Plate movement and plate type determine what happens at a boundary: new crust, subduction, mountains or sideways fault movement.
A plate boundary is where tectonic plates meet. At divergent boundaries they move apart. At convergent boundaries they move towards each other. At transform boundaries they slide past. Read the arrows first, then identify the plates.
Dense oceanic lithosphere can sink beneath another plate: subduction. When two relatively buoyant continents collide, the crust instead compresses and thickens into fold mountains. Convergence can therefore produce different landforms depending on plate type.
Earthquakes occur at all three main boundary types. Stress builds in deforming rock or along locked faults until sudden slip releases energy. Volcanoes commonly form at divergent boundaries and subduction zones. They are not a usual result of continental collision or transform movement. Hotspots can also produce volcanoes away from boundaries.
Step by step
Read movement
Do the plates move apart, towards each other or sideways past each other?
Identify plate types
Oceanic lithosphere can subduct; buoyant continents tend to collide and thicken.
Link process to landform
Spreading, subduction, folding and faulting produce different landforms and hazards.
Worked example: Andes and Himalayas: both converge, different processes
At the Andes, the oceanic Nazca Plate subducts beneath the continental South American Plate, producing a trench and a volcanic mountain belt. At the Himalayas, continental India collides with Eurasia; compression and thickening build mountains without a typical subduction volcanic arc.
Watch out for this
All convergent boundaries produce volcanoes.
Check the plate types. Continental collision builds fold mountains and causes earthquakes, but does not usually produce volcanoes.
Check your understanding
Two continental plates converge. Which prediction is best supported?
- A mid-ocean ridge forms as new seafloor spreads.
- A volcanic island arc forms as an oceanic slab subducts.
- The crust compresses and thickens, producing fold mountains and earthquakes.