Question: I usually use "glacial" to denote something as very slow-moving, but this time I am actually talking about a glacier so it can't be "the glacial glacier".

[These](http://thesaurus.com/browse/glacial) are the synonyms of "glacial" (They all mean cold)

[These](http://thesaurus.com/browse/slow-moving) are for "slow-moving", but none seem to actually imply the persistent slow movement of a glacier.

Answer: 
I have encountered ***creeping*** in the context of glaciers before.

[***creeping***](http://www.merriam-webster.com/dictionary/creeping)

> 
> advancing or developing gradually.
> 
> 
> moving very slowly at a steady pace.
> 
> 
> 

Another suitable adjective is ***sluggish***.
May I submit ***relentless*** which dodges the question slightly; but, in my defence, I feel glaciers are not known for their startling pace, quite yet, anyway.

Closer to your request is ***restless*** to suggest movement, unrelieved.