Plural of alluvium; deposits of sediment (sand, silt, clay) left behind by flowing water, such as rivers and streams.
From Latin 'alluvium' (material washed against), from 'alluere' (to wash against). The term describes geological deposits formed over thousands of years.
The rich farmland of the Nile Valley, Mississippi Delta, and Yangtze River valley all exist because of alluvia—ancient rivers dropped nutrients for thousands of years, creating super-fertile soil!
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