Gatheringsand

Gatheringsand is a term used in some granular physics and sedimentology writings to describe a cohesive, aggregating state of sand grains in which individual grains coalesce into small, mobile clusters or gatherings. The term is informal and not standardized, but it is used to discuss how moisture, electrostatic forces, or binding agents can create transient cohesive groups within otherwise loose sand.

Physical characteristics: Gatheringsand consists mainly of silica grains typically ranging from fine to medium sand, about 0.1 to 2 millimeters in diameter. In dry conditions, grains behave like a granular fluid with minimal cohesion; when moisture or salts are present, capillary bridges and electrostatic forces increase cohesion, enabling clusters to form and persist under low shear. This cohesion can alter the material's angle of repose and flow behavior compared with unsorted sand.

Formation and dynamics: Gatherings form during moisture fluctuations, wetting–drying cycles, or in environments where adhesion is enhanced by surface textures. Transport by wind or water can move gatherings and accumulate them into larger deposits, influencing dune morphology and sediment transport models.

Applications and significance: In research, gatheringsand provides a framework for incorporating cohesion into granular-media models, contributing to predictions of slope stability, dune evolution, and sediment transport. Field observations of cohesive gatherings help explain deviations from classical dry-sand behavior.

See also: granular material, sand dune, sedimentology, angle of repose.