Description: Low elevation flank eruptions represent highly hazardous events due to their location near, or in, communities. Their potentially high effusion rates can feed fast moving lava flows that enter populated areas with little time for warning or evacuation, as was the case at Nyiragongo in 1977. The January–March 1974 eruption on the western flank of Mount Etna, Italy, was a low elevation effusive event, but with low effusion rates. It consisted of two eruptive phases, separated by 23 days of quiescence, and produced two lava flow fields. We describe the different properties of the two lava flow fields through structural and morphological analyses using UAV-based photogrammetry, plus textural and rheological analyses of samples. Phase I produced lower density (∼2,210 kg m−3) and crystallinity (∼37%) lavas at higher eruption temperatures (∼1,080°C), forming thinner (2–3 m) flow units with less-well-developed channels than Phase II. Although Phase II involved an identical source magma, it had higher densities (∼2,425 kg m−3) and crystallinities (∼40%), and lower eruption temperatures (∼1,030°C), forming thicker (5 m) flow units with well-formed channels. These contrasting properties were associated with distinct rheologies, Phase I lavas having lower viscosities (∼103 Pa s) than Phase II (∼105 Pa s). Effusion rates were higher during Phase I (≥5 m3/s), but the episodic, short-lived nature of each lava flow emplacement event meant that flows were volume-limited and short (≤1.5 km). Phase II effusion rates were lower (≤4 m3/s), but sustained effusion led to flow units that could still extend 1.3 km, although volume limits resulted from levee failure and flow avulsion to form new channels high in the lava flow system. We present a petrologically-based model whereby a similar magma fed both phases, but slower ascent during Phase II may have led to greater degrees of degassing resulting in higher cooling-induced densities and crystallinities, as well as lower temperatures. We thus define a low effusion rate end- member scenario for low elevation effusive events, revealing that such events are not necessarily of high effusion rate and velocity, as in the catastrophic event scenarios of Etna 1669 or Kilauea 2018.

Description: This research was financed by the Agence Nationale de la Recherche through the project LAVA (Program: DS0902 2016; Project: ANR-16 CE39-0009). This is ClerVolc publication 443 and ANR-LAVA publication 16.

Description: Published

Description: 590411

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: Digital Elevation Models (DEMs) are fruitfully used in volcanology as the topographic base for mapping and quantifying volcanic landforms. The increasing availability of free topographic data on the web, decreasing production costs for high-accuracy data and advances in computer technology, has triggered rapid growth of the number of DEM users in the volcanological community. DEMs are often visualized only as hill-shaded maps, and while this is among the major advantages in using them, the possibility of deriving a very large number of parameters froma single grid of elevation datamakes DEMs a powerful tool formorphometric analysis. However, many of these parameters have almost the sameinformative content, and before starting to elaborate topographic data it is recommended to knowa-prioriwhat parameters best visualize the investigated landform, and therefore what is necessary and what is redundant. In thiswork,we reviewa number of analytical procedures used to parameterize and represent DEMs. A LIDAR-derived DEM matrix acquired over the Valle del Bove valley, on Mt. Etna, is used as test-case elevation data for deriving the parameters.Wefirst reviewwell known parameters such as hill-shading, slope and aspect, curvature, and roughness, before extending the review to some less common parameters such as Sky View Factor (SVF), openness, and Red Relief Image Maps (RRIM). For each parameter a description is given emphasizing how it can be used for identifying and delimiting specific volcanic elements. The analyzed surface parameters are then cross-compared in order to infer which of them is most uncorrelated, and the results are represented in the formof a correlation matrix. Finally, the reviewed DEM-derived parameters and the correlationmatrix are used for analyzing the volcanic landforms of two case studies:Michoacán-Guanajuato volcanic field and a phonolitic lava flow at the Island of Tenerife.

