Integration between data collection through field and UAV-based surveys in volcano-tectonic environments: an example from the Krafla Fissure Swarm (NE Iceland)

<p>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.</p><p>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.</p><p> 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.</p>

Reconstruction of the entire rift architecture of Theistareykir Fissure Swarm (northeast Iceland): integration between extensive UAV and field surveys

<p>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.</p><p>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 σ<sub>hmin</sub> 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.</p><p>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.</p>

Structural analysis of the Theistareykir Fissure Swarm (NE Iceland) using field survey integrated with UAV-based - Structure from Motion techniques

<p>Due to its position at the boundary between American and European plates, Iceland represents an ideal natural laboratory to study active rifting processes, where rifting mechanisms are complicated by the superimposition of tectonic and magmatic stresses. In order to contribute to the study of such processes, we focused our attention on the southern sector of the Theistareykir Fissure Swarm (ThFS), an active volcanic rift belonging to the Northern Volcanic Zone of Iceland, affected by both volcanic and seismic hazard.</p><p>We studied an area which is about 22 km<sup>2</sup>-large, situated 12 km south of the intersection of the ThFS with the Husavik Flatey Fault (HFF), a dextral strike-slip lineament belonging to the Tjornes Fracture Zone (TFZ). The area is characterized by the presence of normal faults and a dense swarm of extension fractures, affecting prevalently post-glacial, Holocene lavas, dated 8-10 and 11-12 ka. Only in the western sector of the area a Late Quaternary interglacial lava crops out, while the northeastern sector is covered by a Weichselian subglacial hyaloclastite. The southern sector of the area has been investigated with classical field survey, whereas in the northern part a 3.87 km<sup>2</sup>-large area has been reconstructed using the Structure from Motion (SfM) techniques, combined with an Unmanned Aerial Vehicle (UAV), obtaining orthomosaics, DSMs and 3D models with a centimetric resolution through 4189 UAV photos, collected in 7 different missions during summer 2018.</p><p>In the whole area, we recognized and mapped a total of 624 structures (comprising 583 extension fractures and 41 normal faults), and we took various measurements at 626 structural stations along extension fractures, and 132 along normal faults. Regarding extension fractures, we collected the strike and, in 441 cases where it was possible, the opening direction and the amount of opening; along normal faults we measured the strike, dip and vertical offset.</p><p>Our approach allowed to calculate stretch values across the rift comprised between 1.002 and 1.013, and an average opening direction value of 104.4°N, normal to the average extension fracture strike measured at the structural stations (14°N), suggesting a pure extensional opening in the studied area. Actually, in 281 cases out of our 441 stations along extension fractures we noticed a lateral component > 5°. Furthermore, 49% of data is not consistent with tectonics, neither with regard to the extensional fracture strike, nor with regard to opening directions. This suggests that stresses linked to regional tectonics are not the only cause of deformation, which could have been affected by different processes like dyke intrusion, deglaciation, and inflation/deflation of the Theistareykir volcano magma chamber.</p>

Advances in field data collection in volcano-tectonic sensitive areas: examples and results from the Northern Volcanic Zone of Iceland

<p>Classical field studies are vital for mapping and understanding volcano-tectonic processes, particularly for those that produce superficial deformation consequently to magmatic and tectonic activity. Unfortunately, very often, key outcrops are inaccessible due to harsh logistic conditions or their location in remote or dangerous areas. In the framework of the ILP Task Force II, we developed and tested modern and innovative methods aimed at overcoming these limitations in field research and data collection, that we combined with classical field mapping. Such methods have been used to provide a more complete picture of the deformation processes that have been taking place in the Theistareykir Fissure Swarm within the Northern Volcanic Zone of Iceland. This rift is characterized by the presence of huge normal faults, several extension fractures and volcanic centres. The modern methods we used derive from the use of UAVs (drones) combined with Structure from Motion (SfM) photogrammetry techniques. The first innovative method consists of analysing UAV-based SfM-derived high resolution orthomosaics and digital surface models where we collected hundreds of quantitative measurements of the amount of opening and opening direction of Holocene extension fractures and measurements of fault scarp height. The second and more innovative method we used is the Immersive Virtual Reality that can be applied to 3D digital outcrop models (DOMs), reconstructed with UAV-based SfM photogrammetry techniques; several sites within the Theistareykir Fissure Swarm have been reconstructed in the framework of the Italian Argo3D project. The reconstructed 3D DOMs were explored using different modalities: on foot, as is often the case during field activity, moving like a drone, above and around the target, as well as flying like an airplane. Thanks to these modes of exploration we were capable of better understanding the geometry of extension fractures, volcanic centres and normal faults. We also measured, in the virtual environment, the opening direction and the amount of dilation along the extensional fractures, the direction of magma-feeding fractures underlying cones and volcanic vents, as well as the amount of vertical offset along normal faults. The quantification and mapping of these features was accomplished through some tools tailored for virtual field activity in the framework of Italian Argo3D project and the Erasmus+ Key Action 2 2017-1-UK01-KA203-036719. Thanks to the merging of classical and modern approaches we are able of providing a complete picture related to the post-LGM deformation field affecting this part of the Icelandic rift, particularly focusing on the spreading direction and the stretch ratio across the whole Theistareykir Fissure Swarm.</p>

UAV- and SfM-related techniques applied to volcano-tectonics for virtual outcrops construction and geoscience communication. Examples from the North Volcanic Zone, Iceland

<p><strong>UAV- and SfM-related techniques applied to volcano-tectonics for virtual outcrops construction and geoscience communication. Examples from the North Volcanic Zone, Iceland</strong></p><p><strong> </strong><strong>Authors:</strong> Federico Pasquaré Mariotto<sup>1</sup>, Alessandro Tibaldi<sup>2,3</sup></p><p><sup> </sup></p><p><sup>1</sup>Insubria University, Department of Human and Innovation Sciences                     <sup>2</sup>University of Milan-Bicocca, Department of Earth and Environmental Science, Milan, Italy <sup>3</sup>CRUST- Interuniversity Center for 3D Seismotectonics with Territorial Applications, Italy</p><p> </p><p>Iceland offers an unparalleled chance to observe the most powerful natural phenomena related to the combination of tectonic and magmatic forces, such as active rifting, volcanic eruptions, sub-volcanic intrusions. We have focused on a number of geosites which are found in the Northern Volcanic Zone (NVZ) of Iceland; here, the following volcano-tectonic features can be observed: i) the Theystareykir  Fissure Swarm (ThFS), an active rift system with a central volcano, several major faults and numerous eruptive fissures; ii) the Krafla Fissure Swarm (KFS), another major rift system marked by the presence of monogenetic cones, dip-slip faults, eruptive fissures, extension fractures and the active Krafla volcano.</p><p>In order to showcase a few, outstanding examples of the above, we have made use of UAVs integrated by the Structure-from-Motion (SfM) Photogrammetry. As is well known, the combination of UAV-digital image collection and SfM techniques has been increasingly applied to geological and environmental research. We have applied this approach to the collection of high-definition images and with the purpose of constructing 3-D models, which may be considered “Virtual Outcrops (VO)”.</p><p>We highlight that such 3-D models can be navigated in immersive Virtual Reality mode, and hence can be a key tool not only for research purposes: in fact, this is a novel, cutting-edge approach which is suitable for improving geosite popularization and geoscience communication, allowing for the engagement of a wider audience, including potential end-users from the younger generation.</p><p> </p><p><strong> </strong></p>