and the phase of the semi-diurnal and biannual solid Earth tides. However, for semi-diurnal and biannual tides limited acquisition times of the MODIS data account for the apparent correlations. Re-examining the data while accounting for the bias introduced by the limited acquisition times, correlations are no longer found. Onset times of eruptive events and times of thermal anomalies show no statistically significant correlation with the fortnightly tide, indicating this is not an influence on activity at OL. Tidal influences on magmatic activity, if at all present, cannot be observed in coarse resolution thermal data on semi-diurnal and fortnightly time scales. Based on the available data, correlations on biannual timescales cannot be ruled out.

Evidence for volcano collapse and debris avalanche deposits (DADs) at Oldoinyo Lengai (OL), Tanzania, has been obtained from mapping and fieldwork. Three major DADs have been identified, named Zebra, Cheetah and Oryx DADs. Field evidence indicates geologically young ages. On this basis a remote sensing (RS) study of the active carbonatite volcano OL and the surrounding rift plain was carried out, using Shuttle Radar Topography Mission (SRTM) digital elevation data, Landsat and ASTER imagery, geological maps and aerial photographs. The SRTM digital elevation model (DEM) allowed morphological characterization of OL and reassessment of the volcano volume to 41±5 km3. This enabled the identification of collapse scars, fields of large hummocks (>300 m across), sharp deposit edges typical of DADs, and estimation of the minimum thickness of the DADs. Multispectral and topographic RS data interpretation allowed mapping of the extent and estimation of the volume of two sector-collapse scars and three DADs. The DADs extend up to 24 km from OL and have volumes ranging from 0.1 to ∼5 km3. Striking radial ridges and grooves were identified in some parts of the DADs. The morphological variability for ridges and grooves in different DADs is attributed to contrasting flow dynamics and avalanching material. A volcano collapse and the corresponding DAD, ∼1 km3 in volume, were also characterized by RS at the nearby Kerimasi volcano. The presence of young DADs highlights the need for routine monitoring of ground deformation and seismicity at OL to anticipate hazardous events.

Applications of remote sensing for studies of volcanic activity and hazards have developed rapidly in the past 40 years. This has facilitated the observation of volcanic processes, such as ground deformation and thermal emission changes, lava flows, eruption clouds, ash and gas emissions, as well as mapping of volcanic structures and hazardous terrain, even for volcanoes in remote regions. Advances in the remote sensing of volcanoes, from ground-based sensors to sensors onboard airborne and spaceborne platforms, are reviewed. A key point made in this review is that volcanic remote sensing could have a much broader impact if the techniques and data were readily available to scientists studying/monitoring potentially hazardous volcanoes in developing countries. Perspectives on particular needs, with regard to sensor types, data availability and training, required to take volcanic remote sensing further in coming years are highlighted.

Mount Cameroon (MC), West Africa's most active volcano, is a typical example of a hazardous volcano in a densely populated area, often inflicting damage by lava flows. The spatial variation of the lava flow hazard has not been mapped systematically at MC and at many other volcanoes in developing countries because they are insufficiently documented and not continuously, systematically monitored with integrated state-of-the-art methods. Sophisticated lava flow models requiring the specification of numerous physical properties cannot yet be applied in such cases. Hence, a low-cost approach is proposed to assess the medium-to long-term spatial variation of lava flow hazard. The 'lava flow zonation system using low-cost methods' (LAZSLO) approach takes advantage of freely available topographic data and moderate-resolution (10-100 m) satellite imagery. For any eruption, the formulation used here expresses the probability of lava flow invasion at any location as a product of the spatial variation of eruption probability and exposure of low-lying terrain to lava flow reach. The last term is derived by determining the upslope area from where lava flows can invade a given site. A standard UNESCO formula is then used to estimate the lava flow risk. Hazard assessment results at MC indicate that the southwest and northeast flanks are the most hazardous from lava flows, whereas the risk of damage is greatest in the area between Limbe, Mapanja and Batoke, where industrial, urban and tourism infrastructures are developing rapidly. The presented approach can be applied to assist local authorities with disaster preparedness and emergency planning at many poorly studied volcanoes, particularly in developing countries with limited financial resources.

