Scarpati Claudio and Perrotta Annamaria

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1 GSA DATA REPOSITORY Supplemental Information Scarpati Claudio and Perrotta Annamaria Dipartimento di Scienze della Terra, Università di Napoli Federico II Erosional characteristics and behaviour of large pyroclastic density currents Unit description Thickness, max (m) Upper Pumice Flow Unit an unlithified, poorly sorted deposit showing a slight normal grading of both pumice and lithic clasts and abundant degassing structures. UPFU is locally found 6 interlayered with the BU/SU deposits. Breccia Unit/Spatter Unit Lower Pumice Flow Unit Coarse Pumice Flow Lithified Yellow Tuff Welded Grey Ignimbrite Piperno Unconsolidated Stratified Ash Flow Plinian Pumice Fall crudely stratified coarse lithic breccia (breccia unit, BU). The minor juvenile component includes pumice, spatter and obsidian clasts. A welded spatter deposit (spatter unit, SU) is interbedded in the basal and middle part of the BU. a stratified deposit, showing from base upwards: unlithified, weakly welded and lithified portions. an unlithified deposit. Coarse pumice clasts up to block-sized are abundant and show pronounced reverse grading within an ashy matrix (CPF). a lithified (zeolitized) deposit of ashy matrix with dispersed rounded lapilli to block pumice clasts. Locally, few and scattered coarse scoriae are present. black scoriae, reverse graded, embedded in an ashy matrix with subordinate lithics and crystals. Small grey pumice clasts are the only coarse juvenile component at the very base of this unit, where welding is less intense. alternating beds of welded ash with flattened scoriae (fiamme) and a monolithologic coarse breccia made up of grey lava fragments. Locally the Piperno is characterized by a lateral transition to a sintered grey ignimbrite (WGI) a stratified and incoherent ash to sandy deposit that changes in colour from whitish at the base to reddish at the top. a crudely stratified, moderately to well sorted coarse 10 m pumice deposit. Table DR1. Main features of the Campanian Ignimbrite stratigraphic units

2 Figure DR1. Architecture of the Campanian Ignimbrite from Campi Flegrei caldera to the Appennine Mountains. Basal pumice fall (PPF) and the lowermost ignimbritic units (USAF and WGI) are ubiquitous, all other ignimbritic units are confined in proximal or distal locations. Some lateral transitions are observed, especially near the caldera rim: e.g. from Piperno to WGI and from Breccia to UPFU. The sketch is not to scale.

Figure DR2. The Campanian lapilli fall deposit (PPF) at Altavilla, 56 km from the source. It occupies a gully cut in the sedimentary rock of the Appennine Chain.

3 Figure DR2. The Campanian lapilli fall deposit (PPF) at Altavilla, 56 km from the source. It occupies a gully cut in the sedimentary rock of the Appennine Chain. PPF original thickness is preserved along the axis of the gully but has been strongly eroded by the overlying Campanian Ignimbrite (note the USAF and WGI facies) on the sides and outside the gully.

4 Substratum characteristics We selected an homogeneous substratum, as the basal lapilli fall deposits associated with both the studied ignimbrites, to avoid any remarkable interference of the basement on the erosional patterns. We have fully characterized (isopachs, outcrops locations, grainsize, components, volumes) the NYT and CI fall deposits in previously published papers cited in text (Scarpati et al., 1993; Perrotta and Scarpati 2003), and reported in figure 1 the features (thicknesses) useful to this paper. Usually, the mechanical characteristics of the fall deposits change downwind, but we consider that both deposits are the product of very large plinian eruptions, so the investigated area is small if compared with the whole distribution (the CI fall deposit is emplaced as far as Cyprus and the NYT fall deposit distal facies lies on the Alps). Consequently physical parameters of both fall deposits are relatively constant throughout the Campanian region. If we consider a synthetic parameter as the density (depending on grainsize, particle densities, particle interlocking and compaction) of the single layers at the base of the Campanian Ignimbrite at different locations, we can observe from the table DR2 that the values are very similar, illustrating a mechanical uniformity of the deposit throughout its thickness and downcurrent. Also the Neapolitan Yellow Tuff basal fall layers show quite constant density values. Campanian Ignimbrite Neapolitan Yellow Tuff Distance (km)* Azimuth* Density (kg/m 3 ) Layer A Unit A3 620 Layer Bbase Unit A4 631 Layer Btop Unit A5 627 Layer C UnitA6 610 Layer Dbase Layer Dtop Table DR2. Measured density of Campanian Ignimbrite and Neapolitan Yellow Tuff basal fall layers. Density values are quite similar vertically and laterally. The thin lithic-rich layer C

5 shows a more pronounced variation laterally but it represents only a small fraction of the whole deposit (1/25 th in volume, Scarpati and Perrotta unpublished data). *Distance and Azimuth respectively from the presumed Campanian Ignimbrite and Neapolitan Yellow Tuff vent location (see figure 1) in Campi Flegrei.

6 Figure DR3 Locations of Campanian Ignimbrite erosive sites (diamond) and Neapolitan Yellow Tuff erosive sites (circle).

Data Repository Item 1

GSA DR 2006031 Burgisser, p. 1 Data Repository Item 1 of Burgisser, A., and Gardner. J., Using Hydraulic Equivalence to Discriminate Transport Processes of Volcanic Flows This Electronic Supplement contains