A natural phenomenon is an noticeable, visible and observable event which is not man-made. Examples include: sunrise, weather, fog, thunder, tornadoes etc.
The migration of millions of red crabs
Every year on Christmas Island about 43 million land crabs rush to the ocean to lay their eggs. At this time, the local government covers most of the roads of the island, so as not to interfere with the migration.
ChinGum 