​Transform Boundaries

• ​Plates slide across each other

• ​No new boundary is made or destroyed

• ​Friction causes a build-up of pressure

• Eventually, the pressure causes a jolt (earthquake)

• ​May occur between any type of plate

• ​Cause shallow-focus earthquakes (less than 70km deep)

​Convergent Boundaries

• Occur when plates colliding head-on

• Generate the most violent earthquakes

• ​Can cause mountain ranges, volcanoes, or trenches to form

• The denser plate will disappear under the less-dense one (subduction zone)​

​Continent to Continent Collision

• Both plates have similar densities, so no subduction occurs​​​

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• ​Instead, both plates push on each other, causing mountain ranges (the Himalayas are an example)

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Ocean to Continent Collision

• ​Oceanic plates are denser, so always disappear underneath the continental plate (known as subduction)

• The ​line where the plates meet is called an ocean trench

• ​Can produce mountain ranges with volcanoes

• ​As oceanic plate subducts and melts, it can be forced into the volcano above

​Ocean to Ocean Collisions

• ​The older crust will be denser, so will disappear under the younger plate

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• ​A deep-ocean trench is formed

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• ​As the denser plate gets hotter in the mantle, it melts and may be forced up, creating a line of undersea volcanoes, called an island arc (Japan and Indonesia are example where this has occurred)

​Australian Earthquakes

• ​The continent of Australia is in the middle of the Australian tectonic plate

• ​New Zealand is on the edge of the Australian and Pacific plates

• ​New Zealand is more likely to have large earthquakes (NZ's largest recorded earthquake was 8.2 on the Richter scale; Au's largest ever was 6.6)

• ​Australia still has about 100 earthquakes (3.0 or larger) every year!

Tsunamis Caused by ​Earthquakes or Volcanoes

• ​Earthquakes or volcanoes under the seabed cause water to be shifted

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• ​This water travels at about 800km/hr through the deep ocean

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• ​As it approaches shallow water and land, it slows down, but increases in height

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• ​Tsunami means "harbour wave" in Japanese

​Diverging Boundaries

• ​Caused by plates spreading apart

• ​Can occur in the middle of the ocean or even in the middle of a continent

• ​Magma from underneath the crust rises up and pushes on the plate

• ​The continental plate is thinned out and a rift valley is formed​

• ​It is thought that Pangaea broke apart due to diverging plates

• ​Eventually, the gap between continental land masses grows large enough for water to flow in, forming a lake, sea, and eventually, an ocean

​Creating New Land

• ​In the same way that converging boundaries can destroy plates (at a subduction zone), diverging boundaries can create new plates

• ​Magma forces up and pushes the plates apart, forming a mid-ocean ridge

• ​As this magma hardens, it becomes part of the tectonic plate

• ​Continental plates tend to be much older than oceanic plates, because the denser plates melt as they subduct