Andrew J. L. Harris’s research while affiliated with University of Clermont Auvergne and other places

Plain Language Summary We present a new method, VRPTIR ${\text{VRP}}_{\text{TIR}}$, for monitoring thermal energy emission at volcanoes using satellite data, overcoming the challenges posed by hazardous ground conditions. This approach measures thermal energy loss from moderate‐to‐low‐temperature volcanic features, such as crater lakes and fumaroles, with temperatures below 330°C. We validated the VRPTIR ${\text{VRP}}_{\text{TIR}}$ by comparing satellite measurements with long‐term data from Mount Ruapehu (New Zealand), El Chichón (Mexico), Taal (Philippines), Vulcano (Italy), Puracé (Colombia), Poás (Costa Rica), and White Island (New Zealand). Results indicate an excellent correlation between satellite‐based VRPTIR ${\text{VRP}}_{\text{TIR}}$ and available ground‐based measurements, confirming its reliability and global monitoring potential. We observed significant variations at multiple locations, including previously unseen thermal unrest at Puracé volcano, highlighting the ability of VRPTIR ${\text{VRP}}_{\text{TIR}}$ to promptly identify changes in volcano thermal state. The VRPTIR ${\text{VRP}}_{\text{TIR}}$ method offers valuable insights into volcano dynamics and is crucial for compiling global thermal energy records, improving monitoring, and mitigating volcanic hazards.

The volcanic island of Stromboli (southern Tyrrhenian Sea, Italy) is renowned for its persistent, periodic, low-intensity explosive activity, whose spectacular manifestations attract tens of thousands of tourists every year. However, sporadic more intense major explosive and effusive eruptions and paroxysms pose serious threats to the island. In addition to direct hazards, granular slides of volcanic debris and pyroclastic avalanches, which can rapidly reach the sea and potentially generate tsunamis, are often associated with such unpredictable eruptive activity. Due to the very fast propagation of the tsunami around the island and the consequent short tsunami warning time (ranging from less than a minute to only a few minutes), mitigation efforts and evacuation from the Strombolian coast must be carefully planned. In this paper, we describe a new GIS-assisted procedure that allows us to combine the outputs of an ensemble of 156 pre-computed landslide-generated tsunami hazard scenarios (with variable landslide volume, position, and density), statistical exposure data (i.e. the number of inhabitants and tourists), and digital geographic information to obtain a quantitative (scenario-based) risk analysis. By means of the analysis of the road network and coastal morphology, we develop a model with routes and times to reach a safe area from every pixel in the inundated area and an appraisal of the time needed to escape versus the wave arrival time. This allows us to evaluate and quantify the effectiveness of potential risk mitigation by means of evacuation. The creation of an impact score linking the predicted inundation extent and the tsunami warning signals is intended, in the long term, to be used to predict the intensity of future tsunamis and to adapt evacuation plans accordingly. The model, here applied to Stromboli, is general and can be applied to other volcanic islands. Evacuating an island hosting several thousand tourists every summer with very little warning time underlines the absolute necessity for such mitigation efforts, aimed at informing hazard planners and managers and all other stakeholders.

At hydrothermal systems, heat transfer across the final surface layer is driven by permeable convection and conduction, so that soil permeability and thermal conductivity play fundamental roles in controlling heat flux to the atmosphere. We build a Rayleigh-number driven heat transfer model for a bottom-heated surface that uses measurements of heat flux density (radiation and convection to the atmosphere in W/m2), surface temperature, and soil temperature to solve for soil conductivity, density, and permeability for such a bottom-heated surface. At Vulcano in 2019, we measured an ASTER-derived heat flux density of 240 ± 70 W/m2 and a difference between soil and surface temperature of 18 ± 6 °C. The surface layer is a 7.5 ± 2.5 cm thick case-hardened crust across which heat transfer is conduction dominated. We invert our heat transfer model using the temperature (T) gradient derived from a trench dug into the soil: T = − 49.7y2 + 113.6y + 35 (R2 = 0.9997), where y is depth in meters between the surface and 70 cm. The result is a conductivity for the case-hardened surface layer of 1.0 ± 0.3 W/(m K) and a density of 2440 ± 120 kg/m3. Below this case-hardened crust, heat transfer is dominated by permeable convection in a soil comprised of highly altered trachytic blocks in an ash matrix. Our model gives permeabilities of 1–19 × 10−10 m2 for this layer in 2019. In 2021, Vulcano entered a phase of unrest. Our model reveals that this was associated with an increase in permeability to 10−7 m2. However, by 2023 permeabilities had reverted to pre-unrest levels. Using simple measurements of surface and soil temperature, coupled with heat flux density from a satellite overpass, the model can be used as a basis to constrain heat transfer and to assess permeability at any hydrothermal system.

