Which ocean ridge spreads fastest, and how fast?

The East Pacific Rise spreads fastest, at up to about 15 cm yr⁻¹. Fast spreading produces a broad, gently sloping ridge with no deep rift valley.

Why is volcanism at ocean ridges effusive rather than explosive?

Magma at a ridge is basaltic, with low silica content and low viscosity. Gas escapes easily, so lava flows out quietly rather than erupting violently.

Why are earthquakes at divergent margins shallow and low in magnitude?

The lithosphere at a ridge is thin and hot, so brittle failure happens only in the top few kilometres. Focal depths are usually under 20 km and magnitudes rarely exceed 6.

Eduqas A-Level Geography A110QS

Coastal LandscapesLandscape

Topic overview The coast as a system: inputs, outputs, stores and transfers Sediment sources, sediment cells and dynamic equilibrium Tides, currents and wave types High and low energy coastal environments Fetch, wave refraction and wave reflection Lithology and structural geology at the coast Sub-aerial weathering and mass movement at the coast Marine erosion processes Cliffs, wave-cut platforms, geos and blowholes Headlands, bays and the cave to stump sequence Coastal transport and longshore drift Coastal deposition, flocculation and sediment sorting Beaches, spits and bars Tombolos, cuspate forelands and sandy coastlines Coastal sand dunes and aeolian processes Estuarine coastlines, tidal flats and salt marshes Coral reefs and mangrove coastlines Storms, seasons and sea level change Coastal processes and human activity Human impacts and coastal management

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Weather and ClimateContemporary theme

Topic overview Structure of the atmosphere The atmospheric heat budget Global atmospheric circulation and the tricellular model Pressure belts and planetary surface winds Oceanic circulation, continentality and altitude The world's major climate types The ITCZ and seasonal migration The monsoon climate The climate of the UK Air masses affecting the UK The jet stream and UK weather ENSO and short-term climate change Vulnerability, resilience and adaptive capacity Hazards of low- and high-pressure systems and their management Urban climates and air quality Climate change: shifting belts, tipping points and response

Geographical Skills

Topic overview Grid references, coordinates and locating a place Distance, area, direction and scale Sampling and sources of error Percentages, ratios, densities and frequencies Measures of central tendency Measures of dispersion Concentration, ratios and development indices Correlation and Spearman Rank Chi-square and significance testing Mapping techniques Graphs and diagrams Digital and qualitative field techniques

Tectonic Hazards

Divergent plate margins

3 things to know
Component 3 Section A

Overview

Ocean ridge formed by the divergent margin in the Atlantic, typical spreading rate for the Mid-Atlantic Ridge and transform faults.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What happens at a divergent plate margin?

Key term

Name the ocean ridge formed by the divergent margin in the Atlantic.

Key term

State a typical spreading rate for the Mid-Atlantic Ridge.

Questions from this subtopic

Each one with the model answer underneath.

1
What happens at a divergent plate margin?
Model answer
Two plates move apart and magma rises to fill the gap. New oceanic crust forms as that magma cools, so the margin is constructive.
2
Name the ocean ridge formed by the divergent margin in the Atlantic.
Model answer
The Mid-Atlantic Ridge runs the length of the Atlantic, separating the Eurasian and North American plates in the north. Iceland sits astride it above a mantle plume.
3
State a typical spreading rate for the Mid-Atlantic Ridge.
Model answer
The Mid-Atlantic Ridge spreads at roughly 2.5 cm yr⁻¹. Slow spreading gives it a deep central rift valley.
4
Which ocean ridge spreads fastest, and how fast?
Model answer
The East Pacific Rise spreads fastest, at up to about 15 cm yr⁻¹. Fast spreading produces a broad, gently sloping ridge with no deep rift valley.
5
Why is volcanism at ocean ridges effusive rather than explosive?
Model answer
Magma at a ridge is basaltic, with low silica content and low viscosity. Gas escapes easily, so lava flows out quietly rather than erupting violently.
6
Why are earthquakes at divergent margins shallow and low in magnitude?
Model answer
The lithosphere at a ridge is thin and hot, so brittle failure happens only in the top few kilometres. Focal depths are usually under 20 km and magnitudes rarely exceed 6.

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