Crustal movement

Contents

1.1 Definition
1.1.1 Theory of plate movement
1.1.2 Interior of the earth

1.2 Different types of plate

1.3 Types of plate movement1.4 Features: Mountain, Rift Valley and Volcano1.5 Impacts: Volcanic eruption and Earthquake





References
1.1 Definition
Crustal movement is the deformation of the lithosphere (lithosphere is the upper layer of Earth's interior, including the crust and the breakable portion at the top of the mantle). The movement of plates is resulted due to the release and redistribution of energy from Earth's core (convection current).
When the plates move it will cause stress where rock might bend, slide or break. As a result, earth's interior will have faults or fractures in rocks, and folds or bends in the rock structure. The effects of this stress can be seen clearly on the surface of the earth in the form of subsidence, either a depression in the crust, or uplift of crustal materials. Deformation of plates also involves the formation of mountain ranges such as mountain (Rockies or Himalayan), which resulted due to folding, faulting, and volcanic activity.
The fastest-moving plates are at a speed of 10cm per year. As example, the ground beneath continental United States and east of the Juan de Fuca is drifting at the rate of 3 cm every year, which means that in a hundred years it will have shifted 3 m.

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1.1.1 Theory of plate movement

Continental Drift Theory (Pangea)

Alfred Wegener, a German geophysicist and meteorologist (1800 - 1930) mentioned that the world continents seem to fit together like pieces of a jigsaw puzzle. Two American geologists supported his theory in the twentienth century, Frank Bursley Taylor (1860-1938) and Howard Baker where Europe, the Americas, and Africa all had been joined at one time.
Taylor and Baker mentioned that “continental drift is based on the idea that the configuration of continents was once different than it is today, that some of the individual landmasses of today once were joined in other continental forms, and that the landmasses later moved to their present locations.”

According to Wegener, the continents of today once formed a single supercontinent called Pangaea, from the Greek words pan ("all") and gaea ("Earth"). Eventually, Pangaea split into two halves, with the northern continent of Laurasia and the southern continent of Gondwanaland, sometimes called Gondwana, separated by the Tethys Sea.
In time, Laurasia split to form North America, the Eurasian landmass with the exception of the Indian subcontinent, and Greenland. Gondwanaland also split, forming the major southern landmasses of the world: Africa, South America, Antarctica, Australia, and India.



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1.1.2. Interior of the earth


Divided into three major parts:
(1) Crust - representing less than 1% of its volume and varying in depth from 5-60 km
(2) Mantle, a thick and dense layer of rock approximately 2,300 km thick.
(3) Core - comprise about 16% of the planet's volume and 32% of its mass. Composed primarily of iron and another, lighter element such as sulfur, it is divided between a solid inner core with a radius of about 1,220 km and a liquid outer core about 2,820 km thick.



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1.2 Different types of plate
There are two types of tectonic plates: lithosphere plate and asthenosphere plate. The lithosphere plate is rigid, rocky outer layer of the Earth, consisting of the crust and the solid outermost layer of the upper mantle. It extends to a depth of about (100 km). It is broken into about a dozen separate, rigid blocks, or plates. Slow convection currents deep within the mantle, generated by radioactive heating of the interior, are believed to cause the lateral movements of the plates (and the continents that rest on top of them) at a rate of several inches per year. Instinctively, the lithosphere is cooler and more rigid.

While, the asthenosphere plate is zone of the Earth’s mantle lying beneath the lithosphere, believed to be much hotter and more fluid than the lithosphere. The asthenosphere is thought to extend from about (100 km) to about (700 km) below the Earth’s surface. The asthenosphere is hotter and flows more easily.


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There are nine huge plates and a number of minor plates. The main plates are:
  • African Plate covering Africa - Continental plate
  • Antarctic Plate covering Antarctica - Continental plate
  • Australian Plate covering Australia - Continental plate
  • Indian Plate covering Indian subcontinent and a part of Indian Ocean - Continental plate
  • Eurasian Plate covering Asia and Europe - Continental plate
  • North American Plate covering North America and north-east Siberia - Continental plate
  • South American Plate covering South America - Continental plate
  • Pacific Plate covering the Pacific Ocean - Oceanic plate

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1.3 Types of plate movement
There are 3 ways that plate can move;

(1) Divergent
Divergent is a process in which two plates are moving away from each other. When the two plates are pulling away from each other, this enables the magma to flow up through the cracks, which later will be solidify and created a new crust.

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(2)Convergent
Convergent is a process in which two plates are moving towards each other. The results are different in each movement according to the types of plates involved.

Oceanic plate and Continental plate- When the oceanic plate (the lighter plate) and the continental plate (heavier plate) moves towards each other, this makes the oceanic plate (lighter plate) to be force and moves under the continental plate. This process is known as subduction.
Two oceanic plates- when the two oceanic plates moves towards each other, this will makes the magma rises and form a volcano.
Two Continental plates- when the two continental plates move towards each other, this will create the mountain ranges due the compression of the rocks upwards.

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(3) Transform Transform is a process where two plates are sliding horizontally past each other. When the two plates slides past each other, this will cause a jerky movement and causes earthquake.
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1.4 Features: Mountain, Rift Valley and Volcano.





When two plates move towards each other, several features can form. Often, one of the plates is forced to go down into the hot asthenosphere at a subduction zone. Volcanoes may form when a subducted plate melts and the molten rock comes to the surface. If neither plate is subducted, the two crash into each other forming huge mountains.

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1. Answer Corporation (2010). Retrieved on 20th September 2010 from WWW.answers.com/topic/plate-tectonics

2. Plate tectonics; plate boundaries. (2010). Retrieved September 20, 2010, from http://www.platetectonics.com/book/page_5.asp.

3. Betty, M. Glossary. (2006). Retrieved September 20,2010, from http://www.alderleyedge.org/Mines/glossary.htm.

4 .All about plate tectonics: Earth’s plates and continental plates. Retrieved September 20, 2010, from http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml.

5. New World Encyclopedia (2008). Retrieved on 21st September 2010, from http://www.newworldencyclopedia.org/entry/Plate_tectonics

6. Answer Corporation (2010). Retrieved on 21st September 2010, from http://www.answers.com/topic/lithosphere