How does the release of elastic potential energy cause earthquakes?

At a locked fault, plate motion bends the surrounding rock, storing elastic potential energy like a loaded spring. When the stored stress exceeds the strength holding the fault shut, the fault slips suddenly and the rock springs back — elastic rebound. The stored energy is transformed into seismic waves (the kinetic energy of the shaking ground) and heat, released in seconds after years of slow charging.

Why are some volcanic eruptions gentle and others explosive?

It depends on the magma’s viscosity and gas content. Hot, low-silica mafic magma from a thermal plume is runny, so gas escapes and it erupts effusively as flowing lava (e.g. Hawaii). Silica-rich felsic magma, formed where water from a subducting plate triggers melting, is sticky and traps gas until pressure bursts out in an explosive eruption. The heat source is similar; the magma composition decides the style.

Why does magma meeting ice produce huge ash clouds?

When magma rises beneath a glacier, its heat is transferred so rapidly to the ice that water flashes to steam. The sudden, violent expansion of steam shatters the magma into very fine ash and lofts it high, producing a large ash cloud even from magma that might otherwise erupt gently — as in the 2010 Eyjafjallajökull eruption in Iceland.

How is energy involved in building mountains?

Raising rock against gravity stores gravitational potential energy. Two processes do the lifting: deformation, where the energy of converging plates folds, faults and thickens the crust (as in the Himalayas), and thermal expansion, where heating rock lowers its density so a buoyant block of lithosphere rises. Both convert plate-motion and heat energy into elevated land.

Energy & the lithosphere

The ground feels permanent, but it is really a battery — plate motion keeps charging it with energy, stored as strain in rock, heat in magma, and height in raised crust. Earthquakes, volcanoes and mountains are all the same thing: that stored energy being released or transformed. This powerbook traces the energy through each.

energy stores

great events

short sections

Energy & the lithosphereSection 1 of 5

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This book has 5 short sections. Read each one, answer the check, then use Next to move on — the bar above tracks how far you've come.

The lithosphere is a battery

The ground feels like the most permanent thing there is. It is not. It is a store of energy being slowly charged. The same internal engine that drives the plates — heat and gravity — keeps doing work on the crust, and that work pumps energy into the rock, where it sits, waiting. Earthquakes, volcanoes and mountains are what happens when that stored energy is released or transformed.

The energy is held in three forms, and it pays to name them now. Rock squeezed at a locked fault stores elastic potential energy, like a bent spring. Heat melts rock and is carried in magma as thermal energy. And rock lifted high against gravity stores gravitational potential energy. Charge the battery in these three ways, and you get the three great geological events.

That is the lens for this whole chapter. We are not asking what shape a mountain is, or where an earthquake happens — that came earlier. We are tracing the energy: where it comes from, what form it is stored in, and how it is transformed when it is finally let go. An energy transformation simply means energy changing form, as stored strain becomes shaking, or heat becomes a blast.

The crust is a battery: plate motion charges it, and geological events are the discharge.

New words

energy transformation

Energy changing from one form to another — e.g. stored strain becoming the shaking of a quake.

elastic potential energy

Energy stored in bent or stretched rock that could spring back, like a loaded spring.

🔒 Lock it in

What is the unifying idea behind earthquakes, volcanoes and mountains in this chapter?

Answer the check to continue

Quick reference & sources

The interactive book above is the lesson. What follows is a plain recap you can revise from, plus the sources and how this maps to the syllabus.

Earthquakes: elastic energy released

At a locked fault, plate motion bends rock and stores elastic potential energy over years. When the stress beats the fault’s strength, the rock springs back — elastic rebound — and the stored energy is transformed in seconds into seismic waves (ground-shaking kinetic energy) and heat.

Volcanoes: heat, magma and eruption style

Heat makes magma; viscosity and gas decide the eruption. Thermal plumes make hot, runny mafic magma → gas escapes → effusive lava (Hawaii). Water from a subducting plate triggers silica-rich felsic magma → gas trapped → explosive eruptions. Magma meeting ice flashes water to steam, whose expansion shatters magma into ash clouds (Eyjafjallajökull, 2010).

Mountains: energy lifted against gravity

Raising rock stores gravitational potential energy. Deformation converts plate-motion energy into folded, thrust-faulted, thickened crust (Himalayas); thermal expansion uses heat to lower rock density so a buoyant block of lithosphere rises. Both bank energy as height, paid back slowly through erosion.

For HSC students

This powerbook covers the Geological Transformations: Earthquakes, Volcanoes and Mountain Ranges thread of Module 3 (Energy Transformations), framed by the inquiry question how do energy transfers and transformations alter the lithosphere? Working through it, you should be able to:

explain how the release of elastic potential energy in rock leads to earthquakes;
describe how heat and its interaction with the lithosphere create different eruption types and magma compositions — thermal plumes and effusive mafic eruptions, partial melting at subduction zones and explosive felsic eruptions, and magma meeting ice producing ash clouds;
represent the energy transformations in mountain building through thermal expansion and deformation of the lithosphere.

This chapter reads earthquakes, volcanoes and mountains through energy; their structures were covered in the landscapes plates build, and the engines behind them in the engines driving the Earth. Explanations here are original and are a study aid, not a copy of the syllabus.

Sources

US Geological Survey — elastic-rebound theory of earthquakes, and volcano types, magma composition and eruption styles.
Smithsonian Global Volcanism Program — effusive vs explosive eruptions and the role of magma viscosity and gas.
Icelandic Meteorological Office / published accounts of the 2010 Eyjafjallajökull subglacial eruption and ash cloud.
NSW NESA Earth and Environmental Science Stage 6 Syllabus (2017) — used only to scope the Module 3 content; explanations above are original.

Keep going

The ground is not permanent — it is energy in slow storage. Quakes, eruptions and mountains are just the three ways the lithosphere lets that energy back out.