Plate tectonics, earthquakes and volcanoes
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Question
Define a tectonic plate.
Answer
A **rigid slab** of the Earth's crust and upper mantle that moves over the soft asthenosphere.
Question
What drives plate movement?
Answer
**Convection currents** in the mantle, driven by heat from the Earth's interior.
Question
Name the three plate margins.
Answer
**Constructive** (divergent - move apart), **destructive** (convergent - subduction), **conservative** (transform - slide past).
Question
What hazards form at a destructive margin?
Answer
**Explosive composite volcanoes** + the **largest, deepest earthquakes** (and tsunamis).
Question
What hazards form at a constructive margin?
Answer
**Gentle shield volcanoes** (runny basaltic lava) + **small, shallow** earthquakes.
Question
What hazards form at a conservative margin?
Answer
**No volcanoes** (no magma made) but **large, shallow earthquakes** (e.g. San Andreas).
Question
Why is destructive-margin lava explosive?
Answer
Subduction makes **high-silica andesitic** magma - thick and sticky, so it traps gas and bursts out violently.
Question
Why does shield-volcano lava spread far?
Answer
It is **low-silica, runny, low-viscosity basaltic** lava that flows a long way before cooling.
Question
What is a hotspot?
Answer
A **mantle plume** producing volcanoes **away from any plate margin** (e.g. Hawaii).
Question
How does a tsunami form?
Answer
A sudden **displacement of the sea floor** (quake/eruption/landslide) displaces water; waves **radiate out** and grow at the coast.
Question
Why are very large earthquakes rare?
Answer
It takes a long time for enough **strain energy** to build between locked plates before a high-magnitude release.
Question
What does a top [10] Examine answer need?
Answer
A contrast of margin types linked to hazard character, a named example, the hotspot/intraplate exception, and a clear judgement.
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Full study notes for Plate tectonics, earthquakes and volcanoes
Topic 10.1 hub
Geophysical systems
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