Studying tectonic and volcanic active areas by geomorphological observations and data collection on high-resolution models, and numerical simulations of tectonic and gravity driven processes


Tectonically and volcanically active areas are subject to faulting, fracturing, volcanic eruptions, caldera or flank collapse, and magmatic intrusions, such as dyking. These events trigger typical geomorphological features and geomorphological changes that researchers can study in the field and remotely. Satellite data using optical or thermal sensors, and ship acoustics datasets, provide first order information about faulting and volcanic activity, however, there is a resolution gap below the meter-scale, critical to detect and to analyse small structures over broad areas and to better assess how faults, magma intrusions and collapses nucleate and evolve. Moreover, during large metrical ground deformations (earthquakes, dyke intrusions, collapses), the near-field area where satellite radar signal (InSAR) becomes incoherent remains poorly studied, likewise happens in deep sea environments using vessel-based acoustics techniques. In addition, classical field surveys and data collection are, very often, not feasible due to difficult logistic conditions and/or inaccessible areas. Therefore, there is a need to collect higher resolution data to better understand geomorphologic, faulting and volcanic processes at scales from cm to a few meters, that complement classical field studies and remote sensing data.
Structure-from-Motion (SfM) photogrammetry techniques have been applied using imagery acquired from field, aerial and underwater survey, using Unmanned Aerial Vehicles (UAVs, i.e. drones), Remotely Operated Vehicles (ROVs), Autonomous Underwater Vehicles (AUVs), balloons, airplanes and helicopters, as well as cameras and mobile phones. This technique produces digital surface models (DSM), ortho-mosaic imagery, dense point clouds and 3-D models, creating a high-resolution environment reconstruction for local outcrops or broader areas.
The session will focus on the application of SfM for research in the field of structural geology, active tectonics, volcano-tectonics, and geomorphology, with particular regard to tectonically and volcanically active areas. The session covers the following topics: i) case studies where the SfM has been employed; ii) SfM methods, 3-D reconstruction and post-processing analysis; iii) integration and comparison of SfM-derived, field and broad-scale data (such as satellites and acoustics techniques); iv) new tools and methods for data analysis on SfM-derived models; and vi) future works and applications of SfM techniques.

Co-organized by GI5/GM9
Convener: Fabio Luca Bonali | Co-conveners: Federico Di Traglia, Joël Ruch, Alessandro Bonforte, Daniele TrippaneraECSECS, Felix GrossECSECS, Irene Manzella, Fabio Marchese
vPICO presentations
| Mon, 26 Apr, 09:00–10:30 (CEST)

vPICO presentations: Mon, 26 Apr

Chairpersons: Fabio Luca Bonali, Federico Di Traglia, Irene Manzella
Riccardo Rocca

This presentation describes the new improvements applied to the display of a model already presented at EGU2020.

The model was describing a strike/slip fault located in the Venezuelan Andes, and it was special because the fault movement could be animated by the user. The animation was achieved by implementing the options provided by the combination of two software, Blender and Sketchfab, that are typically used for computer games.

The new version allows a better understanding of the fault evolution by expanding the area represented in the model and by graphically highlighting the various elements of the topography. The first improvement is achieved by integrating the portion of the model acquired with a drone, with the DTM and imagery acquired by satellites. The second improvement is achieved by colouring the topography with false colours that can be switched on by the user by pressing a button.

This new version further improves the initial drone SfM model, so that it can be didactically more effective.

How to cite: Rocca, R.: Fault animation with 3D model integrating drone and satellite images., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8084, https://doi.org/10.5194/egusphere-egu21-8084, 2021.

Noemi Corti, Fabio Luca Bonali, Alessandro Tibaldi, Luca Fallati, and Elena Russo

Quantifying the extension rate and the spreading direction in a rift zone is fundamental for several reasons, like the assessment of seismic and volcanic hazard. However, this work requires the collection of a huge amount of precise data along a rift zone, which sometimes can be difficult to obtain, due to hard logistic conditions or to the large width of the study area. In our work we show how the use of UAVs, coupled with Structure-from-Motion (SfM) photogrammetry, allows to overcome these problems and to collect plenty of data even in difficult terrains, where field survey can be affected by the logistics.

We applied this technique in a 2.7 km2 – large area located in the NW part of the Krafla Fissure Swarm (NE Iceland), an active volcanic rift in the Northern Volcanic Zone of Iceland composed of extension fractures, normal faults, eruptive fissures and a central volcano. The study area is situated about 7 km north of the central caldera, and it is characterized by the presence of extension fractures and normal faults, affecting two lava flows dated 11-12 ka BP, and a hyaloclastite ridge dated back to the Weichselian High Glacial (29.1-12.1 ka BP).

The area has been surveyed through 9 different missions, carried out during summer 2019, which allowed to collect a total of 6068 photos. Thanks to the SfM workflow, we obtained a high quality Orthomosaic (2.59 cm/pixel resolution), a DSM (10.40 cm/pixel resolution), and a 3-D Tiled model. By importing the resulting models in a GIS environment, we were able to redraw the geological map of the area, tracing the limits with very high detail, and thus to recognize and map a total of 1355 fractures, classified as normal faults (86) and extension fractures (1269). Moreover, we took structural measurements along both extension fractures and normal faults: at extension fractures, we measured opening directions, local strike and amount of opening in 568 sites, for a total of 1704 structural data, whereas at normal faults we quantified vertical offset in 284 sites. Finally, we interpolated the σhmin values, using the unpublished software ATMO-STRESS, prepared in the framework of the EU NEANIAS project (https://www.neanias.eu/), to plot the strain field.

