Federico A. Pasquarè

Volcanism in Reverse and Strike-Slip Fault Settings

Traditionally volcanism is thought to require an extensional state of stress in the crust. This review examines recent relevant data demonstrating that volcanism occurs also in compressional tectonic settings associated with reverse and strike-slip faulting. Data describing the tectonic settings, structural analy- sis, analogue modelling, petrology, and geochemistry, are integrated to provide a comprehensive presenta- tion of this topic. An increasing amount of field data describes stratovolcanoes in areas of coeval reverse faulting, and shield volcanoes, stratovolcanoes, and monogenic edifices along strike-slip faults, whereas calderas are mostly associated with pull-apart struc- tures in transcurrent regimes. Physically-scaled ana- logue experiments simulate the propagation of magma in these settings, and taken together with data from subvolcanic magma bodies, they provide insight into the magma paths followed from the crust to the sur- face. In several transcurrent tectonic plate boundary regions, volcanoes are aligned along both the strike- slip faults and along fractures normal to the local least principal stress (σ3). At subduction zones, intra- arc tectonics is frequently characterised by contrac- tion or transpression. In intra-plate tectonic settings, volcanism can develop in conjunction with reverse faults or strike slip faults. In most of these cases, magma appears to reach the surface along fractures striking parallel to the local σ1. In some cases, there is a direct geometric control by the substrate strike- slip or reverse fault: magma is transported beneath

Geological‐Structural Framework of Stromboli Volcano, Past Collapses, and the Possible Influence on the Events of the 2002–2003 Crisis

We delineate the geological―structural framework of Stromboli volcano through the description of the deposits and structures that developed during the various phases of buildup and morphostructural reorganization of the edifice. Piling of lava and minor pyroclastic deposits was repeatedly interrupted by summit caldera collapses during the late Pleistocene and by nested flank and sector collapses towards the NW in the Holocene. Field data suggest a strong instability of this volcano flank, and numerical modeling contributes to describing the process. In the Holocene, fissuring and dyking along a main NE-trending weakness zone crossing the island interacted with other magma paths with a horseshoe-shaped geometry in plan view. A brief discussion is aimed at deciphering the possible influence of the previous geological―structural history of the volcano on the location and type of events which occurred during the 2002―2003 crisis.

Dykes, Sills, Laccoliths, and Inclined Sheets in Iceland

Dykes and inclined sheets are extremely common in the volcanic systems of Iceland, both the fossil ones as well as the active systems. Until recently, comparatively few sills and laccoliths were known, but recent studies show that many laccoliths occur in the lava pile and that sills are also very common. Many, perhaps most, shallow magma chambers in Iceland (including laccoliths) develop from sills, so that understanding the conditions for sill formation is of great volcanotectonic importance. Some of the laccoliths described here are felsic, others are mafic, and reach a maximum thickness of several hundred metres. They were emplaced at shallow depths (several hundred metres below the surface) and presumably acted as short-lived shallow magma chambers. Most sills in Iceland are mafic. The largest sills reach at least 120 m in thickness and presumably many kilometres in diameter. Inclined sheets and vertical dykes supply magma to essentially all eruptions in Iceland. Sheet swarms are confined to central volcanoes (stratovolcanoes, calderas), whereas regional dykes occur outside central volcanoes. Most inclined sheet are injected from shallow magma chambers. Individual swarms of inclined sheets are circular to slightly elliptical in plan view (with a maximum diameter of about 18 km), contain up to tens of thousands of sheets, generating a crustal dilation of as much as 80 % (measured in a profile roughly perpendicular to the average sheet attitude), the sheets being mostly <1 m thick and dipping 30°–60o towards the shallow magma source chamber. By contrast, the regional dyke swarms are highly elongated (elliptical) in plan view (with common maximum lengths of 50 km and widths of 5–10 km), contain hundreds of dykes at the level of exposure, mostly subvertical and 2–6 m thick. Recent studies suggest that many regional dykes were emplaced through inclined or vertical magma flow. We conclude that, while much progress has been made, we still do not have reliable models for forecasting the likely paths of sheet-like intrusions during volcanic unrest periods with magma-chamber rupture.

The Detection of Volcanic Debris Avalanches (VDAs) Along the Hellenic Volcanic Arc, Through Marine Geophysical Techniques

Recent marine oceanographic surveys using geophysical techniques have revealed a number of volcanic debris avalanche deposits (VDAs) on the external flanks of Antimilos, Santorini and Nisyros volcanoes in the South Aegean Sea. Swath bathymetry and side-scan sonar surveys led to the recognition of characteristic hummocky topography on all of these deposits. On seismic profiles the VDAs are identified by chaotic facies, with incoherent areas bordered by continuous undisturbed seismic reflectors. High-resolution examination of the morphological characteristics of the VDAs was accomplished by using Remotely Operated Vehicles (ROVs), in order to distinguish them from other clastic deposits. In some cases the VDAs can be traced upslope to horseshoe-shaped collapse depressions and represent the expression of the complex evolution of these volcanic edifices. Recognition of VDAs at these volcanic centers has important implications for geohazard assessments as flank collapses have the potential for triggering of large-scale tsunamis. The relationship between the distribution/emplacement mechanisms of the VDA deposits and the source flank collapses remains an area of ongoing research.