Matthieu Kervyn

Revisiting the question of how cinder cones grow suggests the possibility of inferring magma supply rates from cinder cones sizes. We start with a conceptual model of cinder cone growth: (1) Eruption volume flux increases rapidly and then decreases exponentially. (2) Cinder cones get steeper during the initiation of the eruption and then maintain a constant steepness. (3) The initial basal diameter varies with volume flux into the cone. Based on these constraints, we propose a general form for the relationship between cinder cone volume and magma supply rate: V = Q(exp(-t/b)/b - exp(-t/a)/a), where V is volume (in m3), Q is the maximum potential magma flux (in m3/s), t is time (in s), a is a damping factor (in s) controlling the decline in volume flux, and b is a factor controlling the initial increase in volume flux. Then we use the data available on the growth of cinder cones from four modern eruptions to show the relevance of our model and to constrain the supply curves. All four modern cones (Paricutin, Mexico which erupted 1943-1974; Tolbachik, Kamchatka which erupted in 1975-1976; Cono del Laghetto, Mount Etna, Italy which formed in 2001; and a small cone on the summit of Oldoinyo Lengai, Tanzania, which formed during the 2007 eruption) show the basic growth pattern: initial rapid growth followed by declining growth (Figure 1). The regression results yeild the following magma supply rates: The southern Tolbachik cones have the largest predicted magma supply at ~100 m3/s. Paricutin and Laghetto are around 9 m3/s. The Oldoinyo Lengai cone has a magma supply of ~0.5 m3/s. The northern Tolbachik cone has the lowest magma supply of ~0.1 m3/s. In contrast, the damping factor a is generally on the order of 107 (it varies from 8 x 106 at southern Tolbachik to 4 x 107 at northern Tolbachik). The parameter b controlling the initial increase is generally small (<1). The predicted magma supply does not seem to be very sensitive to either parameter. Thus we suggest that final cone volume can be used to estimate the magma flux based on the assumption that the damping factor is 107 and that the duration of the eruption was sufficiently long for the cone to reach its maximum volume (that is the incremental increase in cone volume with continuing eruption is insignificant compared to the total cone volume). As an example application, we use the estimated magma supply curves from the historical eruption to predict the magma supply rates for cinder cones in the back arc volcanic field of Guatemala. Figure 1. The growth of cinder cones during historical eruptions.

Oldoinyo Lengai (OL) is the only active volcano in the world that produces natro-carbonatite lava. These carbonate-rich lavas are unique in that they have relatively low temperatures (500-600 C) compared with typical silicate lavas (600-1100 C), and they have a low viscosity, behaving more like a mud flow than a lava flow. OL has been erupting on and off since

Mt. Cameroon is an elongated lava-dominated volcano with a morphology comprising a broad summit plateau, ~30° steep upper flanks, sharp slope breaks and topographic terraces around its base. Despite recent lava eruptions along its rift zone (i.e. 1999, 2000), little geological or geophysical data are available to constrain the structure, and ongoing unrest of this large volcanic system. Here we

Nyamulagira volcano (3058m a.s.l.), located in the Virunga volcanic province in the western branch of the East Africa Rift, is Africa&amp;amp;amp;#39;s most active volcano with one eruption every 2-4 years, the most recent one starting in January 2010. Despite such an intense activity, Nyamulagira remains poorly studied. Based on up-to-date remote sensing imagery, a new map of the lava flows

ABSTRACT Revisiting the question of how cinder cones grow suggests the possibility of inferring magma supply rates from cinder cones sizes. We start with a conceptual model of cinder cone growth: (1) Eruption volume flux increases rapidly and then decreases exponentially. (2) Cinder cones get steeper during the initiation of the eruption and then maintain a constant steepness. (3) The initial basal diameter varies with volume flux into the cone. Based on these constraints, we propose a general form for the relationship between cinder cone volume and magma supply rate: V = Q(exp(-t/b)/b - exp(-t/a)/a), where V is volume (in m3), Q is the maximum potential magma flux (in m3/s), t is time (in s), a is a damping factor (in s) controlling the decline in volume flux, and b is a factor controlling the initial increase in volume flux. Then we use the data available on the growth of cinder cones from four modern eruptions to show the relevance of our model and to constrain the supply curves. All four modern cones (Paricutin, Mexico which erupted 1943-1974; Tolbachik, Kamchatka which erupted in 1975-1976; Cono del Laghetto, Mount Etna, Italy which formed in 2001; and a small cone on the summit of Oldoinyo Lengai, Tanzania, which formed during the 2007 eruption) show the basic growth pattern: initial rapid growth followed by declining growth (Figure 1). The regression results yeild the following magma supply rates: The southern Tolbachik cones have the largest predicted magma supply at ~100 m3/s. Paricutin and Laghetto are around 9 m3/s. The Oldoinyo Lengai cone has a magma supply of ~0.5 m3/s. The northern Tolbachik cone has the lowest magma supply of ~0.1 m3/s. In contrast, the damping factor a is generally on the order of 107 (it varies from 8 x 106 at southern Tolbachik to 4 x 107 at northern Tolbachik). The parameter b controlling the initial increase is generally small (

