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1. Divergent plate boundaries
a) plates move away from each other
b) results in mid-oceanic ridges, volcanoes including submarine volcanoes and volcanic islands, rift systems and earthquakes
2. Convergent plate boundaries
a) plates move towards each other
b) results in fold mountains, volcanoes including submarine volcanoes, oceanic trenches and earthquakes
3. Transform plate boundaries
a) plates slide past each other
b) results in faults and earthquakes
Click on the layers menu and tick the checklist box of the different types of plate boundaries. (just click cancel on the popup menu - no need to sign in)
Check out the age of the rocks by clicking sea floor to see the evidence of sea floor spreading.
Check out the subduction zone and oceanic trenches - what type of plate boundary are they found at?
1. Divergent plate boundaries
a) plates move away from each other
b) results in mid-oceanic ridges, volcanoes including submarine volcanoes and volcanic islands, rift systems and earthquakes
Oceanic-oceanic plate divergence: Mid-oceanic ridge, submarine volcanoes and Volcanic islands
As the plates move apart due to convection currents inside the Earth,magma rises from the mantle to fill the gap between the plates as they diverge.
New sea floor is formed when the magma cools and solidifies. This process is called sea-floor spreading.
Magma rises at the zone of divergence/spreading zone to form a ridge of new ocean floor called mid-oceanic ridge.
The newly formed (youngest) rocks are closest to the middle of the ridge/plate boundaries.
At various points along the ridge, magma builds up above the ocean floor to form submarine volcanoes and volcanic islands.
E.g. the Mid-Atlantic Ridge is found in the middle of the Atlantic Ocean cutting across Iceland, a volcanic island.
Can you locate the mid-oceanic ridges in the map showing the typography of the Mid- Atlantic below?
Is there a relationship between the location of earthquakes and volcanoes (including submarine volcanoes and volcanic islands) as shown by the maps below?
Above maps from EOS workshop I attended.
Continental–continental plate divergence
• Can result in the formation of linear sea
• When two plates move away from each other, the plates are subjected to tensional force and faulting occurred.
• The land in between two faults collapsed/subsided and form the rift valley.
• E.g. Red Sea and Gulf of Aden near the Great Rift Valley
Great Rift Valley (East Africa)
– a lowland with steep sides and flat valley floor
– formed by Somalian boundary of the African Plate moving away from the Nubia plate boundary of the African Plate
– 6,000 kilometres long
– between 30 to 100 kilometres wide
– Evidence of tectonic activity: active volcanoes and earthquake fractures found
Will the diverging plates lead to the widening of the East African Rift to the extent of splitting Africa into 2?
2. Convergent plate boundaries
a) plates move towards each other
b) results in fold mountains, volcanoes including submarine volcanoes, oceanic trenches and earthquakes
Can you location where the fold mountains and volcanoes are from the map showing the topography of Southeast Asia?
Is there a relationship between the location of earthquakes and volcanoes as shown by the maps below?
Why does the depth of earthquakes vary at the convergent plate boundary shown?
Above maps from EOS workshop I attended.
Oceanic-continental plate convergence: oceanic trench, fold mountains and volcano
When an oceanic plate meets a continental plate, the denser oceanic plate subducts under the less dense continental plate.
A subduction zone forms, creating a deep oceanic trench along the plate boundary.
The subduction of the continental plate causes the soild mantle material to melt and magma is formed.
The magma rises through the mantle and crust to emerge as lava which cools and solidifies to volcanoes on land.
The edge of thick continental plate buckles to form fold mountains.
Earthquakes may also occur.
E.g. the Australian Plate subducting under a section of the Eurasian Plate near Sumatra formed the Sunda Trench.
Oceanic–oceanic plate convergence
When two oceanic plates converge, one subducts under the other.
A subduction zone forms, creating a deep oceanic trench.
The subduction of the oceanic plate causes the solid mantle material to melt and magma is formed.
The magma rises through the mantle and ocean floor to emerge as lava which cool and solidify to become volcanoes.
Eventually a chain or arc of islands called island arc is formed.
Earthquakes may also occur.
• E.g. the Pacific Plate converging with the slower-moving Philippine plate forming the Mariana trench and the Mariana islands.
Ever wonder how the Himalayas are formed?
The presence of the Himalayan salt mine is a results of tectonic movement?
Continental-continental plate convergence: Fold mountains
Plates made largely of continental crust may collide with other plates made largely of continental crust.
However, both plates have similar densities and hence, resist subduction.
Instead, the plates break, slide along fractures in the crust and fold, the land is uplifted to form fold mountains.
E.g. the Himalayas - convergence of the Indian Plate and the Eurasian Plate.
The uplifted folds of Wildhauser Schafberg, Switzerland, are part of the Alps.
PHOTOGRAPH BY JAMES P. BLAIR, NATIONAL GEOGRAPHIC
3. Transform plate boundaries
a) plates slide past each other
b) results in faults and earthquakes
Plates slide past each other.
As they do so, tremendous stress builds up.
This stress is eventually released, often as a violent earthquake.
E.g. San Andreas Fault, United States of America - In 1906, an earthquake occurred in San Francisco, southern California between the Pacific Plate and the North American Plate. This caused several hundred km of North American Plate to move an average of 2.5 m, and at one point almost 7 m all in less than 1 minute
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