DOWNFLOW code and Lidar technology for lava flow analysis and hazard assessment at Mount Etna
Favalli M., Tarquini S., Fornaciai A.
2011, Annals of Geophysics 54, 552-566.
The use of a lava-flow simulation (DOWNFLOW) probabilistic code and airborne light detection and ranging (LIDAR)... more The use of a lava-flow simulation (DOWNFLOW) probabilistic code and airborne light detection and ranging (LIDAR) technology are combined to analyze the emplacement of compound lava flow fields at Mount Etna (Sicily, Italy). The goal was to assess the hazard posed by lava flows. The LIDAR-derived time series acquired during the 2006 Mount Etna eruption records the changing topography of an active lava-flow field. These shorttime-interval, high-resolution topographic surveys provide a detailed quantitative picture of the topographic changes. The results highlight how the flow field evolves as a number of narrow (5-15 m wide) disjointed flow units that are fed simultaneously by uneven lava pulses that advance within formed channels. These flow units have widely ranging advance velocities (3-90 m/h). Overflows, bifurcations and braiding are also clearly displayed. In such a complex scenario, the suitability of deterministic codes for lava-flow simulation can be hampered by the fundamental difficulty of measuring the flow parameters (e.g. the lava discharge rate, or the lava viscosity of a single flow unit). However, the DOWNFLOW probabilistic code approaches this point statistically and needs no direct knowledge of flow parameters. DOWNFLOW intrinsically accounts for complexities and perturbations of lava flows by randomly varying the preeruption topography. This DOWNFLOW code is systematically applied here over Mount Etna, to derive a lava-flow hazard map based on: (i) the topography of the volcano; (ii) the probability density function for vent opening; and (iii) a law for the expected lava-flow length for all of the computational vents considered. Changes in the hazard due to the recent morphological evolution of Mount Etna have also been addressed.
Morphometry of scoria cones, and their relation to geodynamic setting: a DEM-based analysis
Fornaciai A., Favalli M., Karátson D., Tarquini S., Boschi E.
2012, J. Volcanol. Geoth. Res. 217-218.
The morphometry of a great number of scoria cones, belonging to volcanic fields of various geodynamic settings, has... more The morphometry of a great number of scoria cones, belonging to volcanic fields of various geodynamic settings, has been measured and analyzed, addressing the question whether there is a relation between the prevalent cone shape in a given field and the geodynamic setting of the field itself. Morphometric analysis was carried out on freely downloadable digital elevation models (DEMs). The accuracy of the used DEMs and the associated error in scoria cone morphometry were determined by cross-comparing high-resolution LIDAR-derived DEMs, USGS NED, TINITALY DEM and ASTER GDEM. The 10-m TINITALY/01 and USGS NED DEMs are proven to be suitable for scoria cone morphometry, whereas ASTER GDEM can be used reliably for cones with volume greater than 30×106 m3. According to a detailed morphometry of all scoria cones, we propose that the cones related to subductional setting show relatively higher values of Hco/Wco and lower values of Wcr/Wco than the cones related to extensional setting. The detected differences can be imputable to peculiar eruption dynamics resulting in slight but systematic changes in shape, and differences in lithological and sedimentological characteristics that govern post-eruptive erosion. To constrain the pathway of scoria cone erosion, the detected morphometric changes were also interpreted using a simple linear degradation model. Utilizing the obtained simulation results, the inferred initial cone base, and the age of scoria cones, we calculated a diffusion coefficient (K) for several dated cones, which are related to the prevalent climate. Our results, despite the high error associated, allow to assess the median K for all volcanic fields. Due to the complexity of the factors behind, it is not easy to understand if the prevalent shape characterizing a certain volcanic field is due mainly to sin-eruptive or post-eruptive mechanisms; however, our distinction between the two main geodynamic settings may be the first step to decipher these factors.
Dispersion index of topographic surfaces
Favalli M., Tarquini S., Fornaciai A., Boschi E.
