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

Abstract

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.

• Journal Article Type: Article
• Acceptance Date: May 12, 2020
• Online Publication Date: Jun 8, 2020
• Publication Date: Jun 8, 2020
• Deposit Date: Jun 8, 2020
• Publicly Available Date: Jun 8, 2020
• Journal: Nature Communications
• Electronic ISSN: 2041-1723
• Publisher: Nature Research (part of Springer Nature)
• Peer Reviewed: Peer Reviewed
• Volume: 11
• Article Number: 2873
• DOI: https://doi.org/10.1038/s41467-020-16657-z
• Keywords: Natural hazards; Sedimentology; Volcanology
• Public URL: https://uwe-repository.worktribe.com/output/6012769
• Publisher URL: https://www.nature.com/articles/s41467-020-16657-z