This approach allowed us to obtain an average spreading direction for this area of N97.7°E, with the majority of data characterized by a right-lateral component of motion, suggesting the influence of dyking at shallow depths on the surface deformation in this area. Furthermore, total extensions of 16.6 m and 11.2 m have been calculated along the fractures affecting Holocene lava units, and an extension of 29.3 m in the hyaloclastites, resulting in an extension rate of 1.4 mm/yr in the Holocene lavas and 1.7 ± 0.7 mm/yr in the Weichselian hyaloclastite. Stretch values are 1.018–1.027 for post-LGM units and 1.049 for the Weichselian unit, suggesting the contribution of both tectonic and magmatic forces in dictating surface deformation in the area.

How to cite: Corti, N., Bonali, F. L., Tibaldi, A., Fallati, L., and Russo, E.: UAV-Based Structure-from-Motion Photogrammetry used for reconstructing Late Pleistocene-Holocene deformation: an example from Krafla Rift (NE Iceland), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3467, https://doi.org/10.5194/egusphere-egu21-3467, 2021.

Hoang Bui, Michael Fyhn, Tuan Nguyen, Toan Do, Jussi Hovikoski, and Long Hoang

Situated in the junction between the Song Hong Basin and the Beibuwan Basin, the Bach Long Vy island exposes Paleogene syn-rift rocks not seen elsewhere in the Gulf of Tonkin. The island underwent a complex geological history related to the Cenozoic SE-ward tectonic escape of Indochina, recorded as deformation features along the outstanding, continuous coastal exposure. To analyze these deformation features in detail and relate them to the regional events, we acquired a high-resolution Unmanned Aerial Vehicle (UAV) dataset covering about 635,000m2 of the 3.5 km long coastal outcrop. In addition, 656 strike and dip measurements were made and 390 photos were taken using smart phone apps, thus on-the-ground data were rapidly acquired and georeferenced. Strike and dip measurements from smart phone apps were periodically checked against traditional Brunton compasses for their reliability. The ground photos were correlated with the UAV image during interpretation. QGIS allows both datasets to be overlain on one another for detailed analysis and interpretation.

We interpreted 2236 deformation features from the dataset, which can be divided into three major types: sand injectites, NW-SE faults, and NE-SW faults. Sand injectites can be divided into three main types: linear dikes, irregular dikes, and massive remobilized sands. Linear dikes trend dominantly N80-100E.

NW-SE faults are closely spaced and have high dip with N110-130E trend. They consistently left-laterally offset sand dikes while most of the time left-laterally offset the gently dipping beds. Apparent right-lateral separation of beddings probably resulted from variation of the slip vector from horizontal pure strike-slip. Occasionally, sand dikes fill in these NW-SE faults. The offsets are small, mostly less than 1 m.

NE-SW faults are larger scale than the NW-SE faults, and are associated with drag folding of the strata. No fault surface kinematic indicators were found, probably due to wave erosion. The drag folds are consistently right-lateral, while the bedding separation can be either left-lateral or right lateral. Left-lateral separation is inferred to indicate a second phase of movement along the same fault. Sand dikes cross-cut the drag folds, thus sand dikes formed after the drag folds and the right-lateral motion on NE-SW faults.

The orientations of these deformation features are consistent with the regional stress field associated with the End-Oligocene inversion, which affected the northern Song Hong Basin and the western Beibuwan Basin due to transpression along the junction between the two basins. The inversion caused regional tilting and NE-SW right-lateral faulting, followed by the main phase of sand injection, and finally the left-lateral NW-SE faults that offset sand dikes. Previously the inversion event was characterized at large scale using industrial seismic and well data. This study provides further evidence of the inversion at the outcrop scale, well below the resolution of the seismic data.

How to cite: Bui, H., Fyhn, M., Nguyen, T., Do, T., Hovikoski, J., and Hoang, L.: Analysis of deformation features using integrated field methods and aerial drone imaging on the Bach Long Vy island, Gulf of Tonkin, Vietnam, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4281, https://doi.org/10.5194/egusphere-egu21-4281, 2021.

Sofia Bressan, Noemi Corti, Valentina Rigoni, and Elena Russo

Due to its strategic position at the boundary between European and American plates, Iceland is extraordinarily well suited for the investigation of various geological processes, like the interaction between active rifting processes and magmatic stresses. In this study, we focused on surveying with very high detail different key areas located within the Krafla Fissure Swarm (KFS), an active volcanic system located in the Northern Volcanic Zone, NE Iceland.

The Krafla volcanic rift is characterized by the presence of a central volcano and by a 100 km-long swarm of extension fractures, normal faults and eruptive fissures mainly affecting post-LGM (Late Glacial Maximum) Holocene lavas. Our work focuses on three different areas, located in the northernmost sector of the rift, about 5 km north of the central caldera, and south of the central volcano. All these areas have been investigated through field surveys performed both with classical methods and through two Unmanned Aerial Vehicles (UAVs), the DJI Phantom 4 PRO and DJI Spark: thanks to Structure from Motion (SfM) photogrammetry techniques, we obtained Orthomosaics, Digital Surface Models (DSMs) and 3D models of the study area, with centimetric resolution.

 The integration of the above cited methodologies allowed us to collect a huge amount of data, also overcoming difficulties due to logistics, which can sometimes impede classical field survey. More in detail, we collected 2476 structural measurements at 918 sites along extension fractures, and at 185 sites along normal faults. At extension fractures, we measured local fracture strike, dilation and, whenever possible, opening direction. On the other hand, along normal faults we measured local fault strike and the vertical offset. From our data, we obtained an average opening direction of N101°E, thus observing the presence of lateral components of motion along extension fractures. Finally, considering both extension fractures and normal faults, we quantified the cumulative dilation along these sectors, in order to assess the stretch value along the rift.

