Wind erosion 2
(Continued from page Wind erosion 1)
10. Inselberg. It is mountain top rising suddenly from the plains or plateaus. Inselberg is a German word. It means island mountain, i.e., inselbergs look like islands situated in seas. Born Hardt tried to explain their origin. Inselbergs are also known as Bornhardt after the scientist who explained its origin.
In East Africa, inselbergs are found on the high land of the plateau.
11. Mushroom Rocks. When wind blows, the heavier sand particles roll down the land but the lighter particles blow above the ground. Hence the upper part of the rocks are eroded less than the lower ones. Due to greater erosion of lower portions, the rocks assume the form of mushroom. Such a rock is known as Gara in Sahara and Pitzfelsen in Germany.
12. Demoiselle. There are many areas which are made of hard rocks. Winds subject the upper parts of the rocks to abrasion but the lower parts remain protected. This gives rise to forms known as demoiselle which appear to be giant like.
13. Needles. Abrasion by winds bearing sand goes on at the mountains tops which are converted into needle-like forms.
14. Castellated Chimneys. A combination of demoiselles and needles formed close to each other look like castles. These are known as castellated Chimneys.
15. Zeugen. The rate of wind erosion is different in areas which have parallel layers of hard and soft rocks. The lower soft portions of rocks are eroded fast and become narrow but the upper portions of hard rocks look like tables on soft rocks. The base of the table of hard rocks is shale or some other rock. They are known as Zeugen, which appear standing separately.
16. Yardang. The rocks resemble ribs with steep slopes. The wind creates holes in the ribs and blows very fast through the holes. These formations are parallel to one another. They are about 7 meters high and 10 to 14 meters broad.
17. Desert domes. If the land is uplifted slowly in arid lands, the upliftment is not much effective. The rain takes the form of cloud-bursts and the water flows in lattice channels. These streams and rills are not ordinary but are such that they are, all of a sudden flooded. The rivers are saturated with sediments. A sheet of alluvium on the uplifted portion slips down as a whole. Such a flood is known as sheet flood. Due to this action, a dome with a convex and steep slope is formed. Its slope is uniformly gentle. These domes are known as desert domes.
18. Rack Fans. Due to cloud-bursts in desert areas, small streams are flooded in a very short time. These rivers make a fast down cutting. Later on, when these rivers broaden their channels by lateral erosion, a fan is formed. These fans are called rock-fans. Their bottoms are light convex. They are formed by a large amount of rock flour.
19. Canyons. The water received from cloud-bursts in arid lands flows in loose sediment and effects a deep down-ward cutting. Many depressions are formed along mountains on account of this action. These depressions take the forms of Canyons.
20. Wadi. Due to the cloud-bursts, water emerges out of canyons in a fast-flowing current and makes a valley 15-2 metre deep and hundreds of metre broad. Such valleys are called Wadi in Sahara and washes in America.
21. Hammada. Sometimes, the sand blown by winds in Sahara exposes the floor of hard rocks. When such floor develop a lot, they are known as hammadas.
22. Desert Pediments. Pediments are found in arid areas, especially where cracks are found. For example, the slope of the higher portion of mountains in south-west of U.S.A. is very steep and measures about 35o but the lower portion records a sudden change of slope which is gentle.
Next: Wind effects on geomorphology