What are they and how did they come to be.
Glaciers are not made of water, but from delicate little snowflakes, which fall from the sky. No snowflake in the world has a twin that looks exactly like it, yet they are all lovely, and they melt if they fall on warm surfaces.
As most of us know, sometimes, in winter, they pile up and make white, soft cloudy mounds all over. Everything is covered in a soft white blanket: the streets, cars, tree branches, roofs, even the rivers and mountains. Anyone who lived in a place where it snows knows that one day of warmer temperatures or sunshine, and some of the fluffy snow melts. This is called ablation. Then it gets very cold and those once lovely clouds turn to ice.
Individual snowflakes may be fragile, but put together, they can create one of the most awesome sights in all of nature: the Glacier.
In places where temperatures are cool or better yet cold year around, and more often than not, surrounded by mountains, the snow keeps accumulating. It never has a chance to melt completely it’s never warm enough for that.
Something else happens. In areas with high mountains covered by snow, there are many avalanches each year. An avalanche is when snow slides suddenly and very rapidly, from a high place in the mountain, gathering speed as it goes. It becomes very fast and strong near the bottom of the mountain, picking up with it everything in its way rocks as big as houses, dirt, trees, more snow. By the time the avalanche stops, it is a large, packed mass of snow and debris. After the next avalanche, the snow slides on top of the first and begins compressing it. Then the process is repeated a great many times, with the newer layers putting enormous pressure on the older, lower ones, turning them hard as metal as they push the air bubbles out of them. The pressure from the soft fresh snow mounds, creates pressure that turns them into hard ice pellets. The more they compress and push by having even more fresh snow fall on top of them, the harder they become.
This same thing can happen even without mountains and avalanches the snow accumulates one layer by the next, each one on top the last snowfall, from day to day, week to week, from winter to winter. There is something else that’s interesting that is the Firn line that separates the layers from one another, the ice from snow, the hardest, oldest layer of ice from the newer, and so on. Depending on the age of the glacier, if you were to slice a glacier in half you’d see many markings, called firms, just like the rings inside the trunk of a tree, a ring for every year. In a glacier they also take about a year to form.
Since the temperatures never rise above the level that could melt the ice completely, whatever melts turns to ice, only to be covered by fresh snow the most amazing, enormous structure is created: the glacier. When the weight of these masses becomes great enough, they begin to move, or flow down. They are in constant motion, most of which is so slow that it’s hard to observe unless you were to climb down and look inside a glacier, by pouring hot water into the solid ice and melting it, to make an ice cave, discovering that the bottom of the glacier is filled with dirt, but the rest is mostly pure water. They also found bits of water inside which helps it move with gravity, and is responsible for the exciting thing you will all see from the boat when you get to Glacier Bay large, very old bits of ice can suddenly break off the glacier with a crack and fall into the water. It is a spectacular sight.
Since glaciers can and often do grow for many years. Some are so large they are the size of the state of Maryland. If it was possible to drive over them, which of course it isn’t, it would take over 5 hours.
Some glaciers are very old: there is one in Antartica which is around eight million years old. Also in Antartica is the biggest glacier in the world its name is the Lambert glacier and it’s 60 miles wide and 250 miles long.
Most glaciers are not this large but lots of them are a stunning sight. Some of them are blue, some purple or white, they have shapes that are hard to describe.
Alaska has 664 Glaciers and the most beautiful of them are in Glacier Bay National Park, where the boat will spend a very long time and the passengers will have a chance to see sixteen magnificent glaciers that seem to pop out of the mountains. And the most beautiful of them, the McBride Glacier is in the middle, deep blue and calving off (breaking off, chipping) little fragments, which make a big splash and a cracking sound as they fall into the blue water.