Plate Tectonics and Landforms
Plate Tectonics and Landforms
Candidates must understand continental drift and its modern form, plate tectonics: the lithosphere is divided into plates moved by mantle convection, ridge push and slab pull. Key evidence includes matching coastlines and fossils across the Atlantic, palaeomagnetic stripes on the ocean floor, sea-floor spreading at mid-ocean ridges, and the distribution of earthquakes and volcanoes along plate margins.
Learn the three margin types and their landforms. Divergent (constructive) margins form mid-ocean ridges, rift valleys and new oceanic crust, with shallow earthquakes and fissure volcanism. Convergent (destructive) margins form ocean trenches, volcanic island arcs, fold mountains and subduction zones; earthquakes range from shallow to deep. Transform (conservative) margins produce conservative faults such as the San Andreas, with strong shallow earthquakes but little or no volcanism. Hotspots create volcanic island chains away from margins, as in Hawaii.
Traps: assuming all volcanoes occur at plate margins (hotspots are exceptions); calling transform margins "constructive"; confusing subduction with sea-floor spreading; muddling fold mountains (collision) with volcanic mountains (subduction); and forgetting that the Caribbean plate's eastern margin is a subduction zone producing the Lesser Antilles arc.
Rule of thumb: ask "are plates moving apart, together, or past each other?" - apart means ridges and rifts, together means trenches and mountains, past means faults.
Worked example: The Andes lie where the oceanic Nazca plate subducts beneath the continental South American plate. Expected features: a deep trench offshore, fold mountains, explosive composite volcanoes, shallow-to-deep earthquakes, and a line of volcanic activity inland of the trench.