Conduit Processes at the Haukadalur Geyser‐Hosting Hydrothermal Field (Iceland) Revealed by In Situ Temperature and High‐Speed Camera Measurements

Geysers fascinate scientists and visitors for several centuries. However, many driving mechanisms such as heat transfer in the conduit and in the subsurface remain poorly understood. We document for the first time transient temperature variations inside the active Strokkur's and nearby quasi-dormant Great Geysir's conduits, Iceland. While recording temperature inside the conduit, we visually monitored Strokkur's activity at the vent with a high-speed camera, providing a high temporal resolution of the eruptions. Our results reveal heat transfer from a bubble trap to and through the conduit. We propose a model for the eruptive cycle of Strokkur that includes vapor slug rise, eruption, and conduit refill. Each water jet of an eruption is marked by an initial pulse of liquid water and vapor, emitted at a velocity between 5 and 28 m/s and generally followed by a second pulse less than a second later. The timing of eruptions coincides with temperature maxima in the conduit. After the eruption, the conduit is refilled by water falling back in the pool and drained from neighboring groundwater-saturated geological units. This results in a temperature drop, the amplitude of which increases with depth while its period is reduced. This reflects faster heat transfer in the deeper than shallower part of the conduit. The amplitude of temperature drop following an eruption also increases with the eruption order, implying larger heat release by higher-order eruptions. Temperature in the conduit subsequently increases until the next eruption, starting then a new cycle

Relative Sea-Level Rise Projections and Flooding Scenarios for 2150 CE for the Island of Ustica (Southern Tyrrhenian Sea, Italy)

The island of Ustica (Italy) is constantly exposed to the effects of sea-level rise, which is threatening its coastal zone. With the aim of assessing the sea levels that are anticipated by 2150 CE under the climatic projections shown in the AR6 report from the IPCC, a detailed evaluation of potential coastal flooding under different climatic scenarios and the ongoing land subsidence has been carried out for three coastal zones. Scenarios are based on the determination of the current coastline position, a high-resolution digital terrain and marine model, and the SSP1-2.6, SSP3-7.0, and SSP5-8.5 climatic projections. Relative sea-level rise projections allowed the mapping of the potential inundated surfaces for 2030, 2050, 2100, and 2150. The results show rising sea levels for 2150, ranging from a minimum of 66 ± 40 cm (IPCC AR6 SSP2.6 scenario) to a maximum of 128 ± 52 cm (IPCC AR6 SSP8.5 scenario). In such conditions, considering the SSP8.5 scenario during storm surges with return times (RTs) of 1 and 100 years, the expected maximum wave run-up along the island may vary from 3 m (RT = 1) to 14 m (RT = 100), according to the coastal morphology. Our results show that adaptation and mitigation actions are required to protect the touristic and harbor installations of the island

What lies beneath

Craig Magee and Chris Jackson examine how geophysical seismic reflection data can be used to study the inner workings of volcanoes and magma plumbing systems

Interaction between transform faults and rift systems: A combined field and experimental approach

We present a detailed field structural survey of the area of interaction between the active NW-striking transform Husavik-Flatey Fault (HFF) and the N–S Theystareykir Fissure Swarm (TFS), in North Iceland, integrated by analog scaled models. Field data contribute to a better understanding of how transform faults work, at a much higher detail than classical marine geophysical studies. Analog experiments are conducted to analyse the fracture patterns resulting from different possible cases where transform faulting accompanies or postpones the rift motions. Different tectonic block configurations are also considered and results are compared with field data in order to study as thoroughly as possible the interaction between the HFF and the TFS as well as the possible prolongation of the HFF into the TFS. West of the intersection between the transform fault (HFF) and the rift zone (TFS), the former splays with a gradual bending giving rise to a leading extensional imbricate fan. The westernmost structure of the rift, the N–S Gudfinnugja Fault (GF), is divided into two segments: the southern segment makes a junction with the HFF and is part of the imbricate fan; north of the junction instead, the northern GF appears right-laterally offset by about 20 m. Southeast of the junction, along the possible prolongation of the HFF across the TFS, the strike of the rift faults rotates in an anticlockwise direction, attaining a NNW–SSE orientation. Moreover, the TFS faults north of the HFF prolongation are fewer and have smaller offsets than those located to the south. Through the comparison between the structural data collected in the field at the HFF–TFS connection zone and a set of scaled experiments, we confirm a prolongation of the HFF through the rift, although here the transform fault has a much lower slip-rate than west of the junction. Our data suggest that transform fault terminations may be more complex than previously known, and propagate across a rift through a modification of the rift pattern

