Building your world: glaciers
This is the first topic of my worldbuilding posts. I'll start with a general introduction about the feature - not too detailed though, you have Wikipedia for that - then I'll tell how you can show this in your novel. Beware: I'm an earth scientist and a human (as far as I know), so don't know everything. Don't ask me what kind of plants you can find here, or animals. Heck, I'm pretty sure I forgot to mention a few things that are close to my field of expertise! The earth is such a big thing with lots of stuff in it, after all...
If you want a glacier, you need snow and a slope. Lots of snow. A fluffy snowflake does not look like much, but turn the stuff into a thick layer and its own weight will cause pressure. This heats the snow just enough to make it melt a tiny bit. It recrystallises as ice - and ice is destructive! Glaciers might look quiet, but don't let that fool you: they are one of the greatest shapers of the landscape. They crawl down the slope, with roughly a 1 metre per day, while the ice carves and erodes. Even here, in the seemingly boring Netherlands, we can see the remnants of big ice sheets...
You can divide glaciers into two groups:
Valley glaciers: see image above. It's an ice tongue that flow down a mountain, with rocky slopes at other side. This is probably the image people have in mind when you say 'glacier'.
Continental glaciers: huge sheets of ice, kilometres thick that cover land masses. Think 'Greenland' or 'Antarctica'. Valley glaciers look rather cute compared to these big guys.
The snow that falls high up the mountain (zone of accumulation) will compact to ice and move down under its own weight. The temperature goes up when you get to lower altitudes, so at some point it can become so warm the ice melts (zone of ablation). You can easily tell the border between the zones, known as the snow line: the glacier high up on the mountain is white and crisp, while the lower part looks rather dirty. The end of a glacier is called the terminus. There, the ice melts to form rivers, a like or it will break apart as icebergs when the terminus reaches a sea.
When you say glacier, people think of ice, but that's only part of the story. The ice picks up rocks (or the rocks fall on top of it), a process called plucking, and scrapes them over other rocks - that's called abrasion. The ice carves out rocks and pushes rubble down the slope. The presence of rocks is why the zone of ablation appears dirtier than the zone of accumulation: the ice melts, leaving behind the rubble that got stuck in it. The amount of rubble on top of a glacier can be so high that the glacier does not appear white any more - it's called a rock glacier in that case. I have some colleagues doing awesome research about them, using UAVs (unmanned aerial vehicles - or just drones, but that word has negative associations so we prefer not to use it) to get a good look at them.
So there you have your glacier basics: time to add terminology:
Glacial till - Ice sheets scrapings. It consists of sediment ranging from silt-sized particles to big boulders.
Moraines - accumulation of till. You have different kinds of moraines, but you can see it the best on top of the glacier as dark stripes and at the terminus where rocks get pushed forward by the ice.
Crevasses - deep fractures in the ice sheet. They can be up to 45 m deep and hundreds of metres wide, but they aren't always clearly visible. Fresh snow can hide them. Ice bridges can cover the gaps, sometimes safe enough to walk on.
Cirques - theatre-shaped valley at the top of a glacier.
Arêtes - a sharp mountain row that lies between two glaciers.
Horns - similar to arêtes, but here glaciers have carved the mountain at all sides. leaving a peak in the shape of a pyramid.
Moulins - circular vertical shafts, meters wide, where surface water plummets down into the glacier. Glaciers have their own plumbing system, you see. You can find rivers in them.
Melt ponds - water ponds of molten ice. water is darker than snow, so instead of reflecting light, it adsorbs it, making warmer, causing nearby ice to melt, etc.
Sandur - outwash plane of melt water streams.
Glaciers are a balance: snow goes in, but that stuff melts and goes out as water. More snow results in glacier growth, less snow or high temperatures in decline. With global warming, the snow melt increases, so most glaciers are dying at the moment. It really depends on the situation though: if global warming causes more precipitation in the form of snow, the glacier can grow. High temperatures can also cause surges, a short moment where the glacier just sprints forward, but consider that its swan song.
Climate change is something you should think about. Earth is a dynamic place, and many people - including writers - do not seem to realise this. Was your world colder thousands of years ago? If yes, you should look at the amount of ice there. So many places that now seem nice and warm used to be covered with ice a couple of times in geological history! The ice sheet made all kinds of features at its bottom, which will be visible when the ice has melted away.
U-shaped valleys - a valley carved out by glaciers. Like the name implies, it has a flat bottom, but steep walls. Valleys created by rivers are V-shaped.
Moraines and glacial till (again) - even when the ice is gone, the till and moraines will remain, forming huge ridges in the landscape. They are particularly big if they are created by continental glaciers. The one close to my parents' place is 70m high! A different word for it is Ice-pushed ridge. Glacial till can be badly permeable, so you can get a locally high water table and bogs.
Drumlins - a hill with a steep and a gentle slope, made of glacial till. The steep side is facing the origin of the glacier.
