Geography- Folding and Faulting

Fold Mountains

-A fold is a bend in the rock strata caused by compressional forces. -Folds often occur at a convergent plate boundary, which contort and fold the crustal rock layers. -Fold mountains are very high and are usually the highest points on the Earth's crust. -Mount Everest, the highest mountain in the world with a height of 8,850m (29,035 ft), is an example of a fold mountain. -Usually, fold mountains range between 1,200m (3,937 ft) to over 8000m (26,247 ft) in height.

Mountains

-A mountain is a large landform with steep and rugged slopes which rises 600m and above surrounding landscape. -It may have a sharp peak. -Mountains are categorized into block mountains and fold mountain according the processes by which they have been formed. -As the processes which led to their formation differ, they also differ in terms of their characteristics and appearance.

Rift valleys

-Other than block mountains, another landform associated with faults is rift valleys. -A rift valley is an elongated deep area of subsidence between two block mountains, with steep fault scarps as its walls. -They are usually between 30 to 60 km wide. -Similar to the block mountains, a rift valley may also be formed by normal and reverse faults. -

Introduction

-The Earth's surface is structured by the tectonic forces and processes. -Tectonic activity refers to forces that build up the Earth's surface. -Tectonic forces act in opposition to denudation. -Denudation are forces that act to reduce the height of the land surface. -Magnificent landforms such as the Andes, the Rockies and the Alps are formed because of the folding of the Earth's crust. -Others such as Mt Fuji, Soufriere Hills volcano and Mt Etna, are created from magma that rise from within the Earth.

The Himalayas

-The Himalayas were formed when the Indo-Australian Plate moved towards the Eurasian Plate -The movement of these two plates forces sedimentary rocks on the sea bed into a series of folds, much the same way a piece of paper folds when pushed together. -The Himalayas are young fold mountains formed between 40 to 50 million years ago.

Block Mountains

-These are formed via a process called faulting. -Faults are cracks or breaks in the rocks which lead to the displacement of rocks on either side of the crack relative to each other. -Where cracks occur without displacement, they are called joints. -The fault plane is the surface where the rocks have been displaced. -An uplifted block with steep fault scraps. It is formed by both normal and reverse faults, depending on movement of the blocks relative to each other.

faults and rift valleys

-Varied movements of the Earth's crust along faults and the difference in vertical displacement of different blocks of rocks relative to each other many give rise to a complex system of block mountains and rift valleys, like the Great East African Rift Valley. -Like folds, faults can exist on very large scales where they stretch for many hundreds and thousands of kms, or on a much smaller scale, where they may only be a few metres long.

Types of folds due to increasing amount of pressure on the rocks

1. Symmetrical fold- A result of equal compressional forces on both sides 2. Asymmetrical fold- When the compressional force on one side is greater than that on the other side. As a result, one limb is steeper than the other 3. Overfold- When the compressional force on one side is so great that both limbs are facing in the same direction 4. Recumbent fold- When one limb has been pushed over the other limb, causing the axis of the fold to become almost horizontal 5. Overthrust fold- When the compressional force on one side is so great that it causes the fold to fracture 6. Nappe- formed after the overthrust fold breaks off along the fracture line.

Folding

Folding leads to the formation of arches called upfolds (anticlines) and troughs called downfolds (synclines). -Over time, anticlines can be eroded while synclines can be deposited with eroded materials. -Depending on the strength of the pressure compressing the rock strata, different types of folds can be formed. -Folds can therefore exist on a very large scale, such as fold mountains (macro folds), but they also exist on a much smaller scale as micro folds.

Types of Faults resultant movements

Normal- One block slides down relative to the other Reverse- One block rides up over the other Transform- Horizontal displacements of rocks

Types of Faults landforms associated

Normal- Steep fault scrap (Cliff), ranging from a few metres to hundreds of metres Reverse-Very steep fault scarps, overhanging escarpment which may be weathered and eroded Transform- Fault lines, like the San Andreas Fault on San Francisco

Types of Faults caused by

Normal- Tensional forces on blocks of rocks (Pulling apart) Reverse- Forces of compression on different blocks of rocks (Pushing together) Transform- Blocks of rock sliding laterally pass each other horizontally

Faults

Three main categories: -Normal (Vertical) -Reverse (Vertical) -Transform (Horizontal)