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GCSE Geography · key term
A fluid's resistance to flowing. High-viscosity magma is thick and sticky; low-viscosity magma flows easily.
Used by Edexcel and OCR
Paper 1
Revise: Causes and Characteristics of Volcanic HazardsViscosity means resistance to flow. Low-viscosity magma is runny and flows easily; high-viscosity magma is thick and sticky. Think of the contrast between water spreading across a surface and thick syrup piling up more slowly.
Specification 1.2a · Paper 1, Paper 3
A measure of a fluid’s resistance to flowing: high-viscosity lava is sticky, while low-viscosity lava is runny.
Revise: Tectonic Plate Movement: VolcanoesThe lava erupted here is commonly basaltic: it has low viscosity, meaning that it flows easily. It can spread a long distance before cooling, so repeated flows can build broad volcanoes with gentle slopes. These are shield volcanoes.
For an explanation, link the characteristic to its cause: low-viscosity lava flows further before solidifying, building a broad volcano with gentle slopes.
When comparing volcanoes, compare the same feature on both sides: magma type, viscosity, gas escape, explosivity or shape.
Keep gas content and viscosity distinct. Viscosity describes resistance to flow; it also affects how easily gas can escape.
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