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