ANALISI MORFOLOGICA DELLO SCAVO IN CORRISPONDENZA DI PILE IN TRATTI FLUVIALI CURVILINEI

Analisi sperimentali sulla evoluzione morfologia in tratti fluviali curvilinei dovuta alla presenza di pile di attraversamenti, con particolare attenzione alle diverse curvature dei corsi d'acqua. Elaborazioni e analisi adimensionale sull'andamento dello scavo e sui depositi a valle della pila in funzione del tempo, della portata, delle dimensioni medie del fondo mobile, delle velocità della corrente, delle dimensioni della pila e dei parametri noti in letteratura. Experimental analysis on the evolution of morphology in fluvial curved sections due to the presence of crossings batteries, with particular attention to the different curvatures of the waterways. Elaborations and dimensionless analysis on the progress of the excavation and on the downstream deposits of the stack as a function of time, the flow rate, the average size of the movable floor, the speed of the current, the size of the stack and the parameters known in the literature

How diking affects the tectonomagmatic evolution of slow spreading plate boundaries: Overview and model

Recent diking episodes along slow spreading boundaries included the generation of normal faults, showing that extension is accommodated, on a scale of a few years or less, by both magma intrusion and fault movement. Here we aim to define how diking may affect the overall rift structure on the longer term (=100 yr). We first summarize the main features of the transient diking episodes as obtained from geological, geophysical, geodetic, and modeling studies. We then put these episodes into a broader context, considering the overall longer term shallow and deep structure of the plate boundaries. The synthesis of the data shows that in Iceland crustal extension at depth largely occurs by means of dikes, with negligible normal faulting; faults focus toward the surface (<1 km depth), forming dike-induced grabens commonly propagating downward; along-rift diking episodes (1 in ~200 yr) may induce all the observed surface deformation. The close similarities with transitional (Afar Rift) and magmatic continental rifts (East African Rift System) suggest that repeated diking induces most of the surface deformation along slowly spreading (≤2 cm/yr) magmatic plate boundaries. The frequency of diking and the induced strain may not allow extension to be accommodated amagmatically, through creep or seismic or aseismic faulting. This implies that a diking episode locks any amagmatic faulting until the strain is released (centuries), when the subsequent diking episode occurs, with the cumulative result of controlling and shaping the evolution of slow spreading magmatic plate boundaries. This process appears independent of the stage of magmatic rifting

Understanding the origin of magmatic necks: insights from Mt. Etna volcano (Italy) and analogue models

Magmatic necks are commonly found in volcanic areas, and they often exhibit a homogeneous structure with a cylindrical shape and a diameter of up to several hundreds of metres. Their massive and uniform structure poses a space problem for their emplacement in the brittle crust. Here, we use field data and analogue models to investigate how necks may emplace at shallow levels. Field analysis focuses on characterising the geometric, structural and magmatic features of two necks outcropping in the eroded portions of Mt. Etna, Italy. These are homogeneous and massive intrusive bodies, related to a single episode of emplacement at 400–600 m below the paleosurface. We further investigated their possible emplacement mechanism through analogue models, injecting vegetable oil within (a) a flat sand pack and (b) a sand cone. Dikes form with both configurations, erupting to the surface through vents. However, dikes injected within the cone are characterised by a larger thickening at shallow levels, in correspondence with the vent, where a neck-like structure forms. This suggests that the gravitational load imposed by a volcanic edifice provides the most suitable conditions for the development of magmatic neck, as the downslope shear stresses enhance the deformation of the cone slope during shallow dike emplacement promoting shallow dilation and thickening of the dike. Therefore, topography should be a further factor enhancing the development of necks, in addition to those mechanisms previously proposed. Our results are consistent with natural examples of feeder dikes thickening towards the surface and dikes transitioning to necks, supporting the reliability of the proposed conceptual model