Edexcel A Level Geography Unit 1.1

Unit 1.1 Revision

The global distribution of tectonic hazards can be explained by plate boundaries and other tectonic processes

Global distribution and causes of TDs

Tectonic hazards are unevenly distributed around the globe. The map shows that they mostly occur at plate boundaries/fault lines, particularly the area surrounding the Pacific plate known as the Ring of Fire. There are exceptions to this rule in the form of hotspot volcanoes and intraplate earthquakes.Most tectonic hazards are caused by the movement of tectonic plates. The earth's crust and lithosphere are divided into plates (see map) which are pushed in various directions by convection currents from the mantle.. It is this coming together or pulling away of tectonic plates that causes most natural disasters - but there are always exceptions!

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Caption: : Fig. 1: global distribution of tectonic disasters

Divergent Boundaries

At divergent boundaries convection currents in the mantle force the plates apart. This can occur between two continental plates, to oceanic plates or a continental and oceanic plate.Continental-continental:Here the plates pulling apart creates a rift valley(EX - East African Rift) because the crust in the middle of the fault sinks into the mantle as the plates either side of it pull apart and allow magma to rise. Any volcanoes here will have basalt eruptions. Gradually this valley will fill with seawater until much of the land is completely submerged.

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Caption: : Fig. 2: Continental divergent margin

Oceanic-oceanic:Here it is the same principle as a continental-continental boundary regarding the formation of a rift valley - this one is just underwater! A mid-ocean ridge (EX - Mid-Atlantic ridge) is formed on either side of the trench as a result. Magma rises through the fissures in the ocean crust and forms a submarine volcano. This can eventually break the surface if enough eruptions occur, but this takes a VERY long time!

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Caption: : FIg., 3 Oceanic divergent margin

Continental-oceanic: