Key ideas

As long ago as 1750, a Scot named James Hutton realised that most of the Earth’s land surface was being weathered and eroded and yet, surprisingly, has never been entirely worn away. He reasoned that, somehow, new hills and mountains were being formed all the time.

We now know that this happens because the Earth’s crust is constantly moving, and mountain ranges are lifted up as continents collide, squashing, folding and faulting the rock layers that are caught up in the process.

If you have read the pages on Deposition and Burial, you know how sediments may become buried and turned to rock – if these rocks are later caught up in continental collisions like those that formed the Alps or Himalayas, then they may even end up at the tops of mountains (previous page)!

Credit: J. Bardet, University of S. Carolina

 
This process – Uplift – is going on all the time in various parts of the world, often accompanied by many earthquakes. Taiwan, a large island off the coast of China, is being uplifted at an average rate of over 1 cm per year. Doesn’t sound much? Look at the photo of the dam!

The Shihkang Dam in Taiwan was destroyed in an earthquake in 1999. The right hand part of the dam has been lifted up 9.5 metres along a fault in one go. Not a good place to build a dam!