How to cite: Bressan, S., Corti, N., Rigoni, V., and Russo, E.: Integration between data collection through field and UAV-based surveys in volcano-tectonic environments: an example from the Krafla Fissure Swarm (NE Iceland), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8414, https://doi.org/10.5194/egusphere-egu21-8414, 2021.

Benoit Deffontaines, Kuo-Jen Chang, Samuel Magalhaes, and Gérardo Fortunato

Volcanic areas in the World are often difficult to map especially in a structural point of view as (1) fault planes are generally covered and filled by more recent lava flows and (2) volcanic rocks have very few tectonic striations. Kuei-Shan Tao (11km from Ilan Plain – NE Taiwan) is a volcanic island, located at the soutwestern tip of the South Okinawa trough (SWOT). Two incompatible geological maps had been already published both lacking faults and structural features (Hsu, 1963 and Chiu et al., 2010). We propose herein not only to up-date the Kuei-Shan Tao geological map with our high resolution dataset, but also to create the Kuei-Shan Tao structural scheme in order to better understand its geological and tectonic history.

Consequently, we first acquired aerial photographs from our UAS survey and get our new UAS high resolution DTM (HR UAS-DTM hereafter) with a ground resolution <10cm processed through classical photogrammetric methods. Taking into account common sense geomorphic and structural interpretation and reasoning deduced form our HR UAS-DTM, and the outcropping lithologies situated all along the shoreline, we have up-dated the Kuei-Shan Tao geological mapping and its major structures. To conclude, the lithologies (andesitic lava flows and pyroclastic falls) and the new structural scheme lead us to propose a scenario for both the construction as well as the dismantling of Kuei-Shan Tao which are keys for both geology and geodynamics of the SWOT.

How to cite: Deffontaines, B., Chang, K.-J., Magalhaes, S., and Fortunato, G.: Volcanoes geological mapping and structural geology with UAS High Resolution Digital Terrain Model : the Kuei-Shan Tao case example (Eastern Taiwan)., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7015, https://doi.org/10.5194/egusphere-egu21-7015, 2021.

Elena Russo, Noemi Corti, Fabio Luca Bonali, Alessandro Tibaldi, Federico Pasquaré Mariotto, Luca Fallati, and Fabio Marchese

Reconstructing the origin and kinematics of structures along active rifts is essential to gain a deeper knowledge on rifting processes, with important implications for the assessment of volcanic and seismic hazard. Here we reconstruct the architecture of an entire rift, the 70-km-long Theistareykir Fissure Swarm (ThFS) within the Northern Volcanic Zone of Iceland, through the collection of an extensive amount of 7500 quantitative measurements along extension fractures and normal faults, thanks to the integration between Unmanned Aerial Vehicles (UAV) mapping with centimetric resolution through Structure from Motion (SfM) techniques and extensive field surveys with classical methods. Quantitative measurements, collected across a wide area during several campaigns, comprise strike, opening direction and amount of opening at extension fractures, and strike and offset values at faults, along 6124 post-Late Glacial Maximum (LGM) and 685 pre-LGM structures.

The extent of the area covered by our data allowed us to pinpoint differences in the structural architecture of the rift. From south to north: i) extension fractures and faults strike ranges from mainly N10°-20°, to N00-10°, to N30-40°; ii) the opening direction starts from N110°, reaches N90-100° in the center and amounts to N125° in the northernmost sector; and iii) the dilation amount is in the range 0.1–10 m, then 0.1–9 m and it finally reaches 0.1–8 m. We explore such differences as due to the interaction with the WNW-ESE-striking Husavik-Flatey transform fault and the Grímsey Oblique Rift (Grímsey lineament), and to the structural inheritance of older NNE- to NE-striking normal faults. The reconstruction of the stress field resulting from such data allows the interpolation of the σhmin values, through the unpublished software ATMO-STRESS, prepared in the framework of the EU NEANIAS project, in order to plot and examine the strain field.

Furthermore, mechanisms of rift propagation and the relation between magma systems are here investigated through the analysis of 281 slip profiles of the main Pleistocene-Holocene faults. Our data show a mechanism of along-axis propagation of the rift outward from the volcano: in fact, north of the volcano, 75% of the asymmetric faults propagated northward, whereas south of the volcano 47% of the asymmetric faults propagated southward. This can be due to the combination between the development of faults following lateral dyke propagation outward from the magma chamber, and faults nucleation near the volcano as a consequence of the different crustal rock rheology produced by a higher heat flux.

How to cite: Russo, E., Corti, N., Bonali, F. L., Tibaldi, A., Pasquaré Mariotto, F., Fallati, L., and Marchese, F.: Reconstruction of the entire rift architecture of Theistareykir Fissure Swarm (northeast Iceland): integration between extensive UAV and field surveys, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5246, https://doi.org/10.5194/egusphere-egu21-5246, 2021.

Lucia Andreuttiova, James Hollingsworth, Pieter Vermeesch, and Thomas Mitchell

Optical image correlation (OIC) is a powerful tool for measuring the 3-D near-field surface displacements produced in large earthquakes. The method compares pre- and post-earthquake orthorectified images; shifts between common pixels in the image pair reflects a 2-D (horizontal) offset. The third dimension (vertical displacement) is calculated by differencing the pre- and post-topography, while accounting for the horizontal displacements. Optical image correlation has a sub-pixel detection capability, and can provide information on the displacement field close to fault ruptures (where InSAR typically decorrelates). Small-scale measurements of the distributed damage provide important constraints on the strain distribution within the fault core and the surrounding damage zone, as well as offering insights into the rupture mechanics.