Description: Published

Description: 69-84

Description: 5V. Dinamica dei processi eruttivi e post-eruttivi

Description: JCR Journal

Description: We present a workflow to create, scale, georeference, and integrate digital elevation models (DEMs) created using open-source structure-from-motion (SfM)multiview stereo (MVS) software into existing DEMs (as derived from the light detection and ranging data in the presented cases). The workflow also maps the root-mean-square error between the base DEM and the SfM surface model. This allows DEM creation from field-based surveys using consumer-grade digital cameras with open-source and custom-built software. We employ this workflow on three examples of different scales and morphology: 1) a scoria cone on Mt. Etna; 2) a lava channel on Mauna Ulu (K¯ılauea); and 3) a flank collapse scar on Mt. Etna. This represents a new approach for rapid low-cost construction and updating of existing DEMs at high temporal and spatial resolutions and for areas of up to several thousand square meters. We assess the self-consistency of the method by comparison of DEMs of the same features, created from independent data sets acquired on the same day and from the same vantage points.We further evaluate the effect of grid cell size on the reconstruction error. This method uses existing DEMs as a georeferencing tool and can therefore be used in limited access and potentially hazardous areas as it no longer relies exclusively on control targets on the ground.

Description: Published

Description: 6687 - 6699

Description: 1V. Storia eruttiva

Description: JCR Journal

Description: Original volcanic edifices of two successive stages of Gran Canaria are reconstructed using a geomorphometric analysis of existent or restored paleosurfaces. In the reconstruction, surface fitting was applied preferably to planèzes (i.e. triangular facets of original volcano flanks) and quasi-planar surfaces, QPS (those occurring on planèzes, or scattered, slightly eroded portions derived from original cone surfaces) with the help of red relief image map (RRIM) analysis. Out of the long-lasting, Mid-Miocene to Holocene subaerial evolution of the island, the Late Miocene Fataga volcano and the subsequent, Pliocene Roque Nublo volcanoes were the largest and highest. The eruptive center of Fataga, a composite edifice (12.2–8.8 Ma) that may have grown up excentrically with respect to the previous Tejeda caldera, iswell-defined by both two planèzes (named Veneguera–Mogán and Fataga–Tirajana) and QPS remnants. Its calculated original volume, ≤1000 km3, is close to the largest stratovolcanoes on Earth. However, its ≥3300 m elevation, obtained by exponential fit, may have been significantly lower due to the complex architecture of the summit region, e.g. a caldera responsible for ignimbrite eruptions. Roque Nublo, a 3.7–2.9 Ma stratovolcanic cone, which was superimposed upon the Fataga rocks ≥3 km west of the Fataga center, has left no considerable paleosurfaces behind due to heavy postvolcanic erosion. Yet, its remnant formations preserved in a radial pattern unambiguously define its center. Moreover, surface fitting of the outcropping rocks can be corrected taking the erosion rate for the past 3 Ma into account. Such a corrected surface fit points to a regular-shaped, ≥3000 m-high cone with a 25 km radius and ca. 940 km3 original volume, also comparable with the dimensions of the largest terrestrial stratovolcanoes.

