Geosite assessment and communication: a review

This work is aimed at reviewing the current state of the art in geosite selection, assessment, and communication. We first highlight the main papers that have defined paramount concepts such as geodiversity, geoheritage, and geosites. We then delve into the theoretical principles and guidelines that have been proposed over the last twenty years by researchers who have thoroughly illustrated how to individuate and assess geosites. In doing so, we illustrate notable field examples of applications of qualitative and quantitative assessments of geosites in places such as Serbia, India, Iceland, Ecuador, Sardinia (Italy), Egypt, Tasmania (Australia), and Brazil. The third part of this work is dedicated to illustrating a list (by no means exhaustive) of works that have tried to come up with innovative tools, strategies, and solutions to promote and communicate geosites. From our work, it appears that geosites can be extremely effective as fully fledged outreach tools capable of bridging the gap between Earth science and the lay public

Along-rift propagation of Pleistocene-Holocene faults from a central volcano

The mechanisms of rift propagation are still not fully understood, especially at mid-oceanic ridges, owing to the inherent difficulty in collecting submarine data. Here, we investigate the fault slip profiles of the 60-km-long Theistareykir rift (northern Iceland) that may suggest the direction of along-axis rift propagation. This is one of the few places on Earth where rifting processes and mid-oceanic ridge formation can be studied directly. Moreover, this rift hosts an active central volcano, and this enables to fully understand the relations between rift propagation and magma systems. We reconstructed the slip profiles of all the 281 main Pleistocene-Holocene faults that compose this N-S rift, by merging measurements performed in the field, collected by Unmanned Aerial Vehicle surveys, and derived from Digital Surface Models. Results indicate that north of the volcano, 75% of the asymmetric faults propagated northward; the value increases to 82% if the cumulated fault length is considered. South of the volcano, 47% of the asymmetric faults propagated southward, 54% if the cumulated fault length is considered. These data point to a dominant mechanism of along-axis propagation of the rift outward from the volcano, suggesting a genetic link with the underlying magma chamber. Two possible processes are suggested, which can also occur in combination: i) faults develop following lateral dyke propagation outward from the magma chamber, and ii) faults nucleate near the volcano as a consequence of the different crustal rock rheology produced by a higher heat flux. The rift architecture is complicated by the presence of tectonic zones with different dominant fault dips, separated by transversal accommodation zones. The latter also play the role of barriers guiding local fault propagation

Geometry, oblique kinematics and extensional strain variation along a diverging plate boundary: The example of the northern Theistareykir Fissure Swarm, NE Iceland

The boundary between the American and European plates emerges in Iceland, an outstanding natural laboratory where it is possible to analyse ongoing rifting processes. In the North Volcanic Zone, we studied with unprecedented detail an active rift, known as the Theistareykir Fissure Swarm (ThFS). We surveyed an area of 85 km(2) with 694 measurement sites along 1537 post-Late Glacial Maximum extension fractures. In the southern sector of the study area, fractures strike N30-40 degrees with opening directions about N120 degrees. Fractures in the central sector strike about N00 degrees and opening directions are N90-100 degrees. In the northern sector, fractures strike about N30 degrees with opening directions about N125 degrees. Through a comparison with older faults cropping out in the substrate at the shoulder of the ThFS, we are able to suggest that variations in fracture strike are the effect of substrate structural inheritance as well as the pothible interaction with the Tjornes Fracture Zone. With regard to kinematics, we highlight that most fractures show a small, but systematic, strike-slip component (a more frequent right-lateral component and a less common, left-lateral one). This cannot be explained as the result of fracture strike rotation relative to the regional, tectonic least principal stress. We conclude that the net opening directions can result from the combination of tectonic offsets and events caused by shallow magma chamber inflation and/ or dyke intrusions. The latter can produce transcurrent components of displacement along new or already existing fractures

Active kinematics of the greater caucasus from seismological and GPS data: A review

In this paper, we describe the active kinematics of the Greater Caucasus (territories of Georgia, Azerbaijan and Russia) through an integrated analysis of seismological, geological-structural and GPS data. Alignments of crustal earthquake epicentres indicate that most seismic areas are located along the southern margin of the mountain belt and in its north-eastern sector, in correspondence of major, active WNW-ESE faults, parallel to the mountain range. Focal Mechanism Solutions (FMS) delineate dominant reverse fault kinematics in most sectors of the mountain belt, though swarms of strike-slip FMS indicate the presence of active transcurrent faulting, especially along the southeastern border of the Greater Caucasus. The mountain belt is characterized by dominant NNE-SSW-oriented P-axes. In the central-southern sector, in correspondence of the local collision between the Lesser and Greater Caucasus, P-axes are mainly NNW-SSE oriented. GPS data show dominant motions to the NNW, with rates increasing in eastward direction. All observations are consistent with a component of eastward escape of the central-eastern part of the Greater Caucasus

Rifting Kinematics Produced by Magmatic and Tectonic Stresses in the North Volcanic Zone of Iceland

