An idiom meaning the visible part is just a small portion of a much larger problem—'the tip of the iceberg.'
表に出てきた不正は氷山の一角に過ぎないかもしれない。
The corruption that has come to light may be only the tip of the iceberg.
今回の検査結果は問題の氷山の一角を示しているにすぎない。
This test result merely indicates the tip of the problem.
メディアに出た情報は氷山の一角で、裏にはもっと多くの事実がある。
The information released in the media is only the tip of the iceberg; there are many more facts behind it.