Page 82 - Caldera Volcanism Analysis, Modelling and Response

CHA P T E R 2

Sedimentology, Depositional Mechanisms

and Pulsating Behaviour of Pyroclastic
Density Currents

Roberto Sulpizio and Pierfrancesco Dellino

Contents

1. Introduction: What are Pyroclastic Density Currents? 58
2. Key Concepts 60
2.1. The flow-boundary zone approach 60
2.2. Pyroclastic flows vs. pyroclastic surges 61
2.3. Steady vs. unsteady currents 62
2.4. Sedimentation vs. deposition 62
3. Sedimentology: Main Particle Support and Segregation Mechanisms in PDCs 63
3.1. Support due to fluid turbulence 63
3.2. Fluid-escape regime and matrix support 66
3.3. Support due to particle interactions 68
4. Depositional Processes in PDCs 70
4.1. En masse freezing vs. progressive aggradation 70
4.2. Development of self-organised pulses in a PDC and stepwise aggradation 72
4.3. Influence of topography on deposition 74
5. Field Evidences of Stepwise Aggradation in Pulsating PDCs 84
5.1. Case studies 84
6. Conclusive Remarks and Future Perspectives 87
Acknowledgements 90
References 90

Abstract
This work is an exploratory effort to address some key concepts about physical
processes that influence the mobility, sedimentology and depositional mechanisms of

Corresponding author. Tel.: +39-0805442608; Fax: +39-0805442591
E-mail address: r.sulpizio@geomin.uniba.it
Dipartimento Geomineralogico, Universita ` di Bari, via Orabona 4, 70125, Bari, Italy.
Developments in Volcanology, Volume 10 r 2008 Elsevier B.V.
ISSN 1871-644X, DOI 10.1016/S1871-644X(07)00002-2 All rights reserved.
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