I understand they’re big ol’ chunks of ice, but are they one solid mass? What is defined as the “border” of a glacier? I’ve seen discussions of the dangers of underground glacial rivers, what’s the deal with those?
In: Planetary Science
To add to what has already been posted the glacier normally forms higher up in a depression called a corrie. As snow consistently fills this depression it compresses to form ice, when it cannot possibly hold anymore it starts to overfill the edge of the corrie and gravity makes it slowly slide downhill. Natural springs and ground temperature can cause a stream to form beneath it, cutting a tunnel through the bottom of it. As the glacier flows downhill crack open up, crevasses.
A glacier is a persistent body of dense ice. Basically, it’s a giant chunk of ice that is so large that it does not fully melt in the summer. We typically see them in the polar regions (the so-called polar ice caps,) and at the tops of mountains elsewhere on the globe. Basically if a mountain collects snow faster than the snow can melt or vaporize, over time that snow will compress under the weight of snow above into a glacier.
A giant frozen river.
Think of the water cycle – water evaporates, condenses into clouds, precipitates, and then makes its way (rivers and streams) back into the ocean.
Glaciers follow the same process: water evaporates, condenses into clouds, and precipitates as snow. The places glaciers form tend to be colder, so the snow never melts. It is compacted by more snowfall and eventually becomes ice. This ice slowly makes its way down into the ocean. Look up glacier flow videos on YouTube at fast speed – you will see the flow.
A glacier is a place in the mountains where more snow falls during winter than melts during summer. The snow then builds up year after year.
As the weight of the new snow presses down on the old snow, the old snow gets compacted into very dense, solid ice. When the pressure rises more and the ice on top of the mountain presses down on the ice further below, the whole glacier starts moving and “flowing” very slowly even though it is all solid.
As the ice flows down the mountain over the course of many years, at some point it reaches an altitude where more ice melts than new ice is pushed down from the mountain top. This is where the glacier ends.
Glaciers are mostly solid ice, but there are cracks and holes in the ice. These can either form from mechanical stress, when the glacier moves. Or water from melting ice can basically “cut” them into the glacier. They are really dangerous because you can fall into them and they are often not visible on the surface when they are covered by a thin layer of ice and snow.
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