In the North Volcanic Zone of Iceland, we studied with the greatest possible detail the complete structural architecture and kinematics of the whole Theistareykir Fissure Swarm (ThFS), an N-S-trending, 70 km long active rift. We made about 7500 measurements along 6124 post-Late Glacial Maximum (LGM) extension fractures and faults, and 685 pre-LGM structures. We have collected the data over the last 6 years, through extensive field surveys and with the aid of drone mapping with centimetric resolution. In the southern sector of the study area, extension fractures and faults strike mainly N10\ub0-20\ub0, the opening direction is about N110\ub0, and the dilation amount is in the range 0.1\u201310 m. In the central sector, faults and extension fractures strike mainly N00-10\ub0, the opening direction is N90-100\ub0, and the dilation amount is 0.1\u20139 m. In the northern sector, extension fractures and faults strike N30-40\ub0, the opening direction is about N125\ub0, and the dilation amount is 0.1\u20138 m. The variations in strike are attributable to two processes: the interaction with the WNW-ESE-striking Husavik-Flatey transform fault and Gr\uedmsey Oblique Rift (Gr\uedmsey lineament), and the structural inheritance of older NNE- to NE-striking normal faults. Most extension fractures show a minor strike-slip component: a systematic right-lateral component can be accounted for by the interaction with the WNW-ESE-striking fault zones and the regional, oblique opening of the rift. We regard dyke propagation as a possible cause for the more complex strike-slip components measured at several other fractures. Cumulated dilation and fracture frequency decrease along the rift with distance away from the Theistareykir volcano, situated in the central sector of the ThFS. This is interpreted as a decrease in the number of dykes that are capable of reaching great distances after being injected from the magma chamber

Slope deformation, reservoir variation and meteorological data at the Khoko landslide, Enguri hydroelectric basin (Georgia), during 2016-2019

The Greater Caucasus mountain belt is characterized by deep valleys, steep slopes and frequent seismic activity, the combination of which results in major landslide hazard. Along the eastern side of the Enguri water reservoir lies the active Khoko landslide, whose head scarp zone affects the important Jvari-Khaishi-Mestia road, one of the few connections with the interior of the Greater Caucasus. Here, we present a database of measurement time series taken over a period of 4 years (2016-2019) that enables us to compare slope deformation with meteorological factors and human-induced perturbations owing to variations in the water level of the reservoir. The monitoring system we used is composed of two digital extensometers, placed within two artificial trenches excavated across the landslide head scarp. The stations are also equipped with internal and near-ground surface thermometers. The dataset is integrated by daily measurements of rainfall and lake level. The monitoring system - the first installed in Georgia - was set up in the framework of a NATO-funded project, aimed at assessing different types of geohazards affecting the Enguri artificial reservoir and the related hydroelectrical plant. Our results indicate that the Khoko landslide displacements appear to be mainly controlled by variations in hydraulic load, in turn induced by lake level oscillations. Rainfall variations might also have contributed, though this is not always evident for all the studied period. The full databases are freely available online at the following DOI: 10.20366/unimib/unidata/SI384-2.0 (Tibaldi et al., 2020)

Feeders vs arrested dikes: A case study from the Younger Stampar eruption in Iceland

Understanding the mechanical conditions for dike arrest and associated surface deformation or, alternatively, dike propagation to the surface to supply magma to an eruption, is of fundamental importance for volcanology in general and for volcanic hazards in particular. Here we present the results of a study of an outcrop located in the Reykjanes Peninsula, SW Iceland, where one dike became arrested only 5 m below the surface of an active volcanic system, without inducing any brittle deformation at the surface. In the same outcrop, at a distance of 30 m, a feeder dike is exposed. Both dikes are associated with the Younger Stampar eruption (1210–1240 CE). We reconstructed a high-resolution 3D model, through drone surveys and Structure from Motion (SfM) techniques, on which we collected detailed structural data combined with field surveys. These data, integrated with petrographic and geochemical analyses, became inputs to Finite Element Method (FEM) numerical models, made using the COMSOL Multiphysics® software. Our results indicate that compression exerted by the intrusion of the feeder dike (inferred to have been emplaced first) can explain the arrest of the second dike and the absence of induced brittle deformation even if the dike tip is only 5 m below the surface. Furthermore, the contrasting mechanical properties of the layers that constitute the outcrop, with alternating stiff lavas and compliant tuffs, raise (concentrate) the compressive stresses in the lava flows ahead of the second dike, thereby encouraging its arrest. Both the dikes are basaltic, but the earlier emplaced feeder dike is crystal poor and slightly more evolved than the later emplaced arrested dike. The results throw a new light on the conditions for dike arrest and (the lack of) dike-induced brittle deformation at very shallow depths in active rift zones, with important implications for volcanic-hazard assessments

How academics and the public experienced immersive virtual reality for geo-education

Immersive virtual reality can potentially open up interesting geological sites to students, academics and others who may not have had the opportunity to visit such sites previously. We study how users perceive the usefulness of an immersive virtual reality approach applied to Earth Sciences teaching and communication. During nine immersive virtual reality-based events held in 2018 and 2019 in various locations (Vienna in Austria, Milan and Catania in Italy, Santorini in Greece), a large number of visitors had the opportunity to navigate, in immersive mode, across geological landscapes reconstructed by cutting-edge, unmanned aerial system-based photogrammetry techniques. The reconstructed virtual geological environments are specifically chosen virtual geosites, from Santorini (Greece), the North Volcanic Zone (Iceland), and Mt. Etna (Italy). Following the user experiences, we collected 459 questionnaires, with a large spread in participant age and cultural background. We find that the majority of respondents would be willing to repeat the immersive virtual reality experience, and importantly, most of the students and Earth Science academics who took part in the navigation confirmed the usefulness of this approach for geo-education purposes