2012, Geomorphology 153-154, 169-178
The dispersion index (dσ) of topography is introduced. This index is a geomorphic parameter which characterizes each... more The dispersion index (dσ) of topography is introduced. This index is a geomorphic parameter which characterizes each point of topography with respect to the stability/instability of the steepest descent path (SDP) originating from it. The procedure for calculating dσ is based on the assessment of SDP variations as the initial topography is also varied within a given elevation Δh, while a length scale L defines the maximum extent of the SDP. As a result, dσ can be derived for different ranges Δh and different bandwidths L. Since at each point the gravitational force would direct a surface flow along the SDP, dσ appears to have a strong influence on the behavior of gravity-driven mass flows, influencing local topographic widening, spreading or channelization. Considering Mount Etna (Italy) as a test case, we present maps of dσ for Δh=3 m and L=1, 2, 4 and 8 km, demonstrating also the relationship between the range Δh=3 m and Etnean lava flows. Focusing on the 2001 lava flow, we show that the presented maps of dσ, besides being a tool for viewing morphologies, have interesting applications for hazard assessment related to lava flows.
Lava flow hazard and risk at Mt. Cameroon volcano
Favalli M., Tarquini S., Papale P., Fornaciai A., Boschi E.
2012, Bulletin of Volcanology 74, 423-439.
Mt. Cameroon is one of the most active effusive volcanoes in Africa. About 500,000 people living or working around its... more Mt. Cameroon is one of the most active effusive volcanoes in Africa. About 500,000 people living or working around its fertile flanks are subject to significant threat from lava flow inundation. Lava flow hazard and risk were assessed by simulating probable lava flow paths using the DOWNFLOW code. The vent opening probability density function and lava flow length distribution were determined on the basis of available data from past eruptions at Mt. Cameroon volcano. Code calibration was performed through comparison with real lava flow paths. The topographic basis for simulations was the 90-m resolution SRTM DEM. Simulated lava flows from about 80,000 possible vents were used to produce a detailed lava flow hazard map. The lava flow risk in the area was mapped by combining the hazard map with digitized infrastructures (i.e., human settlements and roads). Results show that the risk of lava flow inundation is greatest in the most inhabited coastal areas comprising the town of Limbe, which constitutes the center of Cameroon’s oil industry and an important commercial port. Buea, the second most important town in the area, has a much lower risk although it is significantly closer to the summit of the volcano. Nonnegligible risk characterizes many villages and most roads in the area surrounding the volcano. In addition to the conventional risk mapping described above, we also present (1) two reversed risk maps (one for buildings and one for roads), where each point on the volcano is classified according to the total damage expected as a consequence of vent opening at that point; (2) maps of the lava catchments for the two main towns of Limbe and Buea, illustrating the expected damage upon venting at any point in the catchment basin. The hazard and risk maps provided here represent valuable tools for both medium/long-term land-use planning and real-time volcanic risk management and decision making.
Tephra architecture, pyroclast texture and magma rheology of mafic, ash-dominated eruptions: the Violent Strombolian phase of the Pleistocene Croscat (NE Spain) eruption.