Although Tanzania, Kenya and Ethiopia contain a number of active and potentially hazardous volcanoes, none of them are routinely or continuously monitored. Of these, Tanzania's Oldoinyo Lengai (OL) has been active almost continuously over the past two decades (since 1983). Recent activity has been confined to small-scale effusive and explosive eruptions of natrocarbonatite within the summit crater, with lava flows occasionally overflowing the crater rim and extending onto the volcano flanks. The automated MODVOLC algorithm falls short of detecting all thermal anomalies within OL's crater. The sensitivity of the algorithm is insufficient to detect anomalies of the size and magnitude presented by those at OL. We explore how Moderate Resolution Imaging Spectroradiometer (MODIS) infrared (IR) bands can still be used to monitor activity. We cross-verify our observations against field reports and higher resolution satellite images (ASTER, Landsat ETM+). Despite the limited extent and low temperature (∼585°C) of natrocarbonatite lavas, relative variations in eruption intensity and periods of increased activity alternating with periods of reduced or no detectable activity can be observed using the MODLEN algorithm. Although activity in the past two decades has been moderate at OL, a more intense explosive eruption is overdue and there is a need for routine monitoring in the future. Our work makes a case for low-cost thermal IR monitoring as an essential component of such a monitoring programme at several Tanzanian, Kenyan and Ethiopian volcanoes. The approach presented here is already available for routine use.

The largest natrocarbonatite lava flow eruption ever documented at Oldoinyo Lengai, NW Tanzania, occurred from March 25 to April 5, 2006, in two main phases. It was associated with hornito collapse, rapid extrusion of lava covering a third of the crater and emplacement of a 3-km long compound rubbly pahoehoe to blocky aa-like flow on the W flank. The eruption was followed by rapid enlargement of a pit crater. The erupted natrocarbonatite lava has high silica content (3% SiO2). The eruption chronology is reconstructed from eyewitness and news media reports and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data, which provide the most reliable evidence to constrain the eruption’s onset and variations in activity. The eruption products were mapped in the field and the total erupted lava volume estimated at 9.2 ± 3.0 × 105 m3. The event chronology and field evidence are consistent with vent construct instability causing magma mixing and rapid extrusion from shallow reservoirs. It provides new insights into and highlights the evolution of the shallow magmatic system at this unique natrocarbonatite volcano.

Most of the hazardous volcanoes, especially those in developing countries, have not been studied or regularly monitored. Moderate-to-high spatial resolution and 3D satellite remote sensing offers a low-cost route to mapping and assessing hazards at volcanoes worldwide. The capabilities of remote sensing techniques are reviewed and an update of recent developments is provided, with emphasis on low-cost data, including optical (Landsat, ASTER, SPOT, CORONA), topographic (3D ASTER, SRTM) and synthetic aperture radar data. Applications developed here illustrate capabilities of relevant remote sensing data to map hazardous volcanic terrain and derive quantitative data, focusing on mapping and monitoring of volcanic morphology. Limitations of the methods, assessment of errors and planned new sensors are also discussed.

In this study, linear spectral mixture analysis (LSMA) is used to characterize the spectral heterogeneity of lava flows from Nyamuragira volcano, Democratic Republic of Congo, where vegetation and lava are the two main land covers. In order to estimate fractions of vegetation and lava through satellite remote sensing, we made use of 30 m resolution Landsat Enhanced Thematic Mapper Plus (ETM+) and Advanced Land Imager (ALI) imagery. 2 m Pleiades data was used for validation. From the results, we conclude that (1) LSMA is capable of characterizing volcanic fields and discriminating between different types of lava surfaces; (2) three lava endmembers can be identified as lava of old, intermediate and young age, corresponding to different stages in lichen growth and chemical weathering; (3) a strong relationship is observed between vegetation fraction and lava age, where vegetation at Nyamuragira starts to significantly colonize lava flows ∼15 years after eruption and occupies over 50% of the lava surfaces ∼40 years after eruption. Our study demonstrates the capability of spectral unmixing to characterize lava surfaces and vegetation colonization over time, which is particularly useful for poorly known volcanoes or those not accessible for physical or political reasons.

