Mapping and evaluating kinematics and the stress and strain field at active faults and fissures: a comparison between field and drone data at the NE rift, Mt Etna (Italy)

We collected drone data to quantify the kinematics at extensional fractures and normal faults, integrated this information with seismological data to reconstruct the stress field, and critically compared the results with previous fieldwork to assess the best practice. As a key site, we analyzed a sector of the northeast rift of Mt Etna, an area affected by continuous ground deformation linked to gravity sliding of the volcano's eastern flank and dike injections. The studied sector is characterized also by the existence of eruptive craters and fissures and lava flows. This work shows that this rift segment is affected by a series of NNE- to NE-striking, parallel extensional fractures characterized by an opening mode along an average N105.7∘ vector. The stress field is characterized by a σHmin trending northwest–southeast. Normal faults strike parallel to the extensional fractures. The extensional strain obtained by cumulating the net offset at extensional fractures with the fault heave gives a stretching ratio of 1.003 in the northeastern part of the study area and 1.005 in the southwestern part. Given a maximum age of 1614 CE for the offset lavas, we obtained an extension rate of 1.9 cm yr−1 for the last 406 years. This value is consistent with the slip along the Pernicana Fault system, confirming that the NE rift structures accommodate the sliding of the eastern flank of the volcano.

Massive data collection in volcanic areas owing to photogrammetry-derived models: a key example from the NE Rift, Mt Etna (Italy).

<p>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.</p><p>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 km<sup>2</sup>. 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.</p>

Multidisciplinary analyses for mapping and evaluating kinematics and stress/strain field at active faults and fissures at NE Rift, Mt Etna (Italy)

<p>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.</p><p>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.</p>

Pre-eruptive magmatic processes and their timescales revealed by crystal zoning

<p>Understanding the processes that occur in the magma plumbing systems prior to eruption and how they relate to monitoring data can lead to improved volcanic hazard assessment. Crystal compositions are witnesses of the architecture and dynamics of the plumbing system, and crystal zoning patterns can inform us of the range of magmatic environments, and of the likely processes that lead to eruption. We have studied the petrology and the geochemistry of the monogenetic historical eruptions occurred in Tenerife (Canary Islands) that come out through the rift zones (NW and NE Rifts) as well as the last mafic intra-caldera monogenetic eruption of Montaña Mostaza (15 ka). The deposits from the NE Rift and the intra-caldera contain complexly zoned olivine crystals suggesting open system and magma mixing, while crystals from the NW Rift are mainly normally zoned. By modelling the zonation patterns of the crystals we have calculated the timescales of the magma intrusions and ascent to the surface. We have found that the magmas erupted along the NW rift are more evolved and vary from basanites to phono-tephrites, while the magmas from the NE rift are basanites recording different mixing events between magma pockets occurred around 1-2 years, 3 months and few days before the eruption. The olivine crystals from the intra-caldera eruption display more variety in the zoning patterns than the eruptions from the rift, suggesting a more complex history. Based on the integration of the petrological and modelling results with gravimetric and geophysical data we propose, at least, three main different ascent histories (paths and timescales) for monogenetic eruptions in Tenerife.</p><p><em>This research has been partially funded by the EUROVOLC project (Horizon 2020 Grant Agreement: 731070).</em></p>

Soil carbon dioxide efflux weekly monitoring network for the volcanic surveillance of Tenerife, Canary Islands

<p>Carbon dioxide (CO<sub>2</sub>) is one of the first gases to escape from the magmatic environment due to its low solubility in basaltic magmas at low pressures. Monitoring of volcanic gases in Tenerife Island (2,304 km<sup>2</sup>) has been focused mainly on diffuse CO<sub>2</sub> degassing and other volatiles due to the absence of visible gas manifestations except fumaroles at the summit of Teide volcano. An inexpensive method to determine CO<sub>2</sub> fluxes based in the absorption of CO<sub>2</sub> through an alkaline medium followed by titration analysis has been used with the aim of contributing to the volcanic surveillance of Tenerife. During summer 2016, a network of 31 closed alkaline traps was deployed along the three volcanic rifts of Tenerife (NE, NW and NS) and at Cañadas Caldera. To do so, an aliquot of 50 mL of 0.1N KOH solution is placed inside the chamber at each station to absorb the CO<sub>2</sub> released from the soil. The solution is replaced in a weekly basis and the trapped CO<sub>2</sub> is later analyzed at the laboratory by titration. Values are expressed as weekly integrated CO<sub>2 </sub>efflux. We present herein the results of one year CO<sub>2 </sub>efflux estimated by closed alkaline traps. The CO<sub>2</sub> efflux values ranged from 1.0 to 14.5 g·m<sup>-2</sup>·d<sup>-1</sup>, with average values of 8.5 g·m<sup>-2</sup>·d<sup>-1</sup> for the NE rift-zone, 5.2 g·m<sup>-2</sup>·d<sup>-1 </sup>for Cañadas Caldera, 6.4 g·m<sup>-2</sup>·d<sup>-1</sup> for NW rift-zone and 6.1 g·m<sup>-2</sup>·d<sup>-1</sup> for NS rift-zone. The estimated CO<sub>2 </sub>efflux values were of the same order than the observed ones in 2016. Relatively high CO<sub>2</sub> efflux values were observed at the NE rift-zone, where maximum values were measured. The temporal evolution of CO<sub>2 </sub>efflux estimated by closed alkaline traps did not show significant variations during 2019. However, small seasonal variations are observed during the period 2016 – 2019. To investigate the origin of the soil CO<sub>2</sub>, soil gas samples were weekly sampled on the head space of the closed chambers. Chemical and isotopic composition of C in the CO<sub>2</sub> were analysed in the gas samples. The concentration of CO<sub>2</sub> on the head space of the closed chambers showed a range of 355-50,464 ppm, with an average value of 1,850 ppmV, while the isotopic composition expressed as d<sup>13</sup>C-CO<sub>2</sub> showed a range from -5.03 to -30.44 ‰, with an average value of -15.9 ‰. The heaviest values of d<sup>13</sup>C-CO<sub>2</sub> are in the NW rift-zone. The systematics of closed static chambers alkaline traps can be a simple and economical tool with volcanic surveillance purposes in system where visible volcanic gases manifestations are absence.</p>