The geomorphic evolution of the Swan Coastal Plain, Western Australia

A change of blog subjects this evening.  Two of my passions is Earth Science and Astronomy, I study these at Uni along with Sustainable Development and social psychology, yet I haven't seemed to be writing any blogs regarding those topics.  So, I decided that I would like to share with you, the geomorphic evolution of the swan coastal plain in WA.
Many people are not aware how fascinating the geological history of the place is!  To many, WA looks very dry, sandy and a rough terrain, people wonder how we could live here, but when you here about the fascinating history of the place it gives you a new appreciation.  If any of the terminology I use is unfamiliar, just google it as this blog will be a fair length as it is.... 

Most of the landmasses that constitutes South-western Australia consists of metamorphic and igneous rock known as the Yilgarn block, which is about 2.5 to 3 billion years old - the Earth is about 4.5, so these rocks are extremely old.  The south-western portion of the yilgarn block which encompasses the Darling Plateau and which is separated from the Swan coastal plain by the Darling Scarp.

During the palaeozoic era, about 500 million years ago, Australia was part of the continent Gondwana. Australia was joined to both India and Antarctica.  The Porongorup range in the south-west is thought to have been formed during the bonding of Australia and Antarctica 1000 million years ago - pretty cool so far huh!

Some subsiding of the yilgarn block during the early permian took place.  During the Triassic period, 230 million years ago rifting and faulting of the yilgarn block caused further sinking and caused rift valley developments.  Sediments accumulated in this low lying region which is now the Perth Basin - this is why our soil is made up mostly of sand. 

The coastline of WA was also much further inland and marine erosion was responsible for eroding sediments in the Perth basin.  However, the very hard rocks of the yilgarn block in the vicinity of the Darling fault resisted erosion.  Just google WA and check out the satellite image and you can distinctly see this.  

During the early mid tertiary, 20-50 million years ago, south-west Australia had a warm, wet, tropical climate.  High rainfall and warm temperatures brought intense chemical decomposition of rocks.  The climate changed 10 million years ago and this dehydrated and hardened the upper iron rich zone of the laterite profile.  Think yellow looking rocks and orange coloured sand!

The geomorphology of this area has been strongly influenced by a series of sea level fluctuations which have occurred during the last 2 million years, caused by tectonic activity, resulting in the tilting of huge areas of rock, land rose and shores were exposed.    About 2 million years ago the shoreline was 80-115 meters higher than today.  As the seas retreated, a wide expanse of sand was exposed.  This is how many of WA's dune systems have been formed such as the Bassendean dune system and the Ridge hill shelf to name a few.

The last glacial period in the world commenced 110,000 years before present and at glacial peak the sea level was 10km west of Rottness.  Australia has never been covered by ice and is very tectonically inactive, therefore the land has never been renewed such as the lands of the UK.  West Australia has plant species that have only adapted to live in WA and are not seen any where else in the world.  So, the next time you think that WA looks a bit rough and the terrain unexciting and dry - I hope you will now appreciate just how amazing this place really is and the amazing geological history it has gone through - it is a beautiful, unique place and I for one love it!