Description: Published

Description: 123-134

Description: 1V. Storia eruttiva

Description: JCR Journal

Description: During an eruption, time scales of topographic change are fast and involve vertical and planimetric evolution of millimeters to meters as the event progresses. Repeat production of high spatial resolution terrain models of lava flow fields over time scales of a few hours is thus a high-value capability in tracking the buildup of the deposit. Among the wide range of terrestrial and aerial methods available to collect such topographic data, the use of an unmanned aerial vehicle (UAV) as an acquisition platform, together with structure from motion (SfM) photogrammetry, has become especially useful. This approach allows high-frequency production of centimeter-scale terrain models over kilometer-scale areas, including dangerous and inaccessible zones, with low cost and minimal hazard to personnel. This study presents the application of such an integrated UAV-SfM method to generate a high spatial resolution digital terrain model and orthomosaic of Mount Etna’s January–February 1974 lava flow field. The SfM method, applied to images acquired using a UAV platform, enabled the extraction of a very high spatial resolution (20 cm) digital elevation model and the generation of a 3-cm orthomosaic covering an area of 1.35 km2. This spatial resolution enabled us to analyze the morphology of sub-meter-scale features, such as folds, blocks, and cracks, over kilometer-scale areas. The 3-cm orthomosaic allowed us to further push the analysis to centimeter-scale grain size distribution of the lava surface. Using these data, we define three types of crust structure and relate them to positions within a channel-fed ʻaʻā flow system. These crust structures are (i) flow parallel shear lines, (ii) raft zones, and (iii) folded zones. Flow parallel shear lines are found at the channel edges, and are 2-m-wide and 0.25-m-deep zones running along the levee base and in which cracking is intense. They result from intense shearing between the moving channel lava and the static levee lava. In zones where initial levees are just beginning to form, these subtle features are the only marker that delimits the moving lava from the stagnant marginal lava. Rafts generally form as the system changes from a stable to a transitional channel regime. Over this 170-m-long zone, the channel broadens from 8 to 70 m and rafts are characterized by topographically higher and poorly cracked areas, surrounded by lower, heavily cracked areas. We interpret the rafts as forming due to breakup of crust zones, previously moving in a coherent manner in the narrow proximal channel reach. Folded zones involve arcuate, cross-flow ridges with their apexes pointing down-flow, where ridges have relatively small clasts and depressions are of coarser-grained breccia. Our folds have wavelengths of 10 m and amplitudes of 1 m; are found towards the flow front, down-flow of the raft zones; and are associated with piling up of lava behind a static or slowly moving flow front. The very high spatial resolution topographic data available from UAV-SfM allow us to resolve surfaces where roughness has a vertical and horizontal scale of variation that is less than 1 m. This is the case over pāhoehoe and ʻaʻā flow surfaces, and thus allows us to explore those new structures that are only apparent in the sub-metric data. Moreover, during future eruptions, the possibility to acquire such information in near-real time will allow a prompt analysis of developing lava flow fields and structures therein, such as developing lava channel systems, so as to contribute to timely hazard assessment, modeling, and projections.

Description: Published

Description: 29

Description: 1V. Storia eruttiva

Description: 3V. Proprietà dei magmi e dei prodotti vulcanici

Description: JCR Journal

Description: Lava flow simulations help to better understand volcanic hazards and may assist emergency preparedness at active volcanoes. We demonstrate that at Fogo Volcano, Cabo Verde, such simulations can explain the 2014–2015 lava flow crisis and therefore provide a valuable base to better prepare for the next inevitable eruption. We conducted topographic mapping in the field and a satellite-based remote sensing analysis. We produced the first topographic model of the 2014–2015 lava flow from combined terrestrial laser scanner (TLS) and photogrammetric data. This high-resolution topographic information facilitates lava flow volume estimates of 43.7 ± 5.2 × 106 m3 from the vertical difference between pre- and posteruptive topographies. Both the pre-eruptive and updated digital elevation models (DEMs) serve as the fundamental input data for lava flow simulations using the well-established DOWNFLOW algorithm. Based on thousands of simulations, we assess the lava flow hazard before and after the 2014–2015 eruption. We find that, although the lava flow hazard has changed significantly, it remains high at the locations of two villages that were destroyed during this eruption. This result is of particular importance as villagers have already started to rebuild the settlements. We also analysed satellite radar imagery acquired by the German TerraSAR-X (TSX) satellite to map lava flow emplacement over time. We obtain the lava flow boundaries every 6 to 11 days during the eruption, which assists the interpretation and evaluation of the lava flow model performance. Our results highlight the fact that lava flow hazards change as a result of modifications of the local topography due to lava flow emplacement. This implies the need for up-to-date topographic information in order to assess lava flow hazards. We also emphasize that areas that were once overrun by lava flows are not necessarily safer, even if local lava flow thicknesses exceed the average lava flow thickness. Our observations will be important for the next eruption of Fogo Volcano and have implications for future lava flow crises and disaster response efforts at basaltic volcanoes elsewhere in the world.

