in recent times the world has seen a sharp increase in earthquake and volcanic eruptions. Make detailed study of global distributions of fold mountains to understand the above statement.
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Answer
Fold Mountains are the mountains formed from the folding of the earth’s crust. These movements are caused due to various factors like movements in the mantle, expansion and contraction of some parts of the Earth. They are formed when two tectonic plates move towards each other leading to the folding of the layers of the Earth. The up folds are called anticlines and the down folds are called synclines.
The Himalayas in Asia, the Andes Mountains in South America and the Alps Mountains in Europe are some examples of Fold Mountains. Orogenesis is the process of building new mountain ranges by the convergence of tectonic plates.
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Fold Mountains are formed at the margins of continents due to:
Fold Mountains are formed from the folding of crust and uprising of the sediments accumulated by rivers along the margins of the continents.
This takes place by ocean-continent collision (e.g., the Andes), continent-continent collision (the Alps and the Himalayas).
All these tectonic processes create sedimentary basins of various types.
The Himalayas are formed at the convergent boundary of the Indo-Australian continental plate and Eurasian continental plate. Both plates are continental ones, and so can neither sink nor be destroyed. The material between them is therefore forced upwards to form the mountains.
The mountains such formed are usually more in length instead of breadth.
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The relation between Fold Mountains and Earthquakes:
Continental-continental convergence is associated with earthquakes as a huge amount of energy is released when the denser plate pushes lighter plate creating a fault zone along the margin.
With the passage of long time the folding continues and crust becomes over folded and strata (layers) of rock develop. It is called Over-thrust fold.
Now, further folding leads to fracture in rock called Nappe.
Upper layer of rock slides over the lower layer leading to the release of tremendous amounts of energy which causes Earthquakes.
Most earthquakes occur in the belt of young-fold Mountains because young fold mountains are formed because of tectonic activities.
In the case of Oceanic-continental convergence, subducting oceanic plate grinds against the surrounding denser medium producing mostly deep-seated earthquakes.
The earthquakes also occur when the plates slide past each other.
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The relation between Fold Mountains and Volcanoes:
Volcanism is observed in Continental -Oceanic convergence and is almost absent in Continental-Continental convergence.
At a destructive plate boundary, the oceanic plate is subducted beneath the continental one.
The molten material then rises to the surface to form volcanoes, either in an island arc (e.g. the West Indies) or on the continental landmass (e.g. the volcanoes of the Andes). In both cases, the Fold Mountains can be formed.
When the Nazca plate dives under the South American one, their motion forward also has been pushing sediment together.
This, over millions of years, has been pushed up into huge fold mountains: The Andes.
Within them, there are also volcanoes as the mountains are above the subduction zone.
If an island arc has been formed, the same idea occurs. Over millions of years, the movement of the two plates together will push the island arc nearer to the continent.
As this occurs the sediments on the seabed are folded up to become huge mountains.
The global distribution of the Fold Mountains is due to the interaction between the various tectonic plates. Thus, there is a close relationship between the volcanoes, earthquakes and the Fold Mountains. Example: The Rocky Mountains, the Andes at the edge of the Pacific Ring of Fire.
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