See plate tectonics for a more complete discussion

Tectonic plate interactions are of three different basic types:

• Divergent boundaries are areas where plates move away from each other, forming either mid-oceanic ridges or rift valleys.
• Convergent boundaries are areas where plates move toward each other and collide. These are also known as compressional or destructive boundaries.
  • Subduction zones occur where an oceanic plate meets a continental plate and is pushed underneath it. Subduction zones are marked by oceanic trenches. The descending end of the oceanic plate melts and creates pressure in the mantle, causing volcanoes to form.
  • Obduction occurs when the continental plate is pushed under the oceanic plate, but this is unusal as the relative densities of the tectonic plates favours subduction of the oceanic plate.
  • Orogenic belts occur where two continental plates collide and push upwards to form large mountain ranges.
• Transform boundaries occur when two plates grind past each other with only limited convergent or divergent activity.

Divergent boundaries

• The Great Rift Valley in eastern Africa
• The Mid-Atlantic Ridge system separates the North American Plate and South American Plate in the west from the Eurasian Plate and African Plate in the east
• The Gakkel Ridge is a slow spreading ridge located in the Arctic Ocean.

Subduction zones

• The oceanic Nazca Plate is being subducted under the continental South American Plate at a rate of 10cm per year.
• The Pacific Plate is being subducted under the Eurasian and Philippine Plates.
• The Pacific Plate is also being subducted under the Indo-Australian Plate north and east of New Zealand, but as this map (109 KB jpg) illustrates, the direction of subduction reverses south of the Alpine Fault where the Indo-Australian Plate starts being subducted under the Pacific Plate.
• The Cascadia subduction zone is where the oceanic Juan de Fuca plate is being subducted under the continental North American plate.

Orogenic belts

• The most dramatic orogenic belt on the planet is the one between the Indo-Australian Plate and the Eurasian Plate. The Himalayas are forming along this boundary.
• The Alps have formed due to the interaction of the African Plate and the Eurasian Plate.

Transform boundaries

• The San Andreas Fault in California is an active transform boundary. The Pacific Plate (carrying the city of Los Angeles) is moving northwards with respect to the North American Plate.
• New Zealand's Alpine Fault is another active transform boundary.