Tectonic Processes and Landforms
Tectonic Processes and Landforms
This domain tests how plate tectonics explains the distribution of earthquakes, volcanoes, fold mountains, rift valleys and oceanic features, and how hazard impacts differ between places. It rewards chain-of-reasoning answers that link plate motion to process, landform and human consequence.
Core rules and concepts
- The lithosphere is broken into rigid plates moving over the ductile asthenosphere; slab pull and ridge push are important drivers, not simple convection currents alone.
- Divergent (constructive) boundaries produce mid-ocean ridges, rift valleys and basaltic fissure eruptions; convergent (destructive) boundaries produce trenches, island arcs, fold mountains and explosive andesitic volcanism; transform boundaries produce conservative faulting.
- Subduction generates magma by flux melting as water-rich oceanic crust descends; continental collision produces fold mountains without volcanic arcs.
- Hazard impact is not the same as hazard magnitude: vulnerability, exposure, preparedness and secondary hazards such as tsunami, landslide and liquefaction shape losses.
Worked example
Explain why the Andes include fold mountains and explosive volcanoes, whereas the Mid-Atlantic Ridge has rift valleys and basaltic lava. Reasoning: the Andes lie above a convergent boundary where the oceanic Nazca plate subducts beneath continental South America. Compression folds sedimentary rocks; water released from the slab lowers the mantle melting point, producing viscous magma and explosive eruptions. The Mid-Atlantic Ridge is divergent: plates separate, pressure release causes partial melting, and low-viscosity basaltic lava builds ridges; extension creates rift valleys. The chain is boundary type, relative motion, melting mechanism, magma type and landform.
Traps
Do not call the asthenosphere liquid magma; it is solid but ductile. Do not place trenches at divergent ridges. Do not assume high magnitude always means high disaster impact. Do not confuse a volcanic arc with an island arc: island arcs are volcanic arcs in an ocean setting.