The creation of fold mountains Learning Objective To

The creation of fold mountains Learning Objective: To learn where fold mountains are and how they are created

STARTER: How do you think these mountains have been formed?

Describe the location of fold mountains.

Fold mountains Young fold mountains form in many parts of the world and they form along the plate margins where great Earth movements have taken place. They are found at destructive plate margins and places where there used to be destructive margins e. g. the West coast of North America. They are found where a continental and oceanic plate collide (e. g. the Andes in South America were formed this way). They form where two continental plates collide e. g. the Himalayas in Asia were formed this way.

Collision plate boundary Collision boundaries occur when two plates of similar densities move together (i. e. a continental plate and a continental plate). This causes the material between them to buckle and rise up, forming fold mountains. The Himalayas are an example of a chain of fold mountains. They have been formed by the African plate colliding into the Eurasian plate.

Collision plate boundary

Fold mountains are formed when tectonic plates collide and the plates fold up and are forced upwards into mountains. 1) There were long periods of quiet between Earth movements during which sedimentary rocks, thousands of metres thick, formed in huge depressions called geosynclines. 2) Rivers carried sediments and deposited them into the depressions. Over millions of years the sediments were compressed into sedimentary rocks such as sandstone and limestone. 3) These sedimentary rocks were then forced upwards into a series of folds by the movement of the tectonic plates. Sometimes the folds were simple upfolds (anticlines) and downfolds (synclines). In such places fold were pushed over on one side, giving overfolds.

Fold mountains have been formed at times in the Earth’s geographical history called mountain-building periods. Recent mountain-building movements have created the Alps, the Himalayas, the Rockies and the Andes, some of which are still rising. For this reason many of these ranges are called young fold mountains. http: //www. bbc. co. uk/schools/gcsebitesize/geography/natural _hazards/fold_mountains_video. shtml

Rivers deposited huge quantities of sediments in depressions called geosynclines

Over millions of years the sediments were compressed into sedimentary rocks such as sandstone and limestone

The plates moved together (a compressional boundary) forcing the sedimentary rocks upwards into a series of folds.

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Ocean Trenches The majority of ocean trenches are located around the sides of the Pacific Ocean. They are associated with destructive plate margins. The subduction zone is an ocean trench. One wall is formed by subducted ocean plate (the Nazca plate), the other by the overriding continental plate (the South American plate). Ocean trenches are very deep, typically 5000 -10 000 metres and narrow. Ocean trenches are inaccessible to humans. The ocean area of greatest importance is the continental shelf, the shallow zone less than 200 metres deep off the coast. The main opportunities here are for fishing and drilling for oil and gas.