Description: Published

Description: 1925–1951

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal

Description: Questo rapporto ha lo scopo di pubblicare il manuale operativo delle operazioni con SAPR (Sistema A Pilotaggio Remoto) in dotazione all’Istituto Nazionale di Geofisica e Vulcanologia sezione di Pisa, redatto con la consulenza della Zefiro Ricerca e Innovazione Srl nell’ambito delle procedure operative, tecniche e di sicurezza nell’utilizzo dei droni. L’orizzonte d’impiego dei droni, o più correttamente dei SAPR, in campo militare, civile, commerciale e scientifico è ormai riconosciuto, non solo tra gli esperti del settore, a dimostrazione dei grandi progressi tecnologici conseguiti in questo ambito. La grande flessibilità d’impiego, la facilità d’utilizzo, l’ampia gamma di modelli dai pochi chili a qualche tonnellata, danno la possibilità di accedere ai SAPR a una vasta platea di utilizzatori a costi di acquisto e di esercizio molto variabili. E questo è molto stimolante ma anche preoccupante. Non solo quindi le istituzioni, gli organismi governativi o le Forze armate, ma anche le aziende, le associazioni, i club, i singoli, possono disporre di un velivolo calibrato sulle proprie esigenze, e capacità per varie finalità.

Description: Published

Description: 1-40

Description: 7A. Geofisica per il monitoraggio ambientale e geologia medica

Description: N/A or not JCR

Description: An innovative wireless sensor network (WSN) based on Ultra-Wide Band (UWB) technology for 3D accurate superficial monitoring of ground deformations, as landslides and subsidence, is proposed. The system has been designed and developed as part of an European Life+ project, called Wi-GIM (Wireless Sensor Network for Ground Instability Monitoring). The details of the architecture, the localization via wireless technology and data processing protocols are described. The flexibility and accuracy achieved by the UWB two-way ranging technique is analysed and compared with the traditional systems, such as robotic total stations (RTSs) and Ground-based Interferometric Synthetic Aperture Radar (GB-InSAR), highlighting the pros and cons of the UWB solution to detect the surface movements. An extensive field trial campaign allows the validation of the system and the analysis of its sensitivity to different factors (e.g., sensor nodes inter-visibility, effects of the temperature, etc.). The Wi-GIM system represents a promising solution for landslide monitoring and it can be adopted in combination with traditional systems or as an alternative in areas where the available resources are inadequate. The versatility, easy/fast deployment and cost-effectiveness, together with good accuracy, make the Wi-GIM system a possible solution for municipalities that cannot afford expensive/complex systems to monitor potential landslides in their territory.

Description: Published

Description: id 2948

Description: 7A. Geofisica per il monitoraggio ambientale

Description: JCR Journal

Description: The Seismic lines Offshore Mount Etna (SOME) database is presented. It consists of multichannel high-resolution seismic data acquired in 2005 off-shore Mount Etna (eastern Sicily). We describe first the acquisition of seismic lines and then the architecture of the data base. Finally we describe a very basic interpretation of some seismic lines to provide clear example of the potentiality of the seismic data sets in addressing relevant issues such as the occurrence of slope instabilities and the deformation style of the continental margin off shore mount Etna.

Description: Published

Description: S0557

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: JCR Journal

Description: Ground displacement monitoring is one of the most important aspects of early warning systems and risk management strategies when addressing phenomena such as landslides or subsidence. Several types of instrumentation already exist, but those able to provide real-time warnings on multiple time series are typically based on expensive technology, highlighting the need to develop a low-cost, easy to install system suitable for emergency monitoring. Therefore, a wireless network based on ultra-wideband impulse radiofrequency technology has been realized. The novelty of this network consists of its ability to measure the distance between nodes using the same signals used for transmission without the need for an actual measurement sensor. The system was tested by monitoring a mudflow in Central Italy and revealed its suitability as an early warning tool. More research on the integration of future low-cost hardware and and eventual industrialization would provide further improvement to this promising technology.

Description: Published

Description: 1-14

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: 4V. Processi pre-eruttivi

Description: JCR Journal