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| Sunday, 14 August 2005 |
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Junior Observer |  |
| News Business Features Editorial
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Moving rivers of ice You may have heard about glaciers which are really moving rivers of ice. Glaciers are made high in the mountain areas. The weather up there is so extreme that the snow doesn't melt completely. Snow falls as tiny flakes. Each snowflake has its own pattern. As the snow settles, the ends of the snowflakes get pressed together, just like when you make a snowball. The snowflakes become rounded and smoother. Then they lose their shapes and the air gets squeezed out. As new snow falls, the old snow gets packed down. Eventually the snow becomes rounded ice crystals. Every winter, the ice grows into millions of interlocking ice crystals. The shapes create a mass of solid ice. As the ice grows, it gets bigger and heavier. V-shaped valleys are made by rivers. They are more narrow at the bottom. Glaciers make U-shaped valleys. Some famous glacier valleys are Yosemite Valley in California and those in the White Mountains of New Hampshire. As glaciers move, the front makes a giant wall of ice. It moves forward because it has a great, weight. The front of the wall can be a mile high. Nothing can stop a glacier, not mountains, forests, lakes, plains or people! As snow keeps falling, the ice gets thicker. When the ice field has grown to about sixty feet in thickness, a strange thing happens. The ice begins to move. A glacier is born! Sometimes, the ice surges and moves one hundred feet in a day, at other times it moves only an inch or two a day, so you can hardly notice the movement. No matter how slowly it moves, when the ice field begins moving, it is officially a "glacier". As the ice moves over the ground, it starts to bend and crack because it is so big and is moving over land that is not flat. The rocks also help crack the ice. Even though glaciers are called "rivers of ice", they do not exactly move like a river. A real river is made of flowing water, but a glacier is made of brittle ice. Scientists have studied glaciers for a long time out of curiousity as to how they move. Using modern equipment, scientists have recently found that glaciers move in two ways. Glaciers slide on water that has melted. They slide along the ground on a thin layer of melted water under the ice. The other way is called "creep". The glacier is extremely heavy that the crystals of ice make layers of ice one on top of the other. Then the different layers of ice start creeping and moving over each other. The thicker the glacier, the faster it will move because the ice crystals creep faster since the ice is heavier. When a glacier is on steep land, it will move much faster than a glacier that is on more level land. The warmer a glacier is, the faster the ice moves because it has more melted water under it to help it move. Only a very few animals can find what they need to survive on glacier ice. Some mice may end up on such an icefield in boxes and bags carried there by mountain climbers and scientists. They might manage to live by stealing food from these people and sleeping hidden in their warm gear. These "stowaway" mice could not live on the ice without people. A closer inspection of a glacier may show you some true "glacier dwellers" such as snow fleas and iceworms. Snow fleas are insects that are about the size of the head of a pin. These tiny creatures are adapted to life on ice. Snow fleas are also called glacier fleas. They are vegetarians and belong to the order of Collembola. They feed on algae and conifer pollen. They get their name because they move in a hopping pattern. Iceworms are dark and are one to three centimetres long. They can live at temperatures that are almost freezing. They dig down into the ice when the air temperature is a few degrees either above or below freezing (32'F). They live in the partially thawed ice. They eat algae whose spores (tiny cells) were caught in the snow as it was carried by the wind. Glacier ice is often a deep blue colour. This is because of how the sunlight passes through the ice and what happens to the sunlight. Sunlight looks white. The light is really made up of all the colours of the rainbow. Each of the sun's colours have different amounts of energy in them. When the sunlight tries to go through the solid glacier ice crystals, the sun gets broken up into lots of colours. Red and yellow have very little energy and the thick ice soaks up the red light more than it soaks up the blue light. The blue light has enough extra energy to get away from the solid ice crystals without getting absorbed or soaked up. This is why the only colour people see is the blue that escaped. The blue light has enough energy to escape the ice so that you can see it. That is why glacial ice is often a deep blue colour. Some glaciers do not look blue to people. If the glacier has a lot of air bubbles inside the ice crystals, the white sunlight gets reflected not soaked up. If the sunlight can get through the ice without all the rainbow colours getting scattered and soaked up, the ice will look white. Glaciers have soil, rocks, snow and dirt mixed up with the ice. Then the ice can look a dirty gray. ########## Types of glaciers Alpine glacier: Formed in the upper elevations of mountains. Compound glacier: Formed when two or more glaciers flowing down different valleys join each other . Icebergs: Large masses of ice which break away from the lower end of a land glacier and fall into the sea or a lake. Ice cap: An ice cap is a permanent glacier over an area that slopes down on all sides from the centre. Ice caps are formed when snow and ice fill a basin. Icecaps are less than 50,000 square kilometres in size. An example is the upper part of Mount Wrangell in Alaska. Ice field: Places where large valley glaciers run into each other and the mountain tops stick through the ice. The Stikine Icefield is northeast of Petersburg, Alaska. Ice sheet: Very thick glacier ice that covers a large area. They have to be bigger than 50,000 square kilometres in size. Antarctica and Greenland have ice sheets. Piedmont glacier: When an ice stream from a mountainous area flows onto flat land, it may spread out into a broad sheet called a piedmont glacier. It is also called a "foot of the mountain" glacier because it looks like a wide, flat boot. Tidewater glacier: When a glacier reaches the ocean, huge pieces of ice fall off into the water with a hiss and a crash. The broken chunks are called icebergs. After they break away from the lower end of the glacier, they float off. Only a little bit of the iceberg shows above the water. The biggest part of the iceberg is hidden under the water. Valley glacier: Starts from snow that collects in a high basin and flows down a mountain valley. |
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