Heat Flux

• How do we know that the Earth’s interior is hot?

  • Hot springs - where magma lies close to the surface, percolating groundwater becomes heated. Boreholes are drilled to tap this source of geothermal energy.
  • Geothermal areas - average geothermal gradient is 25 degrees C. Geothermal areas show a much higher gradient.
• Where does the heat come from?

  • Accretionary heat - internal heat left over from Earth’s formation by countless particles colliding into each other and sticking together.
  • Core formation - heat from the gravitational potential energy of the dense core material sinking into the centre of the planet + heat released when the material solidified
  • Radioactive decay - heat generated by radioactive decay of elements such as uranium and thorium and their decay products.
• • Conduction - as molecules in a medium are heated, they vibrate and pass on their energy to neighboring molecules. Rock’s don’t conduct very well. It is, however, the main mechanism of heat transfer.
  • Convection - liquid or gas is heated, it expands and takes up more space. It rises and the denser and cooler material sinks, creating convection currents.
• • Advection - upward part of convection where movement of a whole region takes heat up with it.
  • Radiation - heat transfer by electromagnetic waves - does not involve particles like conduction and convection so it can transmit heat through the vacuum of space.
• What is Earth’s heat flux?

  • Heat flux is the rate at which heat flows from the Earth’s interior through one square metre of Earth’s surface.
  • Measured in watts per square metre.
  • Heat flux varies with depth and across the Earth’s surface.
  • Geothermal gradient = change in temperature (degrees C)/ change in depth (km)