C. Cimarelli, F. Di Traglia, A, Vona, and J. Taddeucci
Tephro- and chemo-stratigraphy of the Vulcanello Peninsula (Vulcano, Aeolian Islands)
New stratigraphic studies of the Vulcanello Peninsula have been used to better define the small-scale evolution of... more New stratigraphic studies of the Vulcanello Peninsula have been used to better define the small-scale evolution of this young (1000 AD and 325±100 BP) volcanic center and to re-investigate the last 1000 years of volcanic history for the Island of Vulcano (Aeolian Islands, Southern Italy). Vulcanello Peninsula is the northern-most part of the Island of Vulcano. It comprises a shoshonitic lava platform and a volcanic edifice made up of three overlying cones, which are shoshonitic to trachytic in composition. Volcanic activity in this area was coeval with the recent eruptions of the La Fossa Cone, the present-day active center of the island. Our goal is to constrain the recent volcanic development of this mafic volcano and to focus on the historic eruptive activity of the two other recent or active centres in the southern Aeolian Islands, Mt. Pilato (Island of Lipari) and La Fossa Cone. In order to do so, we reconstructed the stratigraphical setting of the proximal deposits of the three Vulcanello cones, through the investigation of 25 outcrops. We analyzed the stratigraphy of the tephra blankets deposited on the lava platform, studying 10 trenches. Our intention is to integrate morphological, textural and chemical data in order to correlate these deposits with the Vulcanello, La Fossa Cone or Mt Pilato. LA-MC-ICPMS (RHUL) analysis of juvenile clasts is underway in order to investigate the evolution of the Vulcanello juvenile clasts. In addition 14C dating is planned on selected organic matter from the volcanostratigraphic sections. Our preliminary data for the Vulcanello proximal deposits suggest that each of the three cones experienced several eruptions, with a wide spectrum of eruptive styles and a diversity of chemistry. The oldest cone (Vulcanello I) is characterised by four different eruptions separated by minor unconformities or reworking material indicative of little or not time breaks in the eruptive cycle. The eruptions shift from Violent Strombolian to Hawaiian in style, testifying to a reduction in fragmentation and dispersal. The second cone (Vulcanello II), contains volcanic deposits from Strombolian eruptions only. The third cone (Vulcanello III), displays a complex evolution with an initial effusive episode of a trachytic lava flow, followed by phreatic explosions, evident as altered fine ash layers. These deposits are interbedded with scoriaceous fall deposits, attesting the occurrence of some mild explosive activity during this eruptive phase. This detailed study of the effusive and explosive products from Vulcanello reveals rapid evolution of Vulcanello during the initial phases (1000 AD to 1200 AD) with voluminous mafic eruptions, both effusive and explosive. A progressive reduction in emitted volume is apparent. The presence of abundant explosive deposits related to phreatic explosions during the Vulcanello III phase, is related to the presence of water, a reduction in magma volume and the presence of intense hydrothermal activity in the latter stage of the evolution of Vulcanello evolution until 1878. This may indicate the presence of a stable shallow thermal anomaly.
Download (.pdf) Basaltic scoria textures from a zoned conduit as precursors to violent Strombolian activity
C. Cimarelli, F. Di Traglia and J. Taddeucci
Pyroclast textures document volcanic conduit processes and may be key to hazard forecasting. Here we show that the... more Pyroclast textures document volcanic conduit processes and may be key to hazard forecasting. Here we show that the relative abundances of mingled, variably crystallized domains in pyroclasts from scoria cone eruptions provide a record of magma ascent velocity and can be used to predict the onset of violent Strombolian activity. Scoria clasts from the Croscat complex scoria cone (Spain) ubiquitously show micrometer- to centimeter-sized, microlite-rich domains (MRD) intermingled with volumetrically dominant, microlite-poor domains (MPD). Glass and bulk composition show that MRDs formed by microlite crystallization of MPDs, the former residing longer in a relatively cooler, degassed zone lining the conduit walls, the latter traveling faster in the central, hotter streamline. MPD and MRD magmas intermingled along the interface between the two velocity zones. The proportion of MPD and MRD in different tephra layers reflects the extent of the fast- and slow-flowing zones, thus reflecting the ascent velocity profile of magma during the different phases. At Croscat, the MPD/MRD volume ratio increased rapidly during the early Strombolian activity, peaked around the Strombolian to violent Strombolian transition, and then decreased smoothly irrespective of shifts in eruptive style. We suggest that magma ascent velocity escalated during the Strombolian phase due to the buoyant push of the underlying, volatile-rich magma that was about to drive the following violent Strombolian activity. Monitoring the MPD/MRD ratio of tephra during ongoing scoria cone eruptions may reveal changes in magma flow conditions and could forecast the onset of hazardous violent Strombolian activity.
Changing eruptive styles in basaltic explosive volcanism: Examples from Croscat complex scoria cone, Garrotxa Volcanic Field (NE Iberian Peninsula)
F. Di Traglia, C. Cimarelli,, D. de Rita, D. Gimeno Torrente
The Croscat pyroclastic succession has been analysed to investigate the transition between different eruptive
styles in basaltic monogenetic volcanoes, with particular emphasis on the role of phreatomagmatism in
triggering Violent Strombolian eruptions. Croscat volcano, an 11 ka basaltic complex scoria cone in the
Quaternary Garrotxa Volcanic Field (GVF) shows pyroclastic deposits related both to magmatic and
phreatomagmatic explosions.
