Earthquakes And Volcanoes (Copy)
6.1 Earthquakes and Volcanoes – Cheat Sheet
Structure of the Earth
| Layer | Description |
|---|---|
| Crust | Thin, solid outer layer (5–70 km thick). Oceanic (dense, basaltic) and Continental (lighter, granitic). |
| Mantle | Semi-molten rock (magma) with convection currents driving plate movement. |
| Core | Outer core = liquid iron & nickel (generates magnetic field). Inner core = solid, very dense, hottest layer (~6000°C). |
Distribution and Causes
| Feature | Cause | Example |
|---|---|---|
| Earthquakes | Sudden release of stress along faults when plates slip | San Andreas Fault (USA) |
| Volcanoes | Magma rises to surface at plate boundaries or hotspots | Mt. Etna (Italy), Mauna Loa (Hawaii) |
| Global Pattern | Most earthquakes/volcanoes occur along plate boundaries (Ring of Fire in Pacific). | 80% of world’s active volcanoes around Pacific Rim |
Plate Boundaries
| Type | Movement | Features | Example |
|---|---|---|---|
| Constructive (Divergent) | Plates move apart → magma rises → new crust formed | Mid-Atlantic Ridge (Iceland volcanoes) | |
| Destructive (Convergent) | Oceanic plate subducts under continental plate → volcanoes, earthquakes, fold mountains | Andes (South America) | |
| Conservative (Transform) | Plates slide past each other → earthquakes only (no volcanoes) | San Andreas Fault (California) |
Magnitude – Richter Scale
- Richter Scale: logarithmic (each step = ×10 increase in wave amplitude).
- Magnitude <4: minor tremors, often unnoticed.
- Magnitude 7+: major earthquakes, widespread destruction.
- Volcano explosivity index (VEI) also used to measure eruption strength.
Quick Pointers
- Plate tectonics explains global distribution of hazards.
- Volcanoes = constructive & destructive boundaries; Earthquakes = all boundaries (especially conservative).
- Impacts depend on magnitude, depth, population density, preparedness.
Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Environmental Management Full Scale Course