Roche moutonnée - also a hill with a steep and a gentle slope, but this one is made of solid rock. The gentle slope is facing the origin of the glacier.
Esker - a ridge of gravel and rock, created by water systems that flowed in and under glaciers.
Glacial lakes - the ice leaves depressions, which can fill up with water when the stuff melts. Think about the great lakes in North America for a rather big example.
Glacial isostasy - the Earth's crust is not as static as you might think. When large sheets of continental ice rest upon the land, it pushes the crust down. Ice is quite heavy when you can express its thickness in kilometres after all. The areas right next to the continental ice get pushed up, as if it was the lighter kid on a seesaw. When this weight gets removed, the crust moves back to its initial position. The ice-covered land becomes lighter and goes up, but land next to it goes down.
Kettle and kame - kettles are small ponds, while kames are irregular hills. Blocks of ice that calve off a receding glacier land in the sandur sediment. Ice is heavy, so the blocks press down the sediment. when the ice melts away, you'll end up with a landscape full of potholes that are usually filled with water. The kames are heaps of rubble on top of a glacier. When the ice melts, they are left behind as hills. Kettles and kames occur together often.
What can you tell in your story:
Glaciers can be found in harsh environments. They are dangerous and they will eat you - crevasses are their mouths! You will only travel across one if there really is no other way - or if you happen to be a mountaineer who likes that kind of stuff. Isn't there a 'mines of Moria' or 'gap of Rohan' in your world? Using that would make more sense than jumping over crevasses and climbing ice bridges.
Maybe your world does not have glaciers, but did it have Ice Ages? Probably, these things are quite natural, even when your world only contains tree-hugging elves who will not kill their own planet with high CO2 emissions. The remnants of glaciers might still be visible.
If you are writing third person omniscient, you can shove additional information in the narrative. But what if you want to stay close to the character, what will he see? Well, that will depend on the level of knowledge of the character. Let's start with a 'Jon Snow' (in other words, he hardly knows what his surname means):
Glaciers can look quite impressive. Let the guy admire them for a moment.
He might be surprised the glacier is not made of snow alone.
It's cold up there. This sounds so obvious, but it's easy to forget your character needs to change his clothes. Sturdy hiking boots are a must as well!
That said, it can be quite pleasant when the sun is shining. Your character can easily end up with a sun burn.
This even surprised me: glacial ice and water can be really, really blue! Like... frozen/liquid smurf! Your character will notice that as well.
Finding your way on a glacier is quite tricky. If your character is clever, he will get a guide - or grow wings...
The moraines form dark stripes on the glacier, making it look like a stretched-out bar code (I hope you'll find better words to describe it).
The top part of glacier is whiter.
Rocks carried by the ice scratches other rocks. The character can see 'scratch marks' if he is perceptive, but he will not realise the ice did it (maybe he blames it on a dragon).
There are big blocks of rock everywhere, and they might even tumble down at inconvenient moments... Jon Snow will not think of that when he starts his ice-hiking trip, of course.
There is a lot of water at the foot of a glacier; braiding rivers, waterfalls, lakes, ponds... Which might cause trouble if the character needs to cross them. The landscape can change drastically within hours too. One shower is enough to turn rivers berserk.
In the case of 'extinct' glaciers: signs of that are much harder to pick up. The character might notice some odd hills - especially if the rest of the landscape is flat - but does not know what caused them.
The Maester (the expert of everything) will notice what Jon Snow sees of course, but has some extra information:
He knows the right terminology.
He knows the physics behind glaciers.
He knows the gear you need to climb them.
He is aware of crevasses and snow bridges and that it's dangerous to cross them. He might even know exactly where they are if he is a local guy. He can use his knowledge to help/kill other characters.
He will notice the end moraine, drumlins and roche moutonnees, and what caused it.
Also knows blocks of ice can fall off at the terminus. An ice cliff is just as dangerous as a rocky version.
And if he is clever, he will admire glaciers from a distance.
Quite some things you can think about. So, do you need to tell all of this?
NO! You don't want to drown the reader with details. Pick out two things that you think are the most important and shove the rest in later parts of the chapter or story. Besides, focus on the feeling of an area, instead of just describing its looks. No matter what your setting looks like, it should affect the character.
Besides, there are other ways to shove the landscape in your story, which might not be so obvious. For example: glaciers leave big rocks behind (glacial erratics). These things have been used in the Netherlands to make burial sites. Many centuries layer a lot of them were blown up with dynamite to get smaller chunks, which were used as building material. Granite is hard to find here, so you need to be creative with what you have. Also, people have their own theories about how those rocks got here. There are still quite some people here who believe the waters of the great flood (the story of Noah's ark) did that. So the landscape is not simply there, it has been used in religion and down-to-earth practicality. You can do something like that as well!
A hunebed, or dolmen.
I think this post is long enough. I probably forgot to mention half the things there is to say about glaciers, but I hope this is still useful.
Next post: dunes!