Dic: scratch the surface

• Officials say they've only scratched the surface of the drug problem.
• We had only two weeks to tour Malaysia, which was hardly enough time to scratch the surface.
• There is no serious damage done to the bench. You only scratched the surface.
• The investigation of the governor's staff revealed some suspicious dealing. It is thought that the investigators have just scratched the surface.
• We don't know how bad the problem is. We've only scratched the surface.

6. PHRASE : V inflects, oft PHR of n | If you only scratch the surface of a subject or problem, you find out or do a small amount, but not enough to understand or solve it.

scratch the surface :

1. Lit. to scratch something just on the surface, not extending the mark below the finish into the wood, stone, marble, below.

2. Fig. to just begin to find out about something; to examine only the superficial aspects of something.

.... Cobuild, McGraw-Hill Dictionary of American Idioms and Phrasal Verbs