Impacts from ash fallout on the environment can be widespread and long lasting, even from moderate-size eruptions. Assessing ash impact on vegetation and the indirect impacts for people is often difficult in the field. Here it is assessed how satellite data can help to map vegetation affected by ash and how temporal analysis enables characterization of vegetation recovery rate. The 2007–08 eruption of Oldoinyo Lengai, north Tanzania, is here used as a case study. An 8 year-long (2005–2012) time series of half-monthly average of the Normalized Differential Vegetation Index (NDVI) is constructed at 250 m spatial resolution from the Moderate Resolution Image Spectro-radiometer (MODIS) sensor. Interpolated rainfall data is used to isolate NDVI values departing from the normal seasonal cycles. Month-to-month NDVI comparison, linear temporal trend analysis and Principal Component Analysis enable to identify a 11 × 4 km area over which ash fallout significantly affected the state of the vegetation. After the eruption’s end, time series of various recovery indices highlight a circumferential pattern in vegetation recovery. The estimated recovery time varies from more than 5 years to less than 6 months with increasing distance from the volcano. A non-linear moderate, but statistically significant, relationship is found between the recovery indices and the spatial variation of ash thicknesses measured in the field. Combining field and remote sensing constraints enable to re-assess the volume of the eruption to ~2 × 107 m3. The spatial pattern of the ash-affected area matches with the spatial contrast in the impact experienced by the local communities. The method applied here opens the scope to document impact and intensity of ash fallout in areas where systematic field work is not possible and to support recovery plans for populations affected by ash fallout., Journal of Applied Volcanology, 4 (1), ISSN:2191-5040

International audience; The monogenetic Lemptégy volcano in the Chaîne des Puys (Auvergne, France) was quarried from 1946 to 2007 and offers the possibility to study scoria cone architecture and evolution. This volcano was originally 50–80 m high, but scoria excavation has resulted in a 50-m-deep hole. eginning in the 1980s, extraction was carried out with the advice of volcanologists so that Lemptégy’s shallow plumbing system and three-dimensional stratigraphy have been preserved. Detailed mapping enabled key stratigraphic units to be distinguished and the constructional phases to be reconstructed. The emplacement and evolution of the shallow plumbing system have also been unraveled. The growth of this monogeneticscoria cone included two temporally well-separated eruptions from closely spaced vents. The activity included Hawaiian, Strombolian and Vulcanian explosions, lava effusion, cryptodome and dome formation, partial collapse, satellite vent formation, eruptive pauses, and intrusion emplacement with consequent uplift. The cone shape, structure, and hence the local stress fi eld, plumbing system, and thermal state were continuously hanging,which in turn infl uenced the eruptive style and location. The plumbing system morphology and microtectonic structures both record local stress fi eld and magmatic fl ow directionchanges. Lemptégy volcano’s internal architecture,stratigraphy, and evolution show howcomplex a monogenetic volcano can be.

International audience; Gravitational deformation strongly infl uences the structure and eruptive behavior of large volcanoes. Using scaled analog models, we characterize a range of structural architectures produced by volcano sagging and volcano spreading. These arise from the interplay of variable basement rigidity and volcano-basement (de-)coupling. From comparison to volcanoes on Earth (La Réunion and Hawaii) and Mars (Elysium and Olympus Montes), the models highlight a structural continuum in which large volcanoes throughout the Solar System lie.

Quantitative characterization of the size and shape of volcanic edifices is an essential step towards the understanding of factors controlling volcano growth and morphology. The recent advent of digital elevation models (DEMs) with worldwide coverage offers the opportunity to systematically document the morphometry of all types of volcanoes using quantitative well-formalized methodologies. We present a methodology for the morphometric characterization of volcanic edifices. After reviewing previous studies on volcano morphometry and the various existing DEM sources, we describe an integrated procedure that uses a DEM and its derived products (slope, curvature) to extract a coherent set of morphometric parameters for a given volcanic edifice. Edifice boundaries are manually defined by searching for breaks in slope around the base. The parameters describe the overall size (basal and summit region area and widths, height, volume), planar shape (ellipticity and irregularity index of elevation contours), profile shape (height–width ratios) and slope of the edifice. Similar parameters for relatively large (depending on DEM spatial resolution) summit craters/calderas are also computed. Slope values and ellipticity and irregularity indexes are extracted for successive height intervals providing detailed information of volcano shape as a function of height. The number of secondary peaks is also estimated. The method is tested on thirteen composite volcanoes in Nicaragua using three DEM datasets (90 m SRTM, 30 m ASTER G-DEM and an 80 m topographic map-derived DEM) and the resulting parameters are evaluated in terms of boundary delineation and DEM source. Finally, the parameters obtained for the Nicaraguan volcanoes are discussed as an illustrative example of the type of data and information that can be extracted systematically for volcanoes worldwide.

