Page 107 - Caldera Volcanism Analysis, Modelling and Response

82 Roberto Sulpizio and Pierfrancesco Dellino

Figure 13 Di¡erent lithofacies association of PDC deposits of Avellino eruption (3.8 ka BP,
Somma-Vesuvius, Italy).The exposures are located in areas free of topographic obstacles or
sheltered by the vertical barrier of the Mount Somma caldera wall.The solid black lines are the
isopachs of Avellino PDC deposits (thickness in cm).

4.3.4. Interaction with town buildings
When gravity-driven currents flow across terrains with significant topographic
obstacles, they develop flow variations, which affect not only the loci of deposition
but also the depositional lithofacies (Kneller and McCaffrey, 1999). The complex
urban morphology, characterised by road networks and agglomerates of buildings
with different heights and shapes, represents a very rough and complex topography
that can greatly affect runout and deposition of gravity-driven currents. Despite
several works that have investigated the impact of different types of gravity-driven
flows on buildings and infrastructures (Newhall and Punongbayan, 1996; Baxter
et al., 1998; Valentine, 1998; Cioni et al., 2000; Gurioli et al., 2002; Druitt and
Kokelaar, 2002; Luongo et al., 2003a, b; Nunziante et al., 2003; Petrazzuoli and
Zuccaro, 2004; Spence et al., 2004; Zanchetta et al., 2004a; Zuccaro and Ianniello,
2004), little quantitative data are available on the influence of urban environments
on transport and deposition behaviours of these flows. The most detailed works
about this topic consider the interaction of PDCs from the AD 79 (Pompeii)
eruption of Somma-Vesuvius (Sigurdsson et al., 1985) with Roman urban
settlements of Herculaneum and Pompeii (Gurioli et al., 2002, 2005). In particular,
these works demonstrated how basal parts of PDCs can experience rapid variations
in both flow direction and temperature when entering an urban area (Cioni et al.,
2004; Gurioli et al., 2005). The effects of this interaction can be modelled