ABSTRACT Karthala volcano on the oceanic island of Grande Comore, West-Indian Ocean, is one of worlds&amp;#39; largest active alkaline basalt shield volcanoes, with 5 eruptions since 1991. In the last century the volcanic activity mainly concentrated within the 3.5 x 2.8 km large area of the summit caldera complex. Limited study has so far been carried out to unravel the structure and geometry of the summit caldera complex, the collapse chronology and the recent changes caused by the 2005 - 2007 eruption phases. Two exploratory missions to the Karthala summit in July 2011 led to an updated overview of the volcano-tectonic structures, evidence of the local orientation of the principle stresses and a preliminary stratigraphy of the 400 m deep rock sequence exposed in the caldera walls. Three overlapping caldera&amp;#39;s build the main structure of the complex, with vertically-subsided blocks forming intermediate terraces along the caldera structures. Within these blocks, several graben-like structures with N-S and N135°E orientations are evidencing a secondary influence of extension during or after the overall vertical collapse. One of the southwestern caldera blocks shows a &amp;#39;tilted block&amp;#39; morphology, with a caldera-inward rotation. &amp;#39;Choungou Changouméni&amp;#39;, a nested pit crater in the Northern caldera, was 30 m deep in 1965 and has now been almost completely filled with pyroclastic deposits and lava flows. Caldera walls in the whole complex consist of massif meter-thick alkali-basalt flows with decimetric intercalations of weathered pyroclastic layers, and are topped by scoria and tuff cones. The caldera floor itself is covered by volcanic ash, lapilli, and massif scoriaceous surfaces of ancient flows. At the intersection of the 3 main caldera structures two deep explosion craters are located, together named &amp;#39;Choungou Chahalé&amp;#39;. These were the centres of recent phreatic activity. Their vertical walls show a sequence of thick alkali basalt flows and hold numerous cross-cutting dykes which fed small-scale eruptive cones, vertical degassing fissures and former caldera levels. Fissures with active fumaroles inside the two explosive craters and in the area between Choungou Chahalé and Changouméni are indicating a focus area in the hydrothermal activity. It is this hydrothermal system that is suggested to have controlled the phreatic nature of recent eruptions (1991, 2005 and 2007). Several pyroclastic beds and cones affected by block and bomb impacts inside the caldera complex and around the summit area testify the high explosive nature of these recent eruptions, in contrast with the effusive Hawaiian-style character generally associated with Karthala. The orientation of caldera-bounding structures, eruption and fumarolic fissures, dykes as well as the orientation of intra-caldera extensional faults indicate one minor (E-W) and two major volcano-tectonic directions (N-S and N135°S). The latter are concurring with previously identified regional stress orientations and rift zone&amp;#39;s orientations on Karthala flanks. Upcoming field work will be dedicated to the exhaustive structural and stratigraphic mapping of Karthala caldera as it provides exceptional exposure to document the internal architecture of an alkali basalt shield volcano and a complex caldera subsidence chronology.

ABSTRACT Mt Meru volcano is located in the Northern Tanzanian Divergence Zone where the East African rift splits into several branches. This 4565 m-high stratovolcano overlooks the highly populated city of Arusha and is breached on the east side by a 4x5 km horse-shoe shaped valley that was attributed to landslides associated with lahars deposits (Wilkinson et al., 1986; Dawson, 2008) and a major collapse (Wilkinson et al., 1986; Roberts, 2002; Dawson, 2008). An ash cone is growing up within the collapse scar, with its last eruption occurring in 1910. Remote sensing, detailed field mapping and facies/lithology description allowed the recognition of more than two collapse events originated from the main eastern scar, as well as at least one collapse from an almost buried scar on the North East flank. No evidence of syn-collapse eruption has been observed. The high distance and large area covered by the bigger deposit up to the foot of Kilimanjaro is partly due to local interaction with water, where debris avalanche behaves like a lahar. Mt Meru has been undergoing several phases of destabilisation events during its history and can be considered as still potentially hazardous, especially with the ongoing Ash Cone growth within the scar.

Morphological parameters of offshore (Gulf of Cadiz, Mediterranean Sea, and Black Sea) and onshore (Azerbeidjan) mud volcanoes are compared with data from magmatic volcanoes. The offshore data series are compiled from multibeam bathymetry measurements (Gulf of Cadiz and Black Sea), and data from literature (Mediterrean Sea). The onshore data series (Azerbeidjan) is derived from Landsat 7 ETM+ and SRTM-DEM data.

