FEATURES OF WIND DEPOSITION AND THEIR MODE OF FORMATION

WEEK 4

SUBJECT: GEOGRAPHY

CLASS:    SS 2  

  DATE: ………………

TOPIC:    ACTION OF WINDS

CONTENTS:

(1) Features of wind deposition and their mode of formation

There are depositional features in the arid and semi-arid region, this includes: Dunes, Barchans, loses and seifs dunes.

DUNES: Dunes are hills or ridges of sand formed by the pilling up of sand into hill-shaped by the action of wind. It is the accumulation of sand and shaped by the movement of winds. They may be active dunes constantly on the move or inactive fixed dunes rooted with vegetation. Dunes are well represented in a TRUEDESERTwhere sea ofsand isbeing continuously re-deposited and reshaped into a variety offeatures. Because of their great contrast in shape, size and alignment, they have been given a long list of names; such as alluvial dunes, head dunes, tail dunes, advanced dune, lateral dune, pyramidal dune, sword dune, parabolic blowout dune, barchans dune, hairpin dune, smoking dune, transverse dune, seifs dune. We shall only consider two which include barchans and seifs.

(a) BARCHANS: These are crescent or moon-shaped sand dunes. They may occur in groups or singly. They have horns which project from the crescent and thin out to become lower in the direction of the wind. They are desert landform. Barchans are formed by wind deposition in deserts. It has a convex shape on windward

side and a concave shape on the leeward side with horns of 15–30m long. Examples are common in Sahara, Chilean and Persian deserts.

Barchans

MODE OF FORMATION

Barchans are formed when an obstacle like rock impedes or prevents the movement of winds . These obstacles may be rock outcrop, a dead animal or a patch of grass which lies in the path of a prevailing wind. The materials carried by the wind are dropped and deposited behind the obstacle. Continuous deposition leads to the growth of the Barchans. The windward side of a barchans is convex and gentle, while the leeward side of a barchans is sheltered in concave and steep.

(b) SEIFS OR LONGITUDINAL DUNES:

Seif is a desert landform. The word seif is Arabic word meaning ‘sword’. These are longitudinal dunes formed into long narrow steep-sided ridges of sand. Examples are in. Examples of seif dunes are found in the great Sand sea of Egypt and Libya (Sahara deserts) and Namib Desert, West Australian Desert and Chad Desert.

Seifs or Longitudinal dunes MODE OF FORMATION

Seif is formed during wind deposition. They lie parallel to the prevailing winds which clear the corridors between dunes of sand and sweep them clean. They stretch up to a hundred kilometres and rise to over 60m. LOESS: These are fine rock particles blown out of the deserts by wind. Loess is a fine loam, very fertile and porous sand. Some are blown into the sea while some are blown to a distance land. Good examples of loess are the extensive loess deposits in North-West China which are blown there from the Gobi Desert and loess plateau of the Hwang-OH. Loess can be formed from fine particles of rock crushed under an ice-sheet and later blown by the wind after the ice-sheet has melted.

ECONOMIC IMPORTANCE OF LOESS DEPOSITS. i. They are usually very fertile hence encourages agricultural development.

1. They have caves which serve as houses.

iii. They are fine loams hence are very rich in lime.

DIFFERENCE BETWEEN BARCHANS AND SEIFS.

a. Barchans are moon-shaped sand dunes while seifs are longitudinal sand dunes. b. Barchans don’t necessarily lie parallel to each other while seifs do.

1. Barchans have horns while seifs do not have horns.
2. Barchans are not separated by corridors while seifs are separated by flat corridors.
3. Barchans lie at 90° to the prevailing winds while seifs lie parallel to the prevailing winds.
4. In barchans, the leeward side is steep and concave, the windward side is convex and gently sloping while in seifs, both sides are steep.
5. Barchans are lower than seifs in height.
6. Barchans are more prone to migration than seifs.
7. Barchans usually develop from the accumulation of sand caused by small obstruction such as rock or a pieces of vegetation while seifs usually develop from small sand ridges.

EVALUATION:

1. List and explain two basic features of wind deposition.
2. With the aid of a diagram explain longitudinal seifs and dune.

WEEKEND ASSIGNMENT

ESSAY

1. With the aid of a diagram, discuss the formation of barchans.

OBJECTIVE TEST

1. The crescent-shaped sand dunes deposited individually or in groups in sandy deserts are called (A) Loess (B) Yardangs (C) Zeugens (D) Barchans.
2. Which of the following landforms is associated with wind deposition? (A) Barchan (B) Rock pedestal (C) Yardang (D) Zeugen.
3. Which of the following pairs are desert landforms? (A) Wave-cut platforms and seif dunes (B) Sandbars and sandpits (C) Yardangs and tombolos (D) Barchans and zeugens.
4. Which of the following is associated with wind deflation in arid regions? (A) Rock pedestals (B) Oasis (C) Barchan (D) Yardangs.
5. Loess is an example of (A) clayey soil (B) loamy soil (C) wind deposited soil (D) montane soil.

READING ASSIGNMENT

Read glacial action in your textbook. REFERENCE TEXT

1. Essential Geography for Senior Secondary Schools by O.A. Iwena.
2. Comprehensive Geography for Senior Secondary Schools by Peter Oluwafemi.