A bedform phase diagram for dense granular currents.

Nature Communications
Gregory SmithSamuel Capon

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.

References

Jul 18, 2006·Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences·S Self
Sep 26, 1969·Science·R V Fisher, A C Waters
Jan 15, 2016·Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics·Thierry Faug
Jan 28, 2017·Scientific Reports·Michiru NishitaYasuhiro Minami

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