OIC is frequently applied to the recent earthquakes where the image footprint is large relative to the rupture extents. However, historical ruptures are documented by aerial photographs which cover a relatively small area. This means that many images are needed to cover the rupture area and all pixels in pre-and post-earthquake images which span the rupture are typically affected by the ground displacement. This creates complications for image co-registration, alignment and correlation of the final mosaics.

To address this problem we developed a workflow that automatically generates a DEM (digital elevation model) and an orthorectified image mosaic. The process uses structure-from-motion (SfM) and stereo-matching approaches, and results in precise and accurate registration between the image pairs.

We applied this method to the 1959 Hebgen Lake earthquake, SW Montana, U.S. This large (Mw 7.2) intraplate normal event re-activated pre-existing faults north of the Hebgen Lake reservoir and created a complex rupture network. We used 20 pre-earthquake photographs from 1947 and 70 post-earthquake images from 1977 and 1982. The final results show a 3-D displacement localized onto several prominent structures: the Hebgen fault and the Red Canyon fault, consistent with field mapping following the earthquake. A significant vertical offset and a large horizontal NS-component agree well with SW extension on NW-SE-striking normal faults. Additionally, we used fault-perpendicular profiles to explore the along-strike variation in fault displacement and to determine the extent of the off-fault damage.

This work demonstrates that the application of OIC techniques to historical earthquakes can provide new information relating to the geometry and displacement of fault ruptures, and isolate the last event from the previously accumulated displacements. Additionally, the method we propose offers potential for the characterisation of historical earthquakes in general, and promises to improve our understanding of rupture behaviour through a statistical analysis of many earthquakes.

How to cite: Andreuttiova, L., Hollingsworth, J., Vermeesch, P., and Mitchell, T.: New 3D constraints on the co-seismic displacement field for the 1959 (Mw 7.2) Hebgen Lake earthquake from optical image correlation of historical aerial images, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11896, https://doi.org/10.5194/egusphere-egu21-11896, 2021.

Fabio Luca Bonali, Luca Fallati, Varvara Antoniou, Kyriaki Drymoni, Federico Pasquaré Mariotto, Noemi Corti, Alessandro Tibaldi, Agust Gudmundsson, and Paraskevi Nomikou

The application of photogrammetry to volcanic areas is usually made using UAVs for collecting pictures aimed at producing high-resolution orthomosaic and digital surface models. In the present work, instead, we use a boat-camera-based photogrammetry approach, as a tool for orthomosaic, digital surface modelling and virtual outcrop production at an almost vertical 300-m-high geological feature: the northern caldera wall of Santorini. This is a geological structure of great interest, where many tens of dykes crop out within a heterogeneous host rock made of sequences of effusive and explosive volcanic deposits. Some active and inactive faults also dissect the caldera wall. Thus, the study area is almost inaccessible for classic field surveys due to challenging logistic conditions and landslide hazard.

We used a 20 MPX camera run by an operator who collected a total of 887 pictures almost continuously, orthogonal to the ground and opposite to the target, during a 5.5-km-long boat survey. We performed the study along the northern caldera wall, at a constant boat velocity and at a distance from the coast/caldera wall that varied between 35.8 m and 296.5 m. The outcomes of the photogrammetry application include: 1) a high-resolution 3D model of the study area, 2) a high-resolution virtual outcrop for two selected parts of the caldera, 3) qualitative and quantitative structural data (dyke attitude, thickness, cross-cutting relationships, host rock lithology) along the vertical caldera cliff. Our method represents a new approach for 3D outcrop building for research under extreme logistic conditions.

How to cite: Bonali, F. L., Fallati, L., Antoniou, V., Drymoni, K., Pasquaré Mariotto, F., Corti, N., Tibaldi, A., Gudmundsson, A., and Nomikou, P.: An application of field-based photogrammetry as a virtual outcrop building target: a key example from Santorini’s northern caldera wall, Greece, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6216, https://doi.org/10.5194/egusphere-egu21-6216, 2021.

Cristina Proietti, Massimo Cantarero, and Emanuela De Beni

Morphological changes of the summit craters of active volcanoes are of pivotal interest in volcano monitoring because they could be the consequences of volcanic activities and represent the prelude of dangerous events.
Several methodologies have been used during the years in the volcanological monitoring, starting from ground measurements and remote sensing techniques such as aerial observation and satellite data analysis.  However, in the last decade UAVs have emerged in monitoring active volcanoes. In fact, they represent tools of indisputable value due to their relatively low cost, speed in mission planning, repeatability of surveys for data acquisition and increased operator safety.
During the last 4 Years we performed 15 UAVs surveys and 3 from helicopter to monitor the four summit craters of ETNA. The acquired data have been processed through structure-from-motion photogrammetric software to extract DEMs and orthomosaics with resolution ranging between 5 and 20 cm. A multi-temporal comparison of the extracted data has been successively performed on a GIS platform with the final aims of performing morpho-structural analyses of Etna summit craters, identifying areas of structural weakness, that could indicate areas of possible lateral collapses, and computing volume balances between gained and lost volumes.
The presented elaborations could help to quantify the hazard related to Etna summit eruptive activity and to mitigate the risk on an area visited by several tourists, especially in summer time.

