Answer:
The answer is: a block of ice as long as a football field.
Explanation:
Appositive is a noun or noun phrase that sits next to another noun and renames or describes it in another way.
In writing an appositive, you offset with a comma or dash.
In the sentence above, the phrase "a block of ice as long as a football field" is the appositive.
This is because it is renaming and describing the noun "glacier."
