Snowball effect

The term, snowball effect, is used to describe a process that starts from an initial small state and rapidly builds on itself, becoming large and potentially dangerous, or even disastrous. The common analogy is with the rolling of a small ball of snow down a snow-covered hillside; the ball will pick up more snow as it rolls, gaining more mass and surface area, and picking up even more snow as it rolls along. In cartoons, this gag is almost a cliche.

See also avalanche, domino effect, butterfly effect