340 million years of history – the world`s oldest caves!
The Jenolan Caves are a leading example of impressive caves in the Blue Mountains of Australia and are included in the Greater Blue Mountains World Heritage Area.
The first Europeans to make their way across the Blue Mountains arrived in this area in 1813. In the 1830’s a colourful legend grew up that an escaped convict named McKeown hid out in the wild valleys of the district, robbing farmers and travellers. Settlers James and Charles Whalan tracked McKeown to this valley, finding not only him but the Grand Arch and Devils Coach House.
A developing interest in geology and natural science at that time was at least in part responsible for the increasing number of visitors to the caves in the 1800’s. Charles Whalan and his sons continued exploring the area and between 1940 and 1860 they had not only discovered the Arch, Elder and Lucas caves but had become unofficial guides to the many tourists who wanted to visit what were then known as the “fish River caves” – later as “Binda Caves” and then Jenolan Caves.
The rocky foundation of the area in which the caves have been formed is limestone, formed very slowly through the accumulation of layer upon layer of sediments that have been compressed and compacted in a process called “bedding”. The sediment that makes up Jenolan’s limestone consists mostly of mineral calcite, or calcium carbonate.
Calcium carbonate is made primarily from fragments of seashells and coral, which tells us the area that is now Jenolan Caves once lay below a warm shallow sea. Fossils of the early sea creatures are clearly visible in sections of the limestone and these fossils suggest that Jenolan’s limestone is very old – possibly around 430 Million years.
The great slow movement of the earth’s continental plates lifted, tilted and folded the limestone and, in some case, cracked the original horizontal layers. You may be able to see some of these cracks (called joints) and the original layers which are now almost vertical.
Landscapes such as this are known as “karst”. The Jenolan karst landscape is dominated by a band of limestone almost 9 kilometres long and 300 metres wide.
In karst regions, most of the drainage is underground. Streams flowing into the area sink through cracks in the rocks, dissolving the limestone, over time, and travelling through subterranean channels creating caves, limestone caves are created when rainwater combined with carbon dioxide and organic acids from plant material in the soil that is passes through.
This carbonic acid, through diluted enough to be drinkable, is able to dissolve limestone, slowly and over many years, as it flows though joints in the rock. The river that carved the Devils Coach House hasn’t gone away. It now runs deep underground and can be seen on several of the cave tours.
Recent studies by geologists, using potassium-argon testing on clay sediments in the caves, have shown that some of these caves are more than 340 Million years old, placing them as the oldest known caves in the world.
In the caves you will see countless numbers of wondrous shapes, some on the walls or floor and others hanging from the roof. They are all called speleothems, or “cave forms’. In all of their beauty we see the results of the interaction between water, limestone, gravity and time.
Slightly acid water containing dissolved carbon dioxide seeps down through the limestone. As it moves slowly down it dissolves the limestone and then deposits it in the caves as the crystal calcite. If the water drips slowly into a cave the crystal is deposited on the ceiling and a stalactite forms. Water dripping more rapidly deposits crystal on the floor and a stalagmite begins to grow slowly upward. These may ultimately join with a stalactite to form a column.
Many other amazing shapes can be formed including canopies, shawls and flowstone. Particularly mysterious and beautiful speleothems, known as helictites, ranging in growth from thin curly whiskers to snake-like formations up to a metre long, can be found in many of the caves.
Please be aware that you will only be able to access the caves between the hours of 9am to 5pm.
1. How do stalactites and stalagmites form and what are their main
Now you can look around a little and admire the beautiful caves.
To finish up, go towards the exit.
If you like, you may go and take a walk around the beautiful lake that appears blue in sunlight.
2. Why do you think the water appears in blue?
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Enjoy this geological expedition very much and good luck!
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