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examBoard: Cambridge
examType: IGCSE
lessonTitle: Earthquake and Volcano Distribution
Earthquakes and volcanoes aren't randomly scattered across the Earth. They follow specific patterns that tell us about what's happening beneath our feet. These patterns are directly linked to the structure of the Earth and the movement of tectonic plates.
Key Definitions:
The Earth consists of four main layers:
The crust and upper mantle form the lithosphere, which is broken into tectonic plates that float on the asthenosphere (upper mantle).
Plates move because of convection currents in the mantle. Hot material rises, spreads out beneath the crust, cools and sinks back down. This creates a circular motion that drags the plates above.
Plates move at different speeds:
This movement creates tension, pressure and friction at plate boundaries, leading to earthquakes and volcanoes.
If you plotted all earthquakes and volcanoes on a world map, you'd notice they form distinct lines and clusters. These aren't random - they mark the boundaries between tectonic plates.
The most significant concentration of tectonic activity occurs in these key areas:
A horseshoe-shaped belt around the Pacific Ocean containing:
Includes Japan, Philippines, New Zealand, western Americas
Stretches from the Mediterranean through the Middle East to Southeast Asia
Underwater mountain chains where seafloor spreading occurs
The way plates interact determines the type of tectonic activity that occurs. There are three main types of plate boundaries, each creating different hazards.
Where plates move toward each other
Hazards: Deep earthquakes, explosive volcanoes, tsunamis
Where plates move away from each other
Hazards: Shallow earthquakes, shield volcanoes, fissure eruptions
Where plates slide past each other horizontally
Hazards: Shallow, frequent earthquakes, ground displacement
Earthquakes occur at all types of plate boundaries but have different characteristics depending on the boundary type.
Occur at all plate boundaries but are most common at:
These tend to be felt more intensely at the surface but affect smaller areas.
Only occur at convergent boundaries where subduction is happening:
These can be very powerful and affect larger areas but may feel less intense directly above.
Unlike earthquakes, volcanoes are not found at all plate boundaries. They mainly occur at convergent and divergent boundaries.
Form explosive stratovolcanoes due to thick, sticky magma:
These volcanoes are typically steep-sided with violent eruptions.
Form shield volcanoes due to runny, fluid magma:
These volcanoes have gentle slopes with less explosive eruptions.
Japan sits at the junction of four tectonic plates: the Pacific, Philippine, Eurasian and North American plates. This location makes it one of the most tectonically active regions on Earth.
Japan has developed advanced early warning systems and strict building codes to reduce the impact of these hazards. Japanese schools regularly practice earthquake drills and most buildings are designed to withstand significant shaking.
Iceland sits directly on the Mid-Atlantic Ridge, a divergent boundary where the North American and Eurasian plates are moving apart at about 2cm per year.
Despite the hazards, Icelanders have adapted to living with active volcanoes, using the geothermal energy for heating, electricity and even tourism.
Not all volcanic activity occurs at plate boundaries. Hotspots are areas where magma from the mantle rises through the crust away from plate boundaries.
The most famous hotspot example:
Several other hotspots exist worldwide:
The distribution of earthquakes and volcanoes reveals the hidden structure of our planet. By understanding these patterns, scientists can:
Remember that while we can't prevent tectonic hazards, understanding where they occur helps us reduce their impact on human lives and infrastructure.
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