geoggers boundary types

Geography Terms Definitions

Geography Terms Definitions

TM- Constructive margin: oceanicRA- Constructive margin: continentalAW- Destructive margin: continentalSPM- Destructive margin: oceanicCW-collision marginSP/AH- Conservative marginJC/CT Hot spotsSH- Fold mountainsGL-Ocean trenchesAO- Island arcsOK, ST- Ocean ridges.

Constructive Margin: Oceanic

Oceanic Constructive Margins are found when two tectonics plates move away from each other in the ocean. Magma then rises to fill the gap created, forming new ocean floor.

An example of this is the Mid-Atlantic Ridge, which is caused by the North Atlantic and the Eurasian Plate moving away from each other, causing new ocean floor to be formed along the ridge. This means that North America and Europe are moving further away from each other

http://www.imperial.ac.uk/earthscienceandengineering/local/forstudents/courses/geoscience/year3/earthsciencesynthesis/coursework/2008/VincentChan/images/constructive_plate.gifTM,1http://www.classroomatsea.net/carlsberg/images/rift_valley.jpgThis type of margin is developed where rising mantle convection currents occur below a continental plate.

The rising hot mantle material causes the overlying continental plate to dome up and stretch.

Stretching of the relatively rigid plate causes brittle fractures to develop, and the plate eventually cracks.

As the mantle convection currents diverge, the plate is gradually pulled apart and the central blocks between the faults sink downwards, forming a rift valley.

Movement between the different fragments of crust in the rift valley causes frequent shallow focus earthquakes.

http://mitchbattros.typepad.com/.a/6a0133ec9febcb970b0177446817b5970d-800wiConstructive Margins: Continental

E.G. Eurasian, North American tectonics plate

RA, 2AW - Destructive Margin Oceanic-Continental

Where the two meet the oceanic crust is more dense than the continental, as such it is subducted.

Example Nazca plate is being subducted under the South American plate forming the Andes mountain range.

Location of many shallow to deep focus quakes as the oceanic plate sticks and slips underneath the continental plate.

Volcanic arc chains on-shore

File:Active Margin.svgAw, 3Oceanic Oceanic Destructive Plate Boundaries

When a convergent boundary occurs between two oceanic plates one of those plates will subduct beneath the other. Normally the older plate will subduct because of its higher density. The subducting plate is heated as it is forced deeper into the mantle and begins to melt. Magma chambers are produced as a result of this melting and the magma is lower in density than the surrounding rock material. Magma chambers that reach the surface break through to form a volcanic eruption cone. Eventually the cones will grow to be higher than sea level. This produces an island chain. With continued development the islands grow larger, merge and an elongate landmass is created.

http://ishmaeljenking.files.wordpress.com/2011/04/marianamap_88058_89661.jpgThe Mariana Trench is an example of a oceanic- oceanic plate boundary

SPM, 4MARGINSWhen two continental crusts collide, neither of them can sink.

This means the force of them pushing into each other all goes upwards. This forms mountain ranges.

This pressure and movement can cause an earthquake, but will not form a volcano.

An example of a major collision is when the Eurasian and Indian Plates collided, forming the Himalayas.

Landmass can also be pushed aside by this. East Asia is still moving away from the collision zone, forced away by the pressure.

COLLISIONCW,5Conservative plate boundaries - San Andreas Fault

http://geomaps.wr.usgs.gov/archive/socal/geology/geologic_history/images/figure1_03.jpgThe San Andreas fault is a conservative plate boundary between the Pacific and North American plates which runs 1200 km across California, in the west of the US.

There have been two large earthquakes caused by the fault: in 1857 and 1906. In the latter 3000 people died.

The main effects of a conservative plate boundary are earthquakes, which can be fairly violent and frequent.

Two plates slide past each other, without creating or destroying any land.

As they move past each other they often get stuck, building up great pressure until finally they jolt past each other. This sudden movement is what causes earthquakes.

AH, 6Hot Spots

Hot spots are areas on the Earths crust above anomalously hot areas of magma. Volcanic activity occurs when the magma rises to the surface and erupts as lava.Sometimes, instead of creating a volcano, the magma will heat groundwater under the Earths surface, which causes water and steam to erupt as geysers.There are around 40-50 hotspots in the world.Hotspots produce Icelands hot springs and are the source of most geothermal energy.The island chain of Hawaii was created by a hotspot continuously spewing lava as the pacific plate it was located on shifted.Scientists can use hotspots to track the movement of tectonic plates.Nobody is entirely clear what causes hotspots.

CT, 7Fold mountains occur near convergent or compressional plate boundaries.

Examples of fold mountains include the Alps, Rockies, Andes and Himalayas

The formation of fold mountainsWhen the two plates move towards each other again, the layers of sedimentary rock on the sea floor become crumpled and folded.

Eventually the sedimentary rock appears above sea level as a range of fold mountains.

Matterhorn, Zermatt, Switzerland Example : Matterhorn, Zermatt, Switzerland

High mountain ranges, e.g. Mont Blanc, which is 4,810 m above sea level.

Glaciated valleys, e.g. the Rhone Valley.

Pyramidal peaks, e.g. the Matterhorn.

Ribbon lakes, e.g. Lake Como.

Fast-flowing rivers.

Contrasting microclimates on north facing and south facing slopes.

Fold Mountains Where an area of sea separates two plates, sediments settle on the sea floor in depressions called geosynclines.

These sediments gradually become compressed into sedimentary rock.

SH,8 http://myweb.cwpost.liu.edu/vdivener/notes/subd_zone.gifOcean Trenches

Narrow, elongated, V-shaped depression in the ocean floor

Formed when oceanic plate dives below overriding plate

Associated with island arcs and high earthquake activity

Examples are the Aleutian islands and the Mariana trench, the deepest in the
world

GL, 9

Island arcs are archipelagos of islands that run along a plate boundary, and are formed when an oceanic plate subducts another oceanic plate, which normally causes magma to rise up and form volcanoes there are examples all over the world, including the South Aegean Volcanic Arc in Greece, and the Philippines. There are also non-volcanic island arcs, such as the Hellenic Arc which is parallel to the South Aegean Arc.

Island Arcshttp://3.bp.blogspot.com/-BZKSSn6Z_rs/UIy6Odo7xmI/AAAAAAAAA20/xLucN0auoXE/s1600/taal.jpgFile:Hellenic arc.pngAO, 10Ocean Ridges

http://www.utexas.edu/tmm/npl/mineralogy/blowups/oceanicridge.jpgA mid ocean ridge is the general term for an underwater mountain system. It is formed when two oceanic plates move away from each other and lava rises. This cools at the surface to form an underwater mountain range.

Example: MID ATLANTIC RIDGEDivergent plate boundary. Split between the North and South of the Atlantic. Around 2.5cm per year (splitting distance)

http://whatonearth.olehnielsen.dk/ocean_img/iceland.jpgST,OK 11

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