Ayers Rock Geology

Both Ayers Rock and Kata Tjuta share a similar geological story and were created at the same time.

The first step in the geological creation of Ayers Rock and Kata Tjuta was the creation of the actual rock substance, this began to form as sediment around 900 million year ago. The area where Ayers Rock is now located was once below sea level and was known as the Amadeus Basin. For about 350 million year rivers from a nearby mountain range to the west dumped a huge amount of sand and gravel into the basin, the sand and gravel sediments eventually turned into rock which in turn turned into Ayers Rock and Kata Tjuta as we know them today.

Between 900 and 550 million years ago there was very little plant life to hold the soil together, so erosion was extensive, the mountain range from which the sediment washed into the Amadeus Basis was huge, some estimates put it as higher than the present day Himalayas! Today to the west near the Western Australian / Northern Territory border, there is a small range called the Peterman Ranges, it is believed that the Peterman Ranges is all that remains of the original huge mountains.

When sediment erodes and washes down from a mountain onto to a flatter landscape or into a basin it forms what are called Alluvial Fans, as viewed from above they form a fan shape. Over this 350 million year period, 2 fans particular fans were created, one mostly consisted of sand material and eventually became Ayers Rock, and the other one was made up of a whole mix of sand, gravel and large smooth rocks, called a conglomerate, and this eventually became Kata Tjuta. Both fans were huge and up to several kilometers thick.

About 500 million years ago, the whole area was covered with in sea and other sediment and the alluvial fans were buried, from around 300 to 400 million year ago, the fans were subjected to a great deal of pressure, both from the sediment and ocean above them, and great forces created as the land mass containing the future Uluru collided with other continents - leading to folding, faulting and more uplift. This slow motion collision squeezed the sand and gravel sediments into rock - and also tipped them on their side, the Uluru rock tipped through nearly 90°, and the Kata Tjuta Rock to about 15 degree.

The landscape was not always flat, as the exposed rocks of the alluvial fans where exposed the whole area was a rugged landscape and much of the rock began to erode as it was exposed to the elements, most of the raised areas mostly just eroded away for the next couple of hundred million years.

A few locations (Uluru, Kata Tjuta and Mount Connor) survived above the surrounding areas, because they were made of harder rock that happened to have been cemented together with quartz. About 65 million years ago, the local climate got a lot wetter. Rivers ran in the area, and sediments filled up the valleys between Uluru and Kata Tjuta, smoothing out the landscape. Not much has happened (geologically speaking) over the last 65 million years except a bit more erosion.

The fan which now forms Kata Tjuta, has cracked and tilted at an angle of around 15 degrees, water has got into the cracks over time and has started to erode the rock, creating the current domes. If you have a close look at the rock which makes up Kata Tjuta, you can see the layers of sediment at 15 degree, and you will see that the rock is made up of small and large smooth rocks and boulders, just like river stones, all cemented together with sand and pebbles, the fact the rocks are smooth indicated that they themselves have been subject to erosion prior to creating the alluvial fan. Most likely this happened as the rocks where being eroded from the Peterman ranges.

The alluvial fan which now forms Uluru when through a more sever folding process and the part of the rock which now sticks out of the ground is vertical, if you look closely you can see the layers running in a vertical direction up and down the rock. The rock it's self is made up of predominantly a sand material unlike to conglomerate of Kata Tjuta. Like an ice berg, most of Uluru is still under the ground. perhaps going down 5 or 6 kilometers!

Why is Ayers Rock Red

And the burning question, why is Uluru Red, and why does it change colour, is answered in Why is Ayers Rock Red

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