... The integration of internet GIS technology with virtual globes is a promising new frontier of disaster management. For instance, after Hurricane Katrina, fine-resolution satellite imagery posted on Google Earth was utilized by rescue teams (see http://earth. google. com/katrina. ...

Volcanism occurs on many planets, from large strato- and shield volcanoes on Earth, Mars, and Venus, to smaller shields and plains volcanism on Io, Mercury, and the Moon. Two important processes that affect the structure of large volcanoes are spreading and sagging. Volcano spreading occurs when a conical edifice is free to gravitationally equilibrate along a basal décollement. This results

ABSTRACT Nyamulagira, located in the western branch of the East African Rift (EAR), is Africa&amp;#39;s most active volcano with one eruption every 2 - 4 years. A map of Nyamulagira lava flows was produced during the 1960&amp;#39;s by Thonnard et al. (1965). This map, which results from the mosaicking of several aerial photographs, contains locally some geographic inaccuracies. The photo-interpretation also led in places to the discrimination of lava units not corresponding to any flow boundaries in the field. Finally, 19 eruptions occurred since this first edition, which causes it to be outdated and of limited use to document the recent eruptive history. Recently, Smets et al. (2010) have produced a new map of lava flows using a combination of optical and radar satellite imagery. This map is GIS-based and can be quickly updated during/after each eruption. Using the new lava flow map of Nyamulagira and a compilation of bibliographic/field information of the last 31 eruptions, the evolution of eruptive activity since the early 1900&amp;#39;s was reconstructed and the volume of erupted lava estimated for each eruption from 1938 to 2010. The spatio-temporal evolution of eruptive activity suggests a strong control from the rift tectonics but also from inherited basement structures on the location, the fissure orientation and the relative lava volume for the successive eruptions. The time lapse after each eruption is strongly correlated with the erupted volume of lava. The 1938-40 eruption is a key event in the volcano recent history, as the corresponding caldera collapse led to an increase of flank eruptions. Nyamulagira flank eruptions systematically destroy large areas of the protected forest of the Virunga National Park, a UNESCO World Heritage in danger since 1994. The lava flows from distal eruptions or from exceptionally high effusion rate or volume events also threaten local population, mainly south of the main edifice near Lake Kivu.

... SRTM90 DEMs are available for &amp;amp;gt;95% of all subaerial historically active volcanoes of the world. ... GROHMAN, G., KROENUNG, G. and STREBECK, J., 2006, Filling SRTM voids: The delta surface fill method. ... GUTH, PL, 2006, Geomorphometry from SRTM: Comparison to NED. ...

Mt Cameroon is a steep lava-dominated volcano located on the coast of the Gulf of Guinea. This ~1400 km3 edifice is one of two active centres in the Cameroon Volcanic Line. Despite recent lava eruptions along its rift zones in 1999 and 2000, little geological or monitoring data are available to understand the structure of this large volcanic system. Here

ABSTRACT Analogue models in the past mainly explored caldera collapse structures by documenting 2D model cross-sections. Kinematic aspects and 3D structures of caldera collapse are less well understood, although they are essential to interpret recent field and monitoring data. We applied high resolution radiography and computerized X-ray micro-tomography (µCT) to image the deformation during analogue fluid withdrawal in small-scale caldera collapse models. The models test and highlight the possibilities and limitations of µCT-scanning to qualitatively image and quantitatively analyse deformation of analogue volcano-tectonic experiments. High resolution interval radiography sequences document &amp;#39;2.5D&amp;#39; surface and internal model geometry, and subsidence kinematics of a collapsing caldera block into an emptying fluid body in an unprecedented way. During the whole drainage process, all subsidence was bound by caldera ring faults. Subsidence was associated with dilatation of the analogue granular material within the collapsing column. The temporal subsidence rate pattern within the subsiding volume comprised three phases: 1) Upward ring fault propagation, 2) Rapid subsidence with the highest subsidence rates within the uppermost subsiding volume, 3) Relatively slower subsidence rates over the whole column with intermittent subsidence rate acceleration. Such acceleration did almost never affect the whole column. By using radiography sequences it is possible in a non-destructive manner to obtain a continuous observation of fault propagation, down sag mechanisms and the subsequent development of collapse structures. Multi-angle µCT scans of the collapse result allow for a full virtual 3D reconstruction of the model. This leads to an unprecedented 3D view on fault geometries. The developed method is a step towards the quantitative documentation of volcano-tectonic models that would render data interpretations immediately comparable to monitoring data available from recent deformation at natural volcanoes. The models carry the potential for a better understanding of the kinematics of caldera collapse amongst a variety of volcano-tectonic processes.

Mt 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 Mt Cameroon. We review the existing geological and geophysical data and morpho-structural features of Mt 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); and ii) models recorded from above with a uniform (Type IIa), iii) and non-uniform 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 gra...