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A bedform phase diagram for dense granular currents

Smith, Gregory; Rowley, Peter; Williams, Rebecca; Giordano, Guido; Trolese, Matteo; Silleni, Aurora; Parsons, Daniel R.; Capon, Samuel


Gregory Smith

Peter Rowley

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Dr Rebecca Williams
Senior Lecturer; Associate Dean for Student Experience

Guido Giordano

Matteo Trolese

Aurora Silleni

Samuel Capon


Pyroclastic density currents (PDCs) are a life-threatening volcanic hazard. Our understanding and hazard assessments of these flows rely on interpretations of their deposits. The occurrence of stratified layers, cross-stratification, and bedforms in these deposits has been assumed as indicative of dilute, turbulent, supercritical flows causing traction-dominated deposition. Here we show, through analogue experiments, that a variety of bedforms can be produced by denser, aerated, granular currents, including backset bedforms that are formed in waning flows by an upstream-propagating granular bore. We are able to, for the first time, define phase fields for the formation of bedforms in PDC deposits. We examine how our findings impact the understanding of bedform features in outcrop, using the example of the Pozzolane Rosse ignimbrite of the Colli Albani volcano, Italy, and thus highlight that interpretations of the formative mechanisms of these features observed in the field must be reconsidered.


Smith, G., Rowley, P., Williams, R., Giordano, G., Trolese, M., Silleni, A., …Capon, S. (2020). A bedform phase diagram for dense granular currents. Nature communications, 11(1),

Journal Article Type Article
Acceptance Date May 12, 2020
Online Publication Date Jun 8, 2020
Publication Date Dec 1, 2020
Deposit Date Jun 9, 2020
Publicly Available Date Jun 11, 2020
Journal Nature Communications
Electronic ISSN 2041-1723
Publisher Nature Publishing Group
Peer Reviewed Peer Reviewed
Volume 11
Issue 1
Article Number 2873
Keywords Natural hazards; Sedimentology; Volcanology
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Additional Information Received: 28 June 2019; Accepted: 12 May 2020; First Online: 8 June 2020; : The authors declare no competing interests.


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