In July and August 2019, two paroxysmal eruptions dramatically changed the morphology of the crater terrace that hosts the active vents of Stromboli volcano (Italy). Here, we document these morphological changes, by using 2259 UAS-derived photographs from eight surveys and Structure-from-Motion (SfM) photogrammetric techniques, resulting in 3D point clouds, orthomosaics, and digital surface models (DSMs) with resolution ranging from 8.1 to 12.4 cm/pixel. We focus on the morphological evolution of volcanic features and volume changes in the crater terrace and the upper part of the underlying slope (Sciara del Fuoco). We identify both crater terrace and lava field variations, with vents shifting up to 47 m and the accumulation of tephra deposits. The maximum elevation changes related to the two paroxysmal eruptions (in between May and September 2019) range from +41.4 to −26.4 m at the lava field and N crater area, respectively. Throughout September 2018–June 2020, the total volume change in the surveyed area was +447,335 m³. Despite Stromboli being one of the best-studied volcanoes worldwide, the UAS-based photogrammetry products of this study provide unprecedented high spatiotemporal resolution observations of its entire summit area, in a period when volcanic activity made the classic field inspections and helicopter overflights too risky. Routinely applied UAS operations represent an effective and evolving tool for volcanic hazard assessment and to support decision-makers involved in volcanic surveillance and civil protection operations.

At active volcanoes recurring eruptive events, erosive processes and collapses modify the edifice morphology and impact monitoring and hazard mitigation. At Etna volcano (Italy) between February and October 2021, 57 paroxysmal events occurred from the South-East Crater (SEC), which is currently its most active summit crater. Strombolian activity and high lava fountains (up to 4 km) fed lava flows towards the east, south and south-west, and caused fallout of ballistics (greater than 1 m in diameter) within 1–2 km from the SEC. The impacted area does not include permanent infrastructure, but it is visited by thousands of tourists. Hence, we rapidly mapped each lava flow before deposits became covered by the next event, for hazard mitigation. The high frequency of the SEC paroxysms necessitated integration of data from three remote sensing platforms with different spatial resolutions. Satellite (Sentinel-2 MultiSpectral Instrument, PlanetScope, Skysat and Landsat-8 Operational Land Imager) and drone images (visible and thermal) were processed and integrated to extract digital surface models and orthomosaics. Thermal images acquired by a permanent network of cameras of the Istituto Nazionale di Geofisica e Vulcanologia were orthorectified using the latest available digital surface model. This multi-sensor analysis allowed compilation of a geodatabase reporting the main geometrical parameters for each lava flow. A posteriori analysis allowed quantification of bulk volumes for the lava flows and the SEC changes and of the dense rock equivalent volume of erupted magma. The analysis of drone-derived digital surface models enabled assessment of the ballistics’ distribution. The developed methodology enabled rapidly and accurate characterisation of frequently occurring effusive events for near real-time risk assessment and hazard communication.

In this body of work, we showcase a historic virtual geotrail on the eastern flank of the iconic Mt. Etna volcano (Italy), along a series of outstanding geological sites and features subsequent to an important eruption that took place in 1928. A geohistoric account of such a major eruption, is of great interest, since it is the only event since 1669 to have caused the destruction of a town (Mascali) in the Etna region. Volcanologists, educators, the lay public, tourists and volcano explorers can now access a series of “virtual geostops” belonging to this virtual geotrail, such that “visitors” can virtually fly above these sites by scanning a QR code on the printed or electronic version of the present manuscript, as well as on the poster provided as additional material for this manuscript. The virtual geostops that comprise the virtual geotrail were developed using the structure-from-motion (SfM) photogrammetry technique from images captured by using unmanned aerial vehicles (UAVs). The main result of our work is the virtual geotrail, subdivided in two parts and composed of eight geostops, each showing outstanding examples of geological features resulting from volcanic phenomena that took place also during 1979. Our approach is designed to support classical field trips, and it can undoubtedly become complementary to traditional field teaching in earth sciences, both now and in the future.

Understanding the dynamics of mild explosive activity is a fundamental tool for hazard assessment at open conduit volcanoes. This is a particularly critical task for Etna volcano. Etna is in fact characterized by frequent, mild explosive activity, punctuated by lava flows and paroxysmal events (‘lava fountains’), which, because of their greater impact, have been the main target for hazard studies, whereas more frequent Strombolian activity has been overlooked. As a result, their impact and associated hazards have been never quantified, despite the extensive monitoring and surveillance activities carried out on this volcano. In this paper, we analyze video recordings of a sequence of Strombolian explosions occurring at the summit craters of Mt. Etna, in Italy, in February 2020. Data were also integrated with a petrographic analysis of collected samples, and drone surveys were performed at the same time as the video recordings. We estimate the frequency of explosions (20–12 per min); particle exit speeds (1–50 m/s), and erupted mass (10⁰–10² kg) of those explosions. A very regular, small-scale activity (marked by a single burst of gas breaking the magma free surface into bombs and lapilli fragments) was occasionally punctuated by larger explosions, (at least one every 5 min), with a longer duration, fed by larger magma volumes, and consisting of two to three distinct pulses followed by a stationary phase. We found that the repose times between explosions follows a log logistic distribution, which is in agreement with the behavior of open vent explosive activity. The four largest explosions of the sequence were analyzed in detail: they emitted particles with median diameters (Mdphi) ranging from −10.1 to −8.8 phi, with bimodal distributions.

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 σ_Hmin 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.