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Nature’s Sandcastle: A Product of Vertical Stacking of Sieve Deposits

This note describes a rare observation of naturally occurring free-falling streams of sand-water mixtures that form vertical sandcastle-like structures with complex interdigitate patterns. These emergent structures and patterns develop on sand dunes during winter via successive stacking of sand-laden flows of snow meltwater. Individual lobes comprising the structures are emplaced via infiltration-induced deposition—a process known as “sieve deposition.” Collectively, the processes and vertical structures documented here provide an expanded context for understanding the behavior and emergent patterns of gravity-driven wet granular slurries in natural, uncontrolled settings.