Rocks of the earth s crust are folded and faulted by forces within the earth

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1 Rocks of the earth s crust are folded and faulted by forces within the earth

2 Name the parts of a fold and draw the main types of fold. Discuss how folding has shaped the landscape of Southern Ireland. Explain what a fault is. Explain and give Irish and international examples of some of the landscapes associated with faults. Describe the landforms created by folding and faulting of the earth s crust.

3 The same forces that move the plates also place huge pressure on the rocks of the earth s surface. When rocks are crumpled up by these forces they are said to be folded. Folds are easily seen in sedimentary rocks. Rocks can be folded because at depth they are subjected to great heat and pressure which allows them to bend without breaking. Different folds are created depending on the strength and direction of the pressure put on the rocks.

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8 1 Caledonian folding 400 million years ago. Mountain ridges trend from northeast to southwest. Eg Leinster mountains and Northwest Ireland. 2 Armorican folding 300 million years ago. Mountain ridges trend from east to west. Eg Munster ridge and valley province. 3 Alpine folding 50 million years ago. Mountain ridges trend from east to west eg Alps and Himalayas.

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10 Caledonian Fold Movement occurred 400mya. The Eurasian and American Continental plates collided during this period leading to the formation of fold mountains. Pressure was exerted from the west so mountains formed are in a North-South trend. The collision caused large amounts of Connaught and Leinster to buckle and wrinkle. Led to the formation of the Nephin Beg Mountains and Maumturk Moutains in the West.

11 The Dublin-Wicklow Mountains and Leinster Batholith formed in the East during this period. These mountains would have been as high as the present day Alps but have been reduced down to present height due to weathering and erosion.

12 Armorican Fold Movement occurred over 250mya. The Eurasian and African Continental plates collided during this period leading to the formation of fold mountains. Pressure was exerted from the South so mountains formed are in a West-East trend. The collision caused large amounts of Munster to buckle and wrinkle. Led to the formation of Munster Ridges and Valleys These mountain ranges were not as high as the ones formed during the Caledonian folding as Ireland was further away from the plate boundaries in collision.

13 Munster Ridges & Valleys Between 350 and 400 million years ago huge amounts of sand were deposited in the south and southwest of Ireland. Today known as Old Red Sandstone. Later, a muddy sea covered the area and limestone was laid down. 300 millions years ago, Ireland s rocks were squeezed by earth movements, creating fold mountains. These mountains stretch from Waterford to Kerry. Anticlines (ridges) Comeraghs, Silvermines and Galtee Mountains. The softer limestone that once covered them has eroded away leaving sandstone mountain ridges, but the synclines are still covered with this limestone and form broad valleys running in an East-West direction. The Blackwater Valley is an example. The River Lee runs through a valley created during this period also

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19 Caledonian Highlands of Scotland formed during this time Armorican The Pyrenees in Southern France were formed during this time. Alpine occurred 60m years ago. Eurasian and African Plates collided. Did not affect Ireland as we were too far prom point of collision. Mountain ranges such as the Alps and the Appenine Moutains formed.

20 Himalayas, the origin of the Himalayas is the impact of the Indian Tectonic Plate travelling northward at 15 cm per year to impact the Eurasian continent, about million years ago. The movement continues and as a result the mountains increase in height by about 5mm each year. Andes Mountains formed due to the collision of the Pacific Ocean plate and the South American continental plate.

21 Near the surface of the earth rock is brittle and will crack or fracture when placed under great stress by earth movements. Rocks contain small fractures or joints, but where a lot of movement has happened along a fracture, it is called a fault.

22 When a sloping fault is created and land slips down along one side of it. These are caused by the land being pulled apart (tension), sometimes making a valley.

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24 If pressure from earth movements (compression) causes land to move up along a sloping fault. Sometimes makes block mountains: eg The Ox Mountains of County Sligo.

25 A type of reverse fault where the angle of the fault plane is very low

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27 Tear faults (transform faults) occur where there is a vertical fault in the landscape but movement has been horizontal. Similar to the movement along the San Andreas Fault in California.

28 When rocks of the earths crust are pulled apart by movement of tectonic plates, they often split. These cracks in the crust are called faults. The first type of fault found in Ireland is a normal fault. Crust can be stretched and thinned due to forced within the earth. Eventually the rocks fractures and the movement of land is downwards. E.g. Near Kingscourt, Co. Cavan.

29 The second type of fault found in Ireland is a reverse fault. These occur when rocks within the crust are subjected to compression (at destructive plate boundaries) The compression causes the rocks to fold upwards. The rocks can only fold upto a certain point before they fracture and the movement of land is upwards. Eg. Fault running from Killarney to Mallow.

30 Sometimes faulting can lead to features known as block mountains forming. E.g. Ox mountains in Connaught These features form when the land between tow parallel faults is forced upwards.

31 Rift Valleys are formed when a block of land between sets of parallel faults slips down due to stretching of the crust. A flat floored valley with steep sloping sides is formed as a result. The steep slopes mark the fault lines and are called fault scarps. Lough Neagh and the lower Bann valley occupy such a rift valley. Larger rift valleys occur in the East African Rift Valley. It is over 5000 km long and varies in width from kms.

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37 Dome mountains are the result of a great amount of melted rock pushing its way up under the earth. The crust is heaved upward into a rounded dome. Weathering and erosion attack the upland formed by the dome, often exposing the igenous rock at the heart of the dome mountains. Common in North America, eg the Black Mountains of South Dakota.

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