Sample Answer - Folding and Faulting 2015 Question 3B PDF

## Chapter 3: Folding and Faulting ### Structures of Deformation #### Landform development: 2015 Question 3B Explain how one of the following influences the development of landforms: - Folding - Faulting **[30 marks]** **Marking scheme:** - Identify landform: 2 marks - Explanation: 14 x SRPs (1...

## Chapter 3: Folding and Faulting ### Structures of Deformation #### Landform development: 2015 Question 3B Explain how one of the following influences the development of landforms: - Folding - Faulting **[30 marks]** **Marking scheme:** - Identify landform: 2 marks - Explanation: 14 x SRPs (14 x 2 marks = 28) **What You Need To Do:** **Answer 1: Folding** - Name a landform caused by folding, e.g. fold mountains. - Explain the formation of fold mountains. - Give an example. - Draw a labelled diagram of a fold mountain. **Answer 2: Faulting** - Name landforms caused by faulting, e.g. rift valleys and block mountains. - Explain the formation of rift valleys and block mountains. - Give an example. - Draw a well-labelled diagram of a rift valley and a block mountain. ### Answer 1: Folding **Landform caused by folding: Fold mountains** **Examples**: the Munster Ridge and Valley Province, Ireland and the Himalaya Mountains, Asia. Folding of rocks occurs when they are compressed or squeezed. Rock can be folded because at depth it is subjected to great heat and pressure which makes the rock flexible and so it can bend without breaking. This compression occurs due to movement and collision of the earth's tectonic plates. As a result of plate collision, the rocks are folded and uplifted and fold mountains are formed. This process is also called orogeny. In Ireland the landscape of Munster is made of fold mountains. About 350 million years ago old red sandstone rock was formed. It was later covered with carboniferous limestone rock. About 300 million years ago these rocks were compressed during the Armorican Fold Mountain building period. The compression came from the north and south and so the folds have an east-west trend. The limestone was easily eroded from the fold anticlines (up-folded rock) exposing the sandstone beneath. The anticlines are seen today as sandstone mountain ridges such as the MacGillycuddy's Reeks and the Comeragh Mountains. Limestone is preserved in the fold synclines (down-folded rock) which are seen in the large east-west trending valleys such as the Blackwater Valley. Globally, three stages of folding (orogeny) have impacted on landscape development. The oldest is the Caledonian Orogeny which occurred 400 million years ago. The trends of these folds are north-east/south-west. They occur in Ireland, e.g. the Wicklow Mountains. The Armorican orogeny occurred 300 million years ago. It formed in Munster and the folds trend east/west. The youngest fold mountains are Alpine. This folding occurred 50 million years ago. This trends east/west and is not found in Ireland. Different types of folds affect the landscape, e.g. symmetric, overfolds and monoclines. Folds can be seen in Loughshinny, County Dublin. | Caledonian mountains | Armorican mountains | Before folding | Today, after weathering and erosion | |---|---|---|---| | | | Fold mountains in Ireland | The formation of the Munster Fold mountains (The Munster Ridge and Valley Province) | ### Answer 2: Faulting **Landforms caused by faulting:** - Rift valleys, e.g. African Rift Valley - Block mountains, e.g. The Ox Mountains, County Mayo - Fault lines, e.g. San Andreas Fault, USA Convection currents in the mantle move the tectonic plates of the earth's crust. When the rocks in the crust are pulled apart or are compressed by plate movement, they crack. The cracks that form are called faults. Reverse faults occur when the land along a fault is moved upwards during compression. If the land is being stretched, land may sink downwards along a fault. In this case the fault is called a normal fault. A landform called a rift valley or graben forms when stretching of the crust causes the land between two parallel faults to sink. The faults in a rift valley are normal faults. The land between the faults forms a flat-floored valley with steep slopes on each side. The slopes mark the fault lines and are called fault scarps. In the African Rift Valley stretching and faulting of the crust is occurring as a hotspot of magma is rising underneath the crust, pushing it up and stretching it. The African Rift Valley is over 5,000 kilometres long and varies in width from 30 to 100 kilometres wide. The edges of the rift valley are marked by fault scarps which run from Ethiopia to Mozambique. Block mountains or 'horsts' form when the earth's crust is compressed. Reverse faults form and further compression forces the land upwards between the reverse faults. Steep-sided upland areas called 'fault-block' mountains are made. The edges of the upland area are fault scarps, e.g. the Ox Mountains of County Mayo. | Block mountain | Fault scarp | Fault scarp | Rift valley | |---|---|---|---| | Uplift | | Sinking | | | Compression of crust | Reverse fault | Reverse fault | Compression of crust | | | | | Stretching of crust | | | | | Normal fault | | | | | Normal fault | | | | | Stretching of crust | **Block mountains in Ireland** Fault lines occur where two plates slide past each other at a transform or conservative plate boundary. Long cracks are visible on the earth's surface. Rivers, roads and fences may be displaced as movement happens along the fault, e.g. the San Andreas fault where the Pacific and North American Plate meet.