Uluru: One Cool Inselberg, Part 1

Uluru at Dawn

A while back I started wondering about the way two famous formations, Devils Tower in Wyoming and Uluru in Australia were formed. Now, I’m sharing what I’ve found with you!

Turns out some similarities but a lot of differences between these two formations, so I’ll have to talk about them separately. Let’s start with the things they have in common.

Both of these mountains are in the class of formations known as Inselbergs from German meaning “island-mountains”.

Many Inselbergs are granite or other hard rocks that were left standing when the softer rock around was washed away. But the two places I’ve chosen out (and others like them around the world) are made of rock that got pushed up from under the ground. They also (surprise, surprise) needed water around to help them take the form we see today. Interestingly, both of these monuments are in very dry areas today, so things must have been different in the past or they wouldn’t be here.

Now, let’s look at Uluru:

CS4K-Uluru

I first heard about how land formations like Uluru in Australia were formed from Dr. Walt Brown’s book. He has a lot to say about it and explains how these kinds of formations are only possible with quiet water covering them. Do check his page out, he has some amazing pictures!

He calls sedimentary stone formations like these “liquifaction mounds (or plumes [if they’re skinny]).”  Liquifaction takes up a large part of Dr. Brown’s book and he gets very detailed.

Basically, water can hold a lot of tiny bits of rock  under the right conditions, and then let them fall in a very quick and orderly way. We see layers like this everywhere in sedimentary rocks, usually laid down like sheets of pastry in a baklava or a torte.

Here at Uluru, something different was happening as well. Uluru is made out of all different kinds of sand cemented together.

Wikipedia tells us Uluru’s sandstones “show little sorting based on grain size, exhibit very little rounding and the feldspars in the rock are relatively fresh in appearance.”

Feldspar is very common rock making up about 60% of the Earth. These bits of sand didn’t have a chance to get rounded like the sand along the ocean or a lake. This shows that they were freshly broken up from whatever rock they came from originally (probably granite) and didn’t spend very long being washed around in water before settling into their form today.

Wikipedia claims that Uluru formed from an “alluvial fan”, which means a river delta.  At least they got the water part right! But have you ever seen a delta with great humps of rock left behind without being worn right back down? To avoid the flood they still have to believe in a unique water event depositing the rock but never happening again to wash it away.

CS4K-Lake_amadeus

Lake Amadeus’ white salt bed

From Dr. Brown’s studies, it seems that layers of wet sand were caught underground with enough pressure to squeeze out of cracks up to the surface when there was a chance.  He figures there were probably lots more of these muddy piles formed during the Flood, but most of them were washed away by the water sloshing around.

But where Uluru is, there was an area of trapped, quiet water which gave the sand time to cement into stone.  We know that a water basin was there because the salt bed, now called Lake Amadeus, these kinds of Flood-water-lakes leave behind is just 31miles [50km] away down the valley.Kat Tjuta Olgas, WikiCommons

If you look at Dr. Brown’s page and this page of Uluru’s 36 sister mounds The Olgas-Kata Tjuta  (25km [16mi] to the west of Uluru) you will see something very interesting about these rocks.  They once had acne really badly… or, rather, they are filled with pock marks all around the sides.

This is what Think Quest is telling kids about Uluru: They start with the “500 million years” bit, then mention that it was formed underwater! I picked this page because it mentions that the Aborigines remember that Uluru was once in an ocean.  Just what we were expecting.

He puts forth his hand upon the rock; he overturns the mountains by the roots. He cuts out rivers among the rocks; and his eye sees every precious thing. He binds the floods from overflowing; and the thing that is hid brings he forth to light.
Job 28:9-11

Article on Devils Tower HERE

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