Idiom: The Tip of Iceberg

If something is said to be ‘the tip of the iceberg’ it means that something is only a small part of a much bigger problem.   The ‘tip of the iceberg’ is the part of a problem that can be easily observed, but not the rest of it, which is hidden.

Example:

The problems that you see here now are just the tip of the iceberg. There are numerous disasters waiting to happen.