Lithofacies analysis, grain size distribution, chemical composition, glass shard morphologies, vesicularity,
bubble-number density and crystallinity of the Croscat pyroclastic succession have been used to characterize
the different eruptive styles. Eruptions at Croscat began with fissural Hawaiian-type fountaining that rapidly
changed to eruption types transitional between Hawaiian and Strombolian from a central vent. A first
phreatomagmatic phase occurred by the interaction between magma and water from a shallow aquifer
system at the waning of the Hawaiian- and Strombolian-types stage. A Violent Strombolian explosion then
occurred, producing a widespread (8 km2
), voluminous tephra blanket. The related deposits are
characterized by the presence of wood-shaped, highly vesicular scoriae. Glass-bearing xenoliths (buchites)
are also present within the deposit. At the waning of the Violent Strombolian phase a second
phreatomagmatic phase occurred, producing a second voluminous deposit dispersed over 8.4 km2
. The
eruption ended with a lava flow emission and consequent breaching of the western-side of the volcano. Our
data suggest that the Croscat Violent Strombolian phase was related to the ascent of deeper, crystal-poor,
highly vesicular magma under fast decompression rate. Particles and vesicles elongation and brittle failure
observed in the wood-shaped clasts indicate that fragmentation during Violent Strombolian phase was
enhanced by high strain-rate of the magma within the conduit.
Understanding conduit dynamics and forecasting major strombolian explosions by groundbased radar interferometry
Federico DI TRAGLIA, Chiara DEL VENTISETTE, Mauro ROSI, Francesco MUGNAI, Emanuele INTRIERI, Sandro MORETTI, Nicola CASAGLI
Ground-based InSAR Monitoring of an Active Volcano and Related Landslides
Nicola Casagli (Florence University, Italy) ・ Filippo Catani (Florence University, Italy) ・ Chiara Del Ventisette (Florence University, Italy) ・ Letizia Guerri (Florence University, Italy) ・ Dario Tarchi (European Commission, Italy) ・ Joaquim Fortuny (European Commission, Italy) ・ Giuseppe Antonello (European Commission, Italy) ・Davide Leva (Ellegi-LiSALab s.r.l., Italy) ・ Carlo Rivolta (Ellegi-LiSALab s.r.l., Italy)
Stromboli volcano (Italy) is characterized by a typical
“Strombolian activity” which consists of very low... more
Stromboli volcano (Italy) is characterized by a typical
“Strombolian activity” which consists of very low energy
explosions, every 10-15 minutes. In December 2002 an
eruption caused a landslide on the NW slope of the volcano
(Sciara del Fuoco slope, SdF) and produced a tsunami.
Concerns over the possibility of further slope collapses of the
SdF led to the set up of a permanent monitoring system of
ground deformations.
The ground-based radar interferometer (GB-InSAR)
system installed on the Stromboli Island (Fig. 1) was
designed by the Joint Research Centre of the European
Commission (Rudolf & Tarchi, 1999; Antonello et al., 2004);
it is continuously active since 20 February 2003 (Antonello et
al., 2003; Casagli et al., 2003 Casagli et a., 2004; Antonello et
al., 2007) and produces, on average, 120 images per day of
the area under investigation (NW flank of crater and the upper
part of the SdF), characterized by a resolution of about 2m ×
2m, with an accuracy of the measurement of less than 1 mm.
Interferograms (obtained using pairs of averaged
sequential images) contain the displacement vector along the
line-of-sight (LoS) in the time interval between two
acquisitions. Negative values of displacement indicate a
movement toward the sensor (shortening along the LoS). On
the crater area this direction of movement correspond to the
inflation of the volcanic cone while, on the SdF, this is
usually related to a local bulging or to the downslope sliding
of the volcano-clastic material accumulated on the SdF slope.
