Plate Boundary Types Flashcards
Collision plate boundary
Two continental places converge. Typical features include fold mountains and plateaus. Produces shallow to intermediate (focal depth) earthquakes of moderate magnitude (6-8) with rare volcanic activity.
Conservative/transform plate boundary
Two plates slide past each other in opposite directions, or in the same direction but at different speeds. Friction is eventually overcome and the plates slip past in a sudden movement. Produces earthquakes of shallow focus of moderate magnitude (6-8). Typical features include ridges and scars on the surface and occasional fissure eruptions.
Constructive plate boundary
Two plates diverge. Typical features include ocean ridges with a central rift valley, transform faults at right angles (due to different spreading rates of ridge blocks), volcanic islands and effusive eruptions (VEI 1-3). Earthquakes produced are usually low magnitude (5-6) and of shallow focus.
Destructive (convergent) plate boundary
Two plates move toward each other and collide. The denser oceanic plate moves under the continental plate and sinks due to gravity into the mantle (undergoes slab pull). Typical features include ocean trenches, batholiths, fold mountains with volcanic peaks and high magnitude (8-9) earthquakes with a range of focal depths from shallow to 700km along the Benioff zone. Produces explosive volcanoes (5-6 VEI scale).
Convergent plate boundary (oceanic and oceanic)
Two plates move toward each other and collide. Subduction and slab pull of the denser oceanic plate occurs. Typical features include island arcs, ocean trenches, fore and back arc zones with explosive volcanoes (VEI 5-6). Produces earthquakes of high magnitude (7-9) with a range of focal depths from shallow to 700km along Benioff zone.
Example of a collision boundary
The Himalayas; Indian plate moving 3.3cm/yr north and Eurasian plate moving 1.4cm/yr south (where the combined continental crust is over 70km in places).
Example of a conservative/transform plate boundary
The San Andreas Fault; 1,300 km through California between the Pacific Plate (moving northwest) and the North American Plate (moving southeast)
Example of a constructive plate boundary
Mid-Atlantic Ridge; Eurasian and North American Plates, average spreading rate of about 2.5 centimetres per year
Example of a destructive (convergent) plate boundary
The Peru-Chile trench; 50km thick South American continental plate moving east to west at 30mm/yr and 7km thick Nazca oceanic plate. Subduction rate 50mm/yr with tearing and deformation, volcanoes about 100km from this plate boundary.
Example of a convergent plate boundary (oceanic and oceanic)
Tonga Trench; 10,880m deep, Pacific oceanic plate and Australian continental plate (with oceanic remnants); Tonga has 169 islands
Transboundary
Across a boundary, e.g. transboundary pyroclastic flows
7 main large plates
African plate, Antarctic plate, Eurasian plate, Indo-Australian plate, North American plate, Pacific plate and South American plate
