Key Idea: Topic 10.1 is the geophysical systems that produce the hazards in Option D — how the Earth's restless crust generates earthquakes, volcanoes and mass movements. It pulls together two ideas: 10.1.1 — plate tectonics, earthquakes & volcanoes: the Earth's plates meet at margins, and the type of margin (constructive, destructive, conservative) controls where these hazards happen and what they are like — runny vs explosive lava, deep vs shallow quakes, and the tsunami sequence. 10.1.2 — mass movement: the downhill movement of rock, soil and debris under gravity, classified by speed and water content, and tipped into failure by physical factors and a trigger — often as a secondary hazard. This is an Option D topic, examined on Paper 1. SL answers 2 options, HL answers 3 (same questions). Expect short data-response reads off a hazard map/graph, a cluster of structured parts (Outline, Identify, Describe), and a [10] Examine essay on plate margins and hazard character.
🌋 10.1.1 — Plate tectonics, earthquakes & volcanoes
The Earth's rigid shell is broken into tectonic plates that drift on the asthenosphere, driven by mantle convection. Almost all earthquakes and volcanoes cluster along plate margins — so the margin type sets the character of the hazard. The skill examiners test is linking a margin type to a hazard's character (lava type, explosiveness, landform; or earthquake depth and magnitude), plus the tsunami sequence and why the largest quakes are rare.
Constructive margins melt the mantle directly → low-silica, runny basaltic lava → gas escapes → gentle eruptions that spread far (shield volcanoes). Destructive margins melt subducted crust → high-silica, sticky andesitic lava → gas is trapped → explosive eruptions that build steep composite cones. Hotspots (e.g. Hawaii) and intraplate quakes occur away from margins, so plate movement is a strong control — not an absolute one.
[Diagram: geo-choropleth]
⛰️ 10.1.2 — Mass movement processes
Mass movement is the downhill movement of rock, soil and debris under gravity — a slope fails when the driving force (gravity) beats the resisting force (friction and material strength). Types are classified by speed and water content, from imperceptible soil creep to a deadly debris flow or rock fall. The examiner skill is reading a classification graph (slowest type = soil creep; a slope-steepness value off the axis) and giving a mechanism in every Outline — a factor plus how it works.
Important: A rock fall or landslide is a secondary hazard when another event triggers it — an earthquake or heavy rain dislodging loose blocks. The quake is the primary hazard; the fall it sets off is the secondary one. This links the two micros: the same earthquakes and eruptions of 10.1.1 are the triggers that set off the mass movements of 10.1.2 (e.g. the Nevado del Ruiz lahar, 1985).
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Exam Tips
- Margin type controls the hazard: destructive = violent (explosive cones + biggest quakes/tsunamis), constructive = gentle (shields + small quakes), conservative = quakes only.
- Lava follows magma: low-silica basaltic = runny shield that spreads far; high-silica andesitic = explosive steep cone.
- Tsunami = sudden sea-floor displacement → waves radiate out → grow at the coast. Large quakes are rare because strain takes a long time to build.
- Mass movement = rock/soil/debris downhill under gravity; slowest = soil creep, fastest/wettest = debris flow / rock fall.
- Outline [2] is never just a name: factor → how it works → effect on the slope. Half the marks are the mechanism.
- On the [10] Examine: contrast two or more margins linked to hazard character + a named example + the hotspot/intraplate exception + a clear judgement.