Credit: Photolibrary
MODERN SOCIETY is totally dependent on reliable energy sources. In particular, we're addicted to fossil fuels. But while media discussion of our energy options is often framed in terms of fossil fuels versus green renewable sources, such as wind and solar, in Australia another abundant energy source lies right beneath our feet.
The Earth is effectively a heat engine, and much of its geological activity is a consequence of heat loss from the deep interior. This heat comes from the decay of naturally occurring radioactive elements like uranium, thorium and potassium, as well as leftover energy from the processes that formed our planet.
Unusually enriched
Heat flow near the Earth's surface is generally highest at mid-ocean ridges, and lowest in areas of old continental rock. But surface heat-flow records in Australia show much higher than average heat throughout the continent's centre: western Queensland, the Northern Territory and South Australia, as well as parts of western Victoria.
In the southeast of this zone, the heat is linked with recent volcanic activity around Portland and Mount Gambier, but elsewhere it comes from high concentrations of radioactive heat-producing elements.
This occurs mainly in Mount Isa, Pine Creek, central Australia and the northern Flinders Ranges, in rocks around one to two billion years old.
In these regions, rocks can have concentrations of radioactive elements 10 to 15 times higher than expected for their age. There are few similarly enriched rocks in other parts of the world (particularly for uranium), and nowhere near the vast volumes of enriched rocks we have in Australia.
This bounty of heat-producing elements represents a vast energy source that has enormous potential to generate both geothermal and nuclear power in Australia. If we engage in debate on our energy future without considering this, then we will sorely miss out.
Vast resource
Nuclear and geothermal power in Australia are intimately linked, arising from the same geochemical enrichment of heat-producing elements. Indeed, despite the amount of attention the local geothermal power industry is starting to receive, it's not well appreciated that this low-emission heat source arises, ultimately, from uranium.
Geothermal power plants work by pumping water to depths of three to five kilometres where rocks reach temperatures of up to 300°C. The heated water returns to the surface as steam which is used to rotate turbines and generate electricity.
Conventionally, the high sub-surface temperatures required come from volcanic activity. New Zealand and Iceland exploit this to generate inexpensive and abundant energy: the fresh produce available year round in snow-covered Iceland is grown in greenhouses heated by geothermal power.
There's a way, but is there a will?
We get comparably high sub-surface temperatures in Australia, where I believe the future for geothermal power is potentially unlimited. It's green and safe, and exploration licences for geothermal power prospects are booming – a pilot plant is already working in the Cooper Basin in northern South Australia.
There is also another option: the enrichments in heat producing elements are what give us our extraordinary uranium resources. Olympic Dam in South Australia is the biggest uranium deposit in the world and it's no coincidence the deposit is found in heat-producing, element enriched rocks.
We export uranium overseas, where it's used to generate enormous amounts of low carbon-emission energy. All over Europe, people live side-by-side with nuclear power plants: they recognise nuclear power as an efficient, cost-effective, carbon neutral energy source.
In Australia, we have the raw materials, but choose not to use them for our own benefit. The potential for both geothermal and nuclear power in Australia is huge. There are almost certainly undiscovered highly lucrative uranium deposits out there, but equally lucrative geothermal resources too.
In exploiting either, though, we will have to overcome obstacles, such as how to deal with nuclear waste, and – for geothermal energy – the engineering advances necessary to extract energy and transfer it to the electricity grid more efficiently.
But the biggest hurdle could be our attitudes. Governments have yet to address our energy potential in a considered, scientific manner. Our reliance on fossil fuels cannot continue given the likely repercussions, and the solution could well lie under our feet.
Sandra McLaren is a Centenary Research Fellow in the School of Earth Sciences at the University of Melbourne.