How to cite: Proietti, C., Cantarero, M., and De Beni, E.: Preliminary morpho-structural analyses of the summit craters of Etna, in the last 4 Years, based on data extracted through SfM technique, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13288, https://doi.org/10.5194/egusphere-egu21-13288, 2021.

Emanuela De Beni, Alessandro Tibaldi, Noemi Corti, Fabio L. Bonali, Susanna Falsaperla, Horst Langer, Marco Neri, Massimo Cantarero, Danilo Reitano, and Luca Fallati

The collection of a conspicuous amount of data in volcanic areas is a key for a deeper understanding of the relationships between faulting, diking and superficial volcanic processes. A way to quickly collect huge amounts of data is to analyse photogrammetry-derived models (Digital surface models, orthomosaics and 3D models) using Unmanned Aerial Vehicles (UAVs) to collect all necessary pictures obtaining final models with a texture ground resolution up to 2-3 cm/pix.

In this work, we describe our approach to build up models of a broad area located in the NE Rift of Mt. Etna, which is affected by continuous ground deformation linked to gravity sliding of the eastern flank of the volcano and dyke injection. The area is characterized by the presence of eruptive craters and fissures, extension fractures, and normal faults, as well as by historical lava flows. The goal was to quantify the kinematics at extensional fractures and normal faults, integrating the latter with seismological data to reconstruct the stress field acting in this peculiar sector of the volcano. By the point of view of UAV surveying, the test area is challenging since it is located at an altitude ranging between 2700 and 1900 m a.s.l., and it is affected by extreme weather conditions, like a strong wind. Resulting models, in the form of DSM and orthomosaic, are characterised by a resolution of 11.86 and 2.97 cm/pix, respectively, obtained from the elaboration of 4018 photos and covering an area of 2.2 km2. Thanks to these models, we recognized the presence of 20 normal fault segments, 250 extension fractures, and 54 single eruptive fissures. Considering all the above mention data, we quantified the kinematics at extensional fractures and normal faults, obtaining an extension rate of 1.9 cm/yr for the last 406 yr.

How to cite: De Beni, E., Tibaldi, A., Corti, N., Bonali, F. L., Falsaperla, S., Langer, H., Neri, M., Cantarero, M., Reitano, D., and Fallati, L.: Massive data collection in volcanic areas owing to photogrammetry-derived models: a key example from the NE Rift, Mt Etna (Italy)., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5875, https://doi.org/10.5194/egusphere-egu21-5875, 2021.

Susanna Falsaperla, Alessandro Tibaldi, Noemi Corti, Emanuela De Beni, Fabio L. Bonali, Horst Langer, Marco Neri, Massimo Cantarero, Danilo Reitano, and Luca Fallati

Strategies for disaster risk reduction in volcanic areas are mostly driven by multidisciplinary analyses, which offer effective and complementary information on complex geomorphological and volcano-tectonic environments. For example, quantification of the offset at active faults and fissures is of paramount importance to shed light on the kinematics of zones prone to deformation and/or seismic activity. This provides key information for the assessment of seismic hazard, but also for the identification of conditions that may favor magma uprising and opening of eruptive fissures.

Here we present the results of a study encompassing detailed geological, structural and seismological observations focusing on part of the NE Rift at Etna volcano (Italy). The area is situated at an elevation ranging between 2700 and 1900 m a.s.l. where harsh meteorological conditions and difficult logistics render classical field work a troublesome issue. In order to bypass these difficulties, high-resolution (2.8 cm) UAV survey has been recently completed. The survey highlights the presence of 250 extension fractures, 20 normal fault segments, and 54 eruptive fissures. The study allows us to quantify the kinematics at extensional fractures and normal faults, obtaining an extension rate of 1.9 cm/yr for the last 406 yr. With a total of 432 structural data collected by UAV along with SfM photogrammetry, this work also demonstrates the suitability of the application of such surveys for the monitoring of hazardous zone.

How to cite: Falsaperla, S., Tibaldi, A., Corti, N., De Beni, E., Bonali, F. L., Langer, H., Neri, M., Cantarero, M., Reitano, D., and Fallati, L.: Multidisciplinary analyses for mapping and evaluating kinematics and stress/strain field at active faults and fissures at NE Rift, Mt Etna (Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4279, https://doi.org/10.5194/egusphere-egu21-4279, 2021.

Giuseppe Puglisi

Flank dynamics is an ensemble of phenomena observable in many volcanoes, caused by shallow (e.g. material erosion) or deep sources (e.g. tectonics or magma dynamics). Whatever its origin, the most evident effect of flank dynamics is the continuous/steady movement of the flanks of the volcano. The interaction between gravity, tectonics and magma dynamics produce deep-seated, steady-state movement of large sectors of the volcanoes (sometimes called “persistent flank motion” or “volcanic spreading”), whose effects may be severe, either when it evolves in sudden transient acceleration (producing flank collapses or landslides) or when the steady movement damages essential infrastructures or inhabited areas.

Before space-based observations begun, the knowledge of flank dynamics was limited in terms of areal dimension, magnitude and evolution. Since the 90s, first the GPS, then the SAR interferometry have produced a dramatic shift in the capacity to measure ground deformations at the scale of the volcano. GPS and InSAR now give a complete picture of the persistent flank motion and allow inferring the processes inducing this phenomenon. All this impacts the ability to improve the Hazard Assessment and Risk Reduction related to the persistent flank dynamics. Some worldwide examples are reported in the presentation, among of which from Supersite volcanoes. In particular, Mt. Etna offers the opportunity to make some considerations on the benefit of these improvements in hazard assessment of the flank dynamics.

