What's the difference between a national monument and a national park?

Question

An ocean area near Hawaii has been named a national monument.
Muir Woods is considered a national monument, but Yosemite is considered a national park.

It doesn't appear a monument is a structure like I thought.

Answer 1

A national monument has a designation due to an individuals dedication to the USA or an individuals service to the USA, and a national park is a particular designated land that serves the greater good of the of the public space.

Answer 2

The monuments tend to be smaller and be centered around a person or object. The parks tend to be larger and be centered around the nature of the area.

The monuments are generally paying tribute to something. I don't see any Nat. Monuments in Hawaii...