Jenolan Caves

Understanding the Science of Earth and Water

October 14, 2021

Earth Science Week logoIt’s Earth Science Week, October 11 to 18. Why is Earth Science celebrated all over the world each year? The answer is to “encourage stewardship of the Earth”[i] and to shine a spotlight on how our planet works. Learning about our planet is relevant to each of us personally, as it lets us make more informed decisions about trending issues such as energy, minerals and water. This year's Earth Science Week theme is "Water Today and For the Future" - relevant to everyone!

You might come to Jenolan for a range of reasons - to experience nature, explore mysterious caves, the wildlife, the quirky history, or to just have a relaxing getaway with great food and wine. But when you leave, you will take home an appreciation of how caves form, and why it’s important to care for natural places. So, exploring Jenolan is not only fun, but you learn without even trying. You can better appreciate the land on which you live, and how it constantly changes.

Slow Change

Here at Jenolan, we were amazed back in 2006, when scientists announced that the huge Jenolan Cave system was the world’s oldest cave system yet discovered. In a study published in the June issue of the Australian Journal of Earth Sciences (Vol. 53, 377-405), scientists from CSIRO, the University of Sydney and the Australian Museum showed that Jenolan Caves has been existing and slowly changing for at least 340 million years.

Previously, geologists thought that the caves were between 90 and100 million years old. Dr Armstrong Osborne, a senior lecturer at Sydney University, had long suspected that the caves are older, but was surprised to find they date back to the Carboniferous (290 to 354 million years ago). To put it into context, the Blue Mountains began to form 100 million years ago and dinosaurs became extinct 65 million years ago.

artists impression of how a coral reef would have looked 430 million years ago, in the Silurian period

Travel Through Deep Time

430 million year old Crinoid and brachiopod fossils which can be seen in the Chiflley Cave at Jenolan.So, next time you go on a tour through one of Jenolan caves, first try to imagine you are snorkling on a vast coral reef – primitive lifeforms swimming around you - crinoids and brachiopods. Think about how the reef gradually got so incredibly thick and heavy that its own incalculable weight changed (compressed) it into rock – limestone. That happened 430 million years ago – the ‘Late Silurian’ period. The Australian climate was hot, and if you walked out of the warm water onto land, you would have only seen rock, rock and more rock! Life was confined to water way back then.[ii]

Next, imagine the waters slowly receeding, and rain gathering into rivers, to slowly change the landscape, carving caves out of solid rock.

You're now standing in a cave, and if you walked outside it, you would have been freezing cold. Ice sheets covered more than half of Australia - and there were volcanos![iii]

volcanic ashImagine them spewing clouds of ash. The ash contains potassium – some of it radioactive! It falls down, drifting and washing thickly into the caves,  and changing (crystalising) into clay minerals. In the clay, the radioactive potassium starts changing into Argon gas, and stays trapped in the crystalised minerals. 

All these changes happened over many millions of years.

Fast forward to 2005. CSIRO scientists wondered if they could use potassium-argon dating to date Jenolan Caves.  Could Argon gas atoms still be trapped in the clay minerals? The Australian Museum identified eight clay areas that were suitable for dating.  Knowing that it takes 1,250 million years for all the potassium isotopes to change into Argon, the scientists could tell that the clay was 340 million years old, and had to have been deposited in the caves after the caves were formed. Therefore, although Jenolan Caves keep forming, ever so slowly, the oldest sections are at least 340 million years old.

It’s all about Water and Change

So, although we may feel that there is nothing as solid and unchanging as the ground beneath our feet, Earth Science shows that the opposite is true. Everything about it moves and changes, even the world’s oldest caves - Jenolan. 

We have quite alot of info on our website about speleothems (all the pretty crystal formation, eg stalactites, stalagmites, etc), cave geological features, surface karst features and limestone. It may sound like 'dry' reading, but our caves are wet!

At Jenolan, we not only care for the caves, and the surrounding wildlife sanctuary, but we care for the water. A steady flow of pure water still makes its way through Jenolan Caves, and will continue to change them far into the future. For thousands of years, the local indignous people brought their sick to be bathed in the Jenolan waters.  Since1837, Jenolan cave water has been used for drinking in our hotel, Jenolan Caves House, and for feeding Jenolan's hydro-electricity system. Jenolan's pure water flows into our Blue Lake (a platypus habitat), down the Jenolan River and eventually into Sydney's water supply, Warragamba Dam.

So, even though we have thousands of visitors each year, many safeguards are in place to ensure that only unpolluted water flows into the catchment, making Jenolan a perfect working illustration of this year's Earth Science Week theme, "Water Today and For the Future".


2006 Media Release

Carboniferous clay deposits from Jenolan Caves, New South Wales: implications for timing of speleogenesis and regional geology




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4655 Jenolan Caves Road, Jenolan Caves, Blue Mountains NSW. Ph: 1300 76 33 11 or +61 2 6359 3911

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