[1] The spatial distribution of eruptive vents around volcanoes can be complex and evolve as a volcano grows. Observations of vent distribution at contrasting volcanoes, from scoria cones to large shields, show that peripheral eruptive vents concentrate close to the volcano base. We use analogue experiments to explore the control of volcano load on magma ascent and on vent location. Results show that the local loading stress field favors eruption of rising magma away from the volcano summit if a central conduit is not established or is blocked. Two sets of scaled experiments are developed with contrasting rheological properties to analyze similarities and differences in simulated magma rise below a volcano: (1) Golden syrup (magma analogue) is injected into a sand-plaster mixed layer (crust analogue) under a cone; (2) water or air (magma analogues) is injected into gelatin under a sand cone. Rising dykes approaching the cone stress field are stopped by the load compressive stress. With continued intrusion, dyke overpressure builds up; dykes extend laterally until their tips are able to rise vertically again and to erupt in the flank or at the base of the volcano. Lateral offset of the extrusion point relative to the edifice summit depends on substratum thickness, volcano slope, and dyke overpressure. The 3D geometry of Golden syrup intrusions varies with experimental parameters from cylindrical conduits to dyke and sill complexes. Experimental results are compared with illustrative field cases and with previously published numerical models. This comparison enables applications and limitations of the analogue models to be highlighted and allows us to propose a conceptual model for the evolution of vent distribution with volcano growth.

Applications of remote sensing for studies of volcanic activity and hazards have developed rapidly in the past 40 years. This has facilitated the observation of volcanic processes, such as ground deformation and thermal emission changes, lava flows, eruption clouds, ash and gas emissions, as well as mapping of volcanic structures and hazardous terrain, even for volcanoes in remote regions. Advances in the remote sensing of volcanoes, from ground-based sensors to sensors onboard airborne and spaceborne platforms, are reviewed. A key point made in this review is that volcanic remote sensing could have a much broader impact if the techniques and data were readily available to scientists studying/monitoring potentially hazardous volcanoes in developing countries. Perspectives on particular needs, with regard to sensor types, data availability and training, required to take volcanic remote sensing further in coming years are highlighted.

Oldoinyo Lengai (OL) is the only active volcano in the world that produces natrocarbonatite lava. These carbonate-rich lavas are unique in that they have relatively low temperatures (495–590 °C) and very low viscosity. OL has been erupting intermittently since 1983, mostly with small lava flows, pools and spatter cones (hornitos) confined to the summit crater. Explosive, ash-producing eruptions are rare, however, on September 4, 2007 the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) captured the first satellite image of an ash plume erupting from OL, which may be indicative of a new phase of more silica-rich products and explosive activity that has not occurred since 1966–1967. In the months prior to the eruption, thermal infrared (TIR) satellite monitoring detected an increasing number of thermal anomalies around OL. Data from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor analyzed with the MODLEN algorithm detected more than 30 hot spots in the last week of August and first week of September 2007, some of which were from bush fires ignited by lava flows or spatter around the volcano. Higher-resolution ASTER data confirmed the location of these burn scars associated with lava flows. ASTER also detected the appearance of an anomalous hot spot at the summit of OL in mid-June with temperatures ~ 440 °C, the presence of several new lava flows in the crater in July and August, and on September 4 measured higher temperatures (~ 550 °C) possibly suggesting a more silicate-rich eruption. ASTER spectral emissivity data were interpreted to indicate a mixture of carbonate and silicate ash in the eruption plume from September 4. Based on the analysis of both ASTER and MODIS data combined with occasional field observations, there appear to have been 2 distinct eruptive events so far in 2007: a typical natrocarbonatite eruption confined to the summit crater in June–July, and a more intense eruption in August–September consisting of natrocarbonatite lava overflowing the crater and explosive events forming ash plumes up to ~ 5 km high, apparently consisting of a mixture of silicate and carbonate ash. OL is one of the many volcanoes in the world, and especially Africa, that is not regularly monitored with in situ instruments. Continued satellite monitoring along with studies of past thermal activity will help determine how future eruptions and ensuing hazards may be forecasted.