Why is the landscape so varied?
Why is the landscape so varied?
Different types of landscapes such as plains, wide valleys, gorges, dunes, rounded hills, and rugged ridges are formed largely by the forces of water, wind, and moving ice, which nibble, sharpen, and polish the surface of the Earth. Experts call this process 'erosion'. These forces are much stronger than they appear. For instance, flowing water can move whole block of rock. The largest bits of rock thus eroded later become sand, which may be fine or coarse in texture and red, white, or grey in colour. Human beings also contribute to the constant changes taking place on the face of landscapes.
How are gorges formed?
Gorges, also called 'ravines', 'flumes' or 'canyons', are deep, narrow valleys with sharply steep cliffs. They are formed mostly due to the action of flowing water when a stream or a river digs into the surrounding rock. The most famous gorge is the Grand Canyon in the USA, Arizona; it is almost 1800 m deep in places. Over a period of 600 million years, the Colorado River carved the Grand Canyon by eroding the surface of the Colorado Plateaus, which are to a large extent made up of sandstone and argillite.
Why is sand of different types?
Sand is not a rough mixture of various rock particles, but a granular material. The size of a sand particle ranges from approximately 0.02 mm to 2 mm. The appearance of the sand particles depends on the rock from which they were formed by erosion. Black sand is made from volcanic rock, and oatmeal sand from quartz and feldspar grains. Red sand contains a lot of iron-rich minerals, which are frequently found in sandstones, and white sand is mostly composed of small, grated seashells, snails or the chalk from coral reefs. If a rock containing gold erodes, the gold particles are freed and get stored in rivers. Such findings led to the so-called gold rush in 1848 in California.
What happens to all the sand?
Sand formed by erosion gets deposited at different places. High sand dunes are formed by the action of wind in deserts and along the coast. On the other hand, the sand transported by rivers gets deposited in low-lying areas or in the sea. As the gradual deposition gathers weight, the pressure on the underlying layers increases and sandstones are formed. If the pressure increases further, the rock changes and becomes more compact. If the rocks then melt due to the movement of tectonic plates (page 14) and magma comes up to the surface as a result of a volcanic eruption, magmatite is formed. These newly formed rocks too fall prey to erosion due to the constant action of wind, water, and ice.
How can ice shape a landscape?
Athick, moving layer of ice acts like a huge plough. In the ice age, thick streams of ice, which were several kilometres long, moved from Scandinavia towards the south, scraping and levelling the land below them. Even today, this is an ongoing natural process in the landscapes of Finland and North Germany. Ice also shapes landscapes by cracking up rocks. In the night or during winters when the temperature falls below 0°C, the water in the crack of rocks freezes, expands, and pushes them from the inside out till they burst with a loud noise.
How do human beings change the surface of the Earth?
Human beings build roads and parking spaces, harness rivers, and remove bushes from margins of fields. As water does not seep through concrete and asphalt, floods increase and the groundwater level drops. The wind blows unhindered over the arable lands shorn of trees and bushes and erode the soil. In some countries, entire stretches of land have become deserts in this way.
You need: Eight small solid sandstones (such as those found in hardware stores), 2 plastic bags, a heater or a sunlit place, an icebox or deep freezer, a small vessel with water
Do as follows: Dry four sandstones for 2 hours on the heater or at a sunny place. Keep the other four sandstones in the vessel with water for 4-15 minutes. Fill the 4 dry sandstones in one plastic bag, and the 4 wet ones in the other. Put both the bags in the icebox or in the deep freezer of your refrigerator. Next day, have a look at both the bags.