Conversely, a positive value of displacement identifies a
movement backward with respect to the sensor (lengthening
along the LoS) that on the crater area could be related to the
deflation of the volcanic cone.
In January 2007, the GB-InSAR showed a progressive
acceleration of deformation on the NE crater. The recorded
velocity progressed from 0.04 mm/h to 0.7 mm/h toward the
radar that suggest an inflation of the upper sector of the
volcanic system. The increase in the deformation rate
successively involves the portion the SdF (15 February 2007)
in which the velocity increased from 0.02 mm/h to 0.25 mm/h,
toward the sensor.
These events are related to the new eruption occurred at
the end of February 2007. The effusive phase (from 27
February to 12 April) started with an explosion to the lower
part of the crater (causing a landslide on the portion of the
crater flank) and with the opening of the effusive vent at 600
m a.s.l. Velocities in the first hours of the eruption were so
high that exceeded the capability of the GB-InSAR device.
After few hours from the effusion onset, the
interferograms returned partly coherent and showed a
complex deformation pattern characterized by:
1. a complete decorrelation on the crater flank due to the
explosion and to morphological changes related to the crater
collapse;
2. concentric interferometric fringes related to the bulging
before the vent opening at 600 m a.s.l.;
3. parallel interferometric fringes related to landslide
movements on the SdF.
During the entire effusive phase, velocity values, on the
SdF slope, constantly decreased from 30 mm/h to 0.2 mm/h
toward the sensor, with the only exception of two limited
periods related to the opening of a new vent (8- 9 March) and
to a major explosion (15 March).
In particular since 8 March the velocity recorded on the
SdF increased again with movements toward the sensor. The
interferogram highlighted a very high deformation rate (more
than 300 mm/h, Fig. 2), which again exceeds the capability of
the correct phase unwrapping. The arrangement of the
interferometric fringes is related to the bulging due to the
opening of a new vent, occurred at 14.30 UT of 9 March.
Following the method proposed by Fukuzono (1985) and
Voight (1988) it has been possible to predict in advance of
one day the opening of the 9 March vent.
After 12 April, the eruption is to be considered concluded
and the velocity recorded by GB-InSAR progressively
decreased down to the values characteristic of the normal
activity of the Stromboli volcano.
The GB-InSAR monitoring allowed us to highlight
different deformation patterns, related to the eruption and to
the associated landslides, suggesting different triggering
mechanisms of the deformation process. Furthermore the
GB-InSAR system has recorded changes in the deformation
patterns, both on the crater area and on the SdF sector, in
advance with respect to the onset of each one of the relevant
events.
The absolute values of velocity recorded are plotted in Fig.
3: the light red line represents movements toward the sensor
(negative radar displacements), while the dark blue line
represents movement backward with respect to the sensor
(positive radar displacements). In Fig. 3 the three different
phases, above mentioned, are shown. The pre-effusive phase
(from 10 January to 27 February) is represented by the first
(light) shaded area, characterized by very low, progressively
increasing, deformation rates; the effusive phase (from 27
February to 12 April) by the second (dark) shaded area,
characterized by very high velocities of deformation and the
post-effusive phase (from 12 April) by the last area in which
the deformation rates decreased down to the pre-crisis values.
Microwave interferometric sensors as a tool for space and time analysis of active volcano deformations: the Stromboli case
Antonello, G. Fortuny, J. ; Tarchi, D. ; Casagli, N. ; Del Ventisette, C. ; Guerri, L. ; Luzi, G. ; Mugnai, F. ; Leva, D.
A Ground Based SAR Interferometer (GB-InSAR) was
installed at Stromboli volcano (Italy) in February 2003 to
installed at Stromboli volcano (Italy) in February 2003 to
continuously monitor the behaviour of the morphological
depression known as Sciara del Fuoco, SdF, with alerting
purposes. This was decided as a consequence of the collapse of a
large landslide from the NW slope of the SdF and the subsequent
tsunami occurred on December 2002. The GB-In SAR system,
working at Ku band, was set up on the stable right flank of the
SdF; it has been continuously working and during this last five
years has permitted to follow the temporal and spatial evolution
of the mass movement in the SdF and the crater. Interferometric
maps have permitted to assess the deformation field over a large
portion of the target area and to characterize different processes.
