Geophysical systems
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Define a tectonic plate.
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All Flashcards in Topic 10.1
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10.1.112 cards
Define a tectonic plate.
A **rigid slab** of the Earth's crust and upper mantle that moves over the soft asthenosphere.
What drives plate movement?
**Convection currents** in the mantle, driven by heat from the Earth's interior.
Name the three plate margins.
**Constructive** (divergent - move apart), **destructive** (convergent - subduction), **conservative** (transform - slide past).
What hazards form at a destructive margin?
**Explosive composite volcanoes** + the **largest, deepest earthquakes** (and tsunamis).
What hazards form at a constructive margin?
**Gentle shield volcanoes** (runny basaltic lava) + **small, shallow** earthquakes.
What hazards form at a conservative margin?
**No volcanoes** (no magma made) but **large, shallow earthquakes** (e.g. San Andreas).
Why is destructive-margin lava explosive?
Subduction makes **high-silica andesitic** magma - thick and sticky, so it traps gas and bursts out violently.
Why does shield-volcano lava spread far?
It is **low-silica, runny, low-viscosity basaltic** lava that flows a long way before cooling.
What is a hotspot?
A **mantle plume** producing volcanoes **away from any plate margin** (e.g. Hawaii).
How does a tsunami form?
A sudden **displacement of the sea floor** (quake/eruption/landslide) displaces water; waves **radiate out** and grow at the coast.
Why are very large earthquakes rare?
It takes a long time for enough **strain energy** to build between locked plates before a high-magnitude release.
What does a top [10] Examine answer need?
A contrast of margin types linked to hazard character, a named example, the hotspot/intraplate exception, and a clear judgement.
10.1.212 cards
Define mass movement.
The **downhill movement of rock, soil and debris under gravity**, when the driving force beats the resisting force.
What is slope stability?
How resistant a slope is to failing — high friction and strong material make a slope stable.
What is a slip surface?
The curved or flat plane along which material **breaks away and moves** during a mass movement.
Primary vs secondary hazard?
A **primary** hazard is the original event (e.g. an earthquake); a **secondary** hazard is one it triggers (e.g. a rock fall).
Which mass movement is the slowest?
**Soil creep** — only millimetres a year; spotted from tilted poles, curved trunks and terracettes.
Which mass movements are fastest / wettest?
**Debris flows** (very high water content) and **rock falls** (very fast) — both move almost instantly.
Why does water content speed a mass movement?
Water **adds weight** and **lubricates the slip surface**, lowering friction, so material moves faster.
Two physical factors that speed mass movement?
Water content and gradient (also sediment size, geology and bare vegetation).
Two human activities that destabilise a slope?
Undercutting the base and deforestation (also building, waste heaps, disturbing drainage).
When is a rock fall a secondary hazard?
When it is **triggered** by another event — an earthquake or heavy rain dislodging loose cliff blocks.
Name a real triggered mass-movement disaster.
Nevado del Ruiz 1985 lahar (Armero), or the Vargas 1999 debris flows, Venezuela.
What does an Outline [2] answer need?
A valid factor (1 mark) **plus** development of how it works — the mechanism (1 mark).
Topic 10.1 study notes
Full notes & explanations for Geophysical systems
Geography exam skills
Paper structures, command terms & tips
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