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: 
You should have stated what register you were writing in. Journalistic (columnistic or newsy?), literary, academic etc. Helpful would've been a specification whether the adjective within your context should denote exclusively the rate of movement, or it can be multihued. Depending on how much you're allowed or inclined to wax poetic, you might decide to chose from among one of these (they're all "googlable"):

### *crawling*

> 
> * These ever changing, ever moving crawling glaciers are very different from the high glacier plateau which they decend from.
> * These had accumulated there over the last few millions of years deposited by the crawling bellies of glaciers long since gone.
> 
> 
> 

### *[torpid](http://www.thefreedictionary.com/torpid)*

> 
> * The arctics down whose voiceless valleys the torpid glaciers creep, the parched deserts of the tropics,...
> 
> 
> 

### *[slothful](http://www.thefreedictionary.com/slothful)*

> 
> * This side glacier, which comes in from the south, slid down its valley out over Sherman Glacier, and ended up almost at the terminal of Sherman, a slothful receding glacier.
> * To the naked eye, glacial activity looks like anything but action. It may put up an appearance of functioning as a stagnant blockage of the water cycle; a stunt of the grunt, if you will, eternally stuck in a rut rather than accomplishing much for its mother to be proud of. In fact, it may be tempting to call a glacier **slothful**, reclusive, just a big hunk (unfortunately not the kind of hunks we've been looking for), and taking up good potential driving passage. We don't mind our Icefield.
> 
> 
> 

### *[languid](http://www.thefreedictionary.com/languid)*

> 
> * down below in the land that forgot time we are eking forwards like a slow languid glacier
> * Overhead, the yellow sun and the green sun circled each other with a languid incessant inevitability
> 
> 
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### *[scant](http://www.thefreedictionary.com/scant) movement*

> 
> * Together with these deposits, and generally at a somewhat lower altitude,
>  there exist deposits that are clearly morainic, either lateral moraines or rock glaciers, with very little fine fraction, due to the scant movement of the glaciers.
> * The luscious green trees were scantily moving to the soft breeze, birds were chirping, it was an amazing scenery.
> 
> 
> 

### *(variations on) slow*

> 
> * Attempts have been made to explain these wide-ranging deposits as being laid down by a **slowly meandering** glacier.
> * Humboldt, a very wide but **slow-moving** and **slow-changing** glacier, lies just to the west of Petermann Glacier
> * It's a slow, **grindingly slow**, tortoise and the hare slow, glacier slide slow, birth of a star slow type of song.
> 
> 
>
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.