The system allowed to observe in particular two main events
occurred on 5 April 2003 (a major explosion) and on 27 February
2007 (beginning of the effusive phase) respectively. The potential
of the use of DInSAR from satellite platforms working at C band
to understand the dynamic of the whole volcano has been also
investigated. Different images acquired from the ERS2,
RADARSAT and ENVISAT satellites before and after the 2003
collapse of the landslide, and before and after the 2007 event,
have been interferometrically processed as well. Notwithstanding
the restricted number of available images, the ground
deformation occurred on the island due to the volcanic activity
has been obtained with spatial and temporal characteristics
complementary to those ones provided by GB-InSAR.
Deformations of the Stromboli volcano using GB-InSAR technique
G. Antonello, N. Casagli , F. Catani, C. Del Ventisette, J.Fortuny-Guasch, L. Guerri, D. Leva, D. Tarchi
Detecting short-term evolution of Etnean scoria cones: a LIDAR-based approach
Fornaciai A., Behncke B., Favalli M., Neri M., Tarquini S., Boschi E
2010, Bulletin of Volcanology 72, 1209-1222.
The 2001 and 2002–2003 flank eruptions on Mount Etna (Italy) were characterized by intense explosive activity which... more
The 2001 and 2002–2003 flank eruptions on Mount Etna (Italy) were characterized by intense explosive activity which led to the formation of two large monogenetic scoria cones (one from each eruption) on the upper southern flank of the volcano. Continuous monitoring of Etna, especially during flank eruptions, has provided detailed information on the growth of these cones. They differ in genesis, shape, and size. A set of high resolution (1 m) digital elevation models (DEMs) derived from light detection and ranging (LIDAR) data collected during four different surveys (2004, 2005, 2006, and 2007) has been used to map morphology and to extract the morphometric parameters of the scoria cones. By comparing LIDAR-derived DEMs with a pre-eruption (1998) 10 m DEM, the volume of the two scoria cones was calculated for the first time. Comparison of the LIDAR-derived DEMs revealed in
unprecedented detail morphological changes during scoria
cone degradation. In particular, the morphologically more exposed and structurally weaker 2002–2003 cone was eroded rapidly during the first few years after its emplacement mainly due to gravitational instability of slopes and wind erosion.
A new approach to risk assessment of lava flow at Mount Etna
Favalli M., Tarquini S., Fornaciai A., Boschi E
2009, Geology 37, 1111-1114
Destruction of human property by lava fl ow invasion is a signifi cant volcanic hazard at Mount Etna (Italy), where... more Destruction of human property by lava fl ow invasion is a signifi cant volcanic hazard at Mount Etna (Italy), where reliable risk maps are important for risk mitigation. We present new high-resolution quantitative risk maps of Mount Etna that are based on lava fl ow simulations starting from more than 70,000 different potential vents, a probability distribution of vent location, an empirical relationship for the maximum length of lavas fl ow, and a database of buildings. In addition to standard risk maps, which classify areas according to the expected damage at each point, we classify each point of the volcano with respect to the damage that would occur if a vent opened at that point. The resulting maps should help local authorities in making the necessary decisions to deal with ongoing eruptions and to plan long-term land use.
Mapping and DOWNFLOW simulation of recent lava flow fields at Mount Etna
Tarquini S., Favalli M.