How to cite: Puglisi, G.: Volcano flank dynamics: breakthroughs delivered by space technologies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16312, https://doi.org/10.5194/egusphere-egu21-16312, 2021.

Viorel Marian Mirea, Alexandru Szakács, and Ioan Seghedi

In poorly-exposed forest-covered volcanic areas, the main challenge in classical geological and geomorphological studies is the interpretations of landforms and volcanic structures. The usage of 3D models provides modern opportunities in visualization of volcanic landforms in volcanological studies in areas with dense vegetation cover.

Geological mapping of the Neogene Călimani-Gurghiu-Harghita (CGH) volcanic chain is challenging due poor exposure of area. The Călimani-Gurghiu-Harghita volcanic chain exhibits ~10 My age range spanning from North (> 10 Ma) to South (< 0.03 Ma) linked to the evolution of the adjacent intra-mountain sedimentary basins (Bilbor, Borsec, Gheorgheni, Upper Ciuc, Lower Ciuc, Brașov and Baraolt basins). The geomorphological analysis of the CGH volcanic chain is currently performed using SRTM data. However, the SRTM data are affected by the vegetation cover. Instead, we used a digital elevation models (DEM) built from topographic maps in combinations with volcanological field observations.

Our method uses a DEM 3D spatial view with overlay standard geological maps, shaded relief complemented with terrain analysis and landform recognition. Then, the study integrates field-based observations and geomorphological mapping results in a new general overview of the complex volcanic topography of the CGH volcanic chain.

Using digital elevation models (DEM) allows the general identification of volcanic facies distribution (proximal, medial and distal) belonging to an individual volcanic structures as well as the regional assemblages of the whole volcanic chain. DEM studies also permit to reconstruct the erosion level of volcanic edifices in conjunctions with field-based volcanological studies. This approach may also help identifying volcanological formations and various types of volcanic facies resulting from both construction and destructions of the edifices in poorly exposed areas.

By using this methodology a broad range of volcanic morphological features have been observed along the CGH volcanic range including the Călimani caldera morphology, features of the old and young debris avalanche deposits of various volcanic edifices and the youngest lava-dome morphology of Ciomadul volcano. Our DEM approach provides better results than those obtained by previous studies pointing out, for instance, that the volcanic edifices are highly to moderately eroded in the north and progressively better preserved toward the south.

Acknowledgements. The research was funded through CNCS – UEFISCDI, project number PN-III-P4-ID-PCCF-2016-4-0014, within PNCDI III.

How to cite: Mirea, V. M., Szakács, A., and Seghedi, I.: An investigation approach of the volcanic geomorphology in the Călimani – Gurghiu – Harghita volcanic chain, Romania, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10745, https://doi.org/10.5194/egusphere-egu21-10745, 2021.

Engielle Mae R. Paguican, Pablo Grosse, Gareth N. Fabbro, and Matthieu Kervyn

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 <10 kmwith means of <1 km3. The small flat cones have mean slopes of <21° (mean = 13°), whereas the small steep cones have mean slopes of 14­–37° (mean = 22°). The large cones have volumes mostly between 1 and 200 km3 (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.

How to cite: Paguican, E. M. R., Grosse, P., Fabbro, G. N., and Kervyn, M.: Morphometric classification, evolution, and distribution of volcanic edifices in the Philippines, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9026, https://doi.org/10.5194/egusphere-egu21-9026, 2021.

Roos van Wees, Pierre-Yves Tournigand, Daniel O’Hara, Pablo Grosse, Gabor Kereszturi, Benjamin Campforts, Pierre Lahitte, and Matthieu Kervyn

Volcanoes are extremely dynamic landforms. They grow by the accumulation of eruptive products and intrusions and degrade by a range of erosion processes such as superficial runoff, chemical and physical weathering, fluvial and glacial incision, and mass movements. In this study, we aim at documenting and quantifying the morphology of natural composite volcanoes using a range of morphometric indices, to better understand the factors that control erosion rates and patterns.

In addition to standard morphometric indices, including edifice ellipticity and irregularity, computed by the MORVOLC algorithm, a fractal dimension tool is developed to quantitatively report the shape complexity of stratovolcanoes. A convex hull approach is used to derive minimal erosion volumes and estimate erosion rates, considering available geochronological constraints. Morphometric parameters are derived from digital elevation models (DEMs) for a few exemplary stratovolcanoes of contrasted ages from the same volcanic region. To analyse the potential bias induced by the selected DEMs and the identification of the volcanic edifice outline, we also conduct a sensitivity analysis. The morphometric parameters are similarly extracted using the freely and globally available ALOS 30m (AW3D30), SRTM 30m (SRTMGL1), and ASTER 30m (GDEM 003), and compared to values obtained with the TanDEM-X 12m. The subjective user-drawn edifice outlines are compared to outlines generated by available algorithms, i.e. NETVOLC and MBOA, and their impact on the accuracy of morphometric indexes is quantified.  

Our results highlight that erosion increases edifice irregularity and fractal dimension. Preliminary trends between volcano fractal dimension, eroded volume, and age suggest that fractal analysis has the potential to be used as a relative age determination tool. The proposed morphometric characterisation paves the way for a comparison between natural volcanoes and controlled lab experiments reproducing the degradation of pristine volcanic cones by surface runoff to be developed later in our project.  

How to cite: van Wees, R., Tournigand, P.-Y., O’Hara, D., Grosse, P., Kereszturi, G., Campforts, B., Lahitte, P., and Kervyn, M.: The role of erosion in the morphometry of composite volcanoes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14500, https://doi.org/10.5194/egusphere-egu21-14500, 2021.

