|The CRYPT Mag|
The Earth Today
The landscape looks as if it's been there forever, solid and unchanging, but parts of it are being worn away by the weather, water and other forces of erosion. As old rock fragments are deposited, other parts of the land are being built up. As it happens too slowly for us to notice, the landscape is being continually reshaped.
Glaciers were widespread during the Ice Ages, beginning as snowfalls in mountainous areas, gradually building up and squeezing the air out, then turning to solid ice. After a while, the weight of the ice makes it slide slowly down the mountain like a river, around 2m (6ft) per day, carrying along fragments of rock, leaving marks on the landscape. More than 75 per cent of the world's water is frozen in glaciers and ice sheets, most of which are in the Antarctic. The longest is the Lambert Glacier in the Antarctic at 250 miles long and parts of it are 37 miles wide.
There have been four Ice Ages in the history of the world, the first known one being 2,400 million years ago in North America, South Africa and Australia. The last one finished 10,000 years ago, during which the land where New York now stands was completely covered in ice. There are signs of glaciation from millions of years ago in the Sahara Desest in Africa. Scientists have not yet discovered what causes Ice Ages, but the most widely accepted theory is that as the earth wobbles on it's orbit around the sun, it tilts closer or further away. The best evidence for this theory comes from the sea bed. Drilling through the sea bed reveal sediment cores which show fossils of marine creatures. By examining these fossils, scientists can discover how much oxygen they contain, they can ascertain the oxygen content of sea water at the time, which would have changed because of the differences in ice sheet thickness, due to freezing or thawing. As thaws occur, ice from them breaks off into the sea becoming icebergs. As the icebergs melt, fresh water from them dilutes the sea water, causing changes in oxygen levels.
As glaciers melt or retreat, they leave behind debris called glacial drift, and carve out U-shaped valleys, different in shape to water eroded valleys which are V-shaped. As the ice is much stronger than water, glaciers travel in a straight line, cutting hills in half, and leaving fragmented peaks in their wake. Many glens in Scotland are U-shaped, indicating that they were once covered by glaciers. In Norway, New Zealand and Canada, glaciers carved out deep valleys well below sea level. When the ice melted, and the sea levels rose, these valleys were flooded becoming fjords.
Beaches formed from erosion of the coastline, by the sea, waves and spray, from soft rock. The coastline is continually changing, often comprising of rock, shifting mud or sand. Sea levels rise and fall constantly and any changes effect the coastline. Volvano eruptions, earthquakes and changes in temperature can alter sea levels. Some coasts have been swamped by rising sea levels while others have emerged. A small increase in sea levels of just a few feet will submerge some islands in the Indian Ocean, and other places have built defences to protect against sea level rises.
Rivers and streams also contribute to land formation, eroding rocks from mountainsides and tumbling them dowsnstream. As they tumble, they grind against each other removing fragments of stone which either get carried onward by the water or, in quieter places, settle into the river bed. A lot of material gets washed down to the mouth of the river, causing deltas and changing the land shape. River erosion lowers the landscape by around 4" (10cm) every 1,000 years. Rivers sometimes empty into lakes, eventually building enough silt to change a lake into swamps and wetlands, if there is no exit for the onward travel of water. Some lakes are man-made, as reserviors for drinking water, by damming rivers.
Deserts cover 20 percent of the world's land surface, Australia is 80 per cent desert. The largest desert is the Sahara, covering 9 million square miles, but only 15 percent of this is covered with sand. Most of the large deserts are in the tropics, and are the hottest places in the world, at 50C during the day. Wind and overgrazing shape the size of deserts shifting the position of deserts over time. Overgrazing is contributing to the growth of deserts at an alarming rate.
Each year, we lose 15 million acres of farmland through erosion from the weather. Wind and rain are the main causes of this, along with over farming. Frost contributes to the changing landscape by splintering rocks and fracturing soils, leaving wind and rain to complete the effects.
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