Tectonic-plate movement creates landforms

Structure of the Earth: crust, mantle and core The crust of the Earth is its thin, solid, outermost layer. Oceanic crust is the part of the crust beneath the ocean. It is the thinnest part of the crust, at about five kilometres thick. Continental crust is the part of the crust that makes up the continents. It varies a great deal in thickness, but is thicker than the oceanic crust. The mantle is the layer below the crust. The mantle is the largest layer and changes significantly from its outer areas to its inner areas. The outermost part of the mantle is solid but, as we descend into the Earth, the mantle becomes partially molten. The core is at the centre of the Earth. The core of the Earth is made up of two distinct layers: a liquid outer layer and a solid inner core.

Diagram of Earth’s internal structure 1: Crust (oceanic and continental) 2: Mantle (upper mantle, including asthenosphere and lower mantle) 3: Core (3a: Outer core; 3b: Inner core) 4: Lithosphere (crust and uppermost solid mantle) 5: Asthenosphere 6: Liquid outer core 7: Solid inner core.

The lithosphere The lithosphere consists of the Earth’s crust and the solid, outer part of the mantle. It is made up of a number of massive plates. These plates are in constant motion. They move in different directions and at different speeds.

The asthenosphere The asthenosphere is the layer of the Earth below the lithosphere. It begins where the mantle becomes more molten. The asthenosphere is much less rigid than the lithosphere. The rigid plates of the lithosphere are able to move around on the less-rigid asthenosphere.

Continental and oceanic plates Continental plates are thicker than oceanic plates, but are much less dense. They have greater buoyancy than oceanic plates. Continental plates are largely made up of granite. Oceanic plates are thinner than continental plates, but are much denser and heavier. They are largely made up of basalt. Continental crust Oceanic crust

Plate boundaries The location where two plates meet is called a plate boundary. Plate boundaries are where events such as earthquakes and the creation of features such as mountains, volcanoes, mid-ocean ridges and oceanic trenches occur. The majority of the world’s active volcanoes occur along plate boundaries.

Tectonic plates ). Courtesy of: Creed, G. Used with Permission. OpenClips(2013)http://pixabay.com/en/volcano-lava-hot-fire-eruption-156872/, Public Domain CC0 Courtesy of: Creed, G. Used with Permission.

Pacific Ring of Fire The Ring of Fire is a 40,000km roughly horseshoe-shaped area where the boundary (or edges) of the Pacific Plate interact with a number of other plates. Approximately 90 per cent of the world’s earthquakes occur along the Ring of Fire. There are 452 volcanoes in the Ring of Fire.

Types of plate boundaries There are three major ways in which the boundary of a plate interacts with the boundary of another plate. Boundaries are described as: Transform Diverging Converging Transform boundary Diverging Converging

Transform boundaries 1. 2. 3. Transform-plate boundaries grind horizontally past each other. Pressure builds up along the boundary and, as pressure releases, earthquakes occur. Transform boundaries neither create nor destroy crust; they just move them. The San Andreas Fault in California is an example of a transform boundary.

Diverging boundaries Diverging plates pull apart from each other. 1. 2. Diverging plates pull apart from each other. Diverging plates create new crust. As the plates pull apart, magma rises to the surface and new crust is formed.

Landforms created at diverging boundaries Diverging oceanic plates create new sea floor. As the plates pull apart, magma rises to fill the fissure and then cools to create new crust. As the process repeats, the ocean basin widens. Diverging oceanic plates also produce mid-ocean ridges. These ridges are areas that are relatively high compared to the surrounding ocean floor. They are created by magma rising between the diverging plates.

Landforms created at diverging boundaries Diverging continental plates create rift valleys. Because continental plates are thicker than oceanic plates, the force of the plates pulling apart does not create a break, but rather an upward bulge. Lines of weakness, called faults, develop along either side of the bulge. If the faults fracture, the bulging area of the plate between the faults drops, creating a valley called a rift valley.

Converging boundaries 1. 2. 3. Converging plates push towards each other. Converging plates destroy crust. As one plate slides under the other, the crust of that plate is returned to the mantle. The area where this happens is called the subduction zone.

Landforms created at converging boundaries When an oceanic plate and a continental plate converge, the oceanic plate is subducted under the continental plate. The edge of the oceanic plate is pushed into the mantle, where it creates a deep trench in the floor of the ocean. The edge of the continental plate is pushed upwards, to create mountains. Often, volcanoes also form along converging boundaries.

Landforms created at converging boundaries When two oceanic plates converge, one is subducted under the other. Converging oceanic plates create undersea volcanoes. As the volcanoes continue to erupt, lava and volcanic debris build up until the volcanoes eventually rise above sea level. Often, chains of volcanoes form along the boundary of converging oceanic plates. These are called island arcs. Anak Krakatau in Indonesia (pictured) is part of an island arc formed at converging-plate boundaries.

Landforms created at converging boundaries When two continental plates converge, one usually moves under or over the other. This is because both of the plates are relatively light. When two continental plates converge, it is called a continental collision. Both plates buckle and fold and the crust is pushed upwards or sideways, forming very large mountains and mountain ranges. This is how the Himalayas (pictured) were formed at the boundary of the Indian plate and the Eurasian plate.

Attributions Slide 1 & 7: USGS http://commons.wikimedia.org/wiki/File:Dds40-097_large.jpeg Slide 3: USGS http://commons.wikimedia.org/wiki/File:Earth-cutaway-schematic-numbered.svg Slide 4: http://commons.wikimedia.org/wiki/File:Mossy_ground.jpg Slide 6: USGS http://commons.wikimedia.org/wiki/File:Terkrusto_sen_vortoj.jpg Slide 8: © DETE Slide 9: http://en.wikipedia.org/wiki/File:Pacific_Ring_of_Fire.svg Slide 10: Adapted from: U.S. Geological Survey http://pubs.usgs.gov/gip/earthq1/plate.html Slide 11 ,12 & 15: Slide 13: NASA http://earthobservatory.nasa.gov/Features/Tectonics/tectonics_3.php Public domain Slide 14: Isa Tsener http://commons.wikimedia.org/wiki/File:PikiWiki_Israel_5980_Great_Rift_Valley.jpg CC BY 2.5 creativecommons.org/licenses/by-sa/2.5/deed.en Slide 16: http://commons.wikimedia.org/wiki/File:Active_Margin.svg Slide 17: NASA http://en.wikipedia.org/wiki/File:Anak_Krakatau.jpg Slide 18: NASA http://www.nasa.gov/multimedia/imagegallery/image_feature_152.html