Avalanche simulator was made for a presentation at a physics camp. It works the following way:
The screen is divided into squares, and at each iteration, the program puts a snowflake on a random square.
There can be multiple snowflakes on one square, the more there are, the whiter that square is. When there are 4
snowflakes on a square, they get pushed to the adjacent four squares. If there are now also four snowflakes on
one of the adjacent squares, they too get pushed to the neighbors, and this can continue, creating an avalanche.
When the program has been running for a while, a lot of large avalanches can be seen.
You can try the program here.