Collision plate margins

Question 1

What happens?

Answer 1

Continental crust can’t sink

Question 2

Mid-ocean ridges

Answer 2

• Faults occur at right angles to plate boundary
• Separating sections of the ridge
• May widen at different rates = frictional stresses building up with shallow-focus earthquakes
  = Release tension
• MR = can rise to 4000m above ocean floor
• Rift valleys -mark middle - widen by magma rising from asthenosphere - cools, solidifies = new crust

Question 3

Rift valley

Answer 3

• Continental divergence = massive rift valleys
• Lithosphere stretches + thins due to magma plume below
  = Fracture into parallel faults
• Land between faults collapse into deep wide valleys - separated by upright blocks of land - horsts

Question 4

Hot spots

Answer 4

• Radioactive decay in core = very hot temps
• Decay concentrated = hot spots
• Heat the lower mantle = localised thermal currents - magma plumes rise vertically
• Plumes occasionally rise and burn thru lithosphere - thermal erosion = volcanic activity
• Plates move over magma plume = chain of active and extinct volcanoes is created = Archipelago