Large historical eruptions at subaerial mud volcanoes, Italy

Abstract

Abstract. Active mud volcanoes in the northern Apennines, Italy, currently have gentle eruptions. There are, however, historical accounts of violent eruptions and outbursts. Evidence for large past eruptions is also recorded by large decimeter rock clasts preserved in erupted mud. We measured the rheological properties of mud currently being erupted in order to evaluate the conditions needed to transport such large clasts to the surface. The mud is wellcharacterized by the Herschel-Bulkley model, with yield stresses between 4 and 8 Pa. Yield stresses of this magnitude can support the weight of particles with diameters up to several mm. At present, particles larger than this size are not being carried to the surface. The transport of larger clasts to the surface requires ascent speeds greater than their settling speed in the mud. We use a model for the settling of particles and rheological parameters from laboratory measurements to show that the eruption of large clasts requires ascent velocities > 1 m s −1 , at least three orders of magnitude greater than during the present, comparatively quiescent, activity. After regional earthquakes on 20 May and 29 May 2012, discharge also increased at locations where the stress changes produced by the earthquakes would have unclamped feeder dikes below the mud volcanoes. The magnitude of increased discharge, however, is less than that inferred from the large clasts. Both historical accounts and erupted deposits are consistent in recording episodic large eruptions.

Conditions for long-lasting gas eruptions: The 2013 event at Fiumicino International Airport (Rome, Italy)

“…All samples show a unimodal distribution with mode ranging between 25 and 10 microns, similar to other mud volcanoes (e.g. Manga and Bonini, 2012); these clay particles largely derive from Holocene clays present at -20 to -40 m below ground level (Fig. 2).…”

Subsurface fluid distribution and possible seismic precursory signal at the Salse di Nirano mud volcanic field, Italy

“…Interestingly, mud outcomes also occurred outside the subsided area that is thought to limit the mud volcanic caldera (Bonini 2008). Manga & Bonini (2012) report that the Regnano and Puianello mud volcanic centres, NW and SE of NMVF, respectively, as well as the NMVF responded to the strongest aftershocks of the Emilia seismic sequence with vigorous mud emissions. Furthermore, local foresters confirmed that the activity of the NMVF was particularly intense before the main shock of the Emilia sequence in 2012.…”

Comparing thixotropic and Herschel–Bulkley parameterizations for continuum models of avalanches and subaqueous debris flows

“…A common observation is that the complexity of the material composition and the effective rheological characteristics play important roles in material movement (Malet et al, 2003;Bisantino et al, 2010;Jeong, 2014;de Haas et al, 2015). This flow complexity is illustrated by the classification of subaqueous mass movements by Locat and Lee (2002) into five types with different behaviors: slides, topples, spreads, falls, and flows.…”

“…Parameterized non-Newtonian fluid models are an obvious approach to approximate these behaviors. Timeindependent rheological models have been widely used to simulate debris flows (e.g., Bovet et al, 2010;Pirulli, 2010;Tsai et al, 2011;Manga and Bonini, 2012); however the realworld flow characteristics include time-dependent behaviors that could be categorized as "thixotropic" (Perret et al, 1996;Crosta and Dal Negro, 2003;Bagdassarov and Pinkerton, 2004;Aziz et al, 2010). Our focus in this paper is examining how a thixotropic model behavior compares to the more common time-independent (Herschel-Bulkley) non-Newtonian fluid model.…”

“…Second, does the non-Newtonian flow (when parameterized) represent a real-world debris flow? To date, successful non-Newtonian models of real-world flows have been parameterized using a time-independent approach, which limits the ability of the model to represent the transition phases, i.e., flow initiation and stalling (e.g., Bovet et al, 2010;Pirulli, 2010;Tsai et al, 2011;Manga and Bonini, 2012). Unfortunately, data on transition phases for real-world flows are lacking and are severely limited even for laboratory-scale flows.…”