AS: Tectonics
Topic 1
Amy Hannam
, Characteristcs of Plate Boundaries
1.1: Plate Boundaries Plate Boundary Plate Seafoor Events Observed Example
& Tectonic Processes Divergent Ocean-
Movement
Apart Forms by seafoor • Ridge forms at spreading center •
Locatons
Mid-
Ocean spreading • Ocean basin expands, plate area Atlantc
The Global Distributon of Earthquakes increases Ridge
• Earthquakes tend to be focused along plate boundaries, • Many small volcanoes and/or shallow
earthquakes
where there are build ups and releases of pressure as • Consequently, tsunamis • East Pacifc
plates collide or diverge. Rise
• 70% of earthquakes are found in the ‘Ring of Fire’ in the Pacifc
Ocean Contnent- New ocean basin • Contnent spreads • East African
• Earthquakes can be found at any plate boundary Contnent may form as • Central rif collapses Rif Valley
contnent splits
• There are a few exceptons: • Ocean flls basin
• Intraplate earthquakes e.g. East Coast of the US. • Red Sea
Convergent Ocean- Together Destroyed at • Dense oceanic lithosphere plunges • Western
Contnent subducton zones beneath less dense contnental South
The Global Distributon of Volcanoes • Earthquakes trace path of down- America
• Volcanoes are located on or near tectonic plate moving plate as it descends into
asthenosphere
boundaries, specifcally destructve and constructve • A trench forms • Cascade
boundaries. • Subducted plate partally melts Mountains
• Magma rises to form contnental in Western
• Most concentrated area is the ring of fre around the volcanoes United
pacifc ocean. States
• There are a few exceptons:
Ocean- • Older, cooler, denser crust slips • Aleutans
• The middle of the Pacifc Ocean (due to hotspots) Ocean beneath less dense crust
• East Coast of Africa (due to the African Plate ripping in half) • Strong earthquakes
• Deep trench forms in arc shape • Marianas
• Subducted plate heats in upper
mantle
The Global Distributon of Plate Boundaries • Magma rises to form curving chains
Divergent Locaton: Mid-Ocean Ridges of volcanic islands
(Constructve) Hazard: Shallow focus and low
magnitude Earthquake events, Contnent- Closure of ocean • Collisions between masses of granitc • Himalayas
mainly under the sea basins contnental lithosphere
Contnent
• Neither mass is subducted
• Plate edges are compressed, folded, • Alps
Convergent Locaton: Actvely deforming uplifed
(Destructve) collision locatons
• One may move beneath the other
Hazard: Volcanoes &
Earthquakes
Conservatve (Transform) Past Each Other Neither created • A line (fault) along which lithosphere • San
nor destroyed plates move past eachother Andreas
Conservatve Locaton: Occur wherever • Strong earthquakes along fault Fault
(Transform) plates are moving
Hazard: Shallow focus
• Transform faults across spreading • Mid-Ocean
center Ridges
Earthquakes
Topic 1
Amy Hannam
, Characteristcs of Plate Boundaries
1.1: Plate Boundaries Plate Boundary Plate Seafoor Events Observed Example
& Tectonic Processes Divergent Ocean-
Movement
Apart Forms by seafoor • Ridge forms at spreading center •
Locatons
Mid-
Ocean spreading • Ocean basin expands, plate area Atlantc
The Global Distributon of Earthquakes increases Ridge
• Earthquakes tend to be focused along plate boundaries, • Many small volcanoes and/or shallow
earthquakes
where there are build ups and releases of pressure as • Consequently, tsunamis • East Pacifc
plates collide or diverge. Rise
• 70% of earthquakes are found in the ‘Ring of Fire’ in the Pacifc
Ocean Contnent- New ocean basin • Contnent spreads • East African
• Earthquakes can be found at any plate boundary Contnent may form as • Central rif collapses Rif Valley
contnent splits
• There are a few exceptons: • Ocean flls basin
• Intraplate earthquakes e.g. East Coast of the US. • Red Sea
Convergent Ocean- Together Destroyed at • Dense oceanic lithosphere plunges • Western
Contnent subducton zones beneath less dense contnental South
The Global Distributon of Volcanoes • Earthquakes trace path of down- America
• Volcanoes are located on or near tectonic plate moving plate as it descends into
asthenosphere
boundaries, specifcally destructve and constructve • A trench forms • Cascade
boundaries. • Subducted plate partally melts Mountains
• Magma rises to form contnental in Western
• Most concentrated area is the ring of fre around the volcanoes United
pacifc ocean. States
• There are a few exceptons:
Ocean- • Older, cooler, denser crust slips • Aleutans
• The middle of the Pacifc Ocean (due to hotspots) Ocean beneath less dense crust
• East Coast of Africa (due to the African Plate ripping in half) • Strong earthquakes
• Deep trench forms in arc shape • Marianas
• Subducted plate heats in upper
mantle
The Global Distributon of Plate Boundaries • Magma rises to form curving chains
Divergent Locaton: Mid-Ocean Ridges of volcanic islands
(Constructve) Hazard: Shallow focus and low
magnitude Earthquake events, Contnent- Closure of ocean • Collisions between masses of granitc • Himalayas
mainly under the sea basins contnental lithosphere
Contnent
• Neither mass is subducted
• Plate edges are compressed, folded, • Alps
Convergent Locaton: Actvely deforming uplifed
(Destructve) collision locatons
• One may move beneath the other
Hazard: Volcanoes &
Earthquakes
Conservatve (Transform) Past Each Other Neither created • A line (fault) along which lithosphere • San
nor destroyed plates move past eachother Andreas
Conservatve Locaton: Occur wherever • Strong earthquakes along fault Fault
(Transform) plates are moving
Hazard: Shallow focus
• Transform faults across spreading • Mid-Ocean
center Ridges
Earthquakes