Federico Di Traglia, Claudio De Luca, Alessandro Fornaciai, Mariarosaria Manzo, Teresa Nolesini, Massimiliano Favalli, Riccardo Lanari, Nicola Casagli, and Francesco Casu

Steep-slope volcanoes are geomorphological systems receptive to both exogenous and endogenous phenomena. Volcanic activity produces debris and lava accumulation, whereas magmatic/tectonic and gravitational processes can have a destructive effect, triggering mass-wasting and erosion.

Optical and radar sensors have often been used to identify areas impacted by eruptive and post-eruptive phenomena, quantify of topographic changes, and/or map ground deformation related to magmatic-tectonic-gravitational processes.

In this work, the slope processes on high-gradient volcano flanks in response to shift in volcanic activity have been identified by means of remote sensing techniques. The Sciara del Fuoco unstable flank of Stromboli volcano (Italy) was studied, having a very large set (2010-2020) of different remote sensing data available.

Data includes LiDAR and tri-stereo PLEIADES-1 DEMs, high-spatial-resolution (HSR) optical imagery (QUICKBIRD and PLEIADES-1), and space-borne and ground-based Synthetic Aperture Radar (SAR) data. Multi-temporal DEMs and HSR optical imagery permits to map areas affected by major lithological and morphological changes, and the volumes of deposited/eroded material. The results lead to the identification of topographical variations and geomorphological processes that occurred in response to the variation in eruptive intensity. The joint exploitation of space-borne and ground-based Differential and Multi Temporal SAR Interferometry (InSAR and MT-InSAR) measurements revealed deformation phenomena affecting the volcano edifice, and in particular the Sciara del Fuoco flank.

The presented results demonstrate the effectiveness of the joint exploitation of multi-temporal DEMs, HSR optical imagery, and InSAR measurements obtained through satellite and terrestrial SAR systems, highlighting their strong complementarity to map and interpret the slope phenomena in volcanic areas.

This work was financially supported by the “Presidenza del Consiglio dei Ministri – Dipartimento della Protezione Civile” (Presidency of the Council of Ministers – Department of Civil Protection); this publication, however, does not reflect the position and official policies of the Department".

How to cite: Di Traglia, F., De Luca, C., Fornaciai, A., Manzo, M., Nolesini, T., Favalli, M., Lanari, R., Casagli, N., and Casu, F.: Remote sensing of steep-slope volcanoes: the Stromboli case study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9539, https://doi.org/10.5194/egusphere-egu21-9539, 2021.

Morelia Urlaub, Alessandro Bonforte, Jacob Geersen, Felix Gross, and Bruna Pandolpho

Collapses of coastal and ocean island volcanoes can cause damaging tsunamis and thus pose ocean-wide hazards. To assess the collapse hazard of an unstable flank, a profound understanding of its structural setting and active deformation is essential. This knowledge is, however, often missing, especially for the remote and submerged offshore part of the edifice. Long before satellite-based techniques were available, observations of extensional structures in the summit region and transpressive to compressional structures farther downslope helped to constrain flank instability onshore at many volcanoes globally. Similar deformation structures are also expected offshore where they might be even better preserved due to the absence of anthropogenic influence, limited weathering and erosion. However, in the offshore realm structures related to flank instability are masked by and interact with other processes that act on underwater slopes, such as bottom currents, downslope sediment transport, and regional tectonics. Furthermore, the remote location of offshore flanks complicates geophysical, geomorphological, and geological investigations. Using (micro-) bathymetric and high-resolution seismic data we analyse the seascape forming processes at the Eastern Sicily continental slope at the foot of Mount Etna's unstable south-eastern flank. We untangle seafloor structures related to volcanotectonic, sedimentary, and regional tectonic processes. This allows singling out patterns and structures related to volcano flank instability, such as the lateral and outward boundaries of the unstable flank. We identify a strike-slip fault that changes its morphological appearance from a sharp linear feature atop a pressure ridge north of Catania Canyon to an almost smooth seafloor further downslope, where gravitational sediment transport outbeats volcanotectonic activity. Sediment transport from the continent to the abyss occurs along several canyons and channels that partly align with fault systems. Furthermore, uplift at the distant toe of Etna‘s south-eastern flank may indicate compression from the downwards moving flank, while at the same time provoking erosional responses, e.g. landslides. This new information provides important constraints for kinematic models that seek to explain the drivers of flank instability. It also forms the base for future studies that will infer the styles and rates of offshore flank deformation from the geological record.

How to cite: Urlaub, M., Bonforte, A., Geersen, J., Gross, F., and Pandolpho, B.: Interplay of volcanotectonic, sedimentary, and regional tectonic processes at Mount Etna’s submerged south-eastern flank, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14689, https://doi.org/10.5194/egusphere-egu21-14689, 2021.

Irene Manzella, Symeon Makris, Federico Di Traglia, Karim Kelfoun, Paul Cole, Daniele Casalbore, and Francesco L Chiocci

As demonstrated by the Anak Krakatau eruption-induced flank collapse in 2018 in Indonesia, tsunamis generated by large mass flows like landslides and pyroclastic density currents can have devastating effects in volcanic areas. However, these phenomena are still poorly understood as they are unusual and complex events, largely unpredictable and often poorly constrained. 

Stromboli is one of the most active volcanoes in the world, extensively monitored and studied in the last few decades. Many tsunamigenic landslides (sub-aerial and/or submarine) have taken place; at least seven have occurred in the last 150 years and a devastating one is believed to have reached the coast of Naples, at more than 200 km distance, during the Middle Ages. Because the level of activity of the volcano has remained similar ever since and the likelihood of such disastrous events is not negligible, the hazard related to tsunamigenic mass flows in this area needs to be carefully assessed.

