Tectonic processes and landforms: the features of volcanoes (shield and composite) and lava types, the characteristics of earthquakes (focus, epicentre, magnitude), primary and secondary hazards, and the landforms of constructive, destructive and collision boundaries.

What this dot point is asking

This is part of Eduqas GCSE Geography A (C111) Theme 3, Tectonic Landscapes and Hazards, the optional theme in Component 1. Eduqas expects you to know the features of volcanoes (shield and composite) and lava types, the characteristics of earthquakes (focus, epicentre, magnitude), the difference between primary and secondary hazards, and the landforms created at constructive, destructive and collision boundaries.

Volcanoes and lava types

The type of lava controls the shape of a volcano.

The characteristics of earthquakes

An earthquake has a precise vocabulary.

• The focus (hypocentre) is the point underground where the earthquake starts and energy is released.
• The epicentre is the point on the surface directly above the focus, where shaking is usually strongest.
• Seismic waves spread out from the focus, shaking the ground; they are recorded by a seismometer.
• Magnitude measures the energy released, on the moment magnitude scale ($M_w$), which is logarithmic: each whole step is about $31.6$ times more energy, so a magnitude $7$ releases roughly $1000$ times the energy of a magnitude $5$.
• A shallow focus generally causes more surface damage than a deep one of the same magnitude.

Primary and secondary hazards

Eduqas wants the two kinds of hazard kept distinct.

• Primary hazards are the direct, immediate effects of the shaking: buildings, bridges and roads collapsing, ground rupture along the fault, and people killed or trapped.
• Secondary hazards are the knock-on effects that follow: tsunamis (waves from an undersea quake), landslides and rockfalls on steep slopes, liquefaction (saturated soil turning to liquid and swallowing foundations), and fires from broken gas and electricity lines.

Secondary hazards often kill more people than the shaking itself, as the 2011 Japan tsunami showed.

Landforms of plate boundaries

Each boundary builds distinctive landforms.

• Constructive boundaries: under the sea, ocean ridges (the Mid-Atlantic Ridge) form where magma rises and cools; on land, a rift valley forms where the crust stretches and the central block drops (the East African Rift).
• Destructive boundaries: an ocean trench marks where the oceanic plate subducts (the Mariana Trench), with a line of composite volcanoes and fold mountains behind (the Andes).
• Collision boundaries: two continents crumple the crust upward into fold mountains (the Himalayas), with no subduction.

A volcano and an earthquake event

Eduqas expects you to study at least one earthquake and one volcanic event, often in contrasting levels of development, so you can compare causes, impacts and responses. Learn your chosen events with named places, dates and figures, ready to apply in the vulnerability and management dot points.

Try this

Q1. Define the focus and the epicentre of an earthquake. [2 marks]

• Cue. The focus is the underground point where the earthquake starts; the epicentre is the point on the surface directly above it.

Q2. Explain how fold mountains form at a collision boundary. [4 marks]

• Cue. Two continental plates of similar density push together; neither subducts, so the crust crumples upward into fold mountains (the Himalayas).