After heavy rain, water flows down any gradients.
As it runs it gathers flotsam – leaves, husks, twigs – and this flows down with the water until it meets an obstacle of any kind, like a small stone.
This forms a small blockage as the flotsam gathers in one place and builds up. Soon the water piles up, but then either flows around the flotsam barrier or leaps over it.
This leads to telltale patterns, often looking like stripes, in the ground:
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