Dynamics of large pyroclastic currents inferred by the internal architecture of the Campanian Ignimbrite

Abstract

Large ignimbrites are the product of devastating explosive eruptions that have repeatedly impacted climate and life on global scale. The assemblage of vertical and lateral lithofacies variations within an ignimbrite sheet, its internal architecture, may help to determine how the parental pyroclastic current evolves in time and space. The 39 ka Campanian Ignimbrite eruption, vented from Campi Flegrei caldera, laid down a thick ignimbrite over an area of thousands of km2. A detailed reconstruction of the vertical and lateral variation of the seven lithofacies recognised in the ignimbrite medial sequence constrains the behaviour of this event. The pyroclastic current flowed over a wide area around Campi Flegrei without depositing (bypass zone), and inundated a huge area during most of the paroxysmal, waxing phase, emplacing a mainly incipiently- to strongly- welded ignimbrite. Following this waxing phase, the leading edge of the current retreated back towards the source as the current waned, impacting a progressively smaller area and leaving an unconsolidated ash and lapilli deposit, later lithified. Our study illustrates how large pyroclastic currents can evolve in time and space and the importance of both internal (eruptive and transport mechanisms) and external (topography, surficial water and rain) factors in governing their behaviour.

Eruption Style, Emplacement Dynamics and Geometry of Peralkaline Ignimbrites: Insights From the Lajes-Angra Ignimbrite Formation, Terceira Island, Azores

“…Interpretation: The massive nature of this lithofacies suggests that particles were predominately deposited from a current with fluid escape-dominated to granular flow-dominated flowboundary zones (Branney and Kokelaar, 2002;Scarpati et al, 2020), similarly to the non-welded lithofacies. The welding of the deposits, together with the coexistence of fiamme and oblate scoriaceous clasts, suggest rapid progressive aggradation from a high temperature PDC, where syn-depositional agglutination of pyroclasts occurred at temperatures exceeding the glass transition, rather than by load compaction (Russell and Quane, 2005;Dávila-Harris et al, 2013;Scarpati et al, 2020).…”

“…Interpretation: The massive nature, poor sorting and absence of stratification suggest rapid progressive aggradation from a sustained high particle concentration, granular fluid-based PDC with a fluid escape-dominated flow-boundary zone, although the presence of clast lenses suggests the development of a granular flow-dominated flow-boundary zone (Druitt, 1998;Branney and Kokelaar, 2002;Scarpati et al, 2020). In a fluid escape-dominated flow-boundary zone clasts are supported by the upward flux of interstitial fluid escaping the matrix as a result of hindered settling, while in a granular flow-dominated flow-boundary zone clast interaction is the main support mechanism due to the high particle concentration and granular shear (Branney and Kokelaar, 2002;Sulpizio and Dellino, 2008).…”

“…Ignimbrites are formed by sedimentation of hot mixtures of ash and vesiculated juvenile (pumiceous) clasts from pyroclastic density currents (PDCs) generated during explosive volcanic eruptions (Sparks et al, 1973;Cas and Wright, 1987;Branney and Kokelaar, 2002). Ignimbrite-forming events can result from a wide range of eruption styles, from caldera-forming eruptions to short-lived explosions, and occur in different geodynamic settings (e.g., Freundt and Schmincke, 1986;Lipman, 1997;Giordano, 1998;Giordano et al, 2002;Sulpizio et al, 2007;Sulpizio et al, 2010;Cas et al, 2011;Pensa et al, 2015;Pimentel et al, 2015;Scarpati et al, 2020).…”

The peperino rocks: historical and volcanological overview

“…The local use of the word piperno can be traced to the earliest written documentation dating to 1428 CE (de' Gennaro et al 2000;GeoPortale 2009). This rock is a proximal deposit of the Campanian Ignimbrite, the highest magnitude explosive eruption of the Mediterranean area in the last 40 ky (Fedele et al 2008;Scarpati et al 2020). It is exposed along the eastern sector of the caldera rim of the Phlegraean Fields and in the city of Naples (Rittmann 1950;Perrotta et al 2006;Fedele et al 2008;Scarpati et al 2020) and consists of alternating beds of welded tuff with flattened scoriae (fiamme) and coarse lithic breccia with grey lava clasts (Fedele et al 2008).…”

Thermodilatometric Study of the Decay of Zeolite-Bearing Building Materials

“…As already established, the zeolite-bearing rocks subjected to thermodilatometric investigation in this work are used as building materials and come from huge outcrops, which makes their cost very low. The features of such zeolite-bearing rocks, as well as those of the outcrops from which they originate, are reported in the literature [36][37][38][39][40][41][42][43].…”