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 Form 2 Geography Online Lessons on Internal Land Forming Processes

Lesson on folding, types of folds and the resultant features of folding

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Answer Text:
-Process in which crustal rocks are distorted by compressional forces by being caused to bend upwards and downwards. It occurs on fairly young sedimentary rocks.
Parts of a Fold
(a) Anticlines (upfolds)-parts of the earth’s surface which bend upwards when folding occurs.
(b) Synclines (down folds)-Parts of the earth’s surface which bend downwards when folding occurs.
(c) Crest-upper most part of Anticline.
(d) Trough-lowest part of a syncline
(e) Limp-rock layers sloping on both sides of a fold
(f) Axis-imaginary line drawn vertically through the centre of the anticline.
Types of Folds
1. Simple Symmetrical Folds
- Which are symmetrical about the anticline.
- Formed by 2 compressional forces of equal magnitude.
2. Asymmetrical Folds
- Which are asymmetrical about the anticlines axis or in which one limp is steeper than the other.
- Formed by two compressional forces of unequal magnitude in which one is stronger than the other.
3. Over Folds
- In which anticline of one fold is pushed over the limp of the other.
4. Isoclinal Folds
- Which are packed closely together and with limps almost parallel to each other.
- Vertical Isoclinal folds are formed by compressional forces of equal magnitude while inclined Isoclinal folds are formed by forces of unequal magnitude.
5. Recumbent Folds
- Which lie in a horizontal manner.
- Formed by two compressional forces one of which is very strong.
6. Nappe/Overthrust Fold
- In which one limp is pushed over the other limp.
- The forces are very strong and they cause a fracture/fault to develop.
7. Anticlinorium and Synclinorium Complex
- Folds characterized by minor upfolds and minor downfolds.
• Land is first subjected to weak compressional forces resulting into minor folds.
• Later the land is subjected to much greater compressional forces resulting into new upfolds with minor folds (Anticlinorium) and new down folds with minor folds (Synclinorium).