* Noun: This is the most common usage. It refers to the act of something bursting forth, like a volcano erupting.
* Example: The volcanic eruption sent ash into the sky.
* Verb: Less common, but it can be used as a verb meaning to burst forth.
* Example: The volcano erupted with a loud roar.
Let me know if you have a specific sentence in mind and I can tell you which part of speech "eruption" is functioning as in that sentence.