When a lava flow enters a body of water, either a lake, sea, river or ocean, explosive interaction may arise. However, when it is an 'a'ā lava flow entering water, a more complex interaction occurs, that is very poorly described and documented in literature. In this paper, we analysed the 2–4 ka San Bartolo lava flow field emplaced on the north flank of Stromboli volcano, Italy. The lava flow field extends from ~ 650 m a.s.l. where the eruptive fissure is located, with two lava channels being apparent on the steep down to the coast. Along the coast the lava flow field expands to form a lava delta ~ 1 km wide characterised by 16 lava ‘Flow’ units. We performed a field survey to characterise the features of lava entering the sea and the associated formation of different components and magnetic measurements to infer the flow fabrics and emplacement process of the lava flow system. We measured the density, porosity and connectivity of several specimens to analyse the effect of lava-water interaction on the content in vesicles and their connectivity and conducted a macroscopic componentry analysis (clast count) at selected sites to infer the character of the eroded offshore segment of the lava flow field and its component flow units. The collected data allowed us to define the main components of a lava delta fed by 'a'ā lava flows, with its channels, littoral units, ramps, lava tubes, and inflated pāhoehoe flows controlled by the arterial 'a'ā flow fronts. The spatial organisation of these components allowed us to build a three-step descriptive model for 'a'ā entering a water. The initial stage corresponds to the entry of channel-fed 'a'ā lava flow into the sea which fragments to form metric blocks of 'a'ā lava. Continued lava supply to the foreshore causes flow units to stall while spreading over this substrate. Subsequent 'a'ā lava flow units ramp up behind the stalled flow front barrier. Lava tubes extending through the stalled flow barrier feed the seaward extension of a bench made of several pāhoehoe flow units.

Based on published and new data for explosive events at Stromboli (Italy), we propose an empirical relation that links mass discharge rate (MDR) and at-vent gas jet velocity (Gv). We use 65 simultaneous measurements of MDR and Gv and find two trends in both the cross-correlation and rank order statistics. Cross-correlation gives a power law relation: $MDR= {10}^{(0.015{G}_{v}+2.434)}$ kg/s, R2 = 0.81, and applies to ash-dominated emissions. Combining this relation with the conservation of mass equation allows at-vent plume density and/or vent area to be derived from MDR = Gv ρ A, ρ being plume density and A being vent cross-sectional area. We find that while a vent radius of 2 m and plume density of 0.35 kg/m3 fits with the “normal” activity at Stromboli, a 290 × 2.5 m vent area likely feeds a 10 kg/m3 jet during paroxysmal activity. Initial tests on available data shows promise in extending the correlation beyond Stromboli and/or to events with higher MDR (> 107 kg/s). However, the exact relation will depend on magma composition, temperature and volatile content, as well as conduit radius and vent overpressure.

When a lava flow enters a body of water, either a lake, sea, river or ocean, explosive interaction may arise. However, when it is an 'a'ā lava flow entering water, a more complex interaction occurs, that is very poorly described and documented in literature. In this paper we analysed the 2–4 ka San Bartolo lava flow field emplaced on the north flank of Stromboli volcano, Italy. The lava flow field extends from ~ 650 m elevation, where the eruptive fissure emplaced following the main structural trend of the island, to the NE coast through two prominent lava channels at middle elevation. Along the coast the lava flow field expands to form a lava delta ~ 1 km wide characterized by 16 lava ‘Flow’ units. We performed a field survey to characterize the features of lava entering the sea and the associated formation of different components, and magnetic measurements to infer the flow fabrics and emplacement process of the lava flow system. We measured the density, porosity and connectivity of several specimens to analyse the effect of lava-water interaction on the content in vesicles and their connectivity, and conducted a macroscopic componentry analysis (clast count) at selected sites to infer the character of the eroded offshore segment of the lava flow field and its component flow units. The collected data allowed us to define the main components of a lava delta fed by 'a'ā lava flows, with its channels, littoral units, ramps, lava tubes, and inflated pāhoehoe flows controlled by the arterial 'a'ā flow fronts. The spatial organization of these components allowed us to build a 3-steps model for 'a'ā entering a water. The initial stage corresponds to the entry of channel-fed 'a'ā lava flow into the sea which fragments to form metric blocks of 'a'ā lava. Continued lava supply to the foreshore causes flow units to stall while spreading over this substrate. Subsequent 'a'ā lava flow units ramp up behind the stalled flow front barrier. Lava tubes extending through the stalled flow barrier feed the seaward extension of a bench made of several pāhoehoe flow units.

The volcanic island of Stromboli (Southern Tyrrhenian sea, Italy) is renowned for its persistent, periodic, low-intensity explosive activity, whose spectacular manifestations attract tens of thousands of tourists every year. However, sporadic more intense major explosive and effusive eruptions, and paroxysms, pose serious threats to the island. In addition to direct hazards, granular slides of volcanic debris and pyroclastic avalanches, which can rapidly reach the sea potentially generating tsunamis, are often associated with such unpredictable eruptive activity. Due to the very fast propagation of the tsunami around the island, and the consequent short tsunami warning time (ranging from less than a minute to only a few minutes) mitigation efforts and evacuation from the Strombolian coast must be carefully planned. In this paper, we describe a new, GIS-assisted procedure that allows us to combine the outputs of an ensemble of 156 pre-computed landslide-generated tsunami hazard scenarios (with variable landslide volume, position, and density), statistical exposure data (i.e., the number of inhabitants and tourists) and digital geographic information, to obtain a quantitative (scenario-based) risk analysis. By means of the analysis of the road network and coastal morphology, we develop a model with routes and times to reach a safe area from every pixel in the inundated area, and appraisal for the time needed to escape versus the wave arrival time. This allows us to evaluate and quantify the effectiveness of potential risk mitigation by means of evacuation. The creation of an impact score linking the predicted inundation extent and the tsunami warning signals is intended, in the long term, to predict the intensity of future tsunamis, and to adapt evacuation plans accordingly. The model, here applied to Stromboli, is general, and can be applied to other volcanic islands. Evacuating an island hosting several thousand tourists every summer with very little warning time supports the absolute necessity for such mitigation efforts, aimed at informing hazard planners and managers, and all other stakeholders.