On the effect of two-direction seasonal flows on barchans and the origin of occluded dunes

Author(s)

Assis, Willian R. ; Borges, Danilo S. ; Franklin, Erick M.

• Document type: Journal article
• Source: Geomorphology; v. 467, p. 8-pg., 2024-11-06.

Abstract

We inquire into the morphodynamics of barchans under seasonal flows. For that, we carried out grain-scale numerical computations of a subaqueous barchan exposed to two-directional flows, and we varied the angle and frequency of oscillations. We show that when the frequency is lower than the inverse of the characteristic time for barchan formation, the dune adapts to the new flow direction and recovers the barchan shape while losing less grains than under one-directional flow. For higher frequencies, the dune has not enough time for adaptation and becomes more round while losing more grains. For both cases, we show, for the first time, the typical dynamics of grains (trajectories and forces). In particular, the round barchans are similar to the so-called occluded dunes observed on Mars, where seasons have very high frequencies compared to the dune timescale, different from Earth. Our results represent a possible explanation for that shape. (AU)

• FAPESP's process: 18/14981-7 - Modeling of dense granular flows: experiments, numerical simulations and stability analyses
• Grantee: Erick de Moraes Franklin
• Support Opportunities: Research Grants - Young Investigators Grants - Phase 2
• FAPESP's process: 19/10239-7 - Bed-load instabilities: granular dynamics and interaction with the fluid flow
• Grantee: Willian Righi Assis
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• FAPESP's process: 22/01758-3 - Turbulent flow interacting with dense granular media: perturbations on the flow structure
• Grantee: Danilo da Silva Borges
• Support Opportunities: Scholarships in Brazil - Post-Doctoral