Chapter 4. Plate Tectonics and Landforms
Earth’s layers: crust, mantle, outer core (liquid) and inner core (solid). The rigid lithosphere (crust plus uppermost mantle) is broken into tectonic plates that move a few centimetres a year on the softer asthenosphere beneath [5].
Plate boundaries
| Boundary | Motion | Typical features |
| Divergent | Plates move apart | Mid-ocean ridges, rift valleys (East African Rift) |
| Convergent | Plates collide | Mountain ranges (Himalayas), trenches, volcanic arcs |
| Transform | Plates slide past | Earthquakes (San Andreas Fault) |
The Pacific Ring of Fire is the zone of frequent earthquakes and volcanoes around the Pacific Ocean basin [5].
Shaping the surface. Weathering breaks rock down in place; erosion moves material by water, wind, ice and gravity; deposition lays it down as deltas, dunes, moraines and floodplains [4].
Notable physical features
Highest point above sea level: Mount Everest (about 8,849 m), in the Himalayas.
Deepest known ocean point: Challenger Deep in the Mariana Trench (about 10,900 m).
Longest mountain chain on land: the Andes. Longest overall: the mid-ocean ridge system.
Largest hot desert: the Sahara (roughly 9 million km²).
Review: Explain why the Himalayas are still rising.