What is a glacier?
A glacier is a large mass of ice that flows slowly. Glaciers form in places where there is enough snow to accumulate, and the summers are mild enough that not all the snow melts away. Year after year, the snow builds up, layer on top of layer, and compresses the snow into ice. Glaciers are made of snow, ice, water, rocks, and sometimes other things that get lost (I once found a ski pole melting out of a glacier)!
Snow is what helps the glacier grow, like our food helps us grow. The more snow the glacier gets, the bigger it gets.
Snow builds up and squeezes the snow into ice (like one of those way-too-hard snow balls but harder). Ice crystals can grow and move over time, making the glacier flow downhill like very slow honey.
With mountain glaciers (think of glaciers in New Zealand, the European Alps, the Rockies), ice flows from high places, where the snow accumulates and it is very cold, down hill to where the ice melts because the temperatures are warmer.
What is it like to be on a glacier?
Each glacier has a slightly different shape, size, look, and sound.
- Sight: Imagine you are up on the side of a mountain, the rock cliffs around you are grey and smooth, the sun is bright and there is a big, blue and white mass of ice, the size of a hill, just sitting there, on the side of the mountain. The glacier moves too slowly for us to see, and you have to put on your sunglasses because the sun reflects off the surface so efficiently you could go blind. My sister also told me to keep my mouth closed while hiking up a glacier because the light reflected off of the snow could burn the roof of your mouth.
- Feel: You are up pretty high in elevation, so you feel that the air is colder. Luckily, it is a warm sunny day, so you are comfortable wearing rain proof pants and a fleece jacket and light gloves (but you have a rain jacket, hat, bigger gloves, and a down jacket in your backpack in case the weather changes). You are excited about walking around on the glacier for the first time and wonder what it will be like: Is the ice strong enough to hold you? Will you be able to jump across the crevasses (breaks in the ice)? Will you trust your gear and ropes to catch you if you fall? Will you remember to walk like a cowboy so the spikes on your boots don’t catch on your pants or on the rope connecting you to your team?
- Sound: You strap the spikes (crampons) onto your boots and take the first step onto the glacier. The ice is firm and strong enough to hold you, like very thick ice should. You hear the crunch, crunch, crunch of your footsteps, you walk like a cowboy with big, wide steps. You notice how easy it is to walk on this wet, blue, slippery ice with your crampons and start listening for other sounds. You hear a slight wind. As you get closer to a crevasse, you hear, but do not see, water. There is a little waterfall and a stream flowing through the crevasse to the glacier bed, you realize the whole surface of the glacier is probably melting a little in the strong, warm sun. You also hear your leader say it’s time to jump a crevasse and to keep the rope between us loose but not too loose so each person can jump one at a time. Ready, aim, JUMP!
- Taste: Well done! Time for a snack. You pull out your water bottle, the water is cold and fresh. You also have a little snack in your side pocket of your jacket. This can be whatever you like (I usually have fruit leather because it is soft even if it freezes, I had a friend chip her front tooth on a cold chocolate bar! Lesson: Keep your chocolate in your coat pocket so it stays warm).
- Smell: Up here, the air is fresh, there aren’t many plants, maybe a few grasses and alpine flowers. All you can smell is yourself (sorry, it’s true).
Why do glaciers matter?
- Water resource: Some places in the world have a wet season and a dry season. Imagine not having water to drink or water your crops during the dry season, it would be bad. Luckily, some places have glaciers that melt during the dry season and keep the rivers flowing, it’s like a water back-up source. But because the glaciers are getting smaller and smaller, the back-up source is failing and the dry season is truly dry without the supply of fresh water from the glaciers.
- Beautiful features: I think glaciers are beautiful to look at, they are dangerous to be on or near, but are incredible forces of nature!
- Thermometers: Most glaciers grow when the air gets cooler, and shrink when the air gets warmer. They also sometimes leave a trace of how big they were in the past, so we can understand when these glaciers were bigger, how much colder it was in the past (20,000 years ago was the last ice age), and then use this information to make a hypothesis about what causes ice ages! AMAZING!
As the air gets warmer, we need to know how the world will respond. People use what has happened to ice, water, air, trees, and land in the past tens of hundreds of years to guess what will happen next. Ice that stays year round in high areas tells us when it was warmer or colder in the past. This works because ice gets bigger and longer when the air is cold and smaller and shorter when the air is warm. Ice moves down from cold high areas to warm low areas. Rocks in the ice fall out at the lower end and leave a line of rocks marking the edge of the ice. So even when the ice is all gone, we can still see the line of rocks and where the ice edge was in the past. I use the line of rocks to learn WHEN the ice was bigger and how much COLDER it was in the past. Ice is great.
What is my favorite thing about glaciers?
I love that you can tell where a glacier has been just by looking around at the landscape: Glaciers can have rocks that freeze to its base and these rocks make scratches (striations) in the bedrock! Rocks can also move with the flow of the glacier (like a conveyor belt) and melt out at the edge. If rocks build up at the edge, they can form a ridge tracing the glacier front (called a moraine), so even when the glacier melts away, the rock ridge remains, and we can tell how big the glacier used to be (and how much colder it was). You can think of these bigger past glaciers like that pair of pants your Uncle Remis used to wear, you can tell how big he was.
This gallery contains images of mountains glaciers and ice sheets to give you an idea of what glaciers look like. Glaciers range in size from <1 km squared to >4,000 km squared (Lambert Glacier in Antarctica).