Loose sedimentary material including clay, silt, sand, and gravel deposited by flowing water, especially in riverbeds, floodplains, and deltas. This fertile material forms some of the world's most productive agricultural soils.
From Latin 'alluvius' meaning 'washed against,' from 'alluere' (to wash against). The geological term was formalized in the 18th century as scientists began systematically studying sedimentary processes and formations.
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