Claudia Corazzato

Deformation at Stromboli volcano (Italy) revealed by rock mechanics and structural geology

Abstract We approach the reconstruction of the recent structural evolution of Stromboli volcano (Italy) and the analysis of the interplay between tectonics, gravity and volcanic deformation. By tying together structural, lithostratigraphic and rock mechanics data, we establish that since 100 ka BP, the edifice has faulted and jointed mainly along NE-striking planes. Faults mostly dip to the NW with normal displacement. Taking also into account the presence of a NW-trending regional least principal stress and of tectonic earthquake hypocenters inside the cone, we suggest that this fracturing can be related to the transmission of tectonic forces from the basement to the cone. Dyking concentrated along a main NE-trending weakness zone (NEZ) across the volcano summit, resembling a volcanic rift, whose geometry is governed by the tectonic field. In the past 13 ka, Stromboli experienced a reorganisation of the strain field, which was linked with the development of four sector collapses affecting the NW flank, alternating with growth phases. The tectonic strain field interplayed with dyking and fracturing related to unbuttressing along the collapse shoulders. We propose that tectonics control the geometry of dykes inside the cone and that these, in turn, contribute to destabilise the cone flanks.

Spatial distribution and structural analysis of vents in the Lunar Crater Volcanic Field (Nevada, USA)

Volcanoes within monogenetic volcanic fields often are arranged in alignments and clusters, which are related to effects of magma source geometry in the upper mantle, principal stress orientations, and crustal structures on their magma feeding systems. We use cluster analysis with dendrogram, vent morphometric analysis, and field structural data to explore the relationships between volcanoes and tectonic features in the Plio-Pleistocene part of the Lunar Crater Volcanic Field (LCVF; Pancake Range, Nevada, USA), which includes 96 monogenetic volcanic edifices totaling 119 vents. Structural analysis identified three main sets of faults with dip-slip kinematics (mostly normal with a few examples of thrust faults), striking N-S, E-W, and NE-SW. The NE-SW set comprises dip-slip faults with a dominant normal component of movement which are consistent with the modern state of stress based upon the World Stress Map database. Spatial distribution pattern analysis suggests a clustered distribution of vents in the LCVF, and GIS-based spatial density analysis shows that these clusters trend mostly NE-SW. Morphometric study of the monogenetic cones, which provides information on feeder dike orientation where dikes are not directly exposed, suggests dominant NNE-SSW to NE-SW orientations of near-surface inferred dikes. An amount of 27 out of 31 inferred feeder dikes within the LCVF is parallel to the present orientation of the greatest principal horizontal stress (σHmax) as suggested by World Stress Map data derived from hydrofracturing and earthquake focal mechanisms. In some cases, dike strike is parallel with that of pre-existing Quaternary dip-slip faults. We suggest that the spatial distribution of vents is related to domains of different scales of partial melting and compositional heterogeneity in the upper mantle source, which is substantiated by geochemical data. The relationship of feeder dikes with respect to shallow tectonic structures, although somewhat ambiguous at LCVF, is consistent with behavior that is intermediate between volcanic fields with high- and low-long-term magma fluxes.

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.

Setting the scene for self-destruction: From sheet intrusions to the structural evolution of rifted stratovolcanoes

We investigate the processes of growth and consumption of rifted stratovolcanoes to better understand their morphostructural and geological evolution in relation to sheet intrusions. Field data collected from four rifted volcanoes, located in Italy and Chile, and representing structural end members, are integrated with scaled physical models and numerical three-dimensional (3D) modeling. Due to preferential along-rift magma pathways, volcanoes grow perpendicular to rift strike mostly by intrusions, and parallel to the rift mostly by effusions. These constructive processes are partially or fully balanced by destructive processes that occur both perpendicular to the rift and along the rift zone, and that are initiated by the sheet intrusions. Field data indicate that sheets and/or flank eruptions increase in number approaching the summit part of a cone. Since dyking within a volcano causes a magmatic driving overpressure and lateral displacement/deformation of the cone flank, this displacement is assumed to be greater where intrusions have the highest frequency. Lateral deformation can also lead to flank failure along a deep-seated slip surface. Symmetrical rifts may produce deep-seated collapses in opposing directions, while asymmetrical rifts can preferentially lead to destruction on the tectonically downthrown side. If the collapse depression is refilled by new volcanism, the cone attains a new critical height (and mass), setting the scene for renewed failure. This sequence inhibits the cone from widening normal to the rift zone. The field examples studied, plus analog and numerical modeling, also indicate that dyking within the rift zone destabilizes the volcano flanks along the rift: where dyke tip stresses approach the slope, surface landsliding might be induced. This in turn produces debuttressing above the dyke, favoring effusive eruptions and lavas flowing within the landslide depression. In this case a balance can occur between new lava outpourings and gravity mass removal, or the volcano can grow along the rift if the emitted magma volume is higher than the collapsed material. From a mechanical point of view, the different behavior of volcanic slopes, both parallel to and perpendicular to dyke strike, is a function of magma forces and the cumulative dyke-induced displacement. The combination of along-rift-strike landsliding and normal-to-rift deep-seated large-scale lateral collapse, characteristically produces in map view four main zones of “consumption” and “rebuilding” on the volcano. These alternate with four triangular sectors where the volcano slopes are relatively more stable. When volcanic activity ends, cone consumption is concentrated along the rift and is favored by fault slip or channeled erosion.