India, Oct. 10 -- There's a lot more to Japan's famous sakura tradition than gathering to admire cherry blossoms.

This delicate annual rite is in fact a form of disaster-preparedness.

Every winter, moisture in the soil near riverbanks would freeze and expand. In centuries gone by, the spring thaw could then loosen the mud, and the slightest rain could trigger landslides.

So, way back in the 8th century, Nara rulers began to encourage spring picnics in April, a practice that spread from the nobility to the general populace over time.

The weight of thousands of people walking about and sitting on blankets by the river helped compact the soil, "creating a man-made solidity, supporting the banks' survival for another year," says Miho Maze...