From the comparative study on the volcanoes Kīlauea (Hawaii), Piton de la Fournaise (La Réunion) and Etna (Italy), the dynamics of the instability of the flank of different volcanic edifices have been identified. The results of this new approach, developed by a team of INGV, USGS, IPGP researchers, have been published in Journal of Volcanology and Geothermal Research
Identified some common mechanisms that trigger and condition the dynamics of persistent and continuous flank instability present on several volcanic edifices, comparing different volcanoes in terms of size, eruptive activity and regional geodynamic context. These are the results of the study, signed by the National Institute of Geophysics and Volcanology (INGV), United States Geological Survey (USGS), French IPGP, published in Journal of Volcanology and Geothermal Research
(http://www.sciencedirect.com/science/article/pii/S0377027317301002).
the dynamics of the sides of volcanic buildings represents an important element of danger. In addition to conditioning the propagation of fractures which can not only generate earthquakes and instability down to the lower slopes but also feed dangerous lateral eruptions (as frequently observed at Etna), flank instability can evolve to such an extent as to generate a real and its lateral collapse of the building, one of the most destructive and dangerous volcanic and natural events in general.
"This work", says Alessandro Bonforte, researcher at the INGV-Catania Section, analyses, through a comparative study of three volcanoes, among the best studied in the world, Kīlauea (Hawaii), Piton de la Fournaise (La Réunion), Etna (Italy), the dynamics of persistent and continuous flank instability observed on several volcanic edifices”.
The aim is to identify the common mechanisms that trigger and condition this dynamic, comparing very different volcanoes in terms of size, eruptive activity and regional geodynamic context.
"The three volcanoes analyzed are very active and all have a complex evolution, mostly characterized by the displacement of the eruptive center over time. Despite this, they are very different from each other, both in terms of size and volume and in terms of geodynamic context Regarding this last aspect, Etna represents the most complex element, having developed in a dynamic context of active collision between Africa and Europe, on the margin between continental and oceanic crust, compared to a simple building that grows undisturbed on a stable substrate that only deforms under its own weight”, continues Bonforte.
All available information, from bibliographic to geological and geophysical data, has been correlated to the measurements, thanks to the monitoring networks, of the different flank movement speeds.
“For the first time, dynamics relating to different volcanoes, albeit characterized by persistent flank instability, have been compared, trying to quantify and parameterize the observed and measured phenomena. A first approach of comparative analysis to understand the triggering elements of instability phenomena and the processes that can condition their possible evolution towards a stable and slow phenomenon or towards a sudden and violent collapse”, concludes the researcher.
Abstract
Persistent motion of the flanks of Kīlauea Volcano, Hawaiʻi, has been known for several decades, but has only recently been identified at other large basaltic volcanoes—namely Piton de la Fournaise (La Réunion) and Etna (Sicily)—thanks to the advent of space geodetic techniques. Nevertheless, understanding of long-term flank instability is based largely on the example of Kīlauea, despite the large differences in the manifestations and mechanisms of the process when viewed through a comparative lens. For example, the rate of flank motion at Kīlauea is several times that of Etna and Piton de la Fournaise and is accommodated on a slip plane several km deeper than is probably present at the other two volcanoes. Gravitational spreading also appears to be the dominant driving force at Kīlauea, given the long-term steady motion of the volcano's south flank regardless of eruptive/intrusive activity, whereas magmatic activity plays a larger role in flank deformation at Etna and Piton de la Fournaise. Kīlauea and Etna, however, are both characterized by heavily faulted flanks, while Piton de la Fournaise shows little evidence for flank faulting. A helpful means of understanding the spectrum of persistent flank motion at large basaltic edifices may be through a framework defined on one hand by magmatic activity (which encompasses both magma supply and edifice size), and on the other hand by the structural setting of the volcano (especially the characteristics of the subvolcanic basement or subhorizontal intravolcanic weak zones). A volcano's size and magmatic activity will dictate the extent to which gravitational and magmatic forces can drive motion of an unstable flank (and possibly the level of faulting of that flank), while the volcano's structural setting governs whether or not a plane of weakness exists beneath or within the edifice and can facilitate flank slip. Considering persistent flank instability using this conceptual structure is an alternative to using a single volcano as a “type example”—especially given that the example is usually Kīlauea, which defines an extreme end of the spectrum—and can provide a basis for understanding why flank motion may or may not exist on other large basaltic volcanoes worldwide.
Images
Figure 1. Map showing locations of large basaltic volcanoes discussed in the text.
Figures 2 and 3. Two aerial photos showing the extent of Etna's unstable eastern flank. The escarpment produced by the S. Leonardello fault which crosses, almost rectilinear, the lower slope of the volcano.
Figure 4. The eastern slope of Etna, with the Valle del Bove and the Ionian coast. In the foreground, a cornerstone for the periodic measurement of ground movements.
Figure 5. Kilauea - A clump of trees lowered below sea level after the 1975 earthquake.