2011, J. Volcanol. Geoth. Res. 204, 27-39
In recent years, progress in geographic information systems (GIS) and remote sensing techniques have allowed the... more In recent years, progress in geographic information systems (GIS) and remote sensing techniques have allowed the mapping and studying of lava flows in unprecedented detail. A composite GIS technique is introduced to obtain high resolution boundaries of lava flow fields. This technique is mainly based on the processing of LIDAR-derived maps and digital elevation models (DEMs). The probabilistic code DOWNFLOW is then used to simulate eight large flow fields formed at Mount Etna in the last 25 years. Thanks to the collection of 6 DEMs representing Mount Etna at different times from 1986 to 2007, simulated outputs are obtained by running the DOWNFLOW code over pre-emplacement topographies. Simulation outputs are compared with the boundaries of the actual flow fields obtained here or derived from the existing literature. Although the selected fields formed in accordance with different emplacement mechanisms, flowed on different zones of the volcano over different topographies and were fed by different lava supplies of different durations, DOWNFLOW yields results close to the actual flow fields in all the cases considered. This outcome is noteworthy because DOWNFLOW has been applied by adopting a default calibration, without any specific tuning for the new cases considered here. This extensive testing proves that, if the pre-emplacement topography is available, DOWNFLOW yields a realistic simulation of a future lava flow based solely on a knowledge of the vent position. In comparison with deterministic codes, which require accurate knowledge of a large number of input parameters, DOWNFLOW turns out to be simple, fast and undemanding, proving to be ideal for systematic hazard and risk analyses.
The regular shape of stratovolcanoes: A DEM-based morphometrical approach
Karátson D., Favalli M., Tarquini S., Fornaciai A., Wörner G.
2010, J. Volcanol. Geoth. Res., 193, 171-181
We studied the shape of the most regular-shaped stratovolcanoes of the world to mathematically define the form of the... more
We studied the shape of the most regular-shaped stratovolcanoes of the world to mathematically define the form of the ideal stratovolcano. Based on the Shuttle Radar Topographic Mission data we selected 19 of the most circular and symmetrical volcanoes, which incidentally all belong to subduction-related arcs surrounding the Pacific. The selection of volcanoes benefitted from the introduction of a new definition of circularity which is more robust than previous definitions, being independent of the erosional dissection of the cone.
Our study on the shape of stratovolcanoes was based on the analysis of the radial elevation profiles of each volcano. The lower half section of the volcanoes is alwayswell fitted by a logarithmic curve, while the upper half section is not, and falls into two groups: it is fitted either by a line (“C-type”, conical upper part) or by a parabolic arc (“P-type”, parabolic/concave upper part). A quantitative discrimination between these groups is obtained by fitting their upper slope with a linear function: C-type volcanoes show small, whereas P-type volcanoes show significant negative angular coefficient. The proposed threshold between the two groups is −50×10−4°/m. Chemical composition of eruptive products indicates higher SiO2 and/or higherH2O content for C-type volcanoes, which could imply a higher incidence of mildly explosive (e.g. strombolian) eruptions. We propose that this higher explosivity is responsible for forming the constant uppermost slopes by the deposition of ballistic tephra and its subsequent stabilisation at a constant angle. By contrast, P-type volcanoes are characterized by a smaller SiO2 andH2O content,which can be responsible for a higher incidence of effusive events and/or a lower incidence of upper flank-forming (i.e. mild) explosive eruptions. Therefore, the concave upper flanks of these volcanoes may be shaped typically by lava flows. Based on this hypothesis, we propose that the morphometric analysis of the elevation profile of stratovolcanoes can provide insights into their dominant eruptive style.
Changes of the susceptibility to lava flow invasion induced by morphological modifications of an active volcano: the case of Mount Etna, Italy
Tarquini S., Favalli M.
2010, Natural Hazards, 54, 537-546
Changes of the susceptibility to lava flow invasion at Mount Etna are quantified by using lava flow simulations on... more
Changes of the susceptibility to lava flow invasion at Mount Etna are quantified by using lava flow simulations on four Digital Elevation Models documenting the morphostructural modifications of the volcano in the time interval 1986–2007. The probabilistic code DOWNFLOW is used to derive the areas invaded by several thousands of lava flows obtaining, for each DEM, maps of the susceptibility to lava flow invasion and of the lava flow hazard. These maps show, for the first time, the evolution of these surficial properties with time, and render a quantitative image of the effects of topographic changes on the preferential lava flow drainage paths. The results illustrate how the emplacement of new lava flows and the growth of scoria cones affect the probability of inundation by lava flows. We conclude that the persistent activity of this volcano requires a frequent updating of the topography for a reliable lava flow hazard
assessment.