How Are You Weathering?

At the moment it may feel that the whole world has stopped, and everything is on hold. But the weather is still here, still changing, and slowly carrying out processes that make our landscapes dynamic. 
High Temperature?
In Australia, one of the most common types of physical weathering is caused by thermal expansion. During the day a rock will start to heat up. Rocks have high specific heat capacity. This means they need a lot of energy for their temperature to change (one reason why a house made of stone will take longer to heat up in the summer than a house made of wood – but also take longer to cool down once they are heated).  Rocks are not particularly good conductors of heat. This means that the outside of the rock will heat up much more than the inside of a rock. As the rock starts to heat up it starts to expand. The outside will expand more than the inside, causing differential expansion.

Feeling stressed?
The rock will cool down again at night as temperatures drop, contracting.  This oscillation between hot and cold, expansion and contraction will create stresses on the rock, weakening it – particularly on the outer layer where the difference is the greatest.

Relax – exfoliate!
The outer layer of the rock will start to crack and peel off. This is known as exfoliation. This type of weathering is often called onion skin or spheroidal weathering. Onion skin – as the rock starts to exfoliate layer by layer, making the rock smaller and smaller. Spheroidal – as the rocks begin to become more spherical and rounded as the outer layers exfoliate.
A simple experiment you can do at home using just some plasticine and a thermometer to investigate temperature differential is described here.

Demonstrating thermal expansion
Thermal expansion can easily be demonstrated as shown in this video.
  • Investigate thermal expansion and the gas laws with this game
    (ABC Education) 
  • Another great interactive
    (University of Colorado)