Associated with the 3rd of July 2019 eruption, at least three mass flows were triggered along the Sciara del Fuoco slope; two subaerial Pyroclastic density currents (PDCs) and a submarine landslide. Simultaneously, three buoys registered the height of the resulting tsunami wave ranging from 0.2 m in front of the Ginostra village to 1.5 m in front of the Sciara del Fuoco. Thanks to the dense monitoring network and the accurate bathymetry survey carried out by the IGAG-CNR, these events have been well constrained. 

The tsunami waves studied here are smaller than those that could constitute a threat for the population living in this area, nevertheless they can be used to characterize the behaviour of the tsunamigenic mass flows. Back analysis of these events were undertaken with the two-fluids version of VolcFlow; this is a continuum mechanics model based on the depth-average approximation that has been developed for the simulation of volcanic flows. VolcFlow can take into account several different rheologies for each of the two fluids. In the present case, one fluid was used for the water body and one for simulating the mass flow. For the latter one, a constant retaining stress type of rheology was used (Dade and Huppert, 1998). Backanalysis suggested that it was the PDC which generated the tsunami wave during the events of July 2019 and best fitting simulations identified a constant retaining stress of 7kPa. With these input parameters it has been possible to run a large number of numerical simulations of possible scenarios. This has allowed to assess threshold values of volume and discharge of mass flows which could generate significant and potentially destructive tsunami waves. This constitutes an important input to improve early warning systems and to reduce the risk related to these unpredictable but extremely dangerous phenomena.

How to cite: Manzella, I., Makris, S., Di Traglia, F., Kelfoun, K., Cole, P., Casalbore, D., and Chiocci, F. L.: Numerical modelling of tsunamis generated by mass flows at Stromboli Volcano, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11042, https://doi.org/10.5194/egusphere-egu21-11042, 2021.

Jorge Romero, Margherita Polacci, Hugo Moreno, Sebastian Watt, Miguel Angel Parada, Kevin Valenzuela, Luis Albornoz, Fabio Arzilli, Giuseppe La Spina, Inés Rodríguez, and Mike Burton

Reconstructing the complex processes triggered by catastrophic destruction of volcanoes on both their own magmatic system and the surrounding landscape, is a fundamental task for evaluating long-timescale volcanic hazards and controls on the development of volcanoes. Antuco stratovolcano (37.4°S, 71.4°W; Chile), is a dominantly basaltic composite edifice which original ca. 3300 m altitude edifice experienced a ca. 5 km3 Bandai-type sector collapse at ~6.2 ka BP. We carried out field studies of its debris avalanche deposit (DAD), which was distributed to the W and consist of chaotic breccias, with a longitudinal facies transformation from 2 large proximal toreva-block facies (4 & 9 km W from the scar) to megablocks, blocks and matrix facies in distal areas (up to 20 km from the scar). Basal facies are fine grained shredded rocks and contain substratum injections and clastic dykes. The surface of the avalanche is hummocky, and the size, internal architecture and lithology of hummocks vary with distance. At El Peñón and Manquel (10 to 20 km W from the scar) the DAD is overlaid by a sequence of dilute pyroclastic density currents (PDCs) containing juvenile ash and highly vesicular porphyritic basalt scoria fine to medium lapilli size. Further W, one of the latest dilute PDC gave ca. 3.4 ky BP in charcoal.  These PDCs are separated from two thick, far-reaching basaltic andesite overlying lava flows (post-collapse Antuco basal flows) by a paleosol, and they show compositional features consistent with mixing of a highly zoned or compartmentalised magma storage system at <5km depth. Subsequently, that event was followed by the initiation of a renewed basaltic magmatic stage and cone regeneration at Antuco during the Late Holocene to the present. These observations plus the detailed study of the composition and texture of post-collapse products suggests a long-lasting reconfiguration of the plumbing system in response to depressurization induced by the sector collapse. The DAD also blocked the natural output of Lake Laja, increasing its level ca. 200 m and then triggering catastrophic outburst floods by dam rupture, preserved as alluvial beds interpreted as debris and hyperconcetrated flow deposits. The ancestral Laja lake outburst, eroded and redeposited tens of meters of basaltic sediments and boulders as far as 120 km within the Central Depression, W from the volcano. Downstream, along the Itata and Biobío rivers (the latter fed by Laja River) at least two fluvial/alluvial terraces are formed by these volcaniclastic materials, 140-170 km WNW from Antuco volcano. These deposits develop laminar, cross bedded and flaser structures. In addition, fragments of pumice, charcoal and archaeological ceramics have been recognised in the sediments. Ceramics where likely produced at the Talcahuano-1 archaeological site (ca. 1.890 BP), in agreement with charcoal that provides a maximum age between 1.8 and 1.85 ky BP for the younger flooding events. The coupled investigation of the impacts produced by massive debris avalanches, especially at basaltic-arc stratovolcanoes, is important to understand their long-term system evolution and hazards.

How to cite: Romero, J., Polacci, M., Moreno, H., Watt, S., Parada, M. A., Valenzuela, K., Albornoz, L., Arzilli, F., La Spina, G., Rodríguez, I., and Burton, M.: Multi-scale impacts of Antuco basaltic stratovolcano (Southern Andes, Chile) ca. 6.2 ka sector collapse: avalanche deposition, eruptive behavior transformation and hydrologic reconfiguration, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16176, https://doi.org/10